Purpose of the study: The anterior rim of the arthroplasty cup can overhang the bone in certain situations: oversized cup, insufficient anteversion, insufficient ace-tabular reaming, cylindrospherical reaming overriding the acetabular opening. The straight or concave shape of the anterior wall of the acetabulum also affects prosthetic overhang. The purpose of this anatomic study was to use a navigation system to quantify, in vitro, the height of the iliopubic psoas notch.

Material and methods: Sixty-eight acetabuli from 34 cadaver pelvi free of osteoarthritis (13 male and 21 female) were analyzed using the Stryker™ hip navigation system. Morphological data were collected for mathematical processing which defined the diameter and the center of the articular surface.

Results: Considerable intra- and inter-individual differences in the shape of the acetabular rim were noted and quantified, particularly concerning the psoas notch. When the lateral view of the acetabular rim is projected onto a plane it produces a succession of three summits and three valleys explaining the difficulty encountered in obtaining a precise mean plane for the acetabular opening.

Discussion: More or less pronounced protrusion of the cup could explain potentially painful anterior impingement of the psoas, especially for certain types of acetabular morphology.

Hip revision failures are partly due to the poor quality of femoral bone stock. Several work showed that bone reconstruction without grafts is possible around a non cemented, stable stem. It is enhanced by a transfemoral approach.

We designed the Restoration TM DLS stem (anatomical, S curved, HA coating and distal locking to ensure a primary stability).

Preoperative planning is necessary. The operative technique is based on a double postero-lateral femoral flaps approach. An innovating and modular instrumentation was developed. It rests on a femoral clamp that solidarises the femur and the trial stem, and allows a precise adjustment of the length and the stem anteversion. A targeting device allows a precise distal locking of the final implant. Osteosynthesis of the flaps is carried out by cerclages in order to bring the bone around the prosthesis.

Forty-seven revisions cases were followed up. No major peroperative incident has occurred. We report one case of locking error. Compared to the planning, the instrumentation was considered to be precise in 94% for the adjustment of the leg length and of the ante-version. The bone adaptation around the implant was generally correct. In 21 cases, it was necessary to carry out metaphysal re-calibration or osteotomies for correction of a femoral deviation. The synthesis of the flaps is stable in 92%. For follow up greater than 3 months, the consolidation of the osteotomies is effective in 90%.

This study made it possible to validate a surgical procedure by transfemoral approach that makes safe implant and cement removal. It also allowed us to validate an innovating, precise yet flexible instrumentation that allows, after preoperative planning, the anatomical reconstruction of the femur around the stem. A perfect proximal adaptation of the femur to the implant is necessary to the good tolerance of the distal locking.