Causes of Supraspinatus Tendon Rupture
Supraspinatus tendon rupture is primarily caused by repetitive mechanical impingement of the coracoacromial arch onto the tendon during overhead activities, compounded by intrinsic hypovascularity in the critical zone near the tendon insertion. 1
Primary Causative Mechanisms
Extrinsic Mechanical Factors
Repeated impingement is the dominant mechanism of supraspinatus tendon injury. 1 The pathophysiology involves:
- Subacromial impingement: The supraspinatus tendon occupies a narrow anatomical space with minimal clearance between the tendon and the coracoacromial arch during normal shoulder abduction 1
- Superior migration of the humeral head: Rotator cuff muscle weakness and improper functioning allow the humeral head to migrate superiorly, resulting in increased mechanical impingement on the supraspinatus tendon 1
- Repetitive overhead activities: Athletes who throw repetitively and laborers who work with their arms overhead are at particularly high risk, affecting approximately 1 in 50 adults 1
Intrinsic Vascular Factors
- Hypovascularity: The region proximal to the insertion of the supraspinatus tendon has inherently poor blood supply, making it vulnerable to degenerative changes and rupture 1
- Tendon degeneration: Most ruptures occur in the setting of chronic tendinosus with collagen fiber disorientation and degeneration, rather than acute inflammation alone 2
Specific Injury Patterns
Traumatic Ruptures
- Acute trauma: Direct injury can cause rupture, particularly at the musculotendinous junction, though this is uncommon 3, 4
- Stretch injuries: High-force eccentric loading can cause complete rupture at the musculotendinous junction, presenting with acute pain and muscular edema on MRI 3
Degenerative Ruptures
- Chronic overuse: The most common pattern involves insidious onset of load-related pain coinciding with increased activity intensity 2
- Progressive tendon degeneration: Structural and biological changes accumulate over time, with cellular and extracellular modifications weakening the tendon 2
High-Risk Populations
- Overhead athletes: Particularly those involved in throwing sports 1
- Manual laborers: Workers requiring repetitive overhead arm positioning 1
- Age-related degeneration: Risk increases with age due to cumulative microtrauma and decreased vascularity 2
Important Clinical Caveat
Musculotendinous junction ruptures are uncommon but clinically significant. 3, 4 These injuries:
- Occur more frequently with acute trauma 3
- Present with acute pain and muscle edema on T2 MRI sequences 3
- Have poor outcomes with nonoperative management when complete rupture with muscle retraction occurs, leading to severe fatty infiltration 3
- Contrast with the more common insertional tears at the bone-tendon interface 3, 4