PROSPECTIVE RANDOMIZED COMPARATIVE WEAR STUDY: CROSSLINKED VERSUS REGULAR POLYETHYLENE FOR TOTAL HIP ARTHROPLASTY

Abstract

Purpose of the study: The purpose of this prospective study was to compare insert wear radiographically at minimum three years comparing crosslinked (Duration, Howmedia) versus regular (Stratec Medical) polyethylene.

Material and methods: We used two types of UHMWPE for a series of 140 total hip arthroplasties (THA) (February 1999 – August 2000). Duration polyethylene (Howmedica) was used for 63 implants. This UHMWPE undergoes gamma ray treatment under nitrogen which leads to a stabilization phase under temperature and time conditions enabling preferential formation of cross links between the molecular chains. Vecteur Orthopedic polyethylene implants exposed to gamma radiation under air were used for 62 implants. Eighty-seven patients were reviewed at minimum three years radiological follow-up. This series included 60 women and 27 men, mean age 64 years (range 32–93 years). The trans-trochanteric approach was used in all cases for insertion of a Charnley-Kerboull cemented femoral stem. All cups were cemented (abnormal implant position was an exclusion criterion). Cups were assigned randomly with a permutation table. Wear measurements were made by graphic construction comparing the immediate postoperative and last follow-up anteroposterior pelvis x-rays.

Results: Follow-up was at least 36 months for 87 patients. Mean follow-up for these 87 patients was 49.9 months. Mean wear was 0.32 mm for crosslinked poly-ethylene and 0.35 mm for regular polyethylene. Five patients presented wear ≥ 1 cm for crosslinked poly-ethylene and there were nine patients with ≥ 1 cm for regular polyethylene.

Discussion: In vitro, crosslinked polyethylene exhibits significantly improved mechanical qualities for wear resistance. Several factors can account for differences in polyethylene wear: the size and composition of the prosthetic head, and patient gender, age, activity level and BMI. These factors were comparable in our two groups. It does however appear that even with crosslinked poly-ethylene, after four years implantation, wear is limited, close to the detection level of the measurement method.

Conclusion: The measurement method used in this prospective randomized study of polyethylene wear comparing crosslinked versus regular polyethylene showed no difference between the two groups at four years follow-up.