Acromioclavicular joint injuries (“separated” shoulder)
- Scott M Koehler, MD
Scott M Koehler, MD
- Physician, Sports Medicine Specialist
- Allina Medical Clinic, Northfield
- Section Editor
- Karl B Fields, MD
Karl B Fields, MD
- Editor-in-Chief — Primary Care Sports Medicine (Adolescents and Adults)
- Section Editor — Biomechanics, Rehabilitation, and Recovery; Sports-Related Injuries; Symptom Assessment and Physical Examination
- Professor of Family Medicine and Sports Medicine
- University of North Carolina at Chapel Hill
The acromioclavicular (AC) joint is situated at the distal end of the clavicle forming an articulation with the acromion of the scapula (picture 1). The AC joint complex is strong, but its location makes it vulnerable to injury from direct trauma. Injuries to the AC joint are classified according to the position of the clavicle with respect to the acromion and coracoid. Treatment is based upon the extent of injury. AC joint injuries are sometimes referred to as sprains or a “separated” shoulder.
The evaluation and management of AC injuries will be reviewed here. A general approach to the patient with shoulder pain and discussions of other specific shoulder injuries are found elsewhere. (See "Evaluation of the patient with shoulder complaints" and "Glenohumeral osteoarthritis" and "Multidirectional instability of the shoulder" and "Rotator cuff tendinopathy".)
ANATOMY AND BIOMECHANICS
A more complete discussion of shoulder anatomy and biomechanics is found separately. The structure and function of the acromioclavicular (AC) joint is described below. (See "Evaluation of the patient with shoulder complaints", section on 'Anatomy and biomechanics'.)
The AC joint is supported by ligaments that span its anterior, superior, posterior, and inferior aspects (picture 1). These ligaments also envelop the distal 1 to 2 cm of the clavicle. In addition to the AC ligaments, the distal clavicle is held in alignment with the acromion by the strong coracoclavicular (CC) ligaments. These ligaments consist of the conoid ligament medially and the trapezoid ligament laterally. The AC joint itself has a cartilaginous disk and synovial membrane.
Joint motion is limited, but the clavicle can rotate a few degrees, and small amounts of translation and slight angulation are possible. The clavicle and scapula tend to move in unison, and investigators have shown fully preserved shoulder range of motion (ROM) with fusion of the AC joint . Anatomic drawings of the shoulder are provided (figure 1 and figure 2 and figure 3).
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- ANATOMY AND BIOMECHANICS
- EPIDEMIOLOGY, MECHANISM, AND CLASSIFICATION
- HISTORY AND EXAMINATION
- DIAGNOSTIC IMAGING
- Plain radiographs
- Additional ultrasound resources
- SPECIFIC AC INJURIES: DESCRIPTION AND RADIOGRAPH APPEARANCE
- DIFFERENTIAL DIAGNOSIS
- General issues
- Rehabilitation during recovery from Type I and II injuries
- Type I (mild injury)
- Type II
- Type III (moderate injury)
- Types IV, V, and VI (severe injury)
- INFORMATION FOR PATIENTS
- SUMMARY AND RECOMMENDATIONS