Abstract
Introduction
Correct alignment is important for a successful result after total knee arthroplasty (TKA). During most activities of daily living, the knee is loaded not only in full extension but also in mid-flexion. However, there are few methods to evaluate mid-flexion varus-valgus alignment, despite its clinical significance. Computer navigation systems are useful for intra-operative monitoring of joint positioning and movements. Knee ligaments contribute to induce kinematics of the joint. It is likely that the presence of posterior cruciate ligament has some effects on kinematics throughout flexion. The purpose of this study was to evaluate changes in the varus–valgus alignment of the femoral–tibial mechanical axis in each flexion angle before and after TKA by using a navigation system, and to evaluate varus–valgus kinematic patterns throughout flexion, and compare preoperative and postoperative changes of kinematic patterns in CR-TKA and PS-TKA procedures.
Material and Method
Forty knees that underwent TKA with computer navigation system were evaluated (CR-TKA 20; PS-TKA 20). CR and PS TKRs were implanted in alternating sequence. The investigator applied manual mild passive knee flexion, while moving the leg from full extension to flexion and the varus-valgus angle of femoral-tibial mechanical axis was measured automatically by the navigation system at every 10 ° throughout flexion. We classified kinematic patterns in the varus–valgus direction throughout flexion.
Results
The mean change in size of the varus–valgus angle associated with full movement was 8.0º preoperatively and 5.3º postoperatively. There was no difference between CR-TKA and PS-TKA. We then evaluated the distribution of changes in size of the varus–valgus angle. Postoperatively, this was limited to 3º or less in many patients, but was also around 6º in many cases, and in some cases it exceeded 10º. For CR-TKA, it was 7º or less in all except one patient, but conversely the change was around 6º in most cases. For PS-TKA, it was limited to 3º or less in most patients, but did exceed 10º in some cases. (Fig.1)
We could classify kinematic patterns throughout flexion movement into five broad types. Type A: Varus movement associated with flexion; Type B: Valgus movement associated with flexion; Type C: Same angle position maintained; Type D: Varus movement in the intermediate flexed position; Type E: Valgus movement in the intermediate flexed position. (Fig.2) Kinematic patterns changed before and after TKA in some patients, but in others they remained similar. Among those who underwent CR-TKA, preoperative and postoperative kinematic patterns were similar in 61% of patients, whereas they were different in 80% of those who underwent PS-TKA.
Discussion)
Our results showed that with respect to postoperative varus–valgus kinematic patterns, the effect of the preoperative varus–valgus kinematic pattern persisted more strongly after CR-TKA compared with PS-TKA. This may have been because in CR-TKA the conserved PCL affects the restriction of varus–valgus movement throughout flexion movements, whereas in PS-TKA it is the post-cam that restricts knee joint movement while also affecting the induction of varus−valgus kinematics with loss of PCL influence.
