New type of hip arthroplasty failure related to modular femoral components: breakage at the neck-stem junction.

Total hip replacements (THR) with modular femoral components (stem-neck interface) make it possible to adapt to extramedullary femoral parameters (anteversion, offset, and length) theoretically improving muscle function and stability. Nevertheless, adding a new interface has its disadvantages: reduced mechanical resistance, fretting corrosion and material fatigue fracture. We report the case of a femoral stem fracture of the female part of the component where the modular morse taper of the neck is inserted. An extended trochanteric osteotomy was necessary during revision surgery because the femoral stump could not be grasped for extraction, so that a long stem had to be used. In this case, the patient had the usual risk factors for modular neck failure: he was an active overweight male patient with a long varus neck. This report shows that the female part of the stem of a small femoral component may also be at increased failure risk and should be added to the list of risk factors. To our knowledge, this is the first reported case of this type of failure.

[Quantitative 3D anatomy of the lumbar spine]. / Anatomie quantitative tridimensionnelle du rachis lombaire.

PURPOSE OF THE STUDY: There are many anatomic descriptions of the spine, but most concentrate on qualitative information. Quantitative data is however important to achieve a better clinical approach, to adapt implant size and to construct geometric models of spine mechanics. MATERIAL AND METHODS: We examined 32 dry spines (160 lumbar vertebrae) obtained from the Orfila Museum anatomy laboratory at the Saints-Pères School of Medicine in Paris. We drew 178 landmarks on the surface of each vertebra and recorded the 3D spatial coordinates of each point using a Fastrack electromagnetic system operating with +/- 0.2 mm precision. The coordinates of the digitalized points were expressed in a local x-y-z axis field (x=posteroanterior axis, y=right-left axis, z=caudocranial axis). The origin O was half way between the "centers" of the vertebral plates. After calculating 112 linear, angular and surface parameters, results were analyzed with the Statview statistics system. RESULTS: All parameters exhibited gaussian distribution. The transpedicular vertebral depth, corresponding to the maximal penetration of a pedicular screw before touching the anterior wall, was nearly constant: 48 mm (mean). The mean height of the pedicle was approximately 16 mm for L1 to L4 and 21 mm for L5. Pedicle width was 7 mm for L1 and L2 then rapidly widened to reach 10 mm for L5. It was noteworthy that the narrowest pedicle (4 mm) was found in 10% of the L1 vertebrae. There was an exponential rise in the sagittal tilt of the pedicles from L1 to L5, measuring approximately 8 degrees for L1 and rising to 24 degrees for L5. DISCUSSION: Our sample of human spines with unknown clinical characteristics (age, sex) is representative of anatomy laboratory populations, generally composed of subjects over 40 years of age, and is thus adapted for studies of the degenerative spine. Our findings are generally in agreement with data reported in the literature and also provided complementary quantitative data concerning the transpedicular vertebral depth that was found to be a rather constant feature of the lumbar spine. It measured between 40 and 56 mm for 95% of the study population. The dimensions of the pedicle is particularly important: the width must be known to determine the size of pedicle screws; it measured between 7 and 12 mm in 95% of the population. The largest mean cross section of the pedicle was found for L5 (82mm(2)), but measured less than 60 mm(2) in 10% of the vertebrae, suggesting predisposition to spondylolysis.

Validation of the non-stereo corresponding points stereoradiographic 3D reconstruction technique.

Several 3D reconstruction techniques deriving from stereoradiographic DLT have been presented during the last 15 years, but these techniques have usually been limited in accuracy because of the small number of corresponding anatomical landmarks identified on both radiographs. A new technique has recently been proposed to perform 3D reconstruction of the spine using not only the stereo-corresponding anatomical landmarks (seen on both frontal and sagittal X-ray films) but also some non-stereo-corresponding ones. This technique (called non-stereo-corresponding points or NSCP) has already been used for cervical dry vertebrae. In the present study, we focus on the validation of this technique for lumbar vertebrae by comparing four techniques: direct measurement, CT scan, 3D reconstruction by stereoradiography using a direct linear transformation (DLT) algorithm and the NSCP technique. The accuracy of the NSCP technique was also evaluated on different vertebral regions. The global results show mean errors of 1.1 mm and maximum of 7.8 mm with regard to direct measurements. These mean errors are close to those obtained using 3D reconstructions from CT scan using 1 mm cuts.

[Dorsal trapezoid-scaphoid luxation. A case report]. / La luxation columnaire trapézo-scaphoïdienne dorsale. A propos d'une observation.

Dorsal trapezoscaphoid dislocations are characterised by posterolateral translation of the trapezium and the distal part of the first finger in relation to the rest of the wrist and hand. The authors found only 7 cases in the literature and they analyse the principal features in the light of a new personal case caused by violent trauma. It was easily reduced orthopaedically, but because of the instability, double pinning was performed to the adjacent bones and plaster immobilisation was maintained for six weeks. An excellent functional and radiological result was obtained and remained stable after two years.