Aims: The purpose of this study was to evaluate primary stability and the time of bony þxation of two different designed cementless titanium hip stems. Therefore we designed a prospective clinical study with high precision RSA and close follow up periods (3, 6,12, 24, 52, 104 weeks). Methods: One stem was a Ç straight stem È (BICONTACT, Aesculap AG, Germany) with a rough pure Titanium surface in the upper part for proximal þxation. The second stem (Image, Smith& Nephew, Germany) was anatomically shaped with additional HA coating. 34 IMAGE stems and 20 BICONTACT stems with RSA markers were implanted. Mean age in both groups was 64 years. In September 2002, 28 patients (14 X BICONTACT and 16 X IMAGE) were followed for more than 1 year and 12 patients (6 X BICONTACT and 6 X IMAGE) for more than 2 years. Results: Subsidence was predominantly observed between the postoperative control and the 6 weeks follow up. (IMAGE 0.83mm, BICONTACT 0,60mm) and decreased up to 12 weeks (IMAGE 0.05mm, BICONTACT 0,29mm). After 12 weeks both stems were stabilized (12–24 weeks: IMAGE 0.05mm, BICONTACT 0.06mm; 6 months -1 year: IMAGE 0.05mm, BICONTACT 0.04mm. Between 1 and 2 years subsidence for the IMAGE stem was 0.05mm compared to 0.16mm in the Bicontact group. Overall subsidence of the IMAGE stem during the þrst year was 0.96mm compared to 0.97mm for the BICONTACT stem. Conclusions: Titanium cementless hip stems with a rough proximal titanium surface or HA coating showed a sufþcient primary and mid-term stability. Bony þxation is achieved between 6 and 12 weeks. No statistical differences were found between both stems.

Aims: The purpose was to evaluate the biomechanical properties of Hamstring graft fixation methods with ability for circumferential graft ingrowth in a standardized experiment with high precision Radiostereometric Analysis (RSA). Methods: We used 30 porcine specimens for the study. A fourstranded graft was sutured with a baseball stitch. Ten trials were performed in each group. The sutured end of the graft was fixed with a Washer-Lock (WL) or two resorbable Cross-Pins (CP). In the Suture-Disc (SD) group 8 polyester sutures (Ethibond 5USP) were knotted over a titanium button. The tibial bone and the tendon-graft were marked with tantalum beads. The grafts were loaded axially under RSA control increasing the force in steps of 50N to load of failure. Micromotion between tendon graft and tibial bone was measured with RSA. Results: Load at failure was significantly higher for the WL and CP fixation (722±173N; 647±129N) compared to SD fixation (445±37N). Stiffness of fixation was significantly higher for WL and CP fixation 492N/mm; 416N/mm) compared to SD fixation 111N/mm). Graft displacement started at low loads for SD fixation (47N) compared to WL and CP (344N; 250N). Graft motion at 200N load was significantly higher in the SD group (1.85mm) than for the WL (0.33mm) and CP (0.3mm) fixation. Bungee cord effect at 200N for the SD was measured 1.32mm, for the CP 0.50mm and for the WL 0.22mm in average. Conclusions: Direct fixation of a quadrupled tendon graft with WL or CP is preferable to SD fixation. Low linear stiffness of SD fixation with linkage suture material allows for a high amount of elastic deformation.