[Cementless femoral neck prosthesis CUT--clinical and radiological results after 5 years].

Aim: With regard to total replacement of the hip, revision arthroplasty poses a challenge especially for younger patients. In spite of substantial improvements, new materials and operation techniques are still not able to prevent a shorter running life of prostheses in this group. The present work aims at evaluating clinical and radiological mid-term results of the femoral neck prosthesis CUT (ESKA Orthodynamics Lübeck) to answer the question of whether this implant is recommendable for younger patients.

Method: Between 2001 and 2005 a consecutive series of 99 CUT prostheses was performed in 86 patients (50 female, 36 male) with a mean age of 50 (17-72) years and again evaluated clinically and radiologically after 5.4 (1.7-6.5) years. 84 cases were operated using a posterior approach and 15 cases were operated according to the anterolateral Watson-Jones approach. For clinical evaluation the Harris hip score and the visual analogue scale (VAS) for pain measurement were applied. Standard anteroposterior radiographs of the pelvis and lateral radiographs of the operated hip were compared to radiographs taken in the recovery room by two independent observers. Interobserver measurement discrepancy of the implant angle was 2.6 +/- 1.4 degrees. With 4 degrees being the maximum discrepancy, it was defined as the threshold of the normal range of 145 degrees (141-149 degrees). Additionally, the amount of femoral neck resection, the contact of the medial corticalis with the proximal stem, and the contact of the lateral corticalis with the distal part of the stem, periarticular ossifications and stable fixation by bone ingrowth according to Engh et al. were evaluated. Five delineated sections around the femoral component for evaluation of looseness or progressive loosening were used according to Gruen et al. Radiological evaluation of the cup was performed according to Charnley and DeLee.

Results: The survival rate according to Kaplan-Meier was 98 % after on average 6.6 years. The Harris hip score significantly improved from 50 (16-83) points preoperatively to 98 (40-100) points at the time of follow-up (p < or = 0.05). 82 % achieved an excellent result (91-100 points), 10% a good (91-90 points), 4% had a moderate (71-80 points) and 4% had a bad (< 70 points) result. Six prostheses had to be revised. One of them had to be changed to a cementless standard stem after 5 years because of aseptic loosening. Another one had to be revised after 2.7 years because of chronic thigh pain. Two painful hips had a capsular revision. In one case the liner had to be changed and one case had an exchange of the femoral ball for a better femoral offset. The VAS revealed a significant reduction of pain in rest and under load (p < or = 0.05). 92% had a correct subcapital neck resection. The recommended implant angle of 145 degrees was seen in 72% while a valgus alignment in 18% and a varus alignment in 10% was measured. Undersizing of the CUT-prosthesis was seen in 27 cases. Nine of these cases developed a varus alignment. Osseous integration of the cup and stem was seen in 100% and in 95%, respectively.

Conclusion: This study demonstrates the CUT prosthesis as a bone-preserving prosthesis with good functional and radiological results and therefore as an alternative joint replacement in younger patients.