This retrospective study reviews fine wire dynamic EMG in 131 shoulders with recurrent instability at a specialist upper limb centre. It asks which non-rotator-cuff muscles show abnormal activation and how those patterns map to the direction of instability. Four muscles were sampled: pectoralis major, latissimus dorsi, anterior deltoid, and infraspinatus.
When a patient with atraumatic or multidirectional instability fails a well-run rotator cuff rehab program or a stabilization procedure, think beyond the cuff. This paper makes the case that superficial torque muscles, chiefly latissimus dorsi and pectoralis major, can actively destabilize the joint through inappropriate recruitment.
The practical decision rule: your clinical exam is good at telling you patterning is present but unreliable at telling you which muscle is the culprit. It named the correct muscle only 11% of the time. That gap matters because rehabilitation must target the specific offending muscle. DEMG localized the problem and uncovered subclinical patterning in 47 shoulders that exam alone missed.
Remember the directional map: PM over-activity leans anterior, IS suppression leans posterior, and LD over-activity crosses both directions, which is why it dominates MDI. As retrospective data without asymptomatic controls, this shows association rather than proven causation.
This retrospective study reviews fine wire dynamic EMG in 131 shoulders with recurrent instability at a specialist upper limb centre. It asks which non-rotator-cuff muscles show abnormal activation and how those patterns map to the direction of instability. Four muscles were sampled: pectoralis major, latissimus dorsi, anterior deltoid, and infraspinatus.
When a patient with atraumatic or multidirectional instability fails a well-run rotator cuff rehab program or a stabilization procedure, think beyond the cuff. This paper makes the case that superficial torque muscles, chiefly latissimus dorsi and pectoralis major, can actively destabilize the joint through inappropriate recruitment.
The practical decision rule: your clinical exam is good at telling you patterning is present but unreliable at telling you which muscle is the culprit. It named the correct muscle only 11% of the time. That gap matters because rehabilitation must target the specific offending muscle. DEMG localized the problem and uncovered subclinical patterning in 47 shoulders that exam alone missed.
Remember the directional map: PM over-activity leans anterior, IS suppression leans posterior, and LD over-activity crosses both directions, which is why it dominates MDI. As retrospective data without asymptomatic controls, this shows association rather than proven causation.