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Year |
2001 |
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Question Number |
201. |
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Category |
Select |
Question
A 49 year-old man with advanced glenohumeral arthritis undergoes total shoulder replacement. Following surgery, he reports pain relief but now has weakness when using his arm for activities in front of his body, He is unable to hold the dorsum of his hand away from his back. The weakness is most likely related to what muscle?
1- Supraspinatus
2- Subscapularis
3- Infraspinatus
4- Deltoid
5- Pectoralis major
Figures
Answer (click for answer)
Answer 2.
Subscapularis Muscle:
- origin: entire anterior surface of the subscapularis fossa;
- insertion: lesser tuberosity of humerus and capsule of shoulder joint;
- action: main action: glenohumeral head depressor and in certain positions
allows extension, adduction and medial rotation of humerus at shoulder; - stabilization of the glenohumeral joint;
- reversed origin insertion action:
- when humerus is stabilized, abducts inferior border of the scapula;
synergists: teres major, pectoralis major, latissimus dorsi; - nerve supply:
- upper & lower subscapular, C5, C6
The lift-off sign is the one described in this question (arm behind back lifted posteriorly) and the inability to do so suggested subscapularis rupture. Subscapularis rupture is one of the complications after shoulder replacement. Other complications include infection, glenoid and humeral loosening, component instability, rotator cuff tears, periprosthetic fractures, nerve injuries, implant dissociation and deltoid dysfunction.
Reference: Gerber C, Farrow MD: Isolated tears of the subscapularis tendon. Orthop Trans 1995; 19: 457
Gerber C, Hershe O, Farron A: Isolated rupture of subscapularis tendon. J Bone Joint Surg Am 1996;78:1015-1023