Fracture of the spina scapulae
The glenosphere and the humeral part of the prosthesis are in normal positions with a firm seating. The spina scapulae is fractured with a wide fracture gap and caudal dislocation of the acromion.
Pathoanatomy: The fracture of the spina scapulae after implantation of an inverse shoulder prosthesis has several biomechanical causes:
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The spina scapulae is subjected to more intensive loading due to the increased use of the deltoid muscle with simultaneous loss of function of the rotator cuff, especially the supraspinatus muscle.
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This results in a strong pull on the spina scapulae during shoulder abduction.
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The lower position of the humeral prosthesis leads to additional strain on the spina scapulae.
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Most patients with an inverse shoulder prosthesis have osteoporosis due to their age.
