UNCEMEMENTED CUSTOM FEMORAL COMPONENTS IN HIP ARTHROPLASTY. A PROSPECTIVE CLINICAL STUDY.

Abstract

18 years ago laboratory studies were started to develop a CT-based uncemented customised femoral stem in order to optimise the fixation and strain distribution to the proximal femur in uncemented femoral components. An individual design also aimed to optimise the biomechanics of the joint and to enable use of uncemented stems in femurs with abnormal shape and dimension. The developed prosthesis has now been in clinical use for 13 years. The aim of this paper is to present the preliminary results of a prospective clinical study of this prosthesis.

Patients and methods: 685 hips have been operated. 58.8 % of the patients were women. Mean age was 51 years (20–69). 42.3 % of the hips were dysplastic. A high number of hips without major anatomic abnormality of the upper femur were included. The prostheses were designed to obtain a neck anteversion of 10 degrees after insertion, optimised medial femoral head offset and correction of leg length discrepancies up to 3 cm. All patients were followed with radiological and clinical examination. Merle d’Aubigné score was used. RSA and DEXA-studies have been performed in some groups of the patients. Finally, study of the gluteal muscular function in hips with optimised medial femoral head offset after insertion of custom stems was compared to hips where optimisation had not been achieved with use of standard stems.

Results: We experienced that use of this type of prosthesis is very simple and offers obvious advantages in abnormal size and geometry of the upper femur. Nine patients sustained a peroperative fissure in the proximal femur (1.3 %). These fissures were treated successfully with cerclage wires. Eight patients sustained a femoral fracture by a fall accident. Four fractures healed after osteosynthesis without loosening of the prosthesis. A long stem pros-thesis had to be used in the other four. No stem loosening was seen except in one case where a non-union after subtrochanteric osteotomy prevented stem fixation. Dislocation occurred in ten hips (1.5%). In four of these the acetabular component had to be replaced. Average total score at 7 years (125 hips) was 17.1 (preop 9.4), at 10 years (56 hips) 17.0 (preop 9.4). The pain scores at the corresponding observations were 5.7 (preop 2.7) and 5.6 (preop 2.8). DEXA-studies showed comparable preservation of femoral bone stock in hips treated with custom and standard stems (ABG). RSA-studies showed no significant stem migration. Superior function of the gluteal muscles was obtained after normalisation of the medial femoral head offset after insertion of a custom stem when compared to hips where normalisation had not been achieved by a standard stem.

Conclusions: Use of custom femoral components enables optimisation of the biomechanics of the hip and eliminates the need for highly modular femoral stems. The rate of peroperative fissures and postoperative instability is relatively low indicating adequate fit of the stem and adequate design of the femoral neck. Use of custom prostheses offers obvious advantages in highly abnormal femurs. The mid-term clinical results up to 10 years are promising with a very low risk of aseptic loosening. However, it remains to see whether use of such pros-theses will give superior long term results compared to standard uncemented stems in “normal” femurs.