Abstract
Introduction:
Recently there has been interest in an alternative method of aligning a total knee arthroplasty (TKA) referred to as kinematic alignment. The theoretical appeal of this method is that alignment of each patient's knee can be individualized through the use of preoperative imaging and computer software, with the goal of achieving pre-arthritic alignment through restoration of the axes of rotation of each particular knee. Clinical studies have evaluated the outcomes of this new alignment technique, but to date there have been no randomized controlled trials comparing kinematic alignment to mechanical alignment. This randomized controlled trial was conducted to compare kinematically aligned and mechanically aligned TKA outcomes of knee pain, function and motion at two years' post-op, along with a comparison of limb, knee, and implant alignment of the two methods.
Methods and Materials:
Forty-four patients were surgically treated with kinematically aligned TKA (figure 1) with the use of patient specific guides, and forty-four patients were surgically treated with mechanically aligned TKA with the use of conventional instruments. All patients underwent CT long leg scanograms after surgery, and outcomes data were collected at a minimum of 2 years. The patient, radiographic evaluator, and clinical evaluator were blinded as to the alignment method.
Results
At a minimum of two years, all outcomes were better in the kinematically aligned group, as determined by the Oxford Knee Score of 41 which was 8 points better (p < 0.001), WOMAC score of 12 which was 13 points better (p = 0.002), Combined Knee Society Score of 164 which was 28 points better (p = 0.001) and flexion of 123 degrees which was 11 degrees better than the mechanically aligned group (p = 0.002). The odds ratio of having a pain free knee at 2 years with the kinematically aligned technique (Oxford and WOMAC pain scores) was 4.1 and 3.53 respectively, compared with the mechanically aligned technique.
The hip-knee-ankle angle (0.3° difference; p = 0.693) and anatomicangle of the knee (0.8° difference; p = 0.131) were similar in the two groups. In the kinematically-aligned group, the angle of the femoral component was 2.4° more valgus (p < .001) and the angle of the tibial component was 2.3° more varus (p < .001) than the mechanically-aligned group (Figure 2).
Discussion:
The Oxford Knee Score, WOMAC Score, Combined Knee Society Score and flexion were significantly better in the kinematic group at a minimum of two years. Oxford Knee and WOMAC pain scores were significantly better, and the number of pain free patients at 2 years was 3–4 times higher in the kinematically aligned group. The obliquity of the joint line was more anatomic in the kinematically aligned total knee replacement.
This study showed that individualizing a total knee arthroplasty using 3-dimensional imaging, preoperative computer planning, and rapid prototyping technology in an attempt to replicate an individual patient's knee kinematics, provided better pain relief and restored better function and flexion compared to the mechanical alignment technique performed with conventional instruments
