Role of Subscapularis in Rotator Cuff Retraining
Typically Subscapularis is thought of as a medial rotator. Comparing the force vector of subscapularis to pectoralis major, teres major, latissimus dorsi and the anterior deltoid muscles it contributes very little to medial rotation. Therefore it is thought that its primary function is to compress the humeral head in the fossa and prevent anterior and superior translation. This is significant as the leading biomechanical causes of shoulder impingement are anterior and superior translation.
It has been demonstrated by David et al that subscapularis is active 10-120 milliseconds prior to the other delto-pectoral muscles during isokinetic medial rotation. Therefore we must retrain subscapularis independently from the delto-pectoral muscle contraction. Retraining must be focused on posterior translation not medial rotation.
Quick and easy clinical test described by Bahram Jam:
Instruct a patient with GH instability or rotator cuff impingement related to an anteriorly translated humeral head to…
Step #1: Actively abduct their arm (note level of pain & ROM) and bring the arm back down
Step #2: This time prior to abducting, visualize taking the shoulder (humeral head) back into its socket
Step #3: Hold that position, and reattempt the abduction (eyes open or closed)
Step #4: Try to keep the "joint back" and slowly bring the arm down from the abducted position (note level of pain and ROM)
References
David G, Jones M, Magarey M. Rotator cuff muscle performances during gleno-humeral joint rotations: An Isokinetic, Electromyographic and Ultrasonographic Study. Manipilative Physiotherapists Association of Australia Conference Proceedings. Melbourne Australia. 1997;34-37
Luft AR, Skalej M, Stefanou A, Klose U, Voigt K. Comparing motion- and imagery-related activation in the human cerebellum: a functional MRI study. Hum Brain Map; 1998;6(2):105-13
Sahrmann SA. Diagnosis and Treatment of Movement Impairment Syndromes. St. Louis: Mosby Inc., 2002