OSTEOLYSIS AFTER PRIMARY THA USING FIRST-GENERATION XLPE: ANALYSIS USING 3D CT SCAN AT MINIMUM TEN-YEAR FOLLOW-UP

Background/Purpose

Cross-linked polyethylene (XLPE) has shown reduced wear rates as compared to conventional polyethylene, but the long-term effect of this on the incidence of osteolysis remains unclear. In addition, the measurement of osteolysis on plain radiographs can underestimate the incidence and extent of osteolysis. Therefore, we evaluated the wear rate, incidence and volume of osteolysis at a minimum follow-up of ten years using three-dimensional computed tomography (3-D CT), a more accurate and sensitive method for detecting and measuring the size of osteolysis than plain radiographs.

Materials and Methods

Between 2000 and 2004, 233 primary THAs were performed using 28-mm cobalt-chrome femoral head on first-generation XLPE (Longevity^®, Zimmer, Warsaw, IN) with cups of identical design. Fifty-five patients (57 hips) deceased, eight patients (8 hips) were lost and four patients (4 hips) were revised due to recurrent dislocation (2 hips) or infection (2 hips). Among the remaining 164 hips, 95 hips underwent 3-D CT scanning (Aquilion® 64, Lightspeed Ultra® 16 or Optima® 660) at minimum 10 years (range, 10.0 to 15.2) and were included in this study. Mean age at the time of THA was 56.2 years and average body mass index was 23.5 kg/m². Average cup size was 55.4 mm whereas mean inclination and anteversion angle of cups on CT scan were 40.1 and 17.4 degrees, respectively. Average follow-up period was 12.8 years. 2D wear rate was measured using PolyWare® 3D Rev 7 software (Draftware Inc, Vevay, IN). Osteolysis was strictly defined as a localized area of trabecular loss with a sclerotic margin. Osteoarthritic cyst and age-related osteoporosis were excluded using perioperative CT scan and magnetic resonance imaging or serial plain radiographs. The incidence, location, and volume of osteolysis were measured.

Results

Mean bedding-in wear rate (<1 yr) was 0.085 mm and average annual wear rate was 0.023 ± 0.012 mm/yr. Seven hips (7.4%) demonstrated osteolysis on 3-D CT scan: Acetabular osteolysis was measured with an average volume of 3.2 cm³ in zone 1 or 2 in three hips whereas femoral osteolysis was demonstrated with a mean volume of 0.7 cm³ in zone 1 or 7 in 5 hips. One hip showed both acetabular and femoral osteolysis.

Conclusion

The results of THA using first-generation XLPE were encouraging with low wear rate as well as low incidence of osteolysis at a minimum follow-up of ten years. Longer follow-up is necessary to determine if this XLPE will continue to demonstrate the improved osteolysis characteristics.

Acknowledgement: This work was supported by Institute for Information & communications Technology Promotion (IITP) grant funded by the Korea government (MSIP) (#B0101-14-1081).