A 59-year-old woman has undergone surgery for ruptures of the rotator cuff (SSP, ISP and LBT). Initially, the procedure was successful, however 6 months later, symptoms recur.
Subsequent X-ray images (true-ap projections) show the course postoperatively (2020-10), after the initial onset of recurrent symptoms (2021-04) and after a further three months (2021-06).
What are the characteristic X-ray findings, which diagnosis results?
Osteonecrosis of the humeral head
Postoperatively (2020-10), the X-ray findings were initially unremarkable. Just six months later (2021-04), the humeral head was deformed with collapse of the joint sphericity. A localized bright zone was found subchondrally directly adjacent to a joint level. Within a further three months (2021-07), this developed into a classic “crescent sign” on the deformed humeral head. This resulted in the diagnosis of humeral head necrosis.
Pathoanatomy: In humeral head osteonecrosis, there is ischemia with a focus in the peripheral, subchondral bone section. The ischemia is caused by occlusion of the intraosseous nutritial vessels, which are supplied by the anterior and posterior circumflex humeral arteries. Due to the retrograde course of the nutritial vessels, the subchondral zone of the humeral head is a vascular terminal zone (“last meadow”) with a predisposition to osteonecrosis.
An inverse shoulder prosthesis was implanted as treatment.
Further course: Eight months later (2022-03), the patient felt a severe, acute pain on the dorsal side of the right shoulder. This was the cause for a new X-ray diagnosis. What is the cause of the pain now?
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.
