Centralization of the femoral component in cemented hip arthroplasty using guided stem insertion

In order to improve the positioning of the stem within the femur, to centralize it within the cement and to achieve a complete and homogeneous cement mantle, a new hip endoprosthesis with guided stem insertion was developed. The femoral component has a longitudinal channel that takes up a guidewire which directs it during insertion into the centre. The guidewire is attached to the cement stopper which is positioned in the marrow cavity before applying the bone cement. The first 100 endoprostheses of this type with an observation period of at least 6 years were assessed radiologically and clinically. The clinical evaluation according to the hip scores of Merle d'Aubigne and Harris revealed a marked improvement between preoperative and postoperative values for all criteria. On radiological assessment 94% of the stems had a neutral position within the femur; 98% of the stems were found to be ideally centred within the cement distally, 80% distally and proximally; 74% of the cement cuffs had a complete and homogeneous cement layer between 2 and 5 mm medially and laterally, while 25% had partially a dimension of more than 5 mm, predominantly proximally. In only 3 cases was one part of the cement mantle found to be less than 2 mm. The radiological follow-up was also documented according to the delineated zones of Gruen. It revealed zonal radiolucent lines in 15 cases, combined in 11 cases with reactive lines, never extending up to 4 zones out of 14. Five prostheses had subsided moderately between 2 and 3 mm, and only one 8 mm. None of these radiological signs was associated with clinical symptoms. There were five cement fractures. Two stems were symptomatic, radiologically loose and revised. Beside these two cases of aseptic loosening there was one septic case, so that in total 97% of the implants are still functioning well.