Table of Contents
- 01. Rotator Cuff
- 1. Anatomy and Function
- 2. Pathogenesis
- 3. Terminology
- 4. Natural History
- 5. Ultrasound Technique
- 6. Spectrum of Findings
- 7. Ultrasound Pitfalls
- 8. References
- 02. Postoperative Rotator Cuff
- 03. Long Head of Biceps Brachii Tendon
- 04. Bursae
- 05. Joint Spaces
- 1. Acromioclavicular Joint
- 2. Glenohumeral Joint
- 3. Sternoclavicular Joint
- 4. Scapulothoracic
- 5. References
- 06. Fractures
- 07. Os acromiale
- 08. Adhesive Capsulitis
- 09. Deltoid
- 10. Pectoralis Major
- 11. Web Exclusive: Sternocostal Joints
- 12. Web Exclusive: Musculoskeletal Ultrasound Educational Videos
- a. Best Original Manoeuver
- b. Snapping Film Direction
- c. Actor in a Leading Role
- d. Actress in a Leading Role
- e. Actor in a Supporting Role
- f. Actress in a Supporting Role
- g. Best Correlation Between Clinical and Sonographic Findings
- h. Joint Instability Short Film Documentary
- i. Unedited Film
- j. Real Time Impingement Short Film
- k. Nerve Compression Short Film
- l. Doppler Feature Special Award for Lifetime Achievements
- m. Interventional Feature Special Award for Distinguished Body of Work
- n. Honorary Award
1.2.4. Acromioclavicular Joint Ultrasound: Traumatic Dislocation
Traumatic acromioclavicular joint (ACJ) dislocation has been described since the time of Hippocrates and results from a sprain or a tear in supporting structures.37 It usually develops from direct trauma and tends to occur in younger physically active individuals. Tossy originally classified ACJ dislocation into three types: mild, moderate, and severe.38 Subsequently, the Tossy classification was expanded by Rockwood to include subtypes of severe dislocation and became the most commonly used classification system to define management (figure 5-10).39
Investigation of suspected ACJ dislocation traditionally involves conventional radiographs because they are widely available and clearly demonstrate moderate and severe lesions, though it has limitations to diagnose mild injuries. In addition to conventional radiographs, weight-bearing views may be used to better differentiate between moderate and severe dislocations, but the evidence for this is controversial40 and some authors recommend that routine use of this technique be abandoned.41
US is also useful for diagnosis and classification of ACJ dislocation according to the well-established Rockwood system (table 5-1). The primary diagnostic criteria are capsular thickening, abnormal alignment of bony structures, and widening of the joint space. In order to objectively assess these findings, bilateral evaluation should be performed to provide a standard reference for the normal ACJ in the uninjured shoulder. The acromioclavicular index is helpful to evaluate joint space widening, and calculated by dividing the acromioclavicular distance on the contralateral asymptomatic side by that on affected side.38 It is important to recognize that the ACJ space is slightly wider anteriorly than posteriorly, and contralateral comparison should be made only at similar levels. In grade 1, or mild dislocation, the acromioclavicular index is close to 1.0, the intrinsic acromioclavicular ligaments are sprained, and the coracoclavicular ligament is intact (figure 5-11). In grade 2, or moderate dislocation, the acromioclavicular index is close to 0.5, the intrinsic acromioclavicular ligaments are completely torn, and the coracoclavicular ligament is intact or sprained (figure 5-12). Grades 3, 4, 5, and 6 have the acromioclavicular index close to 0.25 and are considered severe dislocations as both intrinsic acromioclavicular and coracoclavicular ligaments are completely torn (figure 5-13). The coracoclavicular index is utilized to differentiate between different subtypes of severe dislocation and obtained in a similar way to the method used to calculate the acromioclavicular index (i.e. by dividing the coracoclavicular distance on the contralateral asymptomatic side by that on affected side). In grade 3 dislocation, coracoclavicular index ranges between 0.8 and 0.5 (figure 5-14); in grade 4, coracoclavicular index may be 1.0 since clavicle is dislocated mainly posteriorly; in grade 5, coracoclavicular index is lower than 0.5 (figure 5-15); in type 6, coracoclavicular index is negative because clavicle is dislocated inferior to the coracoid process. Doppler US may be used to increase diagnostic confidence to detect low-grade injuries because it depicts reparative process to injured ligament (video 5-1). Detection of vacuum phenomenon also increases diagnostic confidence as it is usually associated to ACJ distraction (see section 1.2.7).
Table 5-1. Rockwood classification of ACJ dislocations adapted for US. See text for details.
Figure 5-14. Grade 3 traumatic dislocation of the ACJ.
Chronic sprains of the intrinsic acromioclavicular ligaments may show varying degrees of calcification (figure 5-16). Such calcifications may be demonstrated as intraligamentous during dynamic evaluation (video 5-2). This finding must be differentiated from small avulsion fractures of the distal clavicle, which are depicted occasionally as an associated finding (figure 5-17). Pleomorphic calcifications must also be differentiated from chondrocalcinosis (see section 1.2.6).
Most cases referred for US in acute trauma setting consist of minor (grade 1) injury with missed or overlooked findings on radiographs. Dynamic US is critical to detect such mild dislocations, especially because they may present as a normal joint in static images. The degree of bone displacement during dynamic evaluation is proportional to the severity of ligament injury, and mild dislocation (video 5-3) shows less instability than moderate (video 5-4) or severe dislocations (video 5-5).
Management for mild (grade 1) and moderate (grade 2) dislocations is usually conservative. Early surgical intervention for acute grade 4, 5, and 6 dislocations is indicated due to the significant morbidity associated with joint instability. The treatment of grade 3 lesions is controversial, although surgery is probably best reserved for those injuries that fail to respond adequately to conservative management.