Unstable total Hip Replacement. are Constrained Liners A Solution? Experience and Literature Review

The purpose of this paper is to assess clinically and radiologically our experience with constrained acetabular components for the unstable hip following total hip replacement. From July 2006 to August 2012 we retrospectively reviewed the clinical and radiographic outcome of 22 arthroplasties, in 20 patients. The mean age at surgery of constrained acetabular component was 73 years (range, 35 to 90 years) and the mean clinical and radiological follow-up period was 35 months (range, 3 to 73 months). Clinical assessment was performed by the Harris Hip Score and the SF-12. The constrained acetabular device eliminated or prevented hip instability in all patients except in 3 hips who had new dislocation. The mean Harris hip score in the last evaluation was 74 points, and SF-12 was 27 points. A constrained acetabular components are simple to use and provides satisfactory mid term results for the treatment of hip instability in primary and revision replacement in those at high risk of dislocation. The potential for aseptic loosening requires evaluation by long term studies and bigger series. Central Coll et al. (2014) Email: Ann Orthop Rheumatol 2(4): 1033 (2014) 2/5 of instability, [2] cases with surgical attempts at stabilization have failed, [3] cases with significant deficiency of soft-tissue attachments around the hip and [4] patients with neuromuscular disorders. The use of constrained acetabular components has gained interest in the last 15 years with multiple short term papers reporting success rates of greater than 80%. Some surgeons believe increased mechanical stresses inherent to these designs may predispose these hips to increased risks of wear, osteolytic processes, loosening and potential dissociation of the components with subsequent re-operation. MATERIALS AND METHODS From July 2006 to August 2012 we retrospectively reviewed the clinical and radiographic outcomes of 22 arthroplasties, in 20 patients, 8 women and 14 men. The right side was the predominant with 14 cases. Of the 22 patients who were identified, 3 patients had been lost because they died for causes unrelated to the arthroplasty. In 18 hips the constrained component was implanted for the treatment of recurrent instability (Figure 1a and 1b), two hips was implanted because grossly deficient soft-tissue attachments were believed to be associated with a high risk for subsequent instability, and in two cases were indicated for neuromuscular disorder, West Syndrome. The primary indications for total hip replacement were arthrosis in 13 cases and femoral neck fracture in 8 cases and, one case of comminuted per-trochanteric fracture. The mean age at surgery was 73 years (range , 35 to 90 years) and the mean clinical and radiological follow-up period was 35 months (range, 3 to 73 months). Clinical assessment was performed by the Harris Hip Score and the SF-12. All radiographs were evaluated for evidence of loosening. The surgical approach was posterolateral in 9 hips and anterolateral in 13. Including the initial arthroplasty, all patients had undergone at least one reconstructive operation on the hip prior to insertion of constrained cup. Table 1 provides an overview of the patient demographics and follow-up details. A constrained liner is a device consisting of a liner and reinforcing ring. The polyethylene liner fits into the acetabular metal shell and articulates with the femoral head. The articular surface opening of the constrained liner is reduced slightly to allow for mechanical capture of the femoral head. The constrained acetabular components used in our series consisted in constrained cementless acetabular component inserted in a press-fit fashion. The metall-back component was secured with three screws at least. In two hips a polyethylene constrained insert was cemented into a well-fixed cup. Four types of constrained acetabular liner were used in the study; The trilogy Acetabular System Constrained Liner (Zimmer) was used in 8 cases, the RingLoc II Constrained (Biomet Orthopedics) was used in 9 hips, one case with Smith & Nephew liner and one hip with Duraloc Constrained Liner (DePuy). Anteroposterior and lateral radiographs of the hip joint were revised to assess the position of the implant and look for signs of loosening or wear prosthesis. Acetabulum was divided into three zones (De Lee and Charnley zones) to evaluated the presence of radiolucent lines. Possible loosening was defined as the location of a radiolucent line occupying >50% but <100% of bone-component interface on any radiograph or the presence of a progressive radiolucent line.