An unusual complication of hip dislocation after total hip replacement

Clinical History

This lady presented three years following a left total hip arthroplasty, with hip dislocation which was reduced in the operating theatre. She had also suffered two prior dislocations. One month later she had persistent left hip discomfort and instability. An x-ray and CT were performed in preparation for revision surgery.

Imaging Findings

Our patient's initial x-ray showed dislocation of the left hip (Figure 1). One month after closed reduction of the dislocation a follow-up x-ray was performed (Figure 2). The femoral component of the left prosthesis was noted to be excessively supero-laterally located within the acetabular cup, with no other abnormality noted. The patient had persistent left hip discomfort and given the recurrent dislocations a CT was ordered by the orthopaedic surgeons as part of a work-up for revision total hip arthroplasty surgery (Figures 3, 4 and 5). An unexpected circular hypo-dense lesion was incidentally seen within the the soft tissues of the posterior left thigh, although the patient had not been experiencing any symptoms in this exact region. This represented the liner component of the total hip arthroplasty which had become dislodged during dislocation reduction one month prior. In retrospect it could also be visualised on the follow-up x-ray (Figure 2).

Discussion

Dislocation is one of the most common serious complications after total hip replacement. It has an annual rate of up to 10% and is a major concern for both patients and surgeons [1, 2]. It is also the most common indication for revision surgery [3].
In total hip arthroplasty, the liner fits into the acetabular component and allows the femoral head component to glide easier and more naturally in the socket. It is usually composed of plastic or ceramic. Common liner-related complications include wear leading to loosening and ceramic fracture [4]. Dissociation of the liner component is rarely seen [5]. Migration of the liner into the soft tissues around the hip following dislocation has not been described however.
In this case the liner cannot be seen within the soft tissues on the initial dislocation x-ray suggesting that migration occurred during reduction of the dislocation. The presence of the liner within the soft tissues of the thigh was not initially noted on the follow-up x-ray and only identified incidentally on CT as part of work-up for revision surgery. Given the patients history the appearances are readily suggestive of the diagnosis despite its extreme rarity. Clinically it was not clear whether the abnormal position of the liner was causing symptoms distinct from the ongoing hip discomfort and instability.
Liner migration such as this requires surgical management. This patient underwent revision left total hip arthroplasty and the liner was removed from an encapsulated pocket in the posterior thigh.
Take Home Message: Migration of the liner component of total hip arthroplasty into the soft tissues around the hip can occur during reduction following dislocation. It is readily visualised on x-ray and CT and requires surgical removal and revision hip surgery.

Differential Diagnosis List

Final Diagnosis

Total hip arthroplasty liner soft tissue migration following dislocation reduction

URL:	https://www.eurorad.org/case/15111
DOI:	10.1594/EURORAD/CASE.15111
ISSN:	1563-4086