Midterm results of "thrust plate" prosthesis.

The aim of this investigation was to analyze the midterm results obtained with the metaphyseal fixation principle of the thrust plate prosthesis (TPP). Survival of 214 implants in 204 patients was analyzed. Clinical (Harris hip score) and radiologic examinations were carried out on 157 of 190 TPP with a postimplantation follow-up period of at least 5 years. Failure rate was 7.0% (9 aseptic and 6 septic loosening). Harris hip score increased from 36.9 +/- 13.5 points preoperatively to 91.2 +/- 13.1 points at follow-up. Eleven TPPs showed radiolucent lines not indicating prosthetic loosening. Thrust plate prosthesis is not an alternative to stemmed endoprostheses. It may be rarely indicated in very young patients where, because of their age, several revision operations can be expected.

High migration rate of two types of threaded acetabular cups.

INTRODUCTION: Survivorship analysis was performed on 479 Link V-type threaded cups and on 110 modified V-type Bad Bramstedt cups (a modification of the Link V-type cup since 1993 with a smaller primary coil) to evaluate the effect of the modifications. MATERIALS AND METHODS: Indication for hip arthroplasty with a Link V-type cup was an inflammatory arthritis in 310 patients, osteoarthritis in 138 patients and dysplastic hip joints in 31 patients. The average follow-up was 8.6+/-3.2 (range 3.0-15.2) years. The 110 modified V-type Bad Bramstedt cups had a mean follow-up period of 4.5+/-0.7 (range 3.0-5.9) years, including 49 with inflammatory arthritis, 49 with osteoarthritis and 12 with dysplastic hip joints. To evaluate the migration rate and radiolucent lines, radiographical examination according to the method of Nunn et al. and Delee and Charnley was performed on 264 Link V-type cups with a mean follow-up period of 8.2+/-2.7 years and 59 modified V-type Bad Bramstedt cups with a mean follow-up period of 4.6+/-0.7 years. Relevant parameters influencing cup migration were analysed. RESULTS: The cumulative survival rate of the former Link V-type acetabular cup was 94.5% after 5 years, 88.1% after 10 years and 70.2% after 15 years. The Bad Bramstedt cup showed a 5-year survivorship rate of 97.9%. Migration of more than 3 mm or tilting of the cup greater than 5 degrees was found in 73% of the former type and in 39% of the modified cup. Radiolucent lines greater than 2 mm and detectable in two zones appeared in 6.4% of the former Link V-type and in 1.7% of the Bad Bramstedt cup design. Among the influencing factors analysed, length of follow-up and primary cup positioning showed a significant correlation to cup migration. CONCLUSION: The modification of the Link V-type cup showed no satisfactory improvement in cup migration. Therefore, both threaded cups were abandoned in favour of cementless press-fit cups.

The thrust plate prosthesis in patients with aseptic osteonecrosis of the femoral head.

BACKGROUND: The thrust plate prosthesis (TPP) is an implant with a metaphyseal fixation at the proximal femur that transmits the load forces of the hip onto the femoral neck. The osseous incorporation of the TPP and the adaptation of the bone to this force transmission depend on the bone quality, which is reduced to minor vitality and stability in patients with osteonecrosis of the femoral head. Depending on the etiology of the femoral head necrosis, the TPP might lead to early failures. METHODS: In a prospective study, 63 patients with 72 cementless TPP due to femoral head osteonecrosis were examined. A clinical and radiological evaluation was performed preoperatively, 3 and 6 months postoperatively, and every year thereafter. The average follow-up period was 4.8+/-1.3 years with a minimum of 3 years. The pathogenesis of femoral head necrosis included alcoholism (n=19), subsequent to renal transplantation (n=11), during cortisone therapy of other dyscrasia (n=9), preceding a polychemotherapy (n=4), diabetes (n=3), sickle cell anemia (n=1), and idiopathic osteonecrosis (n=25). RESULTS: The Harris Hip Score increased continuously from 50.0 points beyond 79.8 points after 3 months to 86.8 points within the 1st year, and subsequently remained stable at this level. Revision was necessary in six cases (8.3%). Of these, three had an aseptic loosening of the implant: 2 cases with renal transplantation and 1 of alcoholism with an extension of the necrotic area to the seating of the TPP. The other three patients showed septic implant loosenings: 2 cases with renal transplantation and 1 of alcoholism. Radiolucent lines were found in 9 cases (12.5%), mostly in zones 1 and 2 underneath the TPP. Of these, 1 with an idiopathic osteonecrosis was assessed to be radiologically loosened. The overall failure rate was 9.7%, with a proportion of 36.4% in patients with renal transplantation. Excluding this specific patient group, the failure rate was 4.9%. CONCLUSIONS: Femoral head necrosis following renal transplantation and extension of the necrotic area into the femoral neck are contraindications for TPP. Excluding these patients, the TPP shows comparable mid-term results to cementless stemmed prostheses and supplies advantages especially for younger patients, because of its metaphyseal, bone-preserving fixation. However, evaluation of the clinical impact of the TPP in comparison with other cementless femoral stem systems requires long-term examinations in the future.