Abstract
Background: In anteromedial osteoarthritis, only the medial compartment of the knee is affected and the collateral ligaments as well as the cruciate mechanism are intact. These preconditions make the knee suitable for UKA. Our hypothesis was that no difference in tibiofemoral kinematics is observed after UKA. In addition we also hypothesised that the results of the image guided surgery would be the same as the normal surgical procedure.
Design/Methods: To test this hypothesis, we conducted a study using 13 normal human cadaveric knees. For kinematic analysis, the SurgeticsTM surgical navigation system (Praxim, France), equipped with custom written tracking software, was used. Reference markers were mounted to the proximal tibia and the distal femur. In a standardised set-up, the knee was positioned in a leg holder and preoperative kinematics of the normal knee was recorded after a para-patellar mini-incision . Joint kinematics were recorded during passive knee flexion and plotted against flexion angle. Oxford UKA was performed; the standard Phase III instrumentation was used for six knees and the image guided procedure was used for seven knees. After the operation postoperative kinematics were recorded using the same measurement protocol. All data were processed using Matlab 6.1 analysis software (The MathWorks Inc., MA, USA). Preoperative and postoperative tibiofemoral kinematics were determined and compared. The mechanical axes of the tibia and femur were determined and kinematics represented as functions of knee flexion range. Over both the flexing and extending cycles of the knee the changes in tibiofemoral rotation (ΔROT), tibiofemoral ab/adduction (ΔABD), and distances between the origins of the mechanical axes (ΔX, ΔY, ΔZ) were calculated between pre and post-operative states.
Results: The mean differences between pre- and postoperative kinematics for all cases are given as the mean and range in parentheses. For the flexing cycle was ΔROT −0.06 (6.08 to −3.93) degrees, ΔABD was −0.04 (3.39 to −5.72) degrees, ΔX was 0.69 (2.69 to −1.84) mm, ΔY was −0.22 (4.13 to −3.41) mm and was ΔZ 0.27 (4.09 to −1.47) mm. For the extending cycle was ΔROT 0.1 (5.87 to −3.61) degrees, ΔABD was −0.06 (5.72 to −5.95) degrees, ΔX was 0.35 (2.73 to −2.39) mm, ΔY was −0.39 (5.58 to −3.08) mm and was ΔZ 0.21 (3.77 to −1.12) mm. There were no observable differences between the standard and image guided changes in kinematics. Overall, no observable differences were found between pre and post-operative kinematics.
Conclusions: The image guidance system used in our study is a valuable tool for assessing pre- and postoperative knee kinematics. Oxford Unicompartmental Knee Arthroplasty with the Phase III instrumentation in the presence of the cruciate mechanism reproduces the normal kinematics of the knee very accurately.
Theses abstracts were prepared by Professor Roger Lemaire. Correspondence should be addressed to EFORT Central Office, Freihofstrasse 22, CH-8700 Küsnacht, Switzerland.
