The supraspinatus footprint: an anatomic study of the supraspinatus insertion.

PURPOSE Management of articular sided partial-thickness rotator cuff tears is controversial. Most management decisions rest on determining the thickness of tendon loss and location of tendon involvement, without any clear guidelines offered on how to make this determination. This study attempts to confirm the normal cuff thickness at its humeral head attachment and correlate the amount of exposed bone at the "footprint" attachment of the supraspinatus as an accurate measurement of the amount of tendon loss. TYPE OF STUDY Anatomic study. METHODS Forty-eight cadaver shoulders with an average age of 71.5 years were examined. Specimens with full- or partial-thickness rotator cuff tears were not measured, leaving 17 specimens with an average age of 70 for analysis. The anterior to posterior width of the supraspinatus was measured with a caliper, as well as the medial to lateral width at the rotator interval, at midtendon, and at the posterior limit determined by the spine of the scapula raphe. The distance from the articular cartilage margin to the supraspinatus tendon insertion was also measured. RESULTS The mean anteroposterior dimension of the supraspinatus insertion was 25 mm. The mean superior to inferior tendon thickness at the rotator interval was 11.6 mm, 12.1 mm at midtendon, and 12 mm at the posterior edge. The distance from the articular cartilage margin to the bony tendon insertion was 1.5 to 1.9 mm, with a mean of 1.7 mm. CONCLUSIONS Articular partial-thickness tears with > 7 mm of exposed bone lateral to the articular margin should be considered significant tears approximating 50% of the tendon substance. Arthroscopic measurement of the exposed bone between the articular margin and the supraspinatus tendon insertion (footprint) is an accurate way to estimate tear depth and provide a rational, reproducible guideline for treatment.