Long-Term Results of Use of the CLS Stem in Primary Total Hip Arthroplasty

Abstract

PURPOSE OF THE STUDY The aim of the study was to evaluate the results of primary total hip arthroplasty with the use of the CLS stem at 11 to 17 years after implantation. MATERIAL AND METHODS A total of 108 patients (122 hips) in whom a CLS stem was used in the 1991-1996 period were evaluated. The group included 34 men and 74 women, with an average age of 48 years (range, 28-63). The CLS stem with a neck-shaft angle of 145 degrees and the CLS expansion cup were used in all patients. Clinical outcomes were evaluated by Merle d'Aubigné-Postel score and Harris hip score, radiological examination was completed on AP and lateral views of the pelvis and the operated hip. RESULTS The average follow-up was 16.4 years (range, 11-17). The average Merle d'Aubigné-Postel score was 14.5 (range, 13.9-17.0) points and the average Harris hip score was 84.8 (range, 70-99) points. Very good or good outcomes were found in 81% of the patients. Three patients underwent revision surgery, in one for septic loosening, in one for aseptic loosening and in one for varus stem position leading to instability. The radiographs evaluated as described by Engh showed 116 stable stems, three fibrous stable and three unstable stems. Subsidence of more than 3 mm, without any further deterioration, was found in five hips at 12 months post-operatively. Seven hips showed one radiolucent line, four showed two radiolucent lines and three hips showed three radiolucent lines, all of them being less than 2 mm wide. DISCUSSION Radiographic evidence of a stable stem in 116 hips (116/122) suggests a high reliability of the implant. Assessment of radiolucent lines showed 108 hips without radiographic demarcation and 11 hips with slight demarcation. The signs of stress-shielding grade 1 were found in 28 hips. Good results of arthroplasty with the CLS stem can be attributed to its three-dimensional wedge-shaped design that allows for an optimal press-fit in the metaphyseal region. The porous surface provides reliable osteointegration. Stress-shielding is prevented by optimal stress distribution in the metaphyseal region and by a modulus of elasticity of titanium alloy which closely approximates the modulus of elasticity of bone. CONCLUSIONS At 15 years post-operatively, the cumulative probability of clinical survivorship of the CLS stem was 98.3 %, and cumulative probability of radiographic survivorship was 87.7 %. The advantages of this stem include a technically simple implantation, reliable osteointegration and long-term stability even in high demanding patients.