Weight bearing mobilisation after cementless total hip arthroplasty - A cup migration analysis.

Purpose: The postoperative mobilisation after cementless total hip arthroplasty is usually non-weight bearing within the first six weeks to achieve bony ingrowth for the implant. Since 1995 weight bearing mobilisation is performed at our clinic even after cementless implantation of the Alloclassic(R) (Zweymiiller-Sulzer(R)) system. The aim of the presented study was the detection of any negative influence of weight bearing mobilisation on the stability of this cementless implant. Method: The horizontal and vertical cup migration of 42 cementless acetabular cups (Alloclassic(R) Zweymiiller-Sulzer(R)) in 40 patients after weight bearing mobilisation and a minimum follow up of 24 months were analysed by a digital migration analysis. The results were compared to a normative migration profile of the same that was recently established. Results: The migration analysis did not exceed the level of accuracy of 1.3 mm in any patient. The mean horizontal cup migration was 0.3 mm in both groups after 24 months, the mean vertical migration was 0.4 mm in both groups. No significant difference of the acetabular stability was detectable. None of the implants showed radiological signs of loosening or migration. Conclusion: The presented data justify an early postoperative weight bearing mobilisation using the cementless Alloclassic(R) threated cup, provided that primary stability of the implant can be achieved.