The influence of the tibial sagittal cut on component position in the Oxford knee.

The alignment of the components of the Oxford knee replacement were analysed before and after modification of technique for performing the sagittal cut. In the 126 knees prior to the change, there was wide variation in the apparent femoral rotation on screened X-rays centred on the tibial component. In the 40 knees after the change, the variability was markedly reduced (traditional technique, mean femoral rotation 7.86 degrees, range -5 degrees to 30 degrees, compared with 3.18 degrees, range 0 degrees to 15 degrees in the modified group, p=0.0001.). We conclude that the apparent rotation of the femur is largely due to variation in position of the sagittal cut. The mean meniscal displacement was not reduced in the modified group but the range was smaller in that no menisci were displaced more than 3.5 mm from the tibial upright compared with 15% in the traditional group. Menisci which were displaced tended to rotate. The mean rotation and range were greater in the unmodified group (5.92 degrees ER range, 20 degrees ER to 25 degrees IR, traditional group, compared with 0.39 degrees ER, range 10 degrees ER to 12.5 degrees IR in the modified group, p=0.001). A simple technique for controlling the direction of the sagittal cut using intra articular landmarks gives reproducible results. The apparent femoral rotation on screened views in extension is reduced as is the range of meniscal displacement and rotation. Application of this technique may be helpful in lateral resurfacing where soft tissue support is less likely to resist meniscal dislocation.