Introduction: Despite advances in endoprosthesis fixation by implant surface alteration, the problem of aseptic implant loosening still exists. Especially in patients with revisions osseointegration and filling of gaps at the bone-implant interface is mandatory for implant survival. Simple BMP-2 immersion has been introduced previously to act as an osteoinductive coating for advanced osseointegration. However, because of the uncontrolled release kinetics and subsequent molecular action and activity of BMP-2, purely osteoinductive actions are hard to differentiate from osteoclastic BMP-actions leading to bone remodelling, which could counteract the implant fixation process and might be the reason for failed attempts to use BMP-2 for implant fixation. In this study we investigated the osteoinductive potency of BMP-2 bound to titanium surfaces by a highly controlled molecular coupling with specifically designed polymers, allowing a slow controlles release kinetics. We present the first results of two different polymers that were implanted in the tibia and femora of New Zealand White Rabbits.

Methods: In this study we designed cylindrical titanium-implants with an inner thread (Ti6-Alï·& #8220;4V, 3 mm hight x 3 mm diameter) and an electropolished outer surface that were coated with different polymers. The polymers were fixed to the surface using the photochemical method of grafting. The implants were implanted in the proximal tibia and distal femora of New Zealand White Rabbits. The anatomical locations of the implants were alternated to test their osseointegration in different quality of bone (cancellous vs. cortical bone). After 4 weeks the animals were sacrificed and DEXA-scans (Dual-energy X-ray absorptiometry), micro-CT and histological analysis were performed. ANOVA and t-test were used for statistic analysis.

Results: In high-resolution DEXA-scans we found a difference in bone mineral density (BMD) between PVBP and a control implant in the distal femora (PVBP 0,720 g/cm², control 0,661 g/cm²) and in the proximal tibia (PVBP 0,633 g/cm², control 0,431 g/cm²) with an increase of bone mineral density. In the histological investigation we found an increase of osteoblasts around the implants coated with PVBP and PVBP-Co-Acryloxysuccimid. Furthermore, the micro-CT scans showed an increase of BV/TV (bone volume/total volume) for both polymers.

Discussion: In this study we present the first results of the investigation of polymer-coated titanium-implants implanted in the proximal tibia and distal femora of New Zealand White Rabbits. The results of DEXA-scans, micro-CT and histological analysis showed an increase of osseointegration. We suggest that controlled release kinetics after coupling of these polymers with BMP-2 can additionally increase osseointegration. To get a closer look on the polymers, their characteristics in-vivo, and coupling with BMP-2 further investigations are conducted.

Aim: Clinical and radiological intermediate-term results of non-cemented Standard- THR in younger patients up to 45 years old. Method: Between 1991 and 1996 forty-nine patients up to 45 years old (22–45, average 39) got 66 THR, 19 of them on both sides. Indications were: 42 Dysplasias (64%), 7 cases with failed osteo-synthesis of femur fracturs (11%), 5 cases of avascular necrosis (8%), 3 cases of Perthesñ disease (4%), 6 cases of rheumatoid arthritis and 3 cases of primary coxarthritis.64% of the patients with dysplasia have already been surgically treated. 51% of all replaced hips have already unterwent surgical treatment. In 35 patients with 50 THR (78%) a follow up (median 7 years, 5,5– 10) with clinical and radiological assessment was obtained. Results: No revision of stem and radiologically no obvious signs of loosening. Two revisions of the cup within the þrst year (one case of aseptic loosening and one case with persisting tendency of luxation)Complications: one intraoperative fracture of proximal femur, treated with a titanium cerclage, 4 luxations (one open reposition, one revision of cup, two closed repositions) no deep infection, 3 cases of incomplete postoperative pareses of femoral or peroneal nerve. WOMAC- score: 42% excellent, 44% good and 14% satisfactory results (average 29)Larson1- Hip-score: 60% excellent, 31% good and 9% satisfactory results (average 73)Conclusion: Non- cemented Standard- THR in younger patients showed good and excellent clinical results in 86 to 91% after intermediate- term follow-up and can therefore be recommended in the above mentioned indications.