Abstract
Introduction
Range of motion (ROM) is one of the important factor for better functional outcome after total knee arthroplasty (TKA). In posterior cruciate ligament (PCL) retaining (CR) TKA, adequate PCL function is suggested to be important for better kinematics and ROM. However, intraoperative assessment of PCL function is relatively subjective, thus more objective evaluation is required to improve the functional outcomes after TKA. In clinical practice, tibial posterior sagging sign is well known to indicate PCL deficiency. Hence, we hypothesized that intraoperative femorotibial antero-posterior (AP) changes at 90° of flexion indirectly reflected the PCL function and associated with postoperative maximum flexion angles in CR TKA. The purpose of this study was to investigate the correlation between intraoperative femorotibial AP changes at 90° of flexion and postoperative maximum flexion range in navigated CR TKA.
Methods
Between March 2014 and March 2015, forty patients with varus osteoarthritis underwent primary TKA. All of the cases were using same types of implant (Triathlon; Stryker Orthopedics, Mahwah, NJ, USA), with an image-free navigation system (Stryker 4.0 image-free computer navigation system; Stryker). PCL was retained and cruciate substituting (CS) inserts were used in all cases. The mean age at the time of surgery was 71.7 ± 6.8 years old (ranging: 62 – 85). The mean follow-up was 10.9 ± 6.4 months. After minimum release of medial and lateral soft tissue, resection of anterior cruciate ligaments, and protection of PCL, registration and kinematic measurements were performed prior to bone resection. The kinematic measurements were performed again after implantation. The center of proximal tibial and distal femur were defined during registration. The point of proximal tibia was projected to the mechanical axis of femur and the distance between the projected point and the distal femur at 90° of flexion were measured and defined as femorotibial AP position. Distal relative to the center of distal femur indicates as minus, and proximal relative to the point indicates as plus. The correlation between the intraoperative changes of AP position and postoperative maximum flexion angles were investigated.
Results
Preoperative flexion angle is 123.6 ± 13.4° on average, and postoperative flexion angle is 120.7 ± 9.4°. The intraoperative changes of AP position were −1.8 ± 3.5 mm. Although there was no correlation between postoperative maximum flexion angle and the intraoperative changes of AP position, improvement of maxmum flexion angle were negatively correlated with the intraoperative changes of AP position (R = −0.34, P < 0.05).
Conclusion
The results found that intraoperative posterior movement of tibia at 90° of flexion predicts worse postoperative flexion angles in CR TKA. It is suggested that navigation systemmay be able to evaluated the PCL function indirectly and predict the postoperative flexion angles in CR TKA. Navigation might be useful tool not only for proper coronal alignment and kinematics assessment, but for evaluating the femorotibial AP position.
