These authors retrospectively identified 92 magnetic resonance arthrography studies of suspected rotator cuff lesions obtained 3 months before shoulder arthroscopy. The myotendinous junction was identified, and the subscapularis tendon and muscle lengths were measured. Findings on arthroscopy performed later were used as the diagnostic gold standard for tendon integrity and compared with the magnetic resonance data.
Arthroscopy showed an intact subscapularis tendon in 43 patients, tendinopathy in 21 patients, and a partial rupture in 28 patients. The mean subscapularis tendon lengths were 40 mm in cases of intact subscapularis musculotendinous units, 45 mm in cases of tendinopathy, and 53 mm in cases of partial tears, whereas the mean subscapularis muscle lengths were 105 mm, 94 mm, and 95 mm, respectively, in these groups.
Partial tears of the subscapularis tendon lead to muscle shortening by approximately 10% and elongation of the tendon by approximately 32%, which may be interpreted as muscle retraction and a tendon rupture in continuity. If the subscapularis tendon has an apparent length of greater than 60 mm, the probability of a tear is 98%.
Comment: The topic of failure in continuity of cuff tears is an interesting one that has been discussed previously in this blog (see this link).
It is of interest that this was not a study of patients suspected of having subscapularis lesions, but rather a retrospective look at shoulders with suspected cuff lesions having subsequent arthroscopy. It would have been of great interest to know the results of physical examination in these patients: Did they have increased external rotation? Did they have diminished strength of internal rotation? Was their palpable thinning of the subscapularis tendon?
The most common clinical situation in which questions arise regarding subscapularis integrity is after shoulder arthroplasty. In this situation, MRI has difficulty in visualizing the integrity of the repaired subscapularis so that physical exam rather than imaginng becomes the main diagnostic tool.
If the tendon is weak and or retracted, it can be reconstructed with a tendon allograft.
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