Primary stability of different plate positions and the role of bone substitute in open wedge high tibial osteotomy.

BACKGROUND: The purpose of this study was to compare the mechanical fixation strengths of anteromedial and medial plate positions in osteotomy, and clarify the effects of bone substitute placement into the osteotomy site. METHODS: Twenty-eight sawbone tibia models were used. Four different models were prepared: Group A, the osteotomy site was open and the plate position was anteromedial; Group B, bone substitutes were inserted into the osteotomy site and the plate position was anteromedial; Group C, the osteotomy site was open and the plate position was medial; and Group D, bone substitutes were inserted into the osteotomy site and the plate position was medial. The loading condition ranged from 0 to 800N and one hertz cycles were applied. Changes of the tibial posterior slope angle (TPS), stress on the plate and lateral hinge were measured. RESULTS: The changes in the TPS and the stress on the plate were significantly larger in Group A than in Group C. These were significantly larger in Group A than in Group B, and in Group C than in Group D. There was no significant difference between Group B and Group D, and no significant difference between knee flexion angles of 0° and 10°. Stress on the lateral hinge was significantly smaller when bone substitute was used. CONCLUSIONS: A medial plate position was biomechanically superior to an anteromedial position if bone substitute was not used. Bone substitute distributed the stress concentration around the osteotomy gap and prevented an increase in TPS angle regardless of the plate position.

Accuracy of Inter Femoral Head Center Distance Measurement and Evaluation for Coronal Alignment of Femoral Component during Total Knee Arthroplasty / 대한정형외과학회잡지

PURPOSE: Alignment is an important factor in the long-term success of total knee arthroplasty. In the total knee arthroplasty, the conventional extramedullary femoral alignment system has significant error in femoral coronal alignment, since it is difficult to find the femoral head center and it is time consuming to determine during the operation. The purpose of our study was to evaluate the accuracy of the newly-designed marker system for extramedullary femoral alignment that uses radiologic distance between the 2 femoral head centers. MATERIALS AND METHODS: Between July 2008 and July 2009, 90 patients (100 knees) with knee osteoarthritis underwent total knee arthroplasty using the femoral extramedullary femoral guide system. We measured the distance between the femoral head centers using the radiologic picture archiving and communication system (PACS, General Electric, Milwaukee, WI) system preoperatively, then plastic rods and metal pegs were used to simulate the inter femoral head center distance. By placing the center of the plastic rod after marking the inter femoral head center distance on the central body line, we could trace the coronal mechanical axis. We measured the angle between the femoral mechanical axis and the femoral component in standing long leg antero-posterior radiograph to assess radiologically the accuracy of coronal alignment postoperatively. RESULTS: The average femoral length in the study group was 402.5+/-16.2 mm. The mean distance between the femoral head and the center of the marker was 49.6+/-17.9 mm. The average error in estimation of the distance between the femoral head center and the metal peg of the marker was 3.78+/-3.14 mm. The positional error in alignment was 1degrees or less in 90% and 2degrees or less in 100% of knees. The average angle of femoral component to femoral mechanical axis was 89.9+/-1.5degrees (range 84.4-93.6degrees). The coronal alignment of the femoral components was within 90degrees+/-3degrees in -96% of cases. CONCLUSION: Our results suggest that the clinical method reported here is a simple and reliable method to localize the center of the femoral head during total knee arthroplasty.