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
4.2.1. Scapulothoracic Joint Ultrasound: Snapping Scapula
Disorders of the scapulothoracic joint (STJ) are not very common and our experience is restricted to snapping scapula.
Snapping scapula was first described in 1867 by Boinet.89 The typical clinical scenario involves a young active individual who presents with snapping or crepitus during shoulder abduction that presents with variable pain, ranging from absent to annoying or disabling. When present, pain is often located to the superomedial angle or inferior pole of the scapula, and may radiate to the cervical region.90
Snapping scapula is usually considered an idiopathic condition, though it may be occasionally caused by skeletal or soft-tissue abnormalities.88 Skeletal abnormalities associated with this syndrome include bone deformities and abnormal scapular angulation.91 The most frequent bone deformity of the superomedial border of the scapula is a bulbous top or anterior hook causing abnormal contact with the thoracic cage.92 Bony projections at the inferior pole of the scapula are also common.93 The superomedial bare area of the anterior aspect of the scapula is another common anatomical variation located between the subscapularis muscle origin and serratus anterior muscle insertion that may cause symptoms. With scapula movement this bare area may impinge serratus anterior muscle against the chest wall, much like the acromion can impinge the supraspinatus tendon against the greater tuberosity of the humerus in patients with subacromial impingement.94 Unfortunately, all these bony changes are inaccessible to US and better assessed by CT.
Soft-tissue causes for snapping scapula include bursitis, muscular abnormalities, and tumors. Bursitis is generally considered an overuse injury from repetitive motion of the scapula over the thorax. Two major (anatomical) and numerous minor (adventitial) bursae have been described in the scapulothoracic region.95 The two major bursae that may become inflamed are the infraserratus and supraserratus, but the latter is inaccessible to US because of shadowing (figure 5-38). Though most of the infraserratus bursa is also occult behind the scapula, fluid distension of its posterior margin may be depicted at US (figure 5-39). The scapular crepitus associated with bursitis is usually much less intense than that associated with a bony change.
Muscular abnormalities associated to snapping scapula include atrophy and anomalous muscle insertions. Postoperative unilateral atrophy of the serratus anterior muscle is not uncommon following anterolateral thoracotomy with posterior extension and is considered the classical example of muscular abnormalities related to snapping scapula (figure 5-40). Clinical and experimental studies suggest stretching or sectioning of long thoracic nerve as the most likely cause.96
Another soft-tissue cause for snapping scapula is elastofibroma dorsi, a benign reactive fibroelastic hyperproliferation first described by Jarvi and Saxen in 1961.97 The typical presentation involves a slow-growing periscapular mass that almost exclusively affects individuals over the age of 40, with sporadic cases arising in children and adolescents.98,99 The lesion is believed to result from repeated mechanical friction between the thoracic wall and the inferior angle of the scapula. However, it may also result as a natural consequence of aging, rather than abnormal elastogenesis or degeneration. Large case series from Japan strongly suggest familial predisposition.100,101 At US, elastofibromas are depicted deep to the musculature as a multilayered pattern of hypoechoic linear areas of fat deposition intermixed with echogenic fibroelastic tissue (figure 5-41).102 The mass often protrudes from the subscapular region upon shoulder abduction, allowing better delineation of the finding.103-105 Elastofibromas can be differentiated from the most common lipoma on the basis of typical location and well-defined multilayered pattern.100 Complete surgical excision is the treatment of choice in symptomatic patients.
Figure 5-41. Elastofibroma dorsi.