Abstract
A customised, uncemented femoral stem was introduced clinically in 1995 after several years of development and pre-clinical testing. All the patients operated in our hospital have entered a prospective clinical study. The aim of this study is to present the short-term clinical data. Furthermore, the measurement of implant migration and the periprosthetic bone remodelling at two years is also reported.
Materials and methods: The femoral stem is designed from preoperative CT-scans, machined in Ti-alloy and circumferentially coated with a 50μm hydroxyapatite (HA) layer in the proximal 50-70%. Fifty-one patients (median age 52 years) have been followed clinically for a minimum of 3 years using the Merle-d’Aubignè score. Migration of the femoral stem has been measured with radiostereometry (RSA), the precision of the measurements is better than 0.080 mm for translations and 0.30° for rotations. Periprosthetic bone remodelling is expressed as the change in bone mineral density (BMD) in seven zones (Gruen) relative to the postoperative values. RSA- and DEXA measurements have been performed postoperatively and then after 3, 6, 12 and 24 months.
Results: One stem had to be revised after 3 months due to a periprosthetic fracture. The clinical scores were as follows (preop/3 years): Pain 2.6/5.5, ROM 3.7/5.7, function 2.7/5.9, total score 9.1/17.1. Six patients complained of thigh pain during the first two years, however, this complication resolved spontaneously in five patients within the three years follow-up. The mean subsidence after two years was 0.055 mm (SE ±0.045 mm) and the mean axial rotation was 0.29° (SE ± 0.12°). The mean bone loss in zone 7 was 34%; in the other zones the bone loss was less than 14%. The mean overall bone loss was 8%.
Discussion: The short-term clinical experiences with this patient-specific, cementless femoral stem are encouraging. The stem seems to be very stable during the first two postoperative years indicating that biological fixation of the femoral stems has been achieved. The change in the BMD was less than 14% in all Gruen zones, except for the proximal medial area where the bone loss was 34%.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
