Spontaneous Dissociation of Prosthetic Humeral Head: A Case Report

Dissociation of a Morse taper arthroplasty is an uncommon occurrence, especially in the shoulder, reported in only one publication in the English literature.1 In response to reported dissociations of Morse taper modular humeral components, Blevins et al. identified conditions that would interfere with the Morse taper interface strength. The relevant cases were reported only in a single component design and occurred between 1988-1992. Subsequent reports of consecutive arthroplasties with this prosthesis failed to document further episodes of Morse taper dissociation.2 In contradistinction, dissociation of the femoral heads in hip arthroplasty has been more commonly reported.4,10-14 It most frequently occurs during reduction of a dislocated prosthesis that then needs to be surgically addressed. The dissociation is not always apparent on postreduction radiographs, underlining the importance of scrutinizing the images for radiolucencies and the position of the head of the prosthesis in the acetabular cup.7 The present case pertains to a DePuy Global Advantage total shoulder prosthesis implanted in 2008. This prosthesis is a third generation anatomical model, unlike the 1988-1992 second generation component previously reported in the literature. Heretofore, there have been no cases of humeral head dissociation in third generation total shoulder prostheses. The authors have obtained the patient’s informed written consent for print and electronic publication of the case report.