Background: There are few biomechanical studies regarding partial-thickness rotator cuff tears and subsequent repair.
Hypothesis: Partial-thickness intra-articular supraspinatus tendon tears increase articular-sided tendon strain as they increase in size. Repair of these tears will return strain to the intact state.
Study design: Controlled laboratory study.
Methods: Twenty fresh-frozen human cadaveric shoulders were prepared by dissecting to the supraspinatus tendon and leaving the native footprint intact. The tendon footprint was measured with digital calipers and divided into thirds (anterior, middle, and posterior). The middle third was the area where a consistent partial tear was created based on the thickness of the specimens' particular footprint. Created were 25%, 50%, and 75% tears. Image analysis software and differential variable reluctance transducers strain gauges were used to measure strain. A 100 N load at 1 Hz for 30 cycles was conducted for glenohumeral angles of 45 degrees, 60 degrees, and 90 degrees. This was completed for the intact tendon, 25%, 50%, and 75% tears. Shoulders were then repaired using the in situ fixation method. The in situ method consisted of either a parachute anchor or metal corkscrew anchor. Eight shoulders were examined for load-to-failure testing with the Materials Testing System.
Results: There was a significant difference (P < .05) in rotator cuff strain between the intact rotator cuff tendon and 50% and 75% partial-thickness tears. The cuff strain was returned to the intact state with repair. This was consistent for 3 different glenohumeral abduction angles and for all 3 intra-articular tendon areas. The bursal strain did not have any significant differences between groups.
Conclusion: Articular-sided tendon strain increases consistently across the supraspinatus tendon with greater partial tears. Repair returned strain close to the intact state.
Clinical relevance: This study may add credence to the clinical practice of repairing intra-articular partial-thickness rotator cuff tears greater than 50%.