Computer-assisted navigated cup placement in primary and secondary dysplastic hips

Aim: The positioning of an acetabular implant has great influence on the range of motion as well as the charger of dislocation of total hip arthroplasty. Using modern CAS systems the reproduction of the cup position after three-dimensional planning based on computed tomography is possible. We investigated the reliability of the position of the acetabular implant in primary and secondary dysplastic cases. Method: Within a prospective randomised study in a total of 100 hip replacements with postoperatively controlled cup position using a computed tomography, we reinvestigated especially the 18 dysplastic and two secondary dysplastic cases. Results: In the dysplastic cases we could realise nearly the same anteversion angles (22.4degrees to 21.5degrees) with a bigger standard deviation ( +/-7.68 to +/-7.29) than in the normal collective. Even the inclination angles (44.5degrees +/-5.47degrees) could be realized nearly the same as in the normal cases (42.3degrees +/- 4.31degrees). The depth of the cup implantation could be realised in 15 of 18 cases. Conclusion: The CAS system is helpful even in dysplastic cases. The advantage of three-dimensional preoperative CT-based planning is apparent. The surgeon is not able to plan and realise the ideal cup position in some individual.