LONG TERM RADIOLOGICAL CHANGES IN ZWEIMULLER FEMORAL STEMS

Abstract

Introduction The Zweymuller tapered cementless titanium femoral stem has been in widespread use since 1986.1 Stress shielding of the proximal femur has been a concern with pressfit cementless femoral stems. Radiolucent lines (RLLs) are signs of stress shielding and possibly over time, may lead to aseptic loosening.2

Aim To evaluate the longterm radiographic bone response in the femur following Zweimuller total hip replacements.

Study Design Consecutive case study (serial radiographic analysis)

Material and Methods 49 Total Hip Replacements in 42 patients (M:F=25:17) with a mean age of 59 years (range 49–70 years), were included in the study. All patients were operated on by the senior surgeon (JRW). 28 Alloclassic and 21 Endoplus stems were implanted. AP and Lateral radiographs were assessed. A gap of 1mm or more at the bone prosthesis interface was recorded as positive for RLLs in the Gruen zones. The mean duration of follow-up was 46 months (range 24–140 months). 17 patients had follow up of more than 5 years. Other measurements included subsidence, bone remodelling and heterotropic ossification.

Results After 2 years there were distinct radiological changes (RLLs), mainly in Gruen zones 1 and 7, in 18/49(36%) femora. Though there was evidence of RLLs in zones 2 and 6, the numbers were insignificant. Subsidence of more than 3mm was noted in 16 stems (33%). Heterotropic ossification was found in 4 patients (8%), one of whom required excision. Persistent pain due to trochanteric bursitis was noted in 10 patients. 4 patients needed revision due to reasons other than aseptic loosening. There were two dislocations, which needed revision of the acetabular component.

RLLs were more common in the Endoplus group (10/21) compared to the Alloclassic group (8/28). There was no clinical compromise (all had pain free mobility) in these patients and no progression of RLLs was noted.

Conclusion Proximal femoral stress shielding following Zweimuller femoral stem implantation is observed in significant number of patients. The RLLs do not correlate with symptoms and patient satisfaction.