Abstract
Background
In measured resection (MR) technique it is sometimes not easy to equalize extension gap (EG) and flexion gap (FG) because the size of femoral component is generally determined only depending on the anteroposterior and mediolateral size of femoral condyle in MR technique. In order to equalize the EG and FG, femoral implant size should be determined so that the FG is similar to the EG. We developed the novel sizing technique of femoral component to equalize the EG and FG in MR technique. The purpose of this study was to examine the usefulness of this technique.
Methods
Before surgery, the condylar twist angle: CTA (angle between the transepicondylar axis and the posterior condylar axis) was determined for individual knees by transepicondylar view (X ray) or CT. During surgery, after osteophyte was removed EG was made and measured. Knee was flexed in 90° and the specially made tensor which upper paddle has the medial inclination angle (same as the CTA) was inserted to FG before posterior femoral osteotomy. Then, the appropriate traction force was applied to FG. Under this condition, the correct rotational alignment of femur relative to tibia was obtained, and then, the size of femoral component could be determined so that the FG was similar to the EG by measuring the distance between tibial cut surface and posterior cut level of the respective size of femoral conponent. 23 knees that undergone TKA for end stage medial osteoarthritis were examined and the final EG and FG were measured. EG and FG were measured at the mediolateral center of the gap without any trial component.
Results
The mean (± SD) and maximum difference between EG and FG was 2.2±0.9 mm (EG>FG) and 3.5 mm, respectively. The mean (± SD) varus-valgus alignment of gap was 2.1 ± 0.8° varus in extension and 0.9 ± 1.2° varus in flexion.
Discussion
As the EG was reduced by about 2mm after implantation of femoral components, the difference between DG and FG in this series was thought to be very small after implantation. Although it was reported that gap balancing technique has superior ability to control EG and FG compared to MR technique, it was indicated that EG and FG were well controlled also in MR technique by this novel sizing method. Further study to examine the relationship between the clinical results and this method was definitely required.
