Subscapularis insufficiency after shoulder arthroplasty

Last revised by Domenico Nicoletti on 12 Mar 2023

Subscapularis insufficiency after shoulder arthroplasty is a complication that can cause severe loss of function and implant longevity. Exposure of the glenohumeral joint during surgical total shoulder arthroplasty (TSA) procedures is associated with a risk of causing iatrogenic damage to the subscapularis muscle (SSC) and tendon that lead to functional implications.

The cause of loss of function of the SSC is due to failure of tendon repair and muscle changes such as atrophy or fat involution resulting in partial or complete insufficiency of the SSC.

The SSC deficiency leads to a decrease in the infraspinatus muscle that restores mechanical balance, which requires an increase in the force exerted by the supraspinatus muscle and middle deltoid. These changes lead to upward migration of the humeral head, eccentric contact patterns, and a 2% decrease in contact pressures.

Failure rates of SSC repairs after shoulder arthroplasty are between 6.7% and 47.2%.

Access to the glenohumeral joint can be obtained by different SSC tendon take-down techniques such as tendon-to-tendon repair, tendon-to-bone repair, and lesser tuberosity osteotomy (LTO).

No SSC repair technique has been identified as clearly superior, but seems better functional outcomes with LTO techniques have been observed. However, even with LTO techniques, after a mean follow-up of 39 months, the tuberosity osteotomy fragment healed anatomically in all cases, but 40% of patients had a postoperative increase in fat infiltration of at least 1 stage and 15% of patients at least 2 stages.

Sudden development of internal rotation weakness or anterior instability, and excessive external rotation.

AP view (Grashey views) and axillary views: anterior subluxation and upward migration of humeral head.

Useful in the postoperative period with regard to tendon healing.

Can be used to detect anterior subluxation of humeral head, tendon tears and grade the fatty degeneration as per Goutallier et al. (Goutallier classification of rotator cuff muscle fatty degeneration).

To evaluate re-tears of the subscapularis tendon, muscle atrophy and fat infiltration; limited by metal artifacts.

Acute subscapularis tendon failure after anatomic total shoulder arthroplasty can be considered for primary repair.

In chronic situations with significant subscapularis muscle atrophy especially in patients older than 65 years, is better to consider revision to reverse total shoulder arthroplasty (RTSA).

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