gms | German Medical Science

Objectives: The increasing demand for primary total hip replacement (THA) in younger and more active patients makes the implant fixation and periprosthetic osteolysis very relevant issues. Uncemented stems were developed to achieve a biologic fixation of the implant and to prevent the loosening in the long term. In the early 1980's, the common principle of fixation was maximum fit and fill and circumferential porous coating resulting in bone ingrowth and distal anchorage. On the other hand, the CLS stem was developed with a three-dimensional tapered wedge straight shape. The taper provides press-fit in the metaphyseal region and prevents a complete fill in the distal diaphyseal portion encouraging a more physiological load transfer in the proximal part of the femur. The grit-blasted surface surface allows the osseointegration through the bone ongrowth leading to the long-term stability. In this single-center case series, the third decade clinical and radiographic results of CLS stem were evaluated.

Methods: From December 1983 to April 1985, 299 consecutive patients (M:F=145:154) (300 hips) underwent primary THA with a mean age of 57.5 (range 21-77). Pre-operative diagnosis was primary osteoarthritis (62%), osteoarthritis secondary to hip dysplasia (23%), post-traumatic arthritis (8%), avascular necrosis of the femoral head (3%) and other (1%). The mean follow-up was 26.2 years (range, 23-32). The Harris Hip Score (HHS) was assessed. Survivorship analysis was performed with stem revision for any reason and aseptic loosening alone as the endpoint.

Results and Conclusion: At the latest follow-up 189 patients died and 40 were lost. Of the remaining 70 patients, 59 (83.1%) reported excellent or good HHS. The Harris Hip Score increased from 42.4±6.4 pre-operatively to 96.3±7.2 post-operatively (p<0.0001). No patient reported thigh pain or clicking/squeaking sounds coming from the prosthesis. At radiographic assessment, the implant bone demarcation was low grade (1-3 zones) in 37.4% and high grade (4-6 zones) in 2.2% of the hips, the endosteal bone formation was observed in 76.2% of the hips, the periprosthetic osteolyses were reported in 40.2% of the hips, mainly in the proximal femur (Gruen zones 2 and 3), and the stress shielding was mild/moderate in 18.9% of the hips. With an average follow-up of 26.2 years, the cumulative survival rates with stem revision for any reason and for aseptic loosening alone were 88.3% and 92.4%, respectively.

In conclusion, CLS stem provides excellent clinical and radiographic results in patients undergoing primary THA with long-term follow-up.