अक्रोमियल

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¶

• In Thai patients with shoulder problems who required MRI evaluation, the prevalence of os acromiale was 2.13% [1].
• Os acromiale is associated with rotator cuff injuries [5].
• A multicenter study determined the prevalence of and factors associated with os acromiale in the Japanese population [6].
• Surgical treatment is usually not indicated for os acromiale in the professional tennis player [7].
• The presence of os acromiale does not appear to have a negative impact on the clinical outcomes after surgery, and reverse total shoulder arthroplasty remains a safe and effective treatment option [4].
• The outcome of reverse total shoulder arthroplasty does not seem to be negatively affected by the presence of an os acromiale [9].
• Postoperative local tenderness at the os acromiale can be expected in 1 out of 4 patients but resolves spontaneously over time in the majority of patients [3].
• Ipsilateral os acromiale may be a relative contraindication to the clavicle hook plate [13].
• Operative management of a symptomatic os acromiale that has failed initial nonoperative treatment leads to decreased symptoms and improvement in clinical outcomes [2].
• Surgical options for symptomatic os acromiale include arthroscopic sub-total excision, arthroscopic subacromial decompression of stable fragments, and open reduction and internal fixation of unstable fragments [10].

Anatomy & Pathophysiology¶

Bony Anatomy¶

• The acromion has three ossification centers: the metacromion (base), the mesoacromion (middle), and the preacromion (tip) [28].
• Failure of fusion of the acromial ossification centers results in os acromiale [28].
• The unfused segment in os acromiale is most commonly the meso-acromion, a configuration often termed a meso-type os acromiale [14].
• The scapula is attached to the axial skeleton by the clavicle, specifically via the acromioclavicular (AC) and sternoclavicular (SC) joints [27].
• The acromion is a flattened bony process that curves forwards from the scapular spine [27].
• The acromion, coracoacromial ligament, and coracoid process form the coracoacromial arch, a rigid bony-ligamentous structure that imparts stability to the shoulder girdle [25].
• The rotator cuff, subacromial bursa, and subdeltoid bursa pass underneath the coracoacromial arch [25].

Pathophysiology¶

• Most diagnoses of os acromiale are made incidentally on axillary view radiographs of the shoulder [14].
• Primary shoulder pain is usually unrelated to the unfused os acromiale [14].
• When os acromiale drives symptoms, the two principal causes are motion at the non-union site or an impingement-type syndrome resulting from flexion of the os fragment during deltoid contraction and arm elevation [14].
• Pain from os acromiale via these mechanisms has been reported in a variety of sports, particularly among throwing athletes and swimmers [14].
• Previously stable non-unions can become unstable following an episode of blunt trauma to the region, such as direct impact to the shoulder during American football [14].
• A tear of the rotator cuff may often be associated with os acromiale, likely due to impingement from abnormal motion at the fibrous union site [8].
• Extrinsic impingement occurs when the space available for the rotator cuff is diminished, with examples including subacromial spurring, acromial fracture, or pathologic os acromiale [37].
• The synchondrosis of an os acromiale can be injured following trauma, though rarely [15].
• The presence of os acromiale does not appear to have a negative impact on the clinical outcomes after reverse total shoulder arthroplasty (rTSA) [4].
• The outcome of reverse total shoulder arthroplasty (RTSA) does not seem to be negatively affected by the presence of an os acromiale [9].
• Postoperative local tenderness at the os acromiale can be expected in 1 out of 4 patients following reverse total shoulder arthroplasty but resolves spontaneously over time in the majority of patients [3].

Classification¶

• Meta–os acromiale is the rarest subtype of os acromiale [18].
• Meso-type os acromiale is a recognized classification variant for which biomechanical evaluation of internal fixation has been performed [23].

Clinical Presentation¶

• Liberson reviewed 1800 shoulder girdles and identified an incidence of os acromiale of 1.4% [16].
• In Liberson's review of 1800 shoulder girdles, the lesion was bilateral in 62% of patients [16].
• The unfused segment in os acromiale is most commonly the meso-acromion [14].
• Any primary shoulder pain is usually unrelated to the unfused os acromiale [14].
• When os acromiale drives symptoms, one principle cause is motion at the non-union site [14].
• When os acromiale drives symptoms, another principle cause is an impingement-type syndrome resulting from flexion of the os fragment during deltoid contraction and arm elevation [14].
• Pain from os acromiale by the mechanism of impingement has been reported in a variety of sports, particularly among throwing athletes and swimmers [14].
• Previously stable non-unions of os acromiale can become unstable following an episode of blunt trauma to the region [14].
• Multicenter study findings support that os acromiale is associated with rotator cuff injuries [5].
• Awareness of os acromiale in the young athlete, appropriate clinical examination, and image studies are crucial to confirm diagnosis [12].
• Postoperative local tenderness at the os acromiale can be expected in 1 out of 4 patients following reverse total shoulder arthroplasty [3].
• Postoperative local tenderness at the os acromiale resolves spontaneously over time in the majority of patients following reverse total shoulder arthroplasty [3].
• The presence of os acromiale does not appear to have a negative impact on the clinical outcomes after surgery and rTSA remains a safe and effective treatment option [4].
• The outcome of RTSA does not seem to be negatively affected by the presence of an os acromiale [9].

Investigations¶

• Liberson reviewed 1800 shoulder girdles and identified an incidence of os acromiale of 1.4%, with the lesion being bilateral in 62% of patients [16].
• Awareness of the os acromiale in the young athlete, appropriate clinical examination, and image studies are crucial to confirm diagnosis [12].
• The synchondrosis of an os acromiale can be injured following trauma, though rarely, and emphasizes the need for appropriate radiographic investigation including axillary views [15].
• At least two X-ray views should be obtained: an anteroposterior in the plane of the glenoid and an axillary projection with the arm in abduction to show the relationship of the humeral head to the glenoid [33].
• Magnetic resonance imaging (MRI) is useful to identify labral tears and rotator cuff tears, although the accuracy for these is enhanced by combining the scan with arthrography [33].
• Ultrasound is a simple and accurate test for identifying rotator cuff tears and calcific tendinitis [33].
• The purpose of imaging of the shoulder is to help establish the diagnosis, determine the severity of the pathoanatomy, assist in surgical planning, and enable the surgeon to illustrate the condition of the shoulder to the patient [21].
• Unless a specific research protocol is in place, the temptation to “overimage” should be resisted, obtaining only the scans or reconstructions that are necessary for the care of the patient [21].
• Standardized plain films are almost always sufficient to garner the information needed, and there is information that can be gathered from properly taken plain films that cannot be obtained from CT scans [21].
• The first key view is the anteroposterior (AP) in the plane of the scapula taken so that the x-ray beam passes through the glenohumeral joint [21].
• The second key view is the axillary view taken with the arm in the functional position of elevation in the plane of the scapula and oriented so that both the spinoglenoid notch and the scapular neck are visible [21].
• The axillary view is referred to as the “truth view” because it demonstrates the glenohumeral relationships in the functional position of elevation [21].
• CT scans have the disadvantage of being taken with the arm in the adducted position, whereas the axillary truth view is taken with the arm in elevation [21].
• A robust approach to imaging the shoulder needs to recognize that the shoulder is a three-dimensional structure that cannot be represented by a single planar view [35].
• Critical relationships—such as the degree of centering of the humeral head—change with the position of the arm [35].
• Shoulder pathology may be found in a large number of different bones and soft tissues [35].
• Overlying and superimposed structures as well as metallic implants may complicate imaging the structures of interest [35].
• Surgeons need to develop a judicious approach that yields the information necessary to treat the patient while avoiding the tendency to "over-image" [35].

Treatment¶

Non-Operative¶

• Any primary shoulder pain is usually unrelated to the unfused os [14].
• Conservative treatment for symptomatic os acromiale can include physical therapy with ice and infiltration of the os acromial joint with Kenacort and Xylocaine 2% [40].

Operative¶

• Meta–os acromiale is the rarest subtype of os acromiale, and special consideration must be given to the type of tension-band construct used to achieve adequate compression and fixation [18].
• Arthroscopic fixation of os acromiale with absorbable screws provides promising clinical, cosmetic, and radiologic results with high patient satisfaction [22].
• A symptomatic os acromiale in a competitive female fastball pitcher was treated successfully with open reduction and internal fixation [41].
• For symptomatic os acromiale treated with osteosynthesis, nine screws (2.7- and 3.5-mm) were used in one case, including six anterior angle-stable screws, two posterior cortical screws, and two angle-stable locking screws [40].
• In cases of congenital or primary pseudarthrosis of os acromiale treated with osteosynthesis, an osteotomy of 1 mm was performed on each side of the osseous non-union including the cranial osteophytes [40].

Complications¶

• Postoperative local tenderness at the os acromiale resolves spontaneously over time in the majority of patients [3].
• Previously stable non-unions of the os acromiale can become unstable following an episode of blunt trauma to the region [14].

Key Evidence¶

• [L3] In Thai patients with shoulder problems who required MRI evaluation, the prevalence of os acromiale was 2.13%. [1] (10.1177/23259671221078806)
• [L4] Operative management of a symptomatic os acromiale that has failed initial nonoperative treatment leads to decreased symptoms and improvement in clinical outcomes. [2] (10.1016/j.jse.2019.05.047)
• [L3] Postoperative local tenderness at the os acromiale can be expected in 1 out of 4 patients but resolves spontaneously over time in the majority of patients. [3] (10.1177/2325967120965131)
• [L4] The presence of os acromiale does not appear to have a negative impact on the clinical outcomes after surgery and rTSA remains a safe and effective treatment option. [4] (10.1016/j.xrrt.2025.01.002)
• [L3] The study supports previous findings that os acromiale is associated with rotator cuff injuries. [5] (10.1016/j.jseint.2025.05.015)
• [L3] This multicenter study aimed to determine the prevalence of and factors associated with os acromiale in the Japanese population. [6] (10.1016/j.jse.2025.01.008)
• [L4] Surgical treatment is usually not indicated for os acromiale in the professional tennis player. [7] (10.1177/2325967118773723)
• [L4] A tear of the rotator cuff may often be associated with os acromiale, likely due to impingement from abnormal motion at the fibrous union site. [8] (10.2106/00004623-198466080-00029)
• [L4] The outcome of RTSA does not seem to be negatively affected by the presence of an os acromiale. [9] (10.1016/j.jse.2017.02.012)
• [L5] Surgical options for symptomatic os acromiale include arthroscopic sub-total excision, arthroscopic subacromial decompression of stable fragments, and open reduction and internal fixation of unstable fragments. [10] (10.5435/jaaos-d-17-00011)
• [L4] Awareness of the os acromiale in the young athlete, appropriate clinical examination, and image studies are crucial to confirm diagnosis. [12] (10.1016/j.jseint.2020.02.008)
• [L4] Ipsilateral os acromiale may be a relative contraindication to the clavicle hook plate. [13] (10.1186/s12891-021-04841-1)
• [L4] [14] (10.1302/2058-5241.4.180100)
• [L4] This case highlights that the synchondrosis of an os acromiale can be injured following trauma, though rarely, and emphasizes the need for appropriate radiographic investigation including axillary views and a flexible surgical approach. [15] (10.1016/j.jse.2008.02.012)
• [L4] Meta–os acromiale is the rarest subtype of os acromiale, and special consideration must be given to the type of tension-band construct used to achieve adequate compression and fixation. [18] (10.1177/03635465211028238)
• [L4] This new arthroscopic technique of fixation of os acromiale with absorbable screws provides promising clinical, cosmetic, and radiologic results with high patient satisfaction. [22] (10.1016/j.jse.2011.12.011)
• [L5] Surgical repair of a simulated, unstable meso-type os acromiale by a combination of cannulated screws inserted in the A-P direction with a tension band leads to significantly improved repair strength at time zero compared with cannulated screws alone. [23] (10.1016/j.jse.2014.09.040)
• [L4] [40] (10.1186/s40634-017-0111-7)
• [L4] A symptomatic os acromiale in a competitive female fastball pitcher was treated successfully with open reduction and internal fixation. [41] (10.1177/0363546506288305)

References¶

[1] Prevalence of Os Acromiale in Thai Patients With Shoulder Problems: A Magnetic Resonance Imaging Study. Orthopaedic Journal of Sports Medicine. 2022. DOI: 10.1177/23259671221078806

[2] Os acromiale: systematic review of surgical outcomes. Journal of Shoulder and Elbow Surgery. 2020. DOI: 10.1016/j.jse.2019.05.047

[3] Os Acromiale in Reverse Total Shoulder Arthroplasty: A Cohort Study. Orthopaedic Journal of Sports Medicine. 2020. DOI: 10.1177/2325967120965131

[4] Clinical implications of reverse total shoulder arthroplasty with an os acromiale: a systematic review. JSES Reviews, Reports, and Techniques. 2025. DOI: 10.1016/j.xrrt.2025.01.002

[5] Prevalence and factors associated with os acromiale: a multicenter study. JSES International. 2025. DOI: 10.1016/j.jseint.2025.05.015

[6] The prevalence and associated factors of os acromiale: a multicenter study. Journal of Shoulder and Elbow Surgery. 2025. DOI: 10.1016/j.jse.2025.01.008

[7] Os Acromiale in Professional Tennis Players. Orthopaedic Journal of Sports Medicine. 2018. DOI: 10.1177/2325967118773723

[8] Rotator cuff tears associated with os acromiale.. The Journal of Bone & Joint Surgery. 1984. DOI: 10.2106/00004623-198466080-00029

[9] Reverse shoulder arthroplasty in patients with os acromiale. Journal of Shoulder and Elbow Surgery. 2017. DOI: 10.1016/j.jse.2017.02.012

[10] Symptomatic, Unstable Os Acromiale. Journal of the American Academy of Orthopaedic Surgeons. 2018. DOI: 10.5435/jaaos-d-17-00011

[12] The unstable os acromiale: a cause of pain in the young athlete. JSES International. 2020. DOI: 10.1016/j.jseint.2020.02.008

[13] Os acromiale may be a contraindication of the clavicle hook plate: case reports and literature review. BMC Musculoskeletal Disorders. 2021. DOI: 10.1186/s12891-021-04841-1

[14] Os acromiale: a review of its incidence, pathophysiology, and clinical management. EFORT Open Reviews. 2019. DOI: 10.1302/2058-5241.4.180100

[15] Fracture of an os acromiale with associated rupture of the coracoclavicular ligaments. Journal of Shoulder and Elbow Surgery. 2008. DOI: 10.1016/j.jse.2008.02.012

[16] Types of os acromiale according to Liberson. 2006.

[18] Rare Symptomatic Meta–Os Acromiale in an Athlete. The American Journal of Sports Medicine. 2021. DOI: 10.1177/03635465211028238

[21] Rockwood And Matsen S The Shoulder. Arthroscopic Management of Prearthritic and Arthritic Conditions of the Shoulder and the Postarthroplasty Shoulder > Radiographic Evaluation.

[22] Arthroscopically assisted internal fixation of the symptomatic unstable os acromiale with absorbable screws. Journal of Shoulder and Elbow Surgery. 2012. DOI: 10.1016/j.jse.2011.12.011

[23] Biomechanical evaluation of internal fixation techniques for unstable meso-type os acromiale. Journal of Shoulder and Elbow Surgery. 2015. DOI: 10.1016/j.jse.2014.09.040

[25] Rockwood And Matsen S The Shoulder. Shoulder and Elbow Specialty Clinic Workers’ Survey > ANATOMY.

[27] Rockwood And Green S Fractures In Adults. 29: Principles of Nonunion and Bone Defect Treatment > Applied Anatomy Related to Scapular Fractures.

[28] Aaos Comprehensive Orthopaedic Review 3. Anatomy of the Shoulder, Arm, and Elbow > I. Shoulder.

[33] Apley And Solomon S Concise System Of Orthopaedics And Trauma. INVESTIGATION.

[35] Rockwood And Matsen S The Shoulder. Developmental Anatomy of the Shoulder and Anatomy of the Glenohumeral Joint > SENIOR EDITOR COMMENTARY.

[37] Campbell S Operative Orthopaedics 4 Volume Set. ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION WITH BONE-PATELLAR TENDON-BONE GRAFT > Developmental Stages of Impingement Syndrome.

[40] Prebending of osteosynthesis plate using 3D printed models to treat symptomatic os acromiale and acromial fracture. Journal of Experimental Orthopaedics. 2017. DOI: 10.1186/s40634-017-0111-7

[41] Surgical Stabilization of Os Acromiale in a Fast-Pitch Softball Pitcher. The American Journal of Sports Medicine. 2006. DOI: 10.1177/0363546506288305