Apparent Young's modulus of vertebral cortico-cancellous bone specimens.

Up to now, due to cortical thickness and imaging resolution, it is not possible to derive subject-specific mechanical properties on the 'vertebral shell' from imaging modalities applicable in vivo. As a first step, the goal of this study was to assess the apparent Young's modulus of vertebral cortico-cancellous bone specimens using an inverse method. A total of 22 cortico-cancellous specimens were harvested from 22 vertebral bodies. All specimens were tested in compression until failure. To compute the apparent Young's modulus of the specimen from the inverse method, the boundary conditions of the biomechanical experiments were faithfully reproduced in a finite element model (FEM), and an optimisation routine was used. The results showed a mean of the apparent Young's modulus of 374 ± 208 MPa, ranging from 87 to 791 MPa. By computing an apparent Young's modulus of a cortico-cancellous medium, this study gives mechanical data for an FEM of an entire vertebra including an external shell combining both bone tissues.

Is the so-called 'French paradox' a reality?: long-term survival and migration of the Charnley-Kerboull stem cemented line-to-line.

We have evaluated the in vivo migration patterns of 164 primary consecutive Charnley-Kerboull total hip replacements which were undertaken in 155 patients. The femoral preparation included removal of diaphyseal cancellous bone to obtain primary rotational stability of the stem before line-to-line cementing. We used the Ein Bild Roentgen Analyse femoral component method to assess the subsidence of the femoral component. At a mean of 17.3 years (15.1 to 18.3) 73 patients were still alive and had not been revised, eight had been revised, 66 had died and eight had been lost to follow-up. The mean subsidence of the entire series was 0.63 mm (0.0 to 1.94). When using a 1.5 mm threshold, only four stems were considered to have subsided. Our study showed that, in most cases, a highly polished double-tapered stem cemented line-to-line does not subside at least up to 18 years after implantation.

[Computer-assisted surgery in total knee replacement. Preliminary results: report of 60 cases]. / Prothèse totale du genou assistée par ordinateur Résultats préliminaires: à propos de 60 cas.

PURPOSE OF THE STUDY: Conventional techniques proposed for total knee arthroplasty (TKA), necessarily require an acceptable alignment of the lower limb. Computer-assisted surgery is becoming increasingly popular in order to improve the precision of the component alignment, an essential element for good long-term results. The purpose of this prospective study was to present our preliminary results with computer-assisted implantation of TKA. MATERIAL AND METHODS: This was a prospective study of 55 patients (60 knees) included at random for computer-assisted TKA between April 2004 and September 2005. Mean age was 70.5 years. The preoperative assessment noted genu varum in 56 knees and genu valgum in four knees. Three knees with unilateral degenerative disease presented a post traumatic tibia malunion. The same surgeon performed all of the operations using the same prosthesis and navigation system (P.F.C. Sigma). Lower limb alignment and orientation of the prosthetic implants were assessed with standard pre- and postoperative gonometry. Sagittal alignment was measured on the standard X-rays (lateral and anteroposterior view). RESULTS: Knee alignment improved from 8.1+/-4.5 degrees varus (10 degrees valgus to 18 degrees varus) preoperatively, to 0.4+/-0.6 degrees varus (1 degrees valgus to 2 degrees varus) postoperatively. In the frontal plane, the mean angle of the femoral component on the anteroposterior (ap) view was 89.7+/-0.7 degrees (88-91 degrees). The mean angle of the tibial component on the ap view was 89.9+/-0.7 degrees (88.5-91 degrees). The femorotibial mechanical axis was within +/-2 degrees for all prostheses. In the sagittal plane, the mean angle of the femoral component on the lateral view was 4.8 degrees (3-6.5 degrees). The mean tibial slope was 2.7 degrees (1-4 degrees) for the prostheses with a fixed tibial plateau and 0.2 degrees (-1 degrees to +1 degrees) for those with a rotating plateau. The mean operative time was 135 min (110-180 min) and was inversely proportional to experience. There was one conversion to conventional surgery due to software dysfunction. There were no complications related to the operative technique. DISCUSSION: The best outcome, particularly in terms of aseptic loosening, is reported for knees with a valgus or varus angle within 3 degrees . The improved accuracy of computer-assisted implantation has enabled better orientation of the components in the frontal, sagittal and horizontal planes with implantations well within this range.

A comparison of the penetration rate of two polyethylene acetabular liners of different levels of cross-linking. A prospective randomised trial.

We carried out a prospective randomised study designed to compare the penetration rate of acetabular polyethylene inserts of identical design but different levels of cross-linking at a minimum of four years follow-up. A total of 102 patients (102 hips) were randomised to receive either highly cross-linked Durasul, or contemporary Sulene polyethylene inserts at total hip replacement. A single blinded observer used the Martell system to assess penetration of the femoral head. At a mean follow-up of 4.9 years (4.2 to 6.1) the mean femoral head penetration rate was 0.025 mm/year (SD 0.128) in the Durasul group compared with 0.106 mm/year (SD 0.109) in the Sulene group (Mann-Whitney test, p = 0.0027). The mean volumetric penetration rate was 29.24 mm(3)/year (SD 44.08) in the Durasul group compared with 53.32 mm(3)/year (SD 48.68) in the Sulene group. The yearly volumetric penetration rate was 55% lower in the Durasul group (Mann-Whitney test, p = 0.0058). Longer term results are needed to investigate whether less osteolysis will occur.

[Linear scleroderma and foot deformity in children]. / Sclérodermie linéaire et déformation du pied chez l'enfant.

Linear scleroderma is a subtype of localized scleroderma generally observed in children, and may produce secondary bone and joint deformities. Its localization at the foot or ankle is rarely reported. A complete review of the literature reveals 21 cases of foot or ankle deformity due to linear scleroderma to which we add one case. The clinical and radiological aspects of the deformity, its pathogenesis, histological findings as well as orthopaedic management are presented and discussed.