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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¶

Bony Anatomy¶

• The wrist is the anatomic region between the forearm and the hand, including the distal radioulnar, radiocarpal, and ulnocarpal joints and the eight carpal bones with their proximal and distal articulations and attached ligaments [7].
• The proximal row of carpal bones consists of the scaphoid, lunate, triquetrum, and pisiform [7].
• The distal row of carpal bones consists of the trapezium, trapezoid, capitate, and hamate [7].
• Carpal bones vary in size from the smallest (pisiform and trapezoid) to the largest (capitate) [7].
• The amount of articular cartilage allowing for articulation varies among carpal bones, with the pisiform articulating with one bone (the triquetrum) and the capitate articulating with seven bones [7].
• The radiocarpal joints are formed by the articulation of the distal radius with the scaphoid and lunate through their respective concave facets on the distal radius, and the triquetrum on the triangular fibrocartilage [7].
• The distal concave articular surfaces of the proximal carpal row form the midcarpal articulations with the distal row [7].
• The distal row articulates with the metacarpals, allowing mobility in the thumb, stability in the index and long finger metacarpals, and increased mobility in the ring and little finger metacarpals [7].
• The distal ulnar convexity articulates at the lesser sigmoid notch of the distal radius [7].
• The sigmoid notch articular surface accommodates the ulnar head through two thirds of its arc [7].
• There is about a 20-degree inclination of the distal ulna at its articulation with the radius [7].
• The ulnar styloid lies dorsal to the ulnar head and extends distally [7].
• The triangular fibrocartilage attaches to the base of the ulnar styloid and separates the hyaline cartilage–covered ulnar head from the styloid [7].
• The wrist functions as two carpal rows with the distal row bones relatively tightly bound to one another and the proximal row bones less so but still moving together [3].
• The carpal arch has a deep palmar concavity which resembles a rigid osseous mass sometimes incorrectly termed the “carpal block” [4].
• In the horizontal classification of carpal bones, the proximal row is intercalated between the radius and the distal row and must constantly adapt to the mobile articular surfaces of both the radius and the second carpal row [4].
• In the vertical classification of carpal bones, only the radial (scaphoid) and central (capitate articulated with the lunate) columns articulate with the radius [4].
• In the ulnar column, there is a gap between the ulna and the triquetrum [4].
• The proximal row of carpal bones is mobile because of its connections to the radius and the distal row [4].
• Each bone in the proximal row (scaphoid, lunate, and triquetrum) has its own distinct movements [4].
• The scaphoid cradles the capitate and articulates distally with the trapezium and the trapezoid, contributing to the stability of the midcarpus [4].
• The transverse arch of the distal carpal row is much more rigid than the proximal row [4].
• The keystone of the distal carpal arch is formed by the capitate, which moves with the fixed metacarpals [4].
• The wrist is more stable in flexion than in extension [4].
• Wrist stability in flexion is due to the strength of the various capsules and ligaments rather than the interlocking of different pieces of the skeleton [4].
• The original description of the carpal arcs applies only on a true neutral PA wrist x-ray where the third metacarpal shaft and the midradius axes are collinear [9].

Ligaments and Soft Tissue¶

• The chondroligamentous supports attaching the distal radius and ulnar side of the carpus to the distal ulna are designated as the triangular fibrocartilage complex (TFCC) [7].
• The TFCC includes the ulnar collateral ligament, the dorsal and volar radioulnar ligaments, the articular disc, the meniscal homologue, the extensor carpi ulnaris sheath, and the ulnolunate and ulnotriquetral ligament [7].
• Interosseous intrinsic ligaments connect the carpal bones in the proximal and distal carpal rows [7].
• The interosseous ligaments include the scapholunate and lunotriquetral interosseous ligaments connecting the proximal carpal row [7].
• The interosseous ligaments include ligaments connecting the trapezium to the trapezoid, the trapezoid to the capitate, and the capitate to the hamate in the distal carpal row [7].
• Extrinsic or crossing ligaments extend from the radius and ulna distally across the carpal rows [7].
• The radial collateral ligament extends from the radial styloid to the scaphoid waist [7].
• The ulnar collateral ligament extends from the base of the ulnar styloid attaching to the pisiform [7].
• The transverse carpal ligament is an extrinsic or crossing ligament [7].
• Volar extrinsic or crossing ligaments include the radioscapocapitate ligament, the radiolunotriquetral ligament, and the radioscapolunate ligament on the radial side [7].
• Volar extrinsic or crossing ligaments include the ulnolunate and ulnotriquetral components of the TFCC on the ulnar side [7].
• On the palmar side of the carpus, between the radiolunotriquetral ligament and the radioscapocapitate ligament, is a relatively thin area called the space of Poirier, overlying the palmar surface of the lunate [7].
• Dorsal extrinsic ligaments include the dorsal radiocarpal and the dorsal intercarpal ligaments [7].
• The trapezoidal dorsal radiocarpal ligament attaches along the dorsal radial articular margin of the lunate fossa, from the Lister tubercle to the lesser sigmoid notch [7].
• The trapezoidal dorsal radiocarpal ligament spans the lunotriquetral joint and inserts on the dorsal surface of the triquetrum [7].
• There are four types of dorsal radiocarpal ligaments [7].
• The dorsal intercarpal ligament is attached to the distal, dorsal surface of the triquetrum and passes across the midcarpal joint to attach to the dorsal surfaces of the scaphoid waist and the trapezoid [7].
• The flexor retinaculum distal to the radial joint forms a roof over the carpal gutter and transforms it into a tunnel [4].
• The flexor retinaculum retains the massive and powerful finger flexor tendons close to the axes of flexion–extension and medial–lateral deviation [4].
• The flexor retinaculum allows the flexors to generate almost no torque at the radiocarpal joint while acting on the digits [4].
• The narrowness of the osteofibrous tunnel formed by the carpal groove and flexor retinaculum explains why syndromes of irritation and compression of the median nerve are common [4].
• The median nerve is more superficial than the tendons in the carpal tunnel and is compressed by them when the wrist is in the flexed position [4].

Musculotendinous Apparatus¶

• Only the extensor tendons are accessible to visual inspection and palpation owing to the thin dorsal skin on the hand [14].
• Extensor tendons are visible with the fingers in active extension and the thumb in abduction [14].
• The abductor pollicis longus and extensor pollicis brevis tendons can be seen between the radial styloid proximally and the base of the first metacarpal distally [14].
• The extensor pollicis longus tendon runs from the radial styloid to the ulnar side of the base of the first metacarpal and is best seen with the thumb in active retropulsion [14].
• The extensor communis and proprius tendons of the fingers lie in the axis of each metacarpal to the level of the proximal phalanx [14].
• The extensor carpi radialis tendons are only palpable for a short distance proximal to the bases of the second and third metacarpals with the wrist in resisted extension [14].
• The extensor carpi ulnaris tendon is palpable during resisted extension and adduction of the wrist, immediately distal to the ulna styloid until the fifth metacarpal [14].
• The flexor carpi ulnaris tendon is felt in active flexion of the wrist immediately proximal to the pisiform [14].
• The flexor carpi radialis and palmaris longus tendons are palpable and visible in resisted flexion of the wrist just proximal to the distal wrist flexion crease [14].

Imaging and Assessment¶

• The A1 angle is formed by the tangent of the inferior aspect of the radius and the radial aspect of the second metacarpal, indicating “radial angulation” [28].
• The A1 angle is normally 120 degrees to 125 degrees [28].
• The A2 angle measures the ulnar deviation of the fingers and is defined by the angle formed between the tangent of the radial aspect of the second metacarpal and the axis of the proximal phalanx of the middle finger [28].
• The A2 angle becomes pathological when it exceeds 25 degrees [28].
• The ratio of L2 (height of the wrist passing through the center of the head of the capitate) to L1 (length of the third metacarpal) is normally 0.54 ± 0.03 [28].
• The ratio of L3 (distance between the center of the head of the capitate and the extended axis of the ulnar epiphysis) to L1 is 0.30 ± 0.03 [28].
• In a strict lateral view in a neutral position, the radial axis usually extends through the lunate axis and the capitate axis [28].
• The scaphoid makes an angle of 30–60 degrees with the radial/capitate axis [28].
• The dorsal or palmar displacement of the lunate is judged at the level of the distal pole and explains its instability [28].
• The DISI or VISI formula signifies that the distal joint surface of the lunate is turned in extension (dorsal) or in flexion (volar) [28].
• In both DISI and VISI cases, the scaphoid tends to become horizontal [28].
• CT scanning is not as useful in the wrist as in other parts of the skeleton but has specific indications [32].
• CT slices can show a fracture of the base of the metacarpals or of the carpal bones that was not evident on plain radiographs [32].
• CT slices of the scaphoid parallel to its long axis, and in the coronal and sagittal plane, are useful for making an early diagnosis of a fracture [32].
• CT scans can assess a pseudoarthrosis of the scaphoid, showing the extent of loss of substance, exact position of the fragments, and necrosis of the proximal pole [32].
• CT scanning can assess the vascularity of the lunate and any bony collapse for staging and choice of surgical procedure in Kienböck’s disease [32].
• CT scanning can demonstrate a limited osteoarthritis and explain a localized tenderness in Kienböck’s disease [32].
• A tumor, particularly an osteoid osteoma, can be seen and precisely localized using a CT scan [32].
• Magnetic resonance imaging (MRI) is the most sensitive technique currently in use for the wrist [32].
• MRI main applications include showing soft tissues, the vascularity of both bones and soft tissues, and assessing the extension of bony tumors into soft tissues [32].
• Using MRI, intrinsic and extrinsic ligaments of the wrist can be seen in the coronal and sagittal planes [32].
• MRI is a very important tool for the diagnosis of TFCC tears [32].
• Interosseous ligaments (scapholunate and lunotriquetral) and extrinsic ligaments (radiocapitate and radiolunate) are elicited in special planes on MRI, providing significant information about carpal instability [32].
• Cartilage erosions and osseous avascular necrosis are evaluated mainly in T1-weighted sequences on MRI and are helpful for surgical indications [32].
• Vascularization of the carpal bones can be assessed on MRI, and enhancement by gadolinium injection can give information on the prognosis for revascularization [32].
• Lateral wrist radiographs can provide a complete picture of the ulnar border of the radius for measuring ulnar variance [30].
• Wrist arthroscopy is an accepted technique for evaluation of intra-articular pathology and treatment of a variety of disorders in the wrist joint [25].
• Wrist arthroscopy has developed into an effective therapeutic tool useful for the treatment of a variety of wrist disorders from arthritis to acute fractures [50].
• Arthroscopic assessment of intercarpal ligament injuries and instability is considered by many the “gold standard” for evaluation of these conditions [50].
• Arthroscopy has been found to be more accurate than arthrography in identifying the location and size of triangular fibrocartilage and interosseous ligament injuries [50].
• Arthroscopy is more accurate than triple-injection cinearthrography in detecting tears of the dorsal sensory branch of the ulnar nerve during arthroscopic repair of the triangular fibrocartilage [50].

Osseous Anatomy¶

Distal Radius and Ulna¶

• The distal radial articular surface has a double obliquity of 12–15 degrees in the lateral view and 15–20 degrees in the anteroposterior view [19].
• The posterior lip and radial styloid of the distal radius provide a buttressing effect [19].
• The distal radial articular surface consists of two concave facets, the scaphoid and lunate facets, separated by the scapholunate ridge [74].
• The sigmoid notch along the ulnar border of the distal radius is a shallow concavity for the articulating ulnar head at the distal radioulnar joint [74].
• The distal ulna is covered with hyaline cartilage on its dorsal, lateral, palmar, and distal surfaces [74].
• The ulnar styloid projects distally, and its base contains the fovea which serves as the insertion for the triangular fibrocartilaginous complex [74].
• The distal ulnar convexity articulates at the lesser sigmoid notch of the distal radius, with the articular surface accommodating the ulnar head through two thirds of its arc [7].
• There is an approximately 20-degree inclination of the distal ulna at its articulation with the radius [7].
• The center of the distal radial articular surface is located palmar to the long axis of the radius, with a mean value of 5.3 mm [27].
• The secondary center of ossification of the distal radial epiphysis becomes radiographically apparent by the first year of life [97].
• The distal ulnar epiphysis becomes radiographically apparent at approximately 6 years of age and often arises from two distinct centers of ossification [97].
• The distal ulnar physis closes at 16 years in females and 17 years in males, while the distal radial physis closes on average 6 months later [97].

Carpal Bones¶

• The carpus comprises eight ossicles traditionally separated into a proximal row (scaphoid, lunate, triquetrum, pisiform) and a distal row (trapezium, trapezoid, capitate, hamate) [74].
• The carpal bones vary in size from the smallest (pisiform and trapezoid) to the largest (capitate) [7].
• The capitate has the largest amount of articular cartilage, articulating with seven bones, while the pisiform articulates with only one bone (the triquetrum) [7].
• The scaphoid's primary vascular supply is a branch of the radial artery at the dorsal ridge, with smaller vessels entering the palmar tubercle to supply the distal 30% [74].
• The transverse carpal ligament attaches to the palmar tubercle of the scaphoid [74].
• The lunate has a dorsal and palmar vascular supply in 80% of wrists, with only a palmar supply found in 20% of wrists [74].
• The lunate is broader palmarly than dorsally [74].
• The triquetrum articulates distally with the hamate, radially with the lunate, and volarly with the pisiform [74].
• The hamate consists of a body and a hook (hamulus) which serves as an attachment for the transverse carpal ligament and origins for the flexor digiti minimi and opponens digiti minimi [74].
• The head of the capitate often relies on a retrograde vascular supply [74].
• Two ridges separate the distal articular surface of the capitate into three facets for articulation with the metacarpals of the index, long, and ring fingers [74].
• The trapezoid has two distal facets which articulate with the metacarpal of the index finger [74].
• The trapezium has a saddle-shaped articulation with the base of the thumb metacarpal and a palmar groove for the flexor carpi radialis bordered laterally by a palmar tuberosity [74].
• The pisiform is a sesamoid bone within the flexor carpi ulnaris tendon and serves as the origin for the abductor digiti minimi [74].
• The scaphoid and lunate articulate with the radius, with the scaphoid presenting a long axis inclined by 45 degrees to the long axis of the radius [19].
• The scaphoid has a distal pole tubercle that lies palmarly, and the lunate also has a palmar tubercle [19].
• The lunate sits on the capitate and has anterior and posterior horns, with a line drawn between these horns lying perpendicular to the long axis of the wrist in neutral position [19].
• The triquetrum is not in contact with the ulnar head; a fibro-cartilage disc (triangular ligament) separates the two bones [19].
• The most common lunate morphology (73%) features a separate medial facet on its distal surface for the hamate [51].
• The capitate has a separate facet for the fourth metacarpal in 86% of wrists [51].
• The capitate and hamate ossification centers typically appear at 6 to 8 months of age [97].
• The triquetrum ossifies at 2 to 3 years of age, followed by the lunate at 4 years [97].
• The scaphoid becomes radiographically apparent at 4 to 5 years of age, followed by the trapezium and trapezoid at 5 years [97].
• The pisiform is the last carpal bone to ossify, typically at 6 to 8 years of age [97].
• The bony scaphoid forms via enchondral ossification from distal to proximal until fully ossified, typically by age 14 to 16 years [97].
• Male wrists are significantly larger than female wrists, but there are no significant differences in relative dimensions between left and right wrists [49].
• Across a wide range of wrist sizes, individual carpal volumes were a consistent percentage of carpus volume that did not differ with gender [35].

Osseous Kinematics and Stability¶

• The carpus does not form a single rigid bony block because the eight small bones have different degrees of movement, with the distal row being quite rigid and the three proximal row bones being relatively mobile [19].
• The carpal articular surface has a smaller diameter of curvature than the radius, and its stability in the medial and palmar aspects depends upon ligamentous and capsular resistance [19].
• Due to its anterior concavity, the carpus is more stable in flexion than in extension [19].
• Carpal stability is largely due to interosseous ligaments and bony configuration rather than tendon insertions, with the exception of the pisiform which is a sesamoid in the flexor carpi ulnaris tendon [19].
• The distance between the distal articular surface of the radius and the base of the metacarpals is constant [19].
• Rotation of the scaphoid and lunate as the wrist moves from extension to flexion has a double "cam" effect, allowing the carpus to act as a "condyle of variable geometric form" [19].
• The ulnar head sits proximal to the distal radius and has only an indirect effect on stability of the wrist [19].
• The center of rotation for most wrist motions is generally considered to be located in the proximate capitate [11].
• During radial-to-ulnar deviation, the proximal carpal row rotates dorsally and intercalates or shifts at the midcarpal and radiocarpal joints [11].
• During ulnar-to-radial deviation, the proximal carpal row tends toward palmar rotation, with most motion occurring in the intercarpal joints [11].
• The proximal carpal row is considered an intercalated segment in the forearm-to-hand connection, with the scaphoid functioning to stabilize the wrist [11].
• With ulnar deviation, the triquetrum translocates radially and dorsally on the slope of the hamate, bringing the lunate coaxially with the capitate [88].
• With ulnar deviation, the triquetrum is translated ulnarly and palmarly on the slope of the hamate, bringing the lunate axis palmar to the axis of the capitate and rotating it into a dorsal facing attitude [88].
• During wrist extension, the scaphoid extension stops before the lunate, which continues to turn by 30 degrees [88].
• During wrist flexion, the flexion of the mid-carpal joint is more important than the radiocarpal joint, and the capitate is flexed more than the lunate [88].
• During dorsiflexion and ulnar deviation, the scaphoid becomes longitudinal and wrist motion is predominantly radiocarpal [88].
• During volar flexion and radial deviation, the scaphoid position is perpendicular to the long axis of the radius, and motion is mainly mid-carpal [88].
• Structures originating from the ulna change their major constraint contribution with forearm orientation, whereas those with a radial origin have a constant contribution independent of forearm rotation [20].

Ligaments and Joint Capsule¶

General Principles and Stability¶

• Wrist stability is a function of the equilibrium of bony morphology at each joint and the passive resistance of the fibrous skeleton [19].
• The stability of the wrist during motion depends on capsuloligamentous integrity and contact surface contours of the carpal bones [11].
• The carpus is more stable in flexion than in extension due to the strength of the various capsules and ligaments [4].
• The carpus is more stable in flexion than extension because of its anterior concavity [19].
• The normal inclination of the radiocarpal joint surface is inherently unstable, consisting of ulnar deviation and volar flexion [22].
• In a normal wrist, the unstable condition of the radiocarpal joint is neutralized by a strong and complex set of anterior wrist ligaments that resist supination of the carpal bones on the distal end of the forearm [22].
• Uncontrolled joint synovitis stretches essential ligaments and eventually erodes cartilage and bone, resulting in a progressive shift of the carpus ulnarward and volarward [22].
• The interosseous ligaments stabilize the semirigid proximal and distal carpal rows in Lichtman's ring concept of wrist kinematics [11].
• Bone or ligament disruption of the carpal ring creates instability deformities, with the lunate tilting either dorsally or volarly [11].
• Division of either of the proximal row’s interosseous ligaments in isolation does not result in a postural deformity of the lunate [18].
• Similar collapse deformities of proximal row alignment (VISI or DISI) can occur with or without disruption of an interosseous ligament [18].
• The proximal row has its own critical intrinsic and extrinsic ligament stabilizers [18].

Volar (Palmar) Ligaments¶

• The strongest part of the wrist capsule lies anteriorly to resist the tendency to anterior subluxation due to the inclination of the distal radial articular surface [62].
• The palmar capsule is thickened to form a strap joining the anterior border of the radial articular surface to the ulnar styloid with attachment to the anterior horn of the lunate and proximal pole of the triquetrum [62].
• The volar radiocarpal ligament arises from the radial styloid and fans out into a number of bands [62].
• A proximal radiolunotriquetral band and a stronger, more distal band passing anterior to the scaphoid neck are recognizable components of the volar radiocarpal ligament [62].
• The distal band of the volar radiocarpal ligament acts as a pivot for the rotation of the scaphoid before inserting on to the capitate [62].
• The distal band of the volar radiocarpal ligament is the only ligament between the radius and the distal carpal row and has a restraining function [62].
• In pronation to supination movements, the distal band of the volar radiocarpal ligament presses on the scaphoid [62].
• An interval corresponding to the lunocapitate joint line exists between the proximal and distal bands of the volar radiocarpal ligament [62].
• The interval at the lunocapitate joint line represents a weak point in the volar capsule which is particularly vulnerable because there is no lunocapitate ligament [62].
• The ligaments from the radius are much stronger than those from the ulna, particularly true of the volar radiocarpal ligament [62].
• The space of Poirier is a relatively thin area on the palmar side of the carpus between the radiolunotriquetral ligament and the radioscapocapitate ligament, overlying the palmar surface of the lunate [7].
• The volar extrinsic or crossing ligaments include the radioscapocapitate ligament, the radiolunotriquetral ligament, and the radioscapolunate ligament on the radial side [7].
• The volar extrinsic or crossing ligaments include the ulnolunate and ulnotriquetral components of the TFCC on the ulnar side [7].
• The extrinsic or crossing ligaments include the radial collateral ligament from the radial styloid to the scaphoid waist [7].
• The extrinsic or crossing ligaments include the ulnar collateral ligament from the base of the ulnar styloid attaching to the pisiform [7].
• The extrinsic or crossing ligaments include the transverse carpal ligament [7].

Dorsal Ligaments¶

• The identifiable dorsal extrinsic ligaments include the dorsal radiocarpal and the dorsal intercarpal ligaments [7].
• The deep limb of the distal radioulnar ligament has a narrow marginal insertion just behind the pole of the distal ulna, suggesting its role as the capsular ligament [23].
• The interosseous membrane insertion at the triangular fibrocartilage supports the weakest part of the dorsal capsule [40].

Triangular Fibrocartilage Complex (TFCC)¶

• The TFCC attaches to the ulnar margin of the lunate fossa of the radius [7].
• The triangular ligament extends the distal radial articular surface to the ulnar styloid and forms the principal link between the two bones [19].
• The triquetrum is not in contact with the ulna head; a fibro-cartilage disc, the triangular ligament, separates the two bones [19].
• The attachment of the interosseous membrane at the triangular fibrocartilage influences the distal radioulnar joint [40].

Intrinsic (Interosseous) Ligaments¶

• The interosseous ligaments include the ligaments connecting the trapezium to the trapezoid, the trapezoid to the capitate, and the capitate to the hamate in the distal carpal row [7].
• Limited mobility occurs between the scaphotrapezial joints and the triquetrohamate joints [11].
• The scaphoid contributes to the stability of the midcarpus by articulating distally with the trapezium and the trapezoid [4].

Extra-Articular Ligaments and Retinacula¶

• The transverse carpal ligament or flexor retinaculum provides extra-articular support to the wrist [79].
• The posterior retinaculum is composed of a transverse portion and an oblique portion [79].
• The transverse portion of the posterior retinaculum has proximal insertions into the distal radius forming six osteofibrous tunnels or compartments that serve as pulleys for the extensor tendons [79].
• The oblique portion of the posterior retinaculum turns around the ulnar part of the carpus and extensor carpi ulnaris tendon and finishes by insertion on the pisiform and triquetrum [79].
• The oblique portion of the posterior retinaculum forms an extra-articular sling [79].
• The distal fibers of the posterior retinaculum are the strongest but lie distal to the ulna head and are unable to contribute to its stability [79].
• The extensor retinaculum distal fibers continue proximally to the pisiform with the proximal fibers of the flexor retinaculum [79].
• The connection between the extensor retinaculum distal fibers and flexor retinaculum proximal fibers occurs deeply with respect to the flexor carpi ulnaris tendon at the floor of the Guyon space [79].
• The role of the flexor retinaculum in effecting stability of the wrist is questionable [4].
• The massive and powerful finger flexor tendons are retained close to the axes of flexion–extension and medial–lateral deviation by the flexor retinaculum [4].
• The narrowness of the osteofibrous tunnel formed by the flexor retinaculum explains why syndromes of irritation and compression of the median nerve are common [4].

Kinematics and Ligament Function¶

• During ulnar-to-radial deviation, the proximal carpal row tends toward palmar rotation, with most of the motion occurring in the intercarpal joints [11].
• The lunate, capitate, hamate, trapezium, and trapezoid function collectively as the “stable central column,” controlled by the scaphoid in a two-gear, four-bar linkage system and stabilized by the triquetrum [18].
• The triquetrum buffers lunate rotation and prevents ulnar translation [18].
• The dart-thrower’s path of radial extension to ulnar flexion defines the transition between flexion and extension of the scaphoid and lunate [18].
• The dart-thrower’s motion occurs almost exclusively through the midcarpal joint [18].
• In FEM, motion at the triquetrum-hamate joint was rotation in an almost flexion-extension plane of the wrist [26].

Muscles and Tendons¶

Wrist Extension Muscles¶

• Wrist extension is dependent on the extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB), and extensor carpi ulnaris (ECU) [48].
• The ECRL inserts on the base of the second metacarpal and extends the wrist while drawing it into radial deviation [48].
• The ECRB inserts on the radial part of the base of the third metacarpal and is considered the primary wrist extensor with a slight action of radial deviation [48].
• The ECU inserts on the base of the fifth metacarpal and crosses the wrist at the level of the ulna, unlike the ECRB and ECRL which cross at the level of the radius [48].
• The ECU tendon rotates around the ulnar head, positioning it on the ulnar side of the styloid process in pronation and on the radial side in supination [48].
• In pronation, the ECU primarily causes ulnar deviation of the wrist and works in synergy with the flexor carpi ulnaris to prevent radial deviation [48].
• The ECRL originates at the supracondylar ridge of the humerus about 4–5 cm proximal to the epicondyle, with its thickest part located proximal to the elbow joint [48].
• The ECRL plays a role in elbow flexion and loses part of its wrist action when the elbow is flexed [48].
• The ECRB originates on the epicondyle and is not affected by the position of the elbow, with all of its action directed at the wrist [48].
• The ECRL and ECRB tendons are congruent along most of their length in the forearm and often have tendinous connections [48].
• Distal to the retinaculum, the ECRL and ECRB tendons diverge so that the center of the ECRL tendon is about 1.5 cm lateral to the center of the ECRB [48].
• The two ECR tendons comprise about 10 per cent of the muscle mass of the forearm and 76 per cent of the muscle mass of the extensors of the wrist [48].
• The muscle mass of the ECRB is 88 per cent when compared with that of the ECRL [48].
• The moment arm for wrist extension is 16.30 mm for the ECRB and 12.50 mm for the ECRL [48].
• The ECRL has longer muscular fibers, mostly at the level of the elbow [48].
• In the ECRL, the moment arm for elbow flexion and radial deviation is more important than that for wrist extension [48].
• The ECRL only becomes a wrist extensor after radial deviation is balanced against the ulnar forces of the ECU [48].
• The ECU has the weakest moment of extension at 6.3 mm in supination, which becomes zero when the wrist is in complete pronation [48].
• The ECRB is the most effective extensor of the wrist due to its greatest tension and most favorable moment arm [48].
• The axis of common wrist movements is oblique between the ECRL and ECRB, which produce extension and radial deviation, and the flexor carpi ulnaris, which produces flexion and ulnar deviation [48].
• The ECU is the antagonist of the extensor pollicis longus, with contraction being synergistic [48].
• The tension of the ECU is felt when the thumb is abducted [48].

Functional Consequences of Extension Loss¶

• Loss of active wrist extension results in a permanent wrist drop that makes gripping with the hand very difficult [48].
• Radial palsy involves only a very small sensory deficit on the dorsal aspect of the hand, while palmar surface sensibility remains uninvolved [48].
• Loss of active wrist extension robs normal palmar sensibility of its functional capacity [48].
• Loss of active wrist movement has serious repercussions on the action of the extrinsic muscles in the hand [48].
• Flexor action in the thumb and fingers is normally reinforced by extension of the wrist [48].
• Palsy of the wrist extensors involves a great loss of grip strength, which can be the most serious sequela of these palsies [48].
• Neither the flexors nor the extensors of the fingers are long enough to allow maximal movements at the wrist and the fingers simultaneously [48].

Palpation and Landmarks¶

• The abductor pollicis longus and extensor pollicis brevis can be seen between the radial styloid proximally and the base of the first metacarpal distally [14].
• The extensor pollicis longus runs from the radial styloid to the ulnar side of the base of the first metacarpal and is best seen with the thumb in active retropulsion [14].
• The flexor carpi ulnaris is felt in active flexion of the wrist immediately proximal to the pisiform [14].

Anatomical Variations and Surgical Considerations¶

• The insertion of the extensor medii digiti tendon into the proximal phalanx suggests it may function as a metacarpal or wrist extensor, as well as a metacarpophalangeal extensor [110].
• In the Haddad and Riordan wrist arthrodesis technique, the extensor carpi radialis longus tendon is divided just proximal to its insertion on the base of the second metacarpal, leaving a stump distally for later suture [2].
• In the Haddad and Riordan wrist arthrodesis technique, the abductor pollicis longus, extensor pollicis brevis, and wrist and finger extensors are mobilized subperiosteally and retracted [2].
• In the Haddad and Riordan wrist arthrodesis technique, the dorsal carpal ligament is closed deep to the abductor pollicis longus and extensor pollicis brevis [2].
• In the Haddad and Riordan wrist arthrodesis technique, the extensor carpi radialis longus tendon is sutured before closing the wound [2].

Neurovascular Anatomy¶

Arterial Supply¶

• The hand is supplied through two main arteries, the radial and the ulnar, which are responsible for virtually the entire arterial supply under normal circumstances [52].
• The deep palmar arch is formed by the terminal part of the radial artery and its anastomosis with the deep branch of the ulnar artery [52].
• The deep palmar arch lies anterior to the upper extremity of the metacarpal shafts [52].
• The deep palmar arch is seldom fully developed, and the deep ulnar branch is often negligible [52].
• The superficial palmar arch is formed from the anastomosis of the terminal branch of the ulnar artery with the superficial palmar branch of the radial artery [52].
• The superficial palmar arch lies under the deep palmar arch and has a smaller caliber [52].
• The superficial palmar arch is fully developed in only 13–19 per cent of cases [52].
• In 60 per cent of cases, the superficial palmar arch is formed from the ulnar artery alone [52].
• In 32 per cent of cases, the superficial palmar arch is formed from the superficial palmar branch of the radial artery [52].
• In 8 per cent of cases, the superficial palmar arch results from the anastomosis of the median with the ulnar artery [52].
• The dorsal carpal arch, when present, is formed by the union of homologous branches from the radial and ulnar arteries [52].
• The dorsal carpal arch can function as a collateral channel between the radial artery and the deep palmar arch [52].
• The dorsal carpal arch often receives a significant contribution from the radial artery [52].
• The palmar carpal arch seldom forms a recognizable arcade and frequently consists of a loose collateral network known as the palmar carpal plexus [52].
• The palmar carpal plexus usually connects the anterior interosseous artery with the radial and ulnar arteries [52].
• The terminal branches of the radial, ulnar, and anterior interosseous arteries provide extraosseous blood supply to the carpus through three dorsal and three palmar transverse arterial arches with longitudinal connections [90].
• The dorsal radiocarpal arch is located at the radiocarpal joint and supplies the lunate and triquetrum [90].
• The dorsal intercarpal arch is the largest of the dorsal arches, located between the proximal and distal carpal rows, and supplies the distal carpal row [90].
• The dorsal intercarpal arch supplies the lunate and triquetrum through anastomoses with the radiocarpal arch [90].
• The basal metacarpal arch is located at the base of the metacarpals, is the most variable of the dorsal arches, and supplies the distal carpal row [90].
• The palmar radiocarpal arch is located at the level of the radiocarpal joint on the palmar surfaces of the lunate and triquetrum [90].
• The intercarpal palmar arch is located between the proximal and distal carpal rows, is the most variable of the palmar arches, and does not contribute to nutrient vessels in the carpus [90].
• The deep palmar arch is located at the level of the metacarpal bases, is consistent, and communicates with the dorsal basal metacarpal arch and the palmar metacarpal arteries [90].
• The blood supply of the thumb comes mainly from the princeps pollicis artery, the terminal branch of the superficial palmar arch, and the first dorsal metacarpal artery [94].
• The dorsal carpal arch was present in all cases in a cadaver study and always ran above the distal carpal row [86].
• The dorsal carpal arch anastomosed to the ulnar artery in 4 cases and to the radial artery in all cases in a cadaver study [86].
• The main cyst of a volar wrist ganglion may be intertwined with bifurcating branches of the radial artery [37].
• The radial artery is frequently intimately attached to the wall of a volar wrist ganglion and may even be completely encircled by the ganglion [37].
• The Allen test should be performed routinely to assess the patency of the radial and ulnar arteries before volar wrist ganglion excision [37].
• The surgeon must be aware of the importance of preserving the radial artery, particularly in patients with a radial-dominant circulation [37].
• Injuries to the radial artery during volar wrist ganglion excision can be repaired microscopically [37].
• Some authors recommend leaving a portion of the cyst wall attached to the radial artery to avoid arterial injury during volar wrist ganglion excision [37].
• A careful approach to the wrist with styloidectomy preserves the superficial branches of the radial nerve, the antebrachial cephalic vein, and the radial artery [44].

Nerve Anatomy¶

• The radial nerve is a continuation of the posterior cord with roots emerging at the C6, C7, C8, and T1 levels [68].
• The radial nerve divides into two terminal branches at the humeroradial joint line: the anterior sensory branch and the posterior motor branch (posterior interosseous nerve) [68].
• The anterior sensory branch of the radial nerve runs into the forearm under the brachioradialis lateral to the radial artery [68].
• The posterior interosseous nerve penetrates the supinator muscle by passing under the arcade of Frohse [68].
• The arcade of Frohse is fibrous in about one-third of cases and may compress the nerve [68].
• In 25 per cent of cases, the posterior interosseous nerve lies flush against the periosteum for about 3 cm (bare area) when the forearm is supinated, making it more vulnerable at this level [68].
• The radial nerve supplies all the extensors of the elbow, the wrist, and the fingers [68].
• The sensory territory of the radial nerve is relatively limited to the lateral half of the dorsum of the hand [68].
• The autonomous zone of the radial nerve is restricted to the dorsal aspect of the first interosseous space [68].
• Sectioning of the small sensory branches of the radial nerve at the wrist can give rise to painful neuromas [68].
• The radial nerve arises from the posterior cord of the brachial plexus (C5–C8; ±T1) [81].
• The superficial branch of the radial nerve descends in the forearm deep to the brachioradialis muscle and pierces the deep fascia ulnar to the brachioradialis tendon approximately 7 cm proximal to the radial styloid [81].
• The superficial branch of the radial nerve provides sensation to the dorsal-radial hand [81].
• The posterior interosseous nerve (PIN) courses perpendicularly through the supinator to lie between the APL/ECU (deep) and EDM/EDC (superficially) [81].
• The PIN arborizes into three branches to the ECU, EDM, and EDC and into two longer branches to the APL, EPL, EPB, and EIP [81].
• The classic order of reinnervation following injury for the PIN is ECU, EDC, EDM, APL, EPL, EPB, EIP [81].
• The PIN innervates the extensor muscles of the forearm and courses distally deep to the fourth dorsal compartment with the posterior interosseous artery to terminate as an afferent nerve to the dorsal wrist capsule [81].
• The ulnar nerve arises from the medial cord of the brachial plexus (C8–T1, ±C7) [81].
• The ulnar nerve runs between the FCU and FDS in the forearm before emerging more superficially, radial to the FCU tendon [81].
• The ulnar nerve lies ulnar (medial) and dorsal to the ulnar artery [81].
• At the wrist, the ulnar nerve is 45% motor and 55% sensory [81].
• The distal ulnar tunnel, or Guyon canal, comprises three zones [81].
• Zone 1 of Guyon canal begins at the proximal edge of the volar carpal ligament and ends at the nerve bifurcation, approximately 1 cm distal to the pisiform [81].
• Zone 1 of Guyon canal lies dorsal to the volar carpal ligament and volar to the transverse carpal ligament [81].
• The ulnar artery bifurcates distal to the ulnar nerve in Zone 1 of Guyon canal [81].
• Zone 2 of Guyon canal has a roof comprising the palmaris brevis and a floor comprising the pisohamate and pisometacarpal ligaments [81].
• The deep motor branch of the ulnar nerve passes around the hook of the hamate and between the abductor digiti minimi and flexor digiti minimi muscles in Zone 2 of Guyon canal [81].
• The deep motor branch of the ulnar nerve pierces the opponens digiti minimi to follow the deep palmar arch in Zone 2 of Guyon canal [81].
• The deep motor branch of the ulnar nerve typically innervates the interosseous, third and fourth lumbrical, adductor pollicis, and flexor pollicis brevis muscles [81].
• Zone 3 of Guyon canal includes the sensory branch, which remains superficial [81].
• The sensory branch of the ulnar nerve innervates the palmaris brevis muscle and is sensory to the little finger and typically to the ulnar ring finger [81].
• The median nerve arises from the medial and lateral cords of the brachial plexus (C5–T1) [81].
• The median nerve enters the forearm between the ulnar and humeral heads of the pronator teres and runs distally between the FDS and FDP muscles [81].
• The median nerve may course within the FDS muscle substance [81].
• The median nerve is separated from the ulnar artery (deep) by the deep head of the pronator teres in the proximal forearm [81].
• The anterior interosseous nerve typically branches immediately distal to the FDS arch and innervates the FDP (index and long fingers), flexor pollicis longus, and pronator quadratus [81].
• The anterior interosseous nerve passes dorsal to the pronator quadratus muscle with the anterior interosseous artery and provides afferent innervation of the volar wrist capsule [81].
• The palmar cutaneous branch of the median nerve arises approximately 5 cm proximal to the volar wrist crease and runs in the median nerve epineurium for 2 cm [81].
• The palmar cutaneous branch of the median nerve runs in the palmaris longus–FCR interval until it passes superficially to the transverse carpal ligament to supply sensory innervation to the thenar eminence [81].
• At the carpal tunnel, the median nerve is 94% sensory and 6% motor [81].
• The recurrent motor branch of the median nerve typically innervates the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis [81].
• The median nerve branches into radial and ulnar divisions [81].
• The radial division of the median nerve branches into the common digital nerve to the thumb and the proper radial digital nerve to the index finger [81].
• The radial digital nerve to the thumb crosses the flexor sheath obliquely in the region of the A1 pulley from proximal-ulnar to distal-radial [81].
• The radial digital nerve to the thumb is at increased risk for inadvertent injury during an A1 pulley release or trigger thumb release [81].
• The ulnar division of the median nerve divides into the common digital nerves to the second and third web spaces [81].
• The first and second lumbrical muscles are innervated by branches of the common digital nerves [81].
• The common digital nerves are dorsal to the superficial palmar arch and volar to the flexor tendons in the palm [81].
• The proper digital nerves become volar to the digital arteries at the level of the metacarpal neck [81].
• A morphological study showed a dorsal displacement of the median nerve during flexion of the wrist in 84.5% of the patients [16, 17].
• A case is presented of an anomalous course of the palmar cutaneous branch of the median nerve [47].
• Branches of the palmar cutaneous branch of the median nerve innervating the scaphoid were typically found in a study [103].
• In no specimen in a study was a ‘typical’ cutaneous branch of the ulnar nerve found [103].
• The study confirms the presence of a transverse radioulnar branch from the dorsal sensory ulnar nerve in approximately 80% of cases [107].
• In no specimen in a study did the authors identify a deep branch of the ulnar artery coursing with the deep motor branch of the ulnar nerve and contributing to a deep palmar arterial arcade [75].
• The authors concluded that the classic description of a deep palmar arterial arch is not valid due to the mistaken identity of hypothenar arterial branches [75].
• This space on the underside of the wrist is bounded by the fibrous bed anteriorly and the anterior ligament of the carpus posteriorly, and contains the ulnar artery and nerve on its posterior wall [106].

Surgical Considerations¶

• The median nerve can be blocked as it courses between the palmaris longus and flexor carpi radialis tendons [72].
• In the absence of the palmaris longus tendon, the needle for a median nerve block is inserted on the ulnar side of the flexor carpi radialis tendon [72].
• After penetration through the flexor retinaculum at a depth of approximately 1 cm, 5 mL of local anesthetic is injected for a median nerve block [72].
• Injecting 1 mL of local anesthetic above the retinaculum as the needle is withdrawn can block a superficial palmar branch supplying the skin over the thenar eminence [72].
• The ulnar nerve is blocked at the wrist at either the radial or the ulnar side of the flexor carpi ulnaris tendon [72].
• The ulnar approach is preferred for ulnar nerve block to avoid intravascular injection, given the location of the ulnar artery on the radial side of the tendon [72].
• At the level of the distal ulna, the needle for an ulnar nerve block is introduced on the dorsoulnar side of the flexor carpi ulnaris [72].
• Subsequent injection of 5 mL of local anesthetic under the flexor carpi ulnaris will result in anesthesia of this distribution [72].
• Additional subcutaneous infiltration of the dorsoulnar area of the wrist blocks the dorsal cutaneous branch of the ulnar nerve [72].
• The radial nerve is superficial and divided into branches running in the subcutaneous fat at the level of the radial styloid process [72].
• The radial nerve can be blocked using 5 to 10 mL of local anesthetic injected in a subcutaneous field block at the level of the radial styloid [72].
• The initial injection for a radial nerve block is just lateral to the radial artery at the level of the proximal wrist crease using 2 to 3 mL of local anesthetic [72].
• The needle is then redirected and advanced within the subcutaneous tissue injecting 5 to 7 mL of local anesthetic across the proximal border of the snuffbox to the midpoint of the dorsal wrist for a radial nerve block [72].
• Several separate injections may be necessary to follow the curvature of the wrist and block the numerous superficial branches of the radial nerve [72].
• The superficial branch of the radial nerve is mobilized and retracted during wrist arthrodesis [2].
• The dorsal branch of the radial artery is located, ligated, and divided to the dorsal carpal arch during wrist arthrodesis [2].
• The extensor carpi radialis longus tendon is divided just proximal to its insertion on the base of the second metacarpal during wrist arthrodesis [2].
• The abductor pollicis longus, extensor pollicis brevis, and wrist and finger extensors are mobilized subperiosteally and retracted during wrist arthrodesis [2].
• The dorsal carpal ligament is incised in the interval between the first and second dorsal compartments during wrist arthrodesis [2].
• The dorsal carpal ligament is left attached to the volar aspect of the radius during wrist arthrodesis [2].
• The dorsal carpal ligament is closed deep to the abductor pollicis longus and extensor pollicis brevis during wrist arthrodesis [2].
• The extensor carpi radialis longus tendon is sutured during wrist arthrodesis [2].
• A dorsal longitudinal incision is made for dorsal synovectomy, curved only slightly ulnarward and long enough to expose the distal ulna and the extensor retinaculum [12].
• The incision for dorsal synovectomy avoids curving sharply because the flap circulation may be impaired [12].
• The larger veins and all identifiable sensory nerves are preserved during dorsal synovectomy [12].
• A laterally based retinacular flap is raised during dorsal synovectomy [12].
• Transverse incisions are made at the proximal and dist

Biomechanics and Function¶

Kinematics and Motion Patterns¶

• The wrist can essentially be considered to be a two-joint system linking the hand to the forearm around the highly mobile bones of the proximal carpal row [18].
• The two principle articulations are the radiocarpal and midcarpal joints, situated proximal and distal to the mobile proximal carpal row [18].
• During flexion and extension, most motion occurs at the radiocarpal joint, with some occurring through the midcarpal area [11].
• Using ultrafast CT in vivo kinematic studies, the radiocarpal and midcarpal joints were found to contribute equally to wrist flexion [11].
• The midcarpal joint contributed more to extension than the radiocarpal joint [11].
• The proximal carpal row is considered to be an intercalated segment in the forearm-to-hand connection [11].
• The scaphoid functions to stabilize the wrist [11].
• Dart-thrower’s motion rotation occurs along the mechanical axis of the wrist [18].
• In most individuals, the proximal carpal row rotates predominantly around the flexion-extension axis during radioulnar deviation [18].
• In a few individuals, there is more radioulnar translation than flexion-extension during radioulnar deviation [18].
• The magnitude of out-of-plane motion during radioulnar deviation varies substantially from one individual to another [18].
• All bones of each row rotate in the same plane during any direction of global wrist motion [18].
• In all but pure flexion/extension of the uninjured wrist, the proximal and distal rows move in divergent directions [18].
• Carpal kinematics cover a spectrum from the "row" theory to the “column" theory which is normally distributed [101].
• Women are more likely to have a column type wrist [101].
• High-speed, three-dimensional kinematic analysis findings alter the understanding of carpal kinematics obtained from previous studies which suggested that the center of rotation was fixed in the capitate [104].
• There is a spectrum of movements of the scaphoid in two planes, where the scaphoid can either flex, translate or supinate on the radius, or more commonly move by combination of two or three of these during radial and ulnar deviation [109].
• In flexion-extension motion, the triquetrum-hamate joint involves rotation in an almost flexion-extension plane of the wrist [26].
• Out-of-plane motions combine to produce in-plane wrist radioulnar deviation [100].

Structural Models and Stability¶

• The stability of the wrist during motion and interrelated motions depends on capsuloligamentous integrity and contact surface contours of the carpal bones [11].
• The concept of a wrist consisting of three columns was popularized by Novarro: the central (force-bearing) column, the radial column, and the ulnar (control) column [11].
• The central column includes the distal articular surface of the radius, the lunate, and the capitate [11].
• Some include the proximal two thirds of the scaphoid, the trapezoid, and the articulations with the second and third metacarpal bases in the central column [11].
• The radial column includes the radius, the scaphoid, the trapezium, the trapezoid, and the thumb carpometacarpal joint [11].
• The ulnar column includes the triangular fibrocartilage (articular disc), the hamate, the triquetrum, and the articulations of the carpometacarpal joints of the ring and little fingers [11].
• Taleisnik proposed that the central column includes the entire distal row and the lunate [11].
• According to Taleisnik's concept, the scaphoid is included as the lateral column and the triquetrum as a rotary medial column [11].
• Lichtman proposed a ring concept of wrist kinematics where interosseous ligaments stabilize the semirigid proximal and distal carpal rows [11].
• Limited mobility occurs between the scaphotrapezial joints and the triquetrohamate joints in the ring concept [11].
• Bone or ligament disruption of the ring creates instability deformities, with the lunate tilting either dorsally or volarly [11].
• The carpus functions as an oval ring formed by four interdependent elements (distal row, scaphoid, lunate, and triquetrum) connected to the adjacent segments by ligamentous links [18].
• The lunate, capitate, hamate, trapezium, and trapezoid function collectively as the “stable central column” [18].
• The stable central column is controlled by the scaphoid in a two-gear, four-bar linkage system [18].
• The triquetrum stabilizes the central column by buffering lunate rotation and preventing ulnar translation [18].
• This stability is due to the strength of the various capsules and ligaments rather than the interlocking of different pieces of the skeleton [4].
• The transverse arch of the distal carpal row is much more rigid [4].
• Each of the bones that make up the proximal row (scaphoid, lunate, and triquetrum) has its own distinct movements [4].
• The carpus does not form a single rigid bony block because the eight small bones of the carpus all have different degrees of movement [19].
• The distal row is quite rigid, but the three proximal row bones are relatively mobile [19].
• Carpal stability is largely due to interosseous ligaments and bony configuration of these carpal bones [19].
• The stability of the carpal bones does not rely upon tendon insertions, with the exception of the pisiform which is a sesamoid in flexor carpi ulnaris tendon [19].
• The normal inclination of the radiocarpal joint surface is an inherently unstable one consisting of ulnar deviation and volar flexion [22].
• In a normal wrist, this unstable condition is neutralized by a strong and complex set of anterior wrist ligaments that resist supination of the carpal bones on the distal end of the forearm [22].
• The human forearm reaches the most sophisticated compromise between strength, mobility and stability [24].

Load Transfer and Mechanics¶

• The dynamic changes in wrist and forearm geometry observed during grasp and isometric contraction are important for an understanding of wrist and forearm force transmission [39].
• Loads greater than 46 pounds were not found to significantly increase the overall contact areas, implying that the cartilage of the wrist joint was maximally compressed at loads of this magnitude [89].
• Rotation of the scaphoid and lunate as the wrist moves from extension to flexion has a double “cam” effect [19].
• Rotation in a sagittal plane allows the persistent adaptation of the carpal articular surface in order to present the correct diameter of curvature to the distal radius [19].
• The carpus is a “condyle of variable geometric form” [19].
• The posterior lip and the radial styloid have a buttressing effect [19].
• The carpal articular surface has a smaller diameter of curvature than the radius [19].
• The precarious stability of the carpal articular surface in the medial and palmar aspects depends upon ligamentous and capsular resistance [19].
• The scaphoid presents a long axis inclined by 45 degrees to the long axis of the radius [19].
• The lunate sits on the capitate and has anterior and posterior horns [19].
• A line drawn between the anterior and posterior horns of the lunate lies perpendicular to the long axis of the wrist in neutral position [19].
• The flexor retinaculum retains finger flexor tendons close to the axes of flexion–extension and medial–lateral deviation [4].
• The flexors generate almost no torque at the radiocarpal joint while acting on the digits [4].
• The median nerve is compressed by the tendons when the wrist is in the flexed position [4].

Common Sites of Injury¶

Bony Anatomy and Kinematics¶

• The carpal arch has a deep palmar concavity that resembles a rigid osseous mass, sometimes incorrectly termed the “carpal block” [4].
• The transverse arch of the distal carpal row is much more rigid, with the capitate forming the keystone of this arch [4].
• The wrist is more stable in flexion than in extension due to the strength of various capsules and ligaments rather than skeletal interlocking [4].
• The distal carpal row may bear more than 10 times the force applied to the fingertips [64].
• About 55% to 60% of the load on the distal carpal row is transmitted through the capitate, scaphoid, and lunate [64].
• At the radiocarpal level, the load on the radioscaphoid joint varies from 50% to 56% [64].
• At the radiocarpal level, the load on the radiolunate joint varies from 29% to 30% [64].
• At the radiocarpal level, the load on the ulnolunate joint varies from 10% to 21% [64].
• The center of the distal radial articular surface was palmar on the long axis of the radius in all 50 radiographs studied, with a mean value of 5.3 mm [27].

Ligamentous Stability and Injury Patterns¶

• Bone or ligament disruption of the carpal ring creates instability deformities, with the lunate tilting either dorsally or toward the volar aspect [11].
• The scaphoid fractures result from wrist extension with the dorsal articular margin of the radius serving as a fulcrum [71].
• Carpal dislocations result from ulnar deviation and intercarpal supination [71].
• Flexion and pronation injuries may contribute more to ligament injuries on the ulnar side of the wrist, especially the lunotriquetral ligament [71].
• Fractures of the radial styloid may be associated with scapholunate ligament injuries because the intra-articular fracture line extends into the joint at that level [59].
• In isolated radial styloid fractures, intercarpal ligament injuries must be suspected [59].
• The degenerative changes in the pisotriquetral joint occur most frequently in the distal, distal-radial, and radial aspect of the pisiform and triquetrum, and additionally in the distal-ulnar aspect of the triquetrum [61].

Pathomechanics and Deformity¶

• In juvenile arthritis, uncontrolled joint synovitis stretches essential ligaments and eventually erodes cartilage and bone, resulting in a progressive shift of the carpus ulnarward and volarward [22].
• This movement of the hand–carpus unit in juvenile arthritis leaves the ulna dorsally dislocated and creates a dorsal wrist step-off because of the subluxed carpus [22].
• The destruction of wrist mechanics in juvenile arthritis is accompanied by loss of active and passive wrist extension and weakness of grip [22].
• In rheumatoid arthritis, the classic pattern of deformity involves the radiocarpal and radioulnar joints with destabilization of the carpus caused by attenuation of the extrinsic wrist ligaments [58].
• The result of rheumatoid arthritis wrist involvement is ulnar-palmar translocation and wrist supination [58].
• In early-to-midstage rheumatoid arthritis wrists, volar flexion of the lunate relative to the scaphoid occurs in 100% of cases due to intrinsic ligament laxity, mainly of the scapholunate ligament [58].
• At later stages of rheumatoid arthritis, the capitate tends to flex dorsally due to midcarpal instability as a result of extrinsic ligament weakening [58].
• The force vector across the rheumatoid wrist predominately acts in a palmar-ulnar direction [58].

Surgical Anatomy¶

Bony Anatomy and Kinematics¶

• In the lateral projection, the radius, lunate, capitate, and third metacarpal should have collinear axes within an approximately 15-degree tolerance [80].
• The distal scaphoid tubercle does not normally articulate with the radial styloid [77].
• The capitate-hamate joint is normally rigid [77].

Neurovascular Anatomy¶

• The superficial branch of the radial nerve averages 16 mm (5 to 22 mm) from the 3-4 portal [83].
• The dorsal sensory branch of the ulnar nerve averages 8 mm (0 to 14 mm) from the 6R portal [83].
• The 1-2 portal carries a high risk of injury to the superficial branch of the radial nerve [83].
• The 6U portal carries a high risk of injury to the dorsal sensory branch of the ulnar nerve [83].
• The radial artery is frequently intimately attached to the wall of a volar wrist ganglion and may be completely encircled by it [37].
• A careful radial approach to the wrist with styloidectomy preserves the superficial branches of the radial nerve, the antebrachial cephalic vein, and the radial artery [44].
• Resection of the anterior interosseous nerve at a point 4 cm proximal to the proximal point of the ulnar head denervates completely the pronator quadratus [38].
• An anomalous course of the palmar cutaneous branch of the median nerve has been described [47].
• No discrete bottleneck was found that could determine scientifically a proximal end point for carpal tunnel release [46].

Ligamentous and Soft Tissue Anatomy¶

• The posterior interosseous nerve terminal branch can be located on the radial floor of the fourth extensor compartment [82].
• The radioscaphocapitate and long radiolunate ligament interval may be the site of origin for the volar wrist ganglion [83].
• Volar wrist ganglions arising from the radiocarpal joint occur under the volar wrist crease between the flexor carpi radialis and abductor pollicis longus tendons [37].
• The extensor carpi ulnaris tendon sheath attaches to the base of the fifth metacarpal [12].
• The distal ulna is attached to the radius and carpus by ligaments that may be intact or disrupted in subluxation [12].

Arthroscopic Portal Anatomy¶

• The ideal working portal for arthroscopic excision of a dorsal wrist ganglion is the 3-4 portal with visualization from the 4-5 or 6R portals [83].
• Visualization of a foveal triangular fibrocartilage complex tear cannot be accomplished from the radiocarpal joint, only from a distal radioulnar joint arthroscopy [83].
• The radial tunnel for triangular fibrocartilage complex reconstruction should exit volarly just distal to the pronator quadratus muscle [42].
• The radial tunnel for triangular fibrocartilage complex reconstruction should be kept 5 mm away from the lunate sigmoid fossae to avoid fracture [42].
• The ulnar tunnel for triangular fibrocartilage complex reconstruction is created at the middiaphyseal point of the ulna, parallel to the ulnar shaft, targeting the fovea [42].

Key Evidence¶

• [L5] The wrist functions as two carpal rows with the distal row bones relatively tightly bound to one another and the proximal row bones less so but still moving together. [3] (10.1016/0363-5023(88)90189-x)
• [L4] The original description of the carpal arcs still applies, but only on a true neutral PA wrist x-ray where the third metacarpal shaft and the midradius axes are collinear. [9] (10.1016/s0363-5023(96)80004-9)
• [L4] The morphological study showed a dorsal displacement of the median nerve during flexion of the wrist in 84.5% of the patients. [16] (10.1016/0266-7681(87)90061-1)
• [L4] The morphological study showed a dorsal displacement of the median nerve during flexion of the wrist in 84.5% of the patients. [17] (10.1016/0266-7681_87_90061-1)
• [L5] Structures originating from the ulna changed their major constraint contribution with forearm orientation, whereas those with a radial origin had a constant contribution independent of forearm rotation. [20] (10.1016/s0363-5023(05)80031-0)
• [L5] The deep limb has a narrow marginal insertion just behind the pole of the distal ulna, suggesting its role as the capsular ligament. [23] (10.1177/1558944716660555x)
• [Paper] The human forearm reaches the most sophisticated compromise between strength, mobility and stability and becomes the hand’s greatest ally. [24] (10.1016/j.main.2015.10.143)
• [L5] Arthroscopy is an accepted technique for evaluation of intra-articular pathology and treatment of a variety of disorders even in the wrist joint. [25] (10.1016/j.main.2006.07.029)
• [L4] In FEM it was rotation in an almost flexion-extension plane of the wrist. [26] (10.1016/s0363-5023(03)00259-4)
• [L4] In all 50 radiographs, the centre of the distal radial articular surface was palmar on the long axis of the radius, with a mean value of 5.3 mm. [27] (10.1016/s0266-7681(02)00398-4)
• [L4] Lateral wrist radiographs can provide a complete picture of the ulnar border of the radius for measuring ulnar variance. [30] (10.1142/s2424835520500137)
• [L4] Across the wide range of wrist sizes studied the individual carpal volumes were a consistent percentage of carpus volume and this percentage did not differ with gender. [35] (10.1016/j.jhsa.2004.08.012)
• [L5] Resection of the AIN at a point 4 cm proximal to the proximal point of the ulnar head would denervate completely the PQ in our cadaver population. [38] (10.1016/j.jhsa.2005.06.010)
• [L4] The dynamic changes in wrist and forearm geometry observed in this study are important for an understanding of wrist and forearm force transmission. [39] (10.1016/0363-5023(92)90320-o)
• [L5] Its attachment at the triangular fibrocartilage influences the distal radioulnar joint, and its insertion at the triangular fibrocartilage and support of the weakest part of the dorsal capsule are of interest. [40] (10.1016/s0266-7681(98)80170-8)
• [L5] A careful approach preserves the superficial branches of the radial nerve, the antebrachial cephalic vein and the radial artery. [44] (10.1016/j.hansur.2017.04.001)
• [L4] No discrete bottleneck was found that could determine scientifically a proximal end point for carpal tunnel release. [46] (10.1016/j.jhsa.2004.12.004)
• [L5] A case is presented of an anomalous course of the palmar cutaneous branch of the median nerve. [47] (10.1016/0266-7681(93)90102-l)
• [L4] Male wrists were significantly larger than female wrists, but there were no significant differences in the relative dimensions between left and right wrists. [49] (10.1016/s0363-5023(05)80138-8)
• [L5] The most common lunate morphology (73%) had a separate medial facet on its distal surface for the hamate, and the capitate had a separate facet for the fourth metacarpal in 86% of the wrists. [51] (10.1016/0363-5023(93)90094-j)
• [L5] The degenerative changes occur most frequently in the distal, distal-radial, and radial aspect of the pisiform and triquetrum, and additionally in the distal-ulnar aspect of the triquetrum. [61] (10.1016/s0363-5023(98)80044-0)
• [L5] In no specimen did the authors identify a deep branch of the ulnar artery coursing with the deep motor branch of the ulnar nerve and contributing to a deep palmar arterial arcade, leading them to conclude that the classic description of a deep palmar arterial arch is not valid due to the mistaken identity of hypothenar arterial branches. [75] (10.1016/s0363-5023(96)80016-5)
• [L5] The dorsal carpal arch was present in all cases and always ran above the distal carpal row, anastomosed to the ulnar artery in 4 cases and to the radial artery in all cases. [86] (10.1016/j.hansur.2017.02.004)
• [L5] Loads greater than 46 pounds were not found to significantly increase the overall contact areas, implying that the cartilage of the wrist joint was maximally compressed at loads of this magnitude. [89] (10.1016/s0363-5023(89)80004-8)
• [L5] The blood supply of the thumb comes mainly from the princeps pollicis artery, the terminal branch of the superficial palmar arch, and the first dorsal metacarpal artery. [94] (10.1016/s0363-5023(88)80085-6)
• [L5] Our study shows how these out-of-plane motions combine to produce in-plane wrist radioulnar deviation. [100] (10.1016/j.jhsa.2005.05.016)
• [L4] It is felt that carpal kinematics thus cover a spectrum from the "row" theory to the “column" theory which is normally distributed and that women are more likely to have a column type wrist. [101] (10.1016/s0266-7681(05)80044-0)
• [L5] Branches of the PCBm innervating the scaphoid were typically found, but in no specimen did we find a ‘typical’ cutaneous branch of the ulnar nerve. [103] (10.1016/s0266-7681(98)80061-2)
• [L5] These findings alter the understanding of carpal kinematics obtained from the results of previous studies which suggested that the center of rotation was fixed in the capitate. [104] (10.1016/s0363-5023(05)80462-9)
• [Paper] This space is bounded by the fibrous bed anteriorly and the anterior ligament of the carpus posteriorly, and contains the ulnar artery and nerve on its posterior wall. [106] (10.1016/j.jhsb.2005.12.008)
• [L4] The study confirms the presence of a transverse radioulnar branch from the dorsal sensory ulnar nerve in approximately 80% of cases, documenting its size, course, and type specificity. [107] (10.1016/0363-5023(94)90013-2)
• [L4] This work confirms that there is a spectrum of movements of the scaphoid in two planes, where the scaphoid can either flex, translate or supinate on the radius, or more commonly move by combination of two or three of these during radial and ulnar deviation. [109] (10.1016/s0266-7681(98)80092-2)
• [L5] The insertion of the tendon into the proximal phalanx, and not into the extensor mechanism of the middle finger, suggests that it may function as a metacarpal or even wrist extensor, as well as metacarpophalangeal extensor. [110] (10.1016/0266-7681(93)90007-3)

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