Abstract
Purpose
Computer navigation system has been reported as a useful tool to obtain the proper alignment of lower leg and precise implantation in TKA. This system alsoãζζhas shown the accurate gap balancing which was lead to implants longevity and optimal knee function. The aim of this study was determine that the postoperative acquired deep knee flexion would be influenced by intraoperative kinematics on navigated TKA even under anesthesia.
Materials & methods
Forty knees from 40 patients, who underwent primary TKA (P.F.C. sigma RPF, DePuy Orhopaedic International, Leed, UK) with computer-navigation system (Ci Knee, BrainLAB / DePuy Inc, Leeds, UK), were recruited in this study. These patients were classified into two groups according to the recorded value of maximum knee flexion at three month after surgery: 15 patients who obtained more than 130 degrees of flexion in Group A, and 25 patients less than 130 degrees in Group B. We retrospectively reviewed about intraoperative kinematics in each group, to obtain the clue for post operative deep-flexion. The measurements of intraoperative kinematics were consisted of 3 points: femoral rotation angle (degree) and antero-posterior translation (mm), which were measured as the translation of the lowest points of femoral component to tibial cutting surface, and the joint gap difference between the medial and lateral components gap (mm). All joint kinematic data were recorded at every 10 degrees of flexion from maximum extension to flexion under anesthesia.
Results
There were no significant differences between two groups about preoperative diagnosis, sex, age, BMI, and preoperative range of motion. At 3 months, the recorded mean value of maximum knee flexion was 134.7 degrees in Group A, and 112.0 degrees in Group B. Femoral components were rotated internally up to 90 degrees flexion, and then rotated externally with flexion to the tibial plateau in the axial plane. There was no significant difference in femoral rotation angle between two groups, but slightly greater in Group A. Regarding to antero-posterior translation, femoral component had an anterior translation up to 50 degrees in both groups. The posterior translation was started at more than 50 degrees, and total amount of posterior displacement was significantly greater in Group A. The gap difference of lateral side was significantly greater in Group A than that in Group B especially at more than 110 degrees of flexion. Discussion
We found two parameters that can obtain greater knee flexion at more than 130 degrees in the early postoperative period. There were significant differences between two groups about the femoral rollback at more than 50 degrees of flexion, and the gap difference at more than 110 degrees of flexion. Navigation system would only suggest that intraoperatively optimal knee kinematics for femoral rollback and slight laxity at more than 110 degrees of flexion to lead the medial pivot motion. The surgeon can keep it in mind for soft tissue release to obtain the ideal postoperative function.
Conclusion
This study showed that the axial rotation and posterior translation of femoral component were important factors for acquisition of postoperative deep flexion.
