Abstract
Introduction
There has been almost universal adoption of highly cross-linked polyethylene as the polyethylene of choice in metal-on-polyethylene articulations in total hip replacement (THR). Although wear of conventional polyethylene has been shown to be related to periprosthetic osteolysis, the relationship between wear of highly cross-linked polyethylene and osteolysis remains uncertain. Our aim was to determine the incidence and volume of periacetabular osteolysis at a minimum of seven years following primary THR with metal on highly cross-linked polyethylene articulations.
Methods
644 patients were enrolled into a randomised controlled trial which examined the effect of articulation size (28 vs 36 mm) on the incidence of dislocation one year following THR. To date, 62 patients (34 patients – 28 mm articulation; 28 patients – 36 mm articulation) have undergone a quantitative computed tomography (CT) scan, with metal artefact reduction protocol, to detect and measure osteolysis at a minimum of seven years following THR. Osteolysis was defined as a localised area of bone loss of at least 1 cm3 that is expansile, with a well-defined sclerotic border, a clear communication between the defect and the joint space and the absence of acetabular cysts. Pre-operative and post-operative plain radiographs were examined to identify the existence of acetabular cysts. Polyethylene wear from one to seven years following THR was also measured, using a computerised edge detection technique (PolyWare Rev 5, Draftware) of analysing standard radiographs.
Results
The median age of the 62 patients at primary THA was 72 years (range 65–86 years). The minimum follow-up was 7 years (median 7.5 years; range 7.0–9.9 years). Five patients with no evidence of acetabular cysts prior to THR were found to have osteolysis adjacent to the acetabular component, three of whom had a 28 mm articulation. The median lesion volume was 1.4 cm3 (range 1.1–2.2 cm3). All osteolytic lesions were located in the ilium adjacent to either fixation screws or empty screw holes. No femoral osteolysis was detected in any of the patients. The median linear wear rate in the patients with osteolysis was 0.04 mm/yr (range 0.03–0.07 mm/yr).
Conclusions
Although the incidence and volume of osteolysis adjacent to metal on highly cross-linked polyethylene articulations at seven years was low, it is of some concern that osteolytic lesions were detected, particularly in the absence of clinically significant wear. Further monitoring of these lesions will determine whether they develop into larger, clinically relevant osteolytic lesions.
