Rotator cuff tears which are incomplete supraspinatus tears will not affect shoulder mechanics like larger tears do, new research finds.
In the study, “Biomechanics in an Incomplete Versus Complete Supraspinatus Tear: A Cadaveric Study,” published online on December 3, 2020 in the Orthopaedic Journal of Sports Medicine, researchers wanted to compare shoulder mechanics between incomplete and complete supraspinatus tears.
They wrote, “We hypothesized that the incomplete supraspinatus tear would lead to an incremental loss of abduction force and preserve vertical position of the humeral head, while a complete supraspinatus tear would cause superior humeral migration, decrease functional deltoid abduction force, and increase passive range of motion.”
For answers, they tested six cadaveric shoulders on three conditions: intact/control; 50%, full-thickness, incomplete supraspinatus tear; and 100% complete supraspinatus tear. They then measured deltoid abduction force, superior humeral head migration, and passive range of motion in static conditions at 0˚, 30˚, and 60˚of glenohumeral abduction, respectively.
The intact supraspinatus had a mean deltoid abduction force of 2.5, 3.3 and 3.8 N at 0˚, 30˚, and 60˚ of abduction, respectively. A shoulder with an incomplete tear didn’t show any significant difference in mean abduction, however, the force was significantly decreased by 52% at 30˚ of abduction force in the complete tear (p = .009).
The complete tear also exhibited significant decreases in abduction force by 3% and 48% (0.9 N and 1.1N) at 0˚and 30˚of abduction, respectively (p = .04 and .004).
In addition, the researchers found that the intact supraspinatus experienced a mean superior humeral head migration of 1.5, 1.4 and 1.1 mm at 0˚, 30˚, and 60˚. The complete tear caused a superior migration of 3.0 and 4.4 mm greater than the intact supraspinatus at 0˚and 30˚of abduction, respectively (p = .001).
The data also showed a 5˚and 10˚increase in abduction range of motion with 50% and 100% tears, respectively (p = .003 and .03).
“An incomplete supraspinatus tear does not significantly alter the biomechanics of the shoulder, while a large, complete supraspinatus tear leads to a significant superior humeral migration, a decreased deltoid abduction force, and a mild increase in passive range of motion,” the researchers wrote.
“Our findings demonstrate the effects of large supraspinatus tears on key biomechanical parameters, as they progress from partial tears.”