This EMG and motion-analysis study compared shoulder muscle firing in normal controls versus patients with matched 2-tendon (supraspinatus + infraspinatus) rotator cuff tears. Half the tear patients were asymptomatic and half symptomatic, letting the study ask why identical tears produce different function. It tests whether muscle activation strategy, rather than tear size, explains symptom status.
Two patients can have the same MRI-documented supraspinatus and infraspinatus tear yet function completely differently. This study explains why: it comes down to how they fire the remaining muscles. The key mental model is the transverse force couple. An intact subscapularis anteriorly can balance a deficient posterosuperior cuff and restore centered glenohumeral mechanics.
Asymptomatic patients up-regulate that intact subscapularis and elevate near-normally. Symptomatic patients fail to recruit it, keep firing the torn tendons, and substitute with an upper trapezius shrug that rotates the scapula inefficiently.
The practical takeaway: for a two-tendon posterosuperior tear you are treating nonoperatively, target subscapularis strengthening and retrain scapular mechanics before assuming the tear itself mandates surgery. Tear size alone does not predict who will compensate.
Remember the sample is small (6 per group) and the asymptomatic patients were older, so read this as a mechanistic rationale rather than definitive outcome evidence.
This EMG and motion-analysis study compared shoulder muscle firing in normal controls versus patients with matched 2-tendon (supraspinatus + infraspinatus) rotator cuff tears. Half the tear patients were asymptomatic and half symptomatic, letting the study ask why identical tears produce different function. It tests whether muscle activation strategy, rather than tear size, explains symptom status.
Two patients can have the same MRI-documented supraspinatus and infraspinatus tear yet function completely differently. This study explains why: it comes down to how they fire the remaining muscles. The key mental model is the transverse force couple. An intact subscapularis anteriorly can balance a deficient posterosuperior cuff and restore centered glenohumeral mechanics.
Asymptomatic patients up-regulate that intact subscapularis and elevate near-normally. Symptomatic patients fail to recruit it, keep firing the torn tendons, and substitute with an upper trapezius shrug that rotates the scapula inefficiently.
The practical takeaway: for a two-tendon posterosuperior tear you are treating nonoperatively, target subscapularis strengthening and retrain scapular mechanics before assuming the tear itself mandates surgery. Tear size alone does not predict who will compensate.
Remember the sample is small (6 per group) and the asymptomatic patients were older, so read this as a mechanistic rationale rather than definitive outcome evidence.