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This is the clinical evidence summary written for health professionals. It is technical, and it lists the research this page was built from. You do not need to read it to understand your treatment or to make a decision about it.

Overview¶

General Anatomy and Function¶

• The hand is both an organ designed to obtain information and an organ of execution [1].
• The hand functions efficiently only if the proximal joints of the limb are stable and yet mobile [1].
• The hand moves within a large volume of space with the shoulder as the apex, reaching any part of the body fairly easily due to the mobility of the shoulder, elbow, and wrist [1].
• The shoulder is the most mobile joint in the body and allows orientation of the upper limb as required [1].
• The movements of the clavicle amplify those of the shoulder [1].
• The elbow brings the hand closer to or moves it away from the body through flexion–extension movements [1].
• Distal to the elbow, there is in effect only one physiological unit where combined movements of the wrist and forearm place the hand in a position for grasping [1].
• For gripping, the wrist is usually in flexion when close to the trunk and in extension when placed at a distance [1].
• Forearm rotation (pronation–supination) plays an important role, particularly for bringing food to the mouth [1].
• The hand’s blood and nerve supplies are continuous with those of the rest of the limb [1].
• Some hand muscles, the extrinsic muscles, arise in the arm and forearm [1].
• The open hand, with fingers extended and in contact, forms a balanced graceful oval in its longitudinal axis [1].
• The proximal “carpometacarpal” half of the hand is flattened, presenting two faces with unique anatomical and functional significance [1].
• The posterior or dorsal aspect of the hand is convex, and the anterior, palmar or volar aspect is concave [1].
• The distal half of the hand is separated into five digits which flex toward the palm [1].
• Digits converge in closing by flexing and adducting, and diverge in opening by extending and abducting [1].
• The thumb has a more proximal and lateral position, allowing movement inward and outward from the palm [1].
• The four fingers are the distal extension of the carpometacarpal part of the hand [1].
• The hinges of finger movements are not at the bases of the digits, but at the thenar crease and at the transverse distal palmar crease [1].
• When digits are fully extended and touching, their tips almost describe a regular curve with peripheral digits being the shortest [1].
• When fingers are extended and separated, their tips lie on the circumference of a circle whose center is the head of the third metacarpal [1].
• The hand consists of 19 bones, 17 articulations, and 19 muscles situated entirely within the hand, and about the same number of tendons activated by the forearm muscles [1].

Kinematics and Articulations¶

• Most structures in the hand glide in relation to neighboring structures [2].
• The dorsal integument must be supple, elastic, and malleable, sliding distally to allow metacarpophalangeal joint flexion [2].
• Interphalangeal flexion is accomplished by a special arrangement of skin folds on the dorsum of each articulation [2].
• Vessels and nerves adapt to differences in length and are surrounded by loose fibroadipose connective tissue [2].
• In unrestricted areas with straight tendon trajectories, tendons are surrounded by paratenon and areolar connective tissue [2].
• In narrow crowded areas, the gliding mechanism is assured by the synovial sheath, which allows considerable amplitude of movement [2].
• Synovial sheaths at specific sites are surrounded by fibrous sheaths that keep the tendon close to the skeleton, acting as a pulley when the tendon changes direction [2].
• The gliding mechanism represented by synovial sheaths is much more developed on the palmar aspect [2].
• There are three digitopalmar synovial sheaths for the flexor tendons of the index finger, long finger, and ring finger [2].
• On the dorsal aspect, extensor synovial tendon sheaths are present only at the level of the wrist [2].
• The articulations of the hand form functional groups arranged in kinetic chains [2].
• The position of each articulation depends on the equilibrium of forces acting at that level, which is subject to the position of the immediately proximal articulation [2].
• The wrist influences the position of the metacarpophalangeal joint, which affects the proximal interphalangeal joint, which in turn affects the distal interphalangeal joint [2].
• Single articular movements around a fixed perpendicular axis simply do not exist in the hand [2].
• Almost all movements are around oblique and variable axes, resulting in combined movements permitting optimal orientation of the phalanges at the time of prehension [2].

Musculature¶

• Control of digital posture requires a complex balance of extrinsic and intrinsic muscle forces [7].
• Extrinsic muscles have their origin outside of the hand and their insertion on the hand or carpus [7].
• Intrinsic muscles have both origin and insertion within the hand [7].
• Extrinsic muscles are either flexors or extensors, whereas intrinsic muscles contribute to both digital flexion and extension [7].
• The extrinsic extensors run through six different fibroosseous retinacular compartments at the wrist level [7].
• The first extensor compartment contains the abductor pollicis longus and the extensor pollicis brevis [7].
• The abductor pollicis longus inserts at the base of the thumb metacarpal and radially abducts the thumb [7].
• The extensor pollicis brevis inserts on the dorsum of the proximal aspect of the proximal phalanx of the thumb and actively extends the metacarpophalangeal joint [7].
• The second extensor compartment contains the extensor carpi radialis longus and the extensor carpi radialis brevis [7].
• The extensor carpi radialis longus inserts on the index metacarpal, dorsiflexes and radially deviates the wrist [7].
• The extensor carpi radialis brevis inserts into the base of the middle metacarpal, providing balanced wrist dorsiflexion [7].
• The third compartment contains the extensor pollicis longus, which turns abruptly radialward about Lister tubercle [7].
• The extensor pollicis longus inserts on the distal phalanx and provides forceful extension of the thumb interphalangeal joint [7].
• The oblique course of the extensor pollicis longus tendon provides a substantial adduction component to its pull [7].
• The fourth extensor compartment contains the extensor indicis proprius lying deep to the four tendons of the extensor digitorum communis [7].
• The fifth compartment contains the extensor digiti quinti [7].
• The principal bony insertion of the extrinsic digital extensors is on the dorsal proximal aspect of the middle phalanx [7].
• Metacarpophalangeal joint extension is provided by extrinsic extensor force transmitted through the sagittal bands [7].
• Distal interphalangeal joint extension is achieved through the conjoined lateral bands composed of tendinous slips from extrinsic and intrinsic tendons [7].
• The extensor digitorum communis tendons of the middle, ring, and little fingers are tethered together by juncturae tendinum over the dorsum of the hand proximal to the metacarpophalangeal joint [7].
• The digital extensor tendons are stabilized over the mid-line of the metacarpophalangeal joint by their attachment to sagittal band fibers [7].
• The sagittal band fibers insert onto the volar proximal phalanx and onto the lateral borders of the volar plate [7].
• The sagittal bands form a sling that allows proximal extrinsic extensor tension to be transmitted to the proximal phalanx, permitting metacarpophalangeal joint extension without a tendinous insertion onto the proximal phalanx [7].
• With rupture or attenuation of the sagittal band fibers, the extrinsic extensor tendon can sublux to the ulnar side of the metacarpal head causing ulnar deviation of the finger [7].
• The extrinsic finger flexors are the flexor digitorum profundus and the flexor digitorum superficialis [7].
• The flexor digitorum profundus inserts on the proximal volar aspect of the distal phalanx, flexing the distal interphalangeal joint as well as the proximal interphalangeal and metacarpophalangeal joints [7].
• There are seven interosseous muscles, four dorsal and three volar [4].
• The dorsal interossei are abductors [4].
• The anatomic axis of the hand coincides with the axis of the third metacarpal [4].
• The dorsal interossei lie to the radial side of the index and middle fingers and the ulnar side of the middle and ring fingers [4].
• The little finger is abducted by the abductor digiti quinti [4].
• The volar interossei are adductors and lie to the ulnar side of the index finger and the radial side of the ring and little fingers [4].
• The middle finger has two dorsal interossei (abductors) and no volar interossei (adductors) because the central axis of the hand lies within it [4].
• Each dorsal interosseous muscle, with the exception of the third, has two muscle heads [4].
• The superficial head of the dorsal interosseous arises from the shaft of the contiguous metacarpals and is inserted onto the lateral tubercle of the base of the proximal phalanx [4].
• The superficial head abducts and weakly flexes the proximal phalanx [4].
• The deep head of each dorsal interosseous muscle forms a lateral tendon, or lateral band, at the level of the MP joint [4].
• The deep head flexes and weakly abducts the proximal phalanx while extending the middle and distal phalanges [4].
• Transverse fibers arch dorsally from each lateral band to join each other over the dorsum of the finger, flexing the proximal phalanx [4].
• Oblique fibers (spiral fibers) from the lateral bands sweep over the distal third of the proximal phalanx to insert onto the lateral tubercles at the base of the middle phalanx [4].
• The oblique fibers extend the middle phalanx (PIP joint) [4].
• The lateral bands are joined by the lateral slips of the extensor tendon to form the conjoined lateral band [4].
• The two conjoined lateral bands to each finger unite at the distal third of the middle phalanx to form the terminal tendon [4].
• The terminal tendon inserts at the base of the distal phalanx to extend it [4].
• The flexor digiti quinti brevis is structurally and functionally similar to the deep head of the dorsal interossei, forming the ulnar lateral band of the little finger [4].
• Each volar interosseous muscle has only one muscle head and none of them insert onto the proximal phalanx [4].
• The volar interossei form the ulnar lateral band of the index finger and the radial lateral band of the ring and little fingers [4].
• The abductor digiti quinti and flexor digiti quinti brevis are similar in structure and function to the superficial and deep heads of the dorsal interossei, respectively, and arise from the fifth metacarpal [4].
• The abductor digiti quinti inserts onto the ulnar lateral tubercle at the base of the proximal phalanx of the little finger [4].
• The flexor digiti quinti forms the ulnar lateral band [4].
• The opponens digiti quinti arises from the pisohamate ligament and the hook of the hamate and inserts onto the ulnar side of the diaphysis of the fifth metacarpal, which it flexes and supinates [4].
• The extrinsic extensor apparatus of the fingers is formed by extensor communis and extensor proprius of the index and little fingers [8].
• The extensor proprii tendons are situated medially to the corresponding communis tendons and join to the communis at the metacarpophalangeal joint [8].
• Extensor tendons run an almost entirely extrasynovial course, which facilitates repair [8].
• Extensor tendons are thin superficial structures that, when damaged, tend rapidly to become adherent to the underlying bones and joints [8].
• The excursion of the extensor tendons of the hand is considerably less than that of the flexors [8].
• On the dorsum of the hand, the extensor communis tendons are interconnected by the juncturae tendinum [8].
• The juncturae tendinum assist extension of adjacent connected fingers [8].
• The extensor communis tendon to the little finger may be absent or replaced by an oblique junctura from the ring finger [8].
• Halfway down the proximal phalanx of each finger, the broad flat extensor tendon splits into three parts: an extensor central band and two extensor lateral bands [8].
• The most important insertion of the extrinsic extensor system is that of the central tendon into the base of the middle phalanx [8].
• The insertion at the base of the proximal phalanx is inconstant [8].
• Under normal physiological conditions, isolated contraction of the long extensors extends only the proximal phalanx [8].
• With isolated contraction of the long extensors, the two distal phalanges remain flexed in a clawlike position [8].

Vascularization¶

• The arteries of the thumb vary in both size and number, making surgical reconstruction delicate [3].
• The most common variations of the palmar arteries can be schematized by dividing the thumb into three segments defined by the metacarpophalangeal and interphalangeal flexion creases [3].
• In the classical layout, the “princeps pollicis” artery crosses the first intermetacarpal space, runs along the ulnar side of the first metacarpal bone, and emerges onto the subcutaneous palmar tissue at the level of the cutaneous flexion crease of the metacarpophalangeal joint [3].
• The “princeps pollicis” divides into two terminal rami, the collateral palmar arteries of the thumb, which run along the digital tunnel symmetrically and are of equal caliber [3].
• An arcade located deep in the flexor tendon joins together the two arteries at the level of the distal metaphysis of the first phalanx [3].
• In anatomical studies, only 15% of dissections fall into the category of the classical description of palmar arteries of the thumb [3].
• In the first segment (between opposition crease and metacarpophalangeal flexion crease), it is rare to find arteries of surgical interest on the volar surface [3].
• In the second segment, the two arteries run alongside the flexor tendon and behind the collateral nerves [3].
• In the second segment, the main artery is the ulnar collateral artery [3].
• In the third segment (pulp segment), the two arteries are of similar size and run through the thick fatty subcutaneous padding [3].
• The dorsal arteries of the thumb are vascularized by two arteries which originate from the palmar arteries at the level of the first metacarpal [3].
• At the level of the neck of the first phalanx, an anastomosis can be found which originates from the palmar arteries [3].

Cutaneous Anatomy¶

• There are “functional cutaneous units” in the hand similar to those described in the face [12].
• One dorsal cutaneous unit extends from the wrist to the proximal interphalangeal joints of the fingers and the interphalangeal joint of the thumb [12].
• The dorsal covering of the interphalangeal articulations of the digits forms a unique cutaneous unit characterized by a considerable excess of skin when the digits are in extension [12].
• The fine tight skin of the dorsal aspect of the middle phalanx forms another unit [12].
• The dorsal integument of the distal phalanx is very special because of the nail bed with its matrix [12].
• The palm forms a cutaneous unit extending from the distal transverse crease of the wrist up to the transverse crease at the base of the digits [12].
• The palmar integument may be subdivided into two separate zones by the oppositional crease of the thumb [12].
• The skin of the radial portion covers the thenar eminence and the external part of the palm and is the mobile portion [12].
• The skin of the ulnar and distal portion covers the hypothenar eminence where the skin has poor mobility [12].
• The distal part of the palm beyond the transverse distal palmar crease is a true hinge just at the level of the metacarpophalangeal articulations [12].
• The central triangular part of the palm has skin that is fixed and poorly vascularized, covering almost directly the superficial palmar aponeurosis [12].
• The integument of the palmar face of the digits may be subdivided into phalangeal units separated by digital flexion folds [12].
• When a digit is completely flexed, the integument of adjacent phalanges comes into contact in the zones of the flexion creases, establishing areas of cutaneous contact in the form of a diamond [12].
• The sides of this diamond do not undergo variations in length during movements of flexion and extension [12].
• Incisions made along the level of the diamond sides present a minimal chance of retraction [

Osseous Anatomy¶

General Skeletal Composition¶

• The skeleton of the hand and wrist consists of 27 bones, of which 19 are long bones [40].
• The hand consists of 19 bones, 17 articulations, and 19 muscles situated entirely within the hand [1].
• The skeleton is divided into five rays, each ray making up a polyarticulated chain comprising the metacarpals and phalanges [40].
• The base of each metacarpal articulates with the distal row of the carpus [40].
• The carpus articulates with the skeleton of the forearm through its proximal row [40].
• The radioulnocarpal articulation has two axes of movement, to which is added a third axis of pronation and supination from the forearm [40].
• The wrist has three axes of movement, permitting the hand to be positioned in any spatial configuration [40].

Ray Structure and Lengths¶

• The radial ray or first ray is the shortest and is made up of only three bones: a metacarpal and two phalanges [40].
• The other four digital rays are formed by four skeletal segments: a metacarpal and three phalanges [40].
• The thumb metacarpal is the shortest metacarpal [40].
• The index finger metacarpal is the longest metacarpal [40].
• Metacarpal lengths decrease from the third to the fifth digits [40].
• The proximal and middle phalanges of the middle and ring fingers are longer than those of the index finger [40].
• The long finger, and usually the ring finger, are longer than the index finger [40].
• The thumb ray is more mobile, shorter, and more proximal than the other rays [40].
• The thumb ray continues the external column of the carpus formed by the scaphoid and trapezium [40].
• The trapezium is angled out in front of the carpal plane so that the first metacarpal makes an angle of about 45 degrees with the second metacarpal in the sagittal plane [40].
• The first metacarpal makes an angle of about 45 degrees with the second metacarpal in the sagittal plane [40].

Spatial Orientation and Axes¶

• The skeleton of the hand presents a longitudinal and transverse concavity, giving it the shape of a cup with a palmar concavity when the thumb is placed next to the index finger [40].
• When the thumb spreads to grasp an object, the cup becomes a gutter whose major oblique axis follows the thumb crease [40].
• The transverse axis of the palm corresponds to the metacarpophalangeal articulations [40].
• The transverse axis of the palm is not perpendicular to the longitudinal axis represented by the median ray [40].
• The transverse axis is oblique, more distal at the metacarpophalangeal joint of the index finger and more proximal at the fifth metacarpophalangeal joint [40].
• The transverse axis forms an acute angle of approximately 75 degrees with the longitudinal axis [40].
• The axes of flexion are arranged so that flexion of all the metacarpophalangeal and proximal interphalangeal joints causes the fingers to converge toward the scaphoid [39].
• The convergence of the palmar digits toward the scaphoid tubercle results from the orientation of their distal segments in flexion [40].
• The more ulnar the digit, the more obliquely it must deviate as it approaches the palm [40].
• Only the index ray flexes in a sagittal plane [40].
• The more ulnar the digit, the more obliquely it flexes toward the median axis [40].

Growth Plates and Palpable Landmarks¶

• The epiphyseal plates are located at the proximal ends of the phalanges and the first metacarpal [40].
• The epiphyseal plates are located at the distal ends of the other metacarpals [40].
• The third metacarpal is the axis of the hand and a landmark of wrist movements [39].
• The styloid process projects from the base of the third metacarpal and marks the line of the carpometacarpal joints [39].
• The metacarpophalangeal joints lie approximately on a transverse line that begins in the distal palmar crease on the ulnar side and runs into the proximal crease on the radial border [39].
• The proximal part of the proximal phalanx is embedded in the soft tissues of the web space [39].

Thumb MCP Joint Anatomy¶

• The ulnar collateral ligament has proper and accessory phalangeal attachments at the base of the proximal phalanx [9].
• The ulnar collateral ligament fossa is located on the metacarpal head [9].

Ligaments and Joint Capsule¶

General Fibrous Skeleton and Stability¶

• The fibrous skeleton provides support by uniting bone segments and stabilizing the transverse and longitudinal arches of the hand [28].
• Stabilization of each of the five rays requires three supports per joint: two collateral ligaments and one volar plate [28].
• The sagittal bands of the common extensor and the check rein ligaments of the volar plates provide restraint to the digit segments [19].
• The fibrous skeleton maintains zones of condensation under tension from a balance of forces exerted in different directions during active hand utilization [19].
• The deep dorsal aponeurosis inserts on the four ulnar metacarpals and forms a posterior intermetacarpal ligament [28].

Metacarpophalangeal (MP) Joint¶

• The MP joint capsule extends from the metacarpal neck to the base of the proximal phalanx [27].
• The dorsal aspect of the MP joint capsule is composed of areolar tissue and reinforced by the loose insertion of the common extensor tendon [27].
• The volar plate of the MP joint is continuous laterally with the deep transverse metacarpal (intervolar plate) ligaments [27].
• The MP volar plate consists of a thick fibrocartilaginous distal portion and a thin membranous proximal portion [27].
• The MP volar plate lacks strong proximal checkrein ligaments comparable to those found at the PIP joint [27].
• Lateral reinforcement of the MP volar plate is provided by collateral and intervolar plate ligaments that insert into its lateral margins [27].
• The MP collateral ligaments are more taut in flexion than in extension due to the cam effect created by the nonspherical shape of the metacarpal head [27].
• The metacarpal head has a longer dorsovolar axis than proximodistal axis, contributing to the cam effect on collateral ligaments [27].
• Broader and more stable articular contact between the metacarpal head and proximal phalanx base occurs beyond 70 degrees of flexion [27].
• The MP joint is stable laterally in full flexion but allows some abduction and adduction in full extension [27].
• The fibrous nucleus (force nucleus) at the palmar aspect of the MP joint is formed by the convergence of the transverse interglenoid ligament, volar plate, sagittal bands, fibrous flexor tendon sheath, and lateral accessory metacarpoglenoid ligaments [19].
• Destruction or displacement of the MP fibrous complex disturbs force balance, flattens the transverse arch, and compromises finger function [19].
• The MP volar plate collapses from one-third to one-half of its length in full extension when moving to full flexion [33].
• The pocket behind the MP volar plate is smaller than at the PIP joint, resulting in the absence of checkreins [33].

Proximal Interphalangeal (PIP) Joint¶

• The PIP volar plate has a thick, resistant structure with a firm distal insertion on the anterior aspect of the base of the phalanx [28].
• The proximal insertion of the PIP volar plate is supple and thin to allow flexion-extension movement [28].
• The thickness of the volar plate increases the distance between flexor tendons and the joint axis, improving flexor efficiency [28].
• The main function of the volar plate reinforcement is to prevent hyperextension [28].
• The PIP volar plate limits extension more than other digital joints due to two firm lateral check attachments proximally [28].
• The two proximal attachments of the PIP volar plate insert into the proximal phalanx on each side of the flexor tendons and blend with their fibrous sheath [28].
• Resistance to rupture is three times greater at the PIP joint than at the MP joint [28].
• The resistance to rupture for the PIP joint is between 16 and 21 kg [28].
• The resistance to rupture for the MP joint is between 5 and 8 kg [28].
• The PIP volar plate slides proximally and distally, with substantial excursion between flexion and extension and minimal collapse of the plate itself [33].
• Limitation or fixation of the proximal volar plate, such as through the development of checkreins, produces significant restriction in PIP joint extension [33].
• At the PIP joint, Cleland’s ligaments attach to the skin, and oblique retinacular ligaments cross the joint obliquely [19].

Distal Interphalangeal (DIP) Joint¶

• The DIP joint capsule is reinforced laterally by collateral ligaments that insert into the sides of the head of the middle phalanx and run distally and volarly to insert into the volar lateral tubercle of the distal phalanx [33].
• Accessory ligaments at the DIP joint are more volar and extend from the sides of the middle phalanx head to the sides of the volar plate [33].
• The DIP volar plate serves as an accessory insertion point for the flexor digitorum profundus [33].
• The DIP volar plate attaches proximally to the neck of the middle phalanx but lacks lateral volar extensions [33].
• The DIP volar plate lacks checkrein ligaments, allowing for hyperextension [33].
• The dorsal aspect of the DIP joint has no reinforcing ligament, but the terminal extensor mechanism attaches from one collateral ligament to the other and blends into capsular fibers and periosteum [33].

Thumb Carpometacarpal (CMC) Joint¶

• The volar oblique ligament is a short reflection of the transverse carpal ligament that maintains the thumb metacarpal within the biconcave contour of the trapezium [37].
• Complete rupture of the thumb CMC joint ligaments permits dorsal dislocation of the thumb metacarpal [37].
• Partial rupture of the thumb CMC joint ligaments permits varying degrees of displacement, with greater tears causing more obvious displacement [37].
• Less severe thumb CMC ligament tears are difficult to diagnose because joint contours maintain gross alignment of the metacarpal base within the trapezium concavity [37].

Operative Reconstruction of Ulnar Collateral Ligament (UCL)¶

• A general criterion of 6 weeks is used to distinguish between acute and chronic UCL injuries [18].
• In chronic UCL injuries, the proximal stump is typically shortened, retracted, and surrounded by fibrous tissue [18].
• Primary repair of chronic UCL injuries is not recommended if the local tissue is of questionable length or quality, which is typical in surgery performed more than 6 to 12 weeks after injury [18].
• Late reconstruction of an incompetent UCL involves replacing the static restraint with a free tendon graft anchored in the medullary canals of the metacarpal and proximal phalanx [18].
• For UCL reconstruction, a unicortical 2.5-mm hole is made in the proximal phalanx 3 mm from the joint and 3 mm from the volar cortex [18].
• For UCL reconstruction, a unicortical hole is made in the metacarpal at the anatomic UCL origin, approximately 7 mm from the joint line and 5 mm from the dorsal cortex [18].
• A Kirschner wire is driven across the joint after reduction in 30 degrees of flexion to correct positioning in coronal and sagittal planes [18].
• Palmaris longus tendon is the preferred graft for UCL reconstruction, with alternatives including EIP, FCR, ECRB, EDM, long toe extensor, or abductor pollicis longus [18].
• In Jobe four-limb reconstruction, two 2.75 mm holes are made in the proximal phalanx with a bone bridge of 3 to 4 mm between them [9].
• In Jobe four-limb reconstruction, two 3-mm holes are made in the metacarpal head, with the most distal hole in the UCL fossa and another approximately 5 mm more proximally [9].
• The Jobe four-limb reconstruction is protected for 4 to 6 weeks postoperatively before Kirschner wire and splint removal [9].

Muscles and Tendons¶

Gliding Mechanisms and Sheaths¶

• The dorsal integument must be supple, elastic, and malleable to allow metacarpophalangeal joint flexion [2].
• Vessels and nerves are surrounded by loose fibroadipose connective tissue to adapt to differences in length [2].
• In unrestricted areas with a straight tendon trajectory, tendons are surrounded by paratenon and areolar connective tissue [2].
• In narrow crowded areas, the gliding mechanism is assured by the synovial sheath [2].
• Fibrous sheaths surround synovial sheaths at specific sites to keep the tendon close to the skeleton [2].
• The fibrous sheath assumes the role of a pulley when the tendon changes direction [2].
• The gliding mechanism represented by synovial sheaths is more developed on the palmar aspect than the dorsal aspect [2].
• There are three digitopalmar synovial sheaths for the flexor tendons of the index, long, and ring fingers [2].
• The superficial and deep flexor tendons of the digits glide over each other [2].
• Each synovial sheath has a visceral and parietal component separated by a potential synovial cavity containing a thin layer of synovial fluid [2].
• The synovial fluid constitutes the basic gliding and nutritional mechanism for tendons [2].

Extrinsic Extensor Muscles¶

• The extrinsic extensor apparatus of the fingers is formed by the extensor communis and extensor proprius of the index and little fingers [8].
• Extensor tendons are thin superficial structures that tend rapidly to become adherent to underlying bones and joints when damaged [8].
• The excursion of extensor tendons is considerably less than that of flexors, making it more difficult to compensate for a loss of length [8].
• The extensor communis and extensor proprius tendons pass under the dorsal retinaculum on the back of the wrist before diverging toward the fingers [8].
• On the dorsum of the hand, extensor communis tendons are interconnected by juncturae tendinum [8].
• Interruption of an extensor tendon proximally may be masked by the effect of the juncturae tendinum [8].
• The extensor tendon splits into three parts halfway down the proximal phalanx: an extensor central band and two extensor lateral bands [8].
• The most proximal insertion of the extrinsic extensor system is at the level of the interglenoid ligament provided by the sagittal bands [8].
• The most distal insertion of the extrinsic extensor system is at the level of the base of the distal phalanx [8].
• The insertion of the extensor tendon at the base of the proximal phalanx is inconstant [8].
• The extensor carpi radialis brevis inserts into the base of the middle metacarpal and provides balanced wrist dorsiflexion [7].
• The third extensor compartment contains the extensor pollicis longus [7].
• The extensor pollicis longus turns abruptly radialward about Lister tubercle, a dorsal prominence on the distal radius [7].
• The fifth extensor compartment contains the extensor digiti quinti [7].
• The extensor indicis proprius inserts on the index finger ulnar to the extensor digitorum communis [7].
• The extensor digitorum communis inserts on the index, middle, ring, and in some cases little fingers [7].
• The extensor digiti quinti tendon inserts on the little finger ulnar to the extensor digitorum communis insertion [7].
• The extensor carpi ulnaris tendon runs through the sixth compartment and inserts at the base of the little finger metacarpal [7].
• The extensor carpi ulnaris provides wrist extension and ulnar deviation [7].
• The extensor indicis proprius tendon possesses the most distal muscle belly of any of the digital extensor tendons at the wrist level [7].
• Digital extensor tendons are stabilized over the mid-line of the metacarpophalangeal joint by their attachment to sagittal band fibers [7].
• Sagittal band fibers insert onto the volar proximal phalanx and onto the lateral borders of the volar plate [7].
• Sagittal band fibers form a sling that allows proximal extrinsic extensor tension to be transmitted to the proximal phalanx, permitting metacarpophalangeal joint extension without a tendinous insertion onto the proximal phalanx [7].
• Sagittal bands keep the extrinsic extensor tendon balanced over the prominence of the metacarpal head, giving it the greatest mechanical efficiency [7].

Extrinsic Flexor Muscles¶

• The flexor digitorum profundus originates from the proximal ulna and the interosseous membrane [11].
• In the forearm, the flexor digitorum profundus divides into a radial component supplying the index finger and an ulnar component supplying the middle, ring, and little fingers [11].
• The flexor digitorum profundus and flexor pollicis longus muscles form the deep compartment of the volar forearm [11].
• As the flexor digitorum profundus and flexor pollicis longus tendons travel through the carpal tunnel, they occupy the floor of the carpal tunnel [11].
• The tenosynovial sheath of the flexor pollicis longus is continuous with the radial bursa [11].
• The tenosynovial sheath to the little finger is continuous with the ulnar digital bursa [11].
• In some patients, the radial and ulnar bursae communicate, allowing a horseshoe abscess to spread between the thumb and little finger if infection occurs in the flexor tendon sheath of either digit [11].
• The lumbricals originate from the radial side of the index, middle, ring, and little fingers in the palm [11].
• The profundus tendon passes through the bifurcation of the flexor digitorum superficialis before inserting into the proximal palmar base of the distal phalanx [11].
• The innervation of the flexor digitorum profundus of the index and middle fingers is through the anterior interosseous branch of the median nerve [11].
• The profundus of the ring and little fingers is innervated by the ulnar nerve [11].
• The flexor digitorum profundus provides digital flexion at both the proximal and distal interphalangeal joints [11].
• The flexor digitorum superficialis has two heads: a radial head originating from the proximal shaft of the radius, and a humeral ulnar head originating from the medial humeral epicondyle and coronoid process of the ulna [11].
• Each digit has a corresponding independent superficialis muscle [11].
• As the superficialis tendons pass through the carpal tunnel, the tendons of the middle and ring fingers are more superficial and central than those of the index and little fingers [11].
• In the proximal aspect of the finger, the flexor digitorum superficialis tendon bifurcates around the flexor digitorum profundus at the beginning of the A2 pulley [11].
• The flexor digitorum superficialis tendon slips reunite distally at the Camper chiasm, with approximately half of the fibers staying on the ipsilateral side and half crossing to the contralateral side of the finger [11].
• The flexor digitorum superficialis tendon inserts via radial and ulnar slips into the proximal metaphysis of the middle phalanx [11].
• The entire flexor digitorum superficialis muscle receives innervation from the median nerve [11].
• The primary function of the flexor digitorum superficialis is digital flexion at the proximal interphalangeal joint [11].
• The flexor pollicis longus originates from two heads: a radial head from the proximal radius and interosseous membrane, and an accessory head from the coronoid process of the ulna and medial epicondyle of the humerus [11].
• In the palm, the flexor pollicis longus tendon transverses between the abductor pollicis brevis and the flexor pollicis brevis [11].
• The flexor pollicis longus inserts into the proximal base of the thumb distal phalanx [11].
• The flexor pollicis longus is innervated by the anterior interosseous branch of the median nerve [11].
• The flexor pollicis longus flexes both the interphalangeal and metacarpophalangeal joints of the thumb [11].
• As the flexor tendons pass distal to the metacarpal neck, they enter the fibroosseous tunnel, or digital flexor sheath [11].
• The fibroosseous tunnel extends distally to the proximal aspect of the distal phalanx [11].
• The tendinous sheath consists of annular pulleys, which provide mechanical stability, and cruciate pulleys, which provide flexibility [11].
• The first, third, and fifth annular pulleys (A1, A3, and A5) are located over the metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints, respectively [11].
• The second and fourth pulleys (A2 and A4) are situated over the middle portion of the proximal and middle phalanges [11].
• The A2 and A4 pulleys are the most essential in maintaining the mechanical advantage of the flexor tendons [11].
• The tenosynovium that lines the fibroosseous tunnel supplies both nutrition and lubrication to the poorly vascularized flexor tendons [11].
• Proximal to the sheath, the tendons are well vascularized by the peritenon [11].
• Within the sheath, tendon vascularity is supplied via the vincula system: the vinculum longus and brevis [11].
• Following injury, flexor tendon healing occurs through both extrinsic and intrinsic mechanisms [11].
• Extrinsic tendon healing occurs via cells brought to the site of repair by ingrowth of capillaries and fibroblasts, followed by formation of adhesions at the repair site [11].
• Intrinsic healing occurs from tenocyte within the tendon [11].
• The goal of flexor tendon repair and postoperative care is to encourage both intrinsic and extrinsic healing without the formation of thick adhesions, which would limit tendon excursion and result in restricted motion of the finger [11].
• The flexor tendons of the fingers cross five well-defined regions from proximal to distal: the wrist, the carpal tunnel, the palm, the common digital canal, and the distal segment of the tunnel [16].
• The tendon of the flexor pollicis longus crosses five regions: the wrist, the carpal tunnel, the palmar region, the digital canal, and the distal segment [16].
• The digital flexor tendons pass through the carpal tunnel before they fan out in the palm toward their respective digits [16].
• The flexor superficialis tendon inserts on the middle phalanx and the flexor profundus tendon inserts on the distal phalanx [16].
• In each digit, the superficial and deep flexor tendons are surrounded by their synovial sheaths for gliding and kept against the phalanges by their fibrous sheaths [16].
• The fibrous sheath plays an essential mechanical role in preventing divergence of the tendons from the axis of the digit in both anteroposterior and lateral directions [16].
• The digital flexor tendon sheath is formed by five annular pulleys and three cruciform bands [16].
• The second and fourth annular pulleys are the most important for function [16].
• At the level of the digital sheaths, the flexor tendons have a precarious blood supply through a vinculum longum at the chiasma level, common for both tendons superficial and profundus [16].
• The vincula brevis supply blood to the profundus tendon [16].
• Lundborg demonstrated the presence of an "avascular segment" of the flexor superficialis just proximal to the chiasma [16].
• Lundborg demonstrated two "avascular segments" of the flexor profundus proximal and distal to the vinculum longum [16].

Intrinsic Muscles¶

• The superficial head of the dorsal interosseous muscle arises most dorsally from the shaft of the contiguous metacarpals and is inserted deeply by a medial tendon onto the lateral tubercle of the base of the proximal phalanx [4].
• The superficial head has no direct effect on the middle or distal phalanges [4].

• At the level of the middle of the proximal phalanx, transverse fibers arch dorsally from each lateral band to join each other over the dorsum of the finger, flexing the proximal phalanx [4].¶

Neurovascular Anatomy¶

General Principles¶

• Recent developments in hand surgery are based on a better understanding of the dynamic anatomy and function of the hand, emphasizing functional rather than static anatomy [1].
• The hand moves within a large volume of space with the shoulder as the apex, reaching any part of the body fairly easily due to the mobility of the shoulder, elbow, and wrist operating in different planes [1].
• Movements of the clavicle amplify those of the shoulder [1].
• The arm assures projection of the limb from the trunk [1].
• The elbow, through flexion–extension movements, brings the hand closer to or moves it away from the body [1].
• The hand must be studied as an integral part of the upper extremity [1].
• The posterior or dorsal aspect of the hand is convex and aesthetically important as it is usually visible [1].
• The anterior, palmar or volar aspect of the hand is concave and is the functional surface, usually hidden [1].
• Digits converge in closing (flex and adduct) and diverge in opening (extend and abduct) [1].

Arterial Supply: Thumb¶

• Before starting any intervention on the thumb, it is necessary to understand clearly the anatomical layout of the arteries, especially for island flaps or microsurgical interventions [3].
• Although no constant arteries exist in anatomy, concepts of segmental division can make research or dissection of vessels easier and less traumatic [3].
• The layout of thumb arteries is the result of innumerable variations regarding origin, transit, connections, and size [3].
• According to the classical layout, the “princeps pollicis” artery is the terminal branch of the radial artery [3].
• The “princeps pollicis” artery crosses the first intermetacarpal space, runs along the ulnar side of the first metacarpal bone and along the volar surface of the adductor muscle [3].
• The “princeps pollicis” artery emerges onto the subcutaneous palmar tissue at the level of the cutaneous flexion crease of the metacarpophalangeal joint [3].
• At the metacarpophalangeal joint level, the “princeps pollicis” artery divides into two terminal rami, the collateral palmar arteries of the thumb [3].
• The collateral palmar arteries of the thumb run along the digital tunnel symmetrically and are of equal caliber, heading distally to unite in the pulp arcade [3].
• During transit in the digital tunnel, the collateral palmar arteries break off into numerous collateral branches, either cutaneous, articular, or osseous [3].
• Vessels originating from the deep flexor tendon arcade and a similar, more narrow and inconstant arcade at the distal tendon insertion enter the “vincula” and irrigate the flexor tendon [3].
• In the first segment (between opposition crease and metacarpophalangeal flexion crease), it is rare to find arteries of surgical interest on the volar surface of the thumb [3].
• In the first segment, arteries of significant size can sometimes be found emerging from the superficial arcade or the commissural artery, but the main artery is located deeply and is more easily accessible from the dorsal surface [3].
• The ulnar collateral artery in the second segment is sometimes absent, in which case it is replaced by the dorsal artery [3].
• The ulnar collateral artery in the second segment is more often easier to dissect than the radial collateral artery and its size enables a more reliable microanastomosis [3].
• At the level of the neck of the first phalanx, a subtendinous anastomosis acts as a “moderator” between the two collateral arteries [3].
• If the palmar ulnar collateral artery is absent, the dorsal artery takes its place by means of a branch through the subtendinous arcade [3].
• In the pulp segment, the arteries cross over and convert into the ends of the digital nerves at the level of the median axis [3].
• The dorsal arteries of the thumb have not yet been the subject of an in-depth anatomical study [3].
• Classical anatomical literature describes dorsal thumb arteries as stemming from terminal branches of the radial artery at the level of the anatomical snuff-box and heading distally to end as periosteal and bony skin rami at first phalanx level [3].
• The classical description of dorsal thumb arteries only partially corresponds to reality, as those arteries are intended for vascularization of the posterior surface of the first metacarpal and metacarpophalangeal joint [3].
• The posterior area of the thumb is vascularized by two arteries which originate from the palmar arteries (princeps, commissural, or anastomoses of the superficial arcade) at the level of the first metacarpal [3].
• These dorsal arteries run laterally along the metacarpophalangeal joint, continue obliquely from volar to dorsal, and head in a distal direction remaining on the side of the two distal phalanges [3].
• Dorsal thumb arteries are joined by three arcades: one inconstant arcade located under the extensor tendon at the level of the neck of the first phalanx, the arcade of the nail matrix, and the arcade of the nailbed [3].
• The ulnar dorso-collateral artery generally stems from the “princeps pollicis” onto the medial border of the neck of the first metacarpal and heads distally remaining on the lateral surface of the finger [3].

Cutaneous Circulation and Flaps¶

• The cutaneous circulation of the hand has special anatomical and physiological features related to its distal situation far from the cardiac impulse and constant exposure to thermal and postural variation [26].
• The general pattern of cutaneous circulation involves muscular arteries running into arterioles forming a plexus superficial to the aponeurosis, a dermal plexus, and a subpapillary plexus, with return through venous loops [26].
• Arterial supply to skin is classified into three groups: longitudinal cutaneous arteries, septal arteries, and myocutaneous arteries [26].
• Longitudinal cutaneous arteries run part of their course through the subcutaneous tissues [26].
• Septal arteries arise from the main artery and pass through the deep fascia to form a subdermal vascular plexus [26].
• Myocutaneous arteries arise from intramuscular arteries and emerge from the muscle belly to supply an area of overlying skin [26].
• Axial pattern flaps are based on longitudinal cutaneous arteries [26].
• Fascio-cutaneous flaps are based on septal arteries and require inclusion of the main vascular pedicle, deep fascia, and intermuscular septum [26].
• Myocutaneous flaps are based on the vascular pedicle of the muscle [26].
• The dorsal aspect of the first webspace is supplied by two arteries: the deep dorsal intermetacarpal artery and the superficial dorsal intermetacarpal artery [26].
• The deep dorsal intermetacarpal artery runs along the diaphysis of the second metacarpal and vascularizes the base of this bone [26].
• The superficial dorsal intermetacarpal artery supplies the skin overlying the proximal phalanx and the metacarpophalangeal joint of the index finger [26].
• The skin supplied by the superficial dorsal intermetacarpal artery can be raised with its artery, known as Foucher’s Kite flaps [26].
• The deep and superficial dorsal intermetacarpal arteries have anastomoses at the metacarpal head, providing reversed flow vascularization to a bone graft taken on the second metacarpal [26].
• Deep anastomoses between other dorsal intermetacarpal arteries and the proximal arterial system allow dorsal intermetacarpal flaps and dorsal webspace flaps [26].
• In the fingers, blood supply comes predominantly from the two palmar collateral digital arteries [26].
• Palmar collateral digital arteries give cutaneous branches for both palmar and dorsal digital skin [26].
• Palmar collateral digital arteries present digital anastomoses arcades in the pulp and in the nail matrix [26].
• Palmar collateral digital arteries also have anastomoses in the digital part of the proximal and middle phalanx, under the flexor tendons [26].
• The vascular configuration of fingers allows heterodigital island flaps, direct homodigital island flaps, and reversed arterial flow island flaps [26].
• In the thumb, anatomical variations of the vascular system are frequent [26].
• The most constant artery on the dorsal aspect of the thumb is the ulnar collateral artery [26].
• The rich vascular supply of the skin of the hand has an important thermoregulatory function [26].
• The blood circuit contains a system of shunts between arterioles, meta-arterioles, and venules, as well as direct arteriovenous anastomoses known as Sucquet-Hoyer anastomoses [26].
• Sucquet-Hoyer anastomoses consist of spiral vessels that run from the arterioles to the venules and are found mostly in the palm, near the roots of the nails, and in the pulps [26].

Clinical Examination of Circulation¶

• A careful study of the circulation is essential both preoperatively and postoperatively, even if the patient has no specific vascular disease [29].
• Recognition of vascular disease is important for appreciating tolerance to a tourniquet (induced ischemia) and assessing the likelihood of postoperative edema [29].
• Vascular disease necessitates a more conservative attitude toward remaining arterial trunks, especially after severe injuries [29].
• The examiner notes whether the skin is pale, red, or cyanosed [29].
• Distal arteriolar flow is measured by the time taken for color to return to the nail bed after pressure [29].
• The radial pulse is classically taken at the radial wrist groove [29].
• The ulnar pulse is usually palpable at the entry to Guyon’s canal [29].
• The radial artery can be felt as it exits from the anatomical snuffbox at the proximal part of the dorsal aspect of the first web space and should remain accessible after a crush injury [29].
• Collateral digital arteries can be felt at the base of the finger, just anterior to the dorsopalmar cutaneous line, in patients with supple skin and a strong pulse [29].
• The Allen test aids in deciding whether the radial or ulnar artery is responsible for the major arterial supply to the hand [29].
• Predominance of the radial artery is common [29].
• The digital Allen test is performed in a manner similar to that at the wrist level [29].
• Venous return is more difficult to measure than arterial flow [29].
• Localized cyanosis is a sign of venous stasis, but edema is the most common feature of abnormal venous return [29].
• Edema is most readily demonstrable on the dorsum of the hand [29].
• Severe dorsal edema is obvious, while less marked edema rounds off the bony contours of the metacarpals [29].
• Minimal dorsal edema causes the disappearance of the shallow transverse furrows that are normally present in dorsal skin [29].
• Edema of the palmar tissues is more easily overlooked than dorsal edema [29].
• Palmar edema becomes obvious when abundant enough to fill the concavity of the palm between the thenar and hypothenar eminences [29].
• Slight infiltration of palmar tissues is just palpable and suggested by limitation of flexion of the fingers [29].

Vascular Assessment Techniques¶

• Obtaining a medical history with particular attention to documented diabetes and/or collagen vascular disease is very important in evaluating vascular disorders [20].
• A habit of smoking will have an impact on vascular health [20].
• Medical management of diseases with pharmacologic agents may mitigate symptoms, particularly in patients with Raynaud appearance [20].
• Physical examination should pay close attention to the appearance of the hands and color of the fingers, looking for evidence of ischemia, gangrene, or ulceration [20].
• The warmth of the fingers is important in physical examination [20].
• Sensation plays a role in examination, with potential for sympathetic overactivity in the presence of nerve compression [20].
• Pulses at the elbow and wrist should be felt [20].
• Doppler ultrasound plays a very important role in the examination of the patient with a vascular disorder [20].
• An Allen test can be done, but performing a similar exam with the pencil Doppler may yield much more information [20].
• With pencil Doppler, the arch is located and the radial and ulnar arteries are compressed sequentially at the wrist [20].
• The Doppler can be moved over the arch to follow the signal, listening for a change in character or flow [20].
• This technique can almost always diagnose the site of arterial occlusion if performed carefully [20].
• An arterial signal should be heard with the Doppler placed on the pulp of the finger; if it is not, there is a significant problem with flow to that finger [20].
• The presence of an audible Doppler arterial signal in one of the wrist’s vessels is not an indication of adequate nutritional flow to the hand [20].
• Computed tomography angiography (CTA) or arteriography is preferred for planning surgical procedures, with arteriography used if fine detail of the hand’s vessels is needed [20].
• Magnetic resonance angiography (MRA) detail is often inadequate in terms of knowing exactly where and how significant the problem is [20].
• Digital subtraction angiography (DSA) remains the gold standard for vascular imaging [20].
• Surgeons must view the vascular studies themselves because the radiologist or vascular specialist may or may not see the lesion [20].
• A familiarity with the upper extremity’s normal and variant anatomy is essential for evaluating vascular problems [20].
• Color-flow ultrasonography can show real-time flow and be used to evaluate an anastomosis, but is of primary use in the venous system [20].
• Cold stress testing evaluates vasospasm by measuring the vascular system’s ability to recover from exposure to cold [20].
• In cold stress testing, digital temperature is measured at baseline and the hand is placed in cold water (5° to 8°C) for 5 minutes [20].
• Thermistor probes or laser Doppler are used to measure the time required for digital rewarming to baseline [20].
• A prolonged rewarming response is often seen in women and can be diagnostic of Raynaud’s [20].
• Smokers often have a delayed rewarming response [20].
• The

Biomechanics and Function¶

General Architecture and Kinematics¶

• The hand functions as both an organ for obtaining information and an organ of execution [1].
• The hand functions efficiently only if the proximal joints of the upper limb are stable yet mobile [1].
• The combined movements of the wrist and forearm place the hand in a position for grasping [1].
• Forearm rotation (pronation–supination) plays an important role in bringing food to the mouth [1].
• The hand contains approximately the same number of tendons activated by forearm muscles as it has intrinsic muscles [1].
• The dorsal aspect of the hand is convex, while the palmar or volar aspect is concave [1].
• The palmar surface is the functional surface of the hand, while the dorsal surface is aesthetically important [1].
• The thumb has a more proximal and lateral position than the fingers, allowing movement inward and outward from the palm [1].
• The web space of the thumb is the largest and deepest web space in the hand [1].

Tendon Mechanics and Excursion¶

• Mechanical advantage is defined as the moment arm of one force acting at a joint divided by the moment arm of a second force acting in the same plane around that joint [6].
• The amplitude of muscle contraction is about one-third the length of the muscle’s resting fleshy belly [6].
• Amplitude of tendon excursion increases if muscle fibers are longer and if the angle they make with the tendon is acute [6].
• The extensor digitorum has an amplitude of approximately 4 mm at the distal interphalangeal joint [6].
• The extensor digitorum has an amplitude of approximately 8 mm at the proximal interphalangeal joint [6].
• The extensor digitorum has an amplitude of approximately 15 mm at the metacarpophalangeal joint [6].
• The extensor digitorum has an amplitude of approximately 45 mm at the wrist [6].
• The flexor digitorum profundus has an amplitude of gliding of 5 mm at the distal interphalangeal joint [6].
• The flexor digitorum superficialis has an amplitude of gliding of 16 mm at the proximal interphalangeal joint [6].
• The flexor digitorum profundus has an amplitude of gliding of 17 mm at the proximal interphalangeal joint [6].
• The flexor digitorum profundus has an amplitude of gliding of 26 mm at the metacarpophalangeal joint [6].
• The flexor digitorum superficialis has an amplitude of gliding of 23 mm at the metacarpophalangeal joint [6].
• The flexor digitorum profundus has an amplitude of gliding of 46 mm at the carpal canal [6].
• The flexor digitorum superficialis has an amplitude of gliding of 38 mm at the carpal canal [6].
• The flexor digitorum profundus has an amplitude of gliding of 88 mm in the distal forearm [6].
• The flexor digitorum superficialis has an amplitude of gliding of 85 mm in the distal forearm [6].
• The motor muscles of the wrist have a tendinous excursion of approximately 3.5 cm [6].
• The common extensor of the fingers and the long flexor of the thumb have an excursion of approximately 4–5 cm [6].
• The tendons of the long flexors of the fingers have the greatest excursion of all the muscles in the hand [6].
• Movements are determined by the modulation of forces between antagonists, a concept known as "synergistic antagonism" [6].

Opposition Mechanics¶

• Thumb opposition involves the ability to oppose the four fingers during the "long range" of the first metacarpal while keeping the first web space open [32].
• Thumb opposition involves the ability to oppose the four fingers during the short range of the first metacarpal with the first commissure closed [32].
• Rotation of the pulp of the thumb determines the efficiency of a pulp grip [32].
• Pulp rotation may reach 90 to 120 degrees between full extension/abduction and opposition with the little finger [32].
• It is normally possible to place the pulps of the thumb and little finger in the same plane at the end of the movement of opposition [32].

Global Hand Movements¶

• The movements involved in opening the hand determine the maximal size of the object that can be grasped [34].
• Grasping cylindrical objects up to 11 cm in diameter usually represents the limit of cylindrical grasp [34].
• One flexed finger is sufficient to prevent the hand from grasping a sizeable object [34].
• Passive opening of the first web space depends on the absence of contracture of the skin and thumb adductor muscle [34].
• Passive opening of the first web space depends on the mobility of the carpometacarpal and metacarpophalangeal joints [34].
• Closing of the fingers involves a sequence wherein the metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints are flexed in turn [34].
• If interphalangeal joints flex before the metacarpophalangeal joints, grasping of a large object becomes impossible [34].
• The amplitude of finger flexion determines the size of the smallest object that closed fingers can hold safely [34].
• In the normal hand, the terminal part of the four digital pulps can be actively brought into contact with the palm along a line joining the ulnar end of the distal palmar crease to the radial end of the proximal palmar crease [34].
• If fingers contact the palm proximal to this landmark, it implies a flexion deficit in the interphalangeal joints compensated by increased metacarpophalangeal flexion [34].
• If fingers contact the palm distal to this landmark, it implies isolated metacarpophalangeal stiffness compensated by interphalangeal hyperflexion [34].

Functional Assessment¶

• Assessment of hand function is useful to detect deterioration and to allow objective assessment of surgical outcomes [5].
• Traditional hand function assessment using activities of daily living is time-consuming and highly subjective [5].
• Using the patient’s opposite hand as a control minimizes the influence of anatomical and psychological factors in objective assessment [5].
• There is an approximately 5–10 per cent difference between dominant and non-dominant hands [5].
• The Jamar grip strength meter measures only a single static reading which may bear little relationship to actual function [5].
• Patients with rheumatoid arthritis of the wrist cannot effectively use the Jamar grip strength meter [5].
• Quantitative objective measurement allows for the assessment of force decay with time [5].
• Quantitative objective measurement allows for the determination of the threshold value below which a specific task, such as turning a key, cannot be performed [5].

Pathological Biomechanics¶

• Swan-neck deformity is characterized by hyperextension of the proximal interphalangeal joint and flexion of the distal interphalangeal joint [36].
• Synovitis of the proximal interphalangeal joint in rheumatoid arthritis may distend the joint and render the volar plate ineffective in preventing hyperextension [36].
• Overly forceful intrinsic muscle contraction transmits an abnormally high force through the central slip, hyperextending the proximal interphalangeal joint [36].
• When the proximal interphalangeal joint is hyperextended, the dorsal hood apparatus is relatively ineffective in extending the distal interphalangeal joint [36].
• The relative ineffectiveness of the dorsal hood apparatus allows the distal interphalangeal joint to fall into flexion [36].

Common Sites of Injury¶

• The upper extremity is the most common anatomic area burned, being involved in up to 89% of burns [22].
• The two main reasons for frequent upper extremity burn involvement are the protective reflex used to guard the face and the fact that the hand is often exposed without protection [22].
• The dorsum of the hand is predominantly involved in flame or explosion injuries [22].
• Injuries to the palm are more frequently found with chemical exposure, friction burns, or high-voltage injuries [22].
• Scalds and contact burns are the major cause of pediatric hand burns [22].
• Mangling injuries of the hand and upper extremity involve multiple critical structures of the fingers, hand, arm, or any combination of these [13].
• Mangling injuries generally include all or nearly all of the major functional systems of an extremity, including skin and soft tissue, vascular, nerve, muscle and tendon, bone, and joint [13].
• The skin is especially thin over the proximal interphalangeal (PIP) joints, where the extensor tendons are at risk [22].
• Attenuation or rupture of the central slip with PIP joint exposure is one of the most frequently encountered complications after deep dorsal burns [22].
• The dorsal skin of the hand is thin and very flexible and lies on a rather thin subcutaneous layer of fatty tissue [22].
• The palmar skin has a thick, subcutaneous fatty layer with a honeycomb-like structure that provides shock-absorbing properties and grip stability [22].
• In the finger, the Cleland ligament is located dorsal to the neurovascular bundle and the Grayson ligament is located palmar to the neurovascular bundle [22].
• The hand contains 38 muscles working in a coordinated fashion to control its motion [35].
• In ulnar nerve palsy, the loss of motor function in a low lesion primarily involves fine dexterity and grip strength [35].
• Ulnar nerve injury at the wrist is the most common cause of ulnar nerve palsy in the United Kingdom [35].
• The early signs of ischemic necrosis of the intrinsic muscles are hyperextension of the fingers at the metacarpophalangeal (MCP) joint with flexion of the interphalangeal joints [21].
• Scar contractures across the dorsum of the hand lead to the claw deformity, which is typical of neglected burns of the hand [21].
• Deep burns over the PIP joint frequently lead to disruption of the central extensor mechanism and development of the boutonnière deformity [21].

Surgical Anatomy¶

Skin Coverage Dimensions¶

• The skin required to cover the thumb distal to the metacarpophalangeal joint is approximately 9 cm wide and 8 cm long [10].
• The skin loss area for the thumb and first metacarpal is 13 cm wide and 12 cm long [10].
• The skin cover for both the palmar and dorsal surfaces of the hand is 12 cm by 10 cm [10].
• The skin covering each finger is 7 cm by 10 cm on both the palmar and dorsal aspects [10].
• Skin grafting or flaps for both sides of the hand and digits require a skin area of 20 cm by 20 cm [10].
• Skin grafting or flaps for one aspect of the forearm from wrist to elbow require skin of 30 cm by 15 cm [10].
• Skin grafting or flaps for both aspects of the forearm require skin of 30 cm by 30 cm [10].
• The skin for the volar surface of the forearm is 28 cm wide and 15 cm long [10].
• The skin for the dorsal surface of the forearm is 28 cm wide and 15 cm long [10].
• The skin for the entire volar and dorsal surface of the forearm is 30 cm wide and 30 cm long [10].

Nerve Anatomy and Repair¶

• The internal arrangement of the nerve in the palm and digits is usually oligofascicular [42].
• An intraneural polyfascicular or group arrangement is found in the median and ulnar nerves at the wrist [42].
• The outlook is better after repair of common digital and proper digital nerves due to their internal arrangement, pure sensory function, and short distance from the injury to the end organ [42].
• Incisions to expose the nerve should not cross flexion creases at right angles [42].
• Skin flaps should not be devascularized during nerve exposure incisions [42].
• Extensive mobilization of the nerve from its surrounding tissues within the digits, palm, and wrist is generally insufficient to cause harm [42].
• Magnification achieved by 2.5× to 4.5× magnifying loupes is usually sufficient for accurate repair in the palm and fingers [42].
• An operating microscope is more helpful for satisfactory anatomic repair in more proximal locations [42].
• The operating microscope may be extremely helpful in repair of the terminal branches of the proper digital nerves distal to the distal flexion crease of the finger [42].
• 8-0 and 9-0 monofilament nylon sutures are generally used in the forearm, wrist, and hand [42].
• 9-0 nylon suture has a more predictable failure via breakage with a failure threshold of 5% to 8% strain compared to 8-0 nylon [42].
• 8-0 nylon suture failed more often at higher strain and with suture pullout from the epineurium in a cadaveric median nerve model [42].
• Literature has not shown perineural repair to be superior to a simpler epineural repair [42].
• Epineural repair is pursued to limit trauma from suture bulk [42].

Metacarpal and Carpal Anatomy¶

• There is 15 to 30 degrees of mobility between the ring and small finger metacarpal bases and the hamate at the CMC joint [43].
• The ring finger and small metacarpal bases share a common articulation with the hamate [43].
• The base of the fifth metacarpal can slide radially if the entire fourth metacarpal is excised [43].
• The fourth metacarpal base lacks tendinous attachments, unlike the remaining metacarpals in the hand [43].
• The carpal bones are intraarticular [41].
• The onset of symptoms for isolated intraosseous carpal lesions is generally associated with synovitis and joint invasion [41].

Tumor Anatomy and Resection Boundaries¶

• Malignancies of the proximal palmar surface of the hand and volar aspect of the wrist often require amputation [41].
• Tumors arising on the dorsum may allow preservation of the hand if staging studies show the lesion has not penetrated into the palm [41].
• Excision margins must verify a safe plane of normal tissue for dorsal tumor preservation [41].
• Isolated intraosseous carpal lesions that have not invaded soft tissue are rare but can be excised locally [41].
• Below-elbow amputation or complete en bloc excision of the entire radiocarpal articulation and carpus is likely necessary for carpal lesions with joint invasion [41].
• Growths on the volar aspect of the distal part of the forearm must be widely excised with negative margins [41].
• If a tumor does not specifically involve the ulnar nerve and artery, it may be possible to save a portion of the hand and wrist along with the neurovascular bundle [41].
• Intracompartmental lesions within the distal radius or ulna can be treated by wide excision of the bone and arthrodesis or autograft replacement [41].
• Transosseous excision for intracompartmental lesions must include biopsy of the medullary canal from the retained segment or segments [41].
• Above- or below-elbow amputation may be required when tumors have invaded tissues or crossed compartments extensively [41].

References¶

[1] Exam Of The Hand Wrist 2Ed. INTRODUCTION.

[2] Exam Of The Hand Wrist 2Ed. 1.3 MOVEMENTS OF THE HAND AND WRIST > Gliding mechanisms.

[3] Exam Of The Hand Wrist 2Ed. Techniques of investigation of the arterial supply by J P Melki > Vascularization of the thumb > Palmar aspect.

[4] Green S Operative Hand Surgery. Interosseous and Hypothenar Muscles.

[5] Exam Of The Hand Wrist 2Ed. Opposition > Functional assessment.

[6] Exam Of The Hand Wrist 2Ed. Mechanical advantage.

[7] A Lange Medical Book Current Diagnosis Treatment In Orthopedics Fifth Edition. 9Hand Surgery > Image DISORDERS OF THE MUSCULATURE OF THE HAND.

[8] Exam Of The Hand Wrist 2Ed. The extrinsic extensor muscles.

[9] Campbell S Operative Orthopaedics 4 Volume Set. FRACTURES, DISLOCATIONS, AND LIGAMENTOUS INJURIES OF THE HAND AND WRIST > JOBE FOUR-LIMB RECONSTRUCTION.

[10] Exam Of The Hand Wrist 2Ed. Planning skin cover of the hand and forearm.

[11] A Lange Medical Book Current Diagnosis Treatment In Orthopedics Fifth Edition. 9Hand Surgery > FLEXOR TENDON INJURY.

[12] Exam Of The Hand Wrist 2Ed. Functional cutaneous units.

[13] Green S Operative Hand Surgery. EVOLUTION IN THE TREATMENT OF MANGLING INJURIES > PRINCIPLES.

[16] Exam Of The Hand Wrist 2Ed. Muscular equilibrium at the level of the digits > The flexor apparatus.

[18] Green S Operative Hand Surgery. Dislocations and Ligament Injuries of the Digits > AUTHOR’S PREFERRED METHOD OF TREATMENT: CHRONIC ULNAR COLLATERAL LIGAMENT INJURIES.

[19] Exam Of The Hand Wrist 2Ed. Restraint.

[20] Green S Operative Hand Surgery. EVALUATION.

[21] Green S Operative Hand Surgery. Control of Edema.

[22] Green S Operative Hand Surgery. EPIDEMIOLOGIC FINDINGS.

[26] Exam Of The Hand Wrist 2Ed. Blood supply of the skin.

[27] Green S Operative Hand Surgery. Dislocations and Ligament Injuries of the Digits > METACARPOPHALANGEAL JOINT OF THE FINGER.

[28] Exam Of The Hand Wrist 2Ed. Functions of the fibrous skeleton > Stability.

[29] Exam Of The Hand Wrist 2Ed. Circulation.

[32] Exam Of The Hand Wrist 2Ed. Opposition.

[33] Green S Operative Hand Surgery. Distal Interphalangeal Joint.

[34] Exam Of The Hand Wrist 2Ed. Global movements in the hand.

[35] Green S Operative Hand Surgery. Tendon Transfers for Median, Radial, and Ulnar Nerve Palsy > Early Tendon Transfers (Internal Splints) for Nerve Injuries > AUTHOR'S PREFERRED METHOD OF TREATMENT: ISOLATED ULNAR NERVE PALSY.

[36] A Lange Medical Book Current Diagnosis Treatment In Orthopedics Fifth Edition. 9Hand Surgery > SWAN-NECK DEFORMITY.

[37] Green S Operative Hand Surgery. Dislocations and Ligament Injuries of the Digits > Carpometacarpal Joint Dislocations > Preoperative Evaluation.

[39] Exam Of The Hand Wrist 2Ed. The digital rays.

[40] Exam Of The Hand Wrist 2Ed. 1.1 SKELETON OF THE HAND > The osseous skeleton.

[41] Green S Operative Hand Surgery. BOX 59.1 Ganglions of the Hand and Wrist > Wrist and Distal Forearm.

[42] Campbell S Operative Orthopaedics 4 Volume Set. NERVE INJURIES AT THE LEVEL OF THE HAND AND WRIST > SUTURING OF NERVES.

[43] Green S Operative Hand Surgery. Ring Finger Ray Amputation Without Transposition.