What’s the Diagnosis – Case 96
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What’s the Diagnosis – Case 96
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What’s the Diagnosis – Case 96
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What’s the Diagnosis – Case 96
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Findings On the initial post operative radiographs there is anatomic positioning of the components and no complication. Similarly, no abnormality is present on the routine postoperative radiographs two months later. On the subsequent radiographs, there is then asymmetric positioning of the femoral head component within the acetabular component. This asymmetric positioning is further corroborated on the CT. In addition, a geometric, low attenuation mass is seen in the soft tissue directly posterior to the hip joint and bony fragments are seen about the posterior wall of the acetabulum.
What’s the Diagnosis – Case 96
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What’s the Diagnosis – Case 96
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Diagnosis: Displaced poly liner The history withheld in this case is that immediately prior to the radiographs and CT of 3/30 the patient had sustained a dislocation with relocation. This case shows the importance of trying to stay current on the hardware that is being used. The Dual Mobility Cup (DMC) is a type of arthroplasty that is utilized for individuals that are thought to be a dislocation risk following total hip arthroplasty. However, when there is a dislocation of the hip in the setting of a DMC with relocation there is a known risk of dislodging of the poyethylene liner which is what occurred in this situation. The geometric, low attenuation mass is the displaced polyethylene liner. This can not be seen on the radiographs because it is sitting directly posterior to the metal components of the hip. A frog leg lateral view was also done but not shown in this case and it too did not show the liner. The key is to realize that in the setting of a DMC with a dislocation and relocation, an asymmetric positioning of the femoral component indicates there has been a displacement of the liner. This prompted the CT to look for the liner. The CT also showed the bone fragments of the posterior wall that are unlikely to represent heterotopic ossifcation related to the recent arthroplasty and much more likely related to a recent dislocation. The patient was subsequently revised to a different type of prosthesis with a constrained acetabular liner again to help prevent against dislocation.
What’s the Diagnosis – Case 96
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What’s the Diagnosis – Case 96
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References The dual mobility cup: what problems does it solve?. Ko LM, Hozack WJ, Bone Joint J. 2016 Jan;98-B(1 Suppl A):60-3. doi: 10.1302/0301620X.98B1.36332. Medacta International.
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