Figure. Anteroposterior radiograph of the right hip.
An 87-year-old woman with dementia presents to the emergency department with right hip pain and deformity after rolling over in bed. She underwent a right total hip replacement with a posterior approach more than 20 years ago. On examination, a noticeably shortened and internally rotated right lower extremity is observed. Anteroposterior radiograph of the right hip (Figure) shows a posterior dislocation. She has had three dislocations over the last two weeks that were all closed-reduced in the operating room. She underwent a computed tomography scan and laboratory work-up during the past week, and no identifiable cause of her hip instability was found. She underwent hip revision surgery one year ago for instability, but all components were found to be well fixed. Her husband states that she can no longer be compliant with her hip dislocation precautions because of her dementia.
Which of the following is the best treatment for this patient?
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Postoperative hip dislocation affects approximately 2% of patients who undergo total hip replacement. More than 50% of dislocations occur within three months of surgery with 75% occurring within the first year. The classic posterior approach has been associated with a higher risk of hip dislocation compared with new surgical techniques such as the anterior approach. An isolated hip dislocation usually heals well with closed reduction if there is no identifiable cause of instability such as loose or malpositioning of the components or fracture. However, multiple dislocations can disrupt the supporting soft tissue, causing the hip to become prone to recurrent instability. Cognitive disorders such as dementia often result in an inability to comply with activity restrictions that help prevent dislocation after a total hip replacement. Recurrent hip dislocations usually require performing a salvage procedure using a device such as a constrained acetabular component. A constrained liner uses a locking mechanism to keep the femoral head in the cup liner. Constrained liners have a success rate of >97% in preventing further instability of the hip. The downside of a constrained liner is that it results in loss of hip motion and increases forces between the head and cup, potentially causing early component failure.1,2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants (JOPA).
1. Shrader M, Parvizi J, Lewallen D. The use of a constrained acetabular component to treat instability after total hip arthroplasty. J Bone Joint Surg Am. 2003;85(11):2179-2183.
2. Su EP, Pellicci PM. The role of constrained liners in total hip arthroplasty. Clin Orthop Relat Res. 2004;(420):122-129