Advantages of custom made prosthesis are the 3D-Planing and correction of the head position using the best possible form fit. Considering these properties we examined several off the shelf systems if they can fulfil the requirements to form fit and head position. By using our fit program we simulated the implantation of five different off the shelf systems in more than 200 individual reconstructed femora. The data of these bones were used for constructing a custom made implant, so the best form fit and head position could be compared with the result of the fit. All of the patients were younger than 65 years. The data of the off the shelf prostheses systems came from 3D measurement. All systems were described as anatomical.

The fit program is an optimization program which can implant a 3D prosthesis model in a reconstructed 3D femur by variation of all six special parameters simultaneously.

Compared to the demands of our custom implants, the results of the virtual implantation of the off the shelf systems, are more or less unsatisfactory. Depending on the acceptable tolerance of the limits in offset, leg lengthening and anteversion up to 50% of the patients could not be treated with a single off the shelf system, when the best form fit was reached sufficiently. Using the results of this examination we enlarged our custom-made prosthesis system with six different sizes of an anatomical like off the shelf prostheses. By perfoming the same fit simulation with our new implants we found that more than 70% of our patients could be treated with this implant sufficiently, when using the same limits.

A good correspondence was found between the computer fit, which was calculated in advance, and the postoperative situation. The combined system of custom and off the shelf prostheses in addition with our 3D planning system based on CT examination, leads to new way of choosing the best implant for a single patient. If the virtual implantation of an off the shelf system does not give a satisfying result, the custom-made CTX prosthesis will be chosen for this patient.

With 3D CT data of proximal femora it is possible to develop a computer programme for optimising femoral component fit and simulation of implantation. The implantation of the femoral stem can be simulated with any femoral component that has cortical press fit.

Five different currently used femoral components were virtually “implanted” in over 200 different femoral bone data. Optimal femoral fit was defined, when the component showed best diaphyseal and metaphyseal congruent contact with all CT data available. Position of neck and head were secondary, since an optimal press fit situation had priority in our set-up. Best fit was considered taken cortical contact and reconstruction of joint geometry into account.

There were numerous failures in all tested standard components, when correct angle of antetorsion, off-set, and leg length were expected. There were considerably better results with the use of CTX standard prosthesis (CTX-S).

The data of this study indicate a high proportion of less optimal fit with femoral standard components tested in this series. Indication for choosing CTX-S femoral components is dependent upon the individual geometry of dysplastic hip joint and the simulation results of standard components using the VIP method.