Radiological evaluation consisted of anteroposterior (AP) views of the hip and pelvis and a true lateral of the hip. These were compared with the radiographs taken immediately after operation and at all subsequent reviews. All radiographs in this study were read by an independent orthopaedic surgeon (JRM), who was not the operating surgeon. The femur was divided into the seven Gruen zones,9 with the corresponding areas on the lateral radiograph. The presence of radiolucencies or osteolysis was assessed in each of the seven zones and recorded in increments of 0.5 mm. Progressive radiolucencies were identified and recorded. Radiolucencies with a scalloped or cystic appearance, or greater than 2 mm in width, were recorded as oseolysis.10 The stability of the femoral component was assessed by the criteria of Engh et al.11 A component was defined as having fixation by bone ingrowth when there was no subsidence and minimal or no formation of a radio-opaque line along the porous-coated portion of the implant. Stable fibrous ingrowth occurred when an implant had no progressive migration irrespective of the presence of a radio-opaque line along the stem. Definitive femoral component loosening was defined as progressive migration of the implant. Subsidence of greater that 3 mm was required for this determination.
While not the focus of this review, we examined the acetabular components used in these patients. The prosthesis used in all cases was a conically shaped, threaded-ring titanium shell without porous coating (T-Tap; Zimmer-Biomet). Ultra-high molecular-weight polyethylene powder HiFax 1900 MG (HiMont, USA) was directly compression-moulded into the shell to form an articulating surface, 28 mm in diameter.