IMPACT OF PRE-OPERATIVE KNEE KINEMATICS ON POST-OPERATIVE KNEE KINEMATICS IN TOTAL KNEE ARTHROPLASTY

Introduction We have previously reported that patients who demonstrated medial pivot kinematics pattern after total knee arthroplasty (TKA) had better clinical results than that of non-medial pivot pattern. However, it is unclear how preoperative kinematics pattern affects postoperative knee kinematics. The aim of this study was to evaluate the relationship between preoperative and postoperative knee kinematics pattern in TKA. Materials and Methods The present study consists of 38 patients with medial osteoarthritis who underwent a primary TKA using a CT-based navigation system from July 2010 to September 2012. All the operations were performed by a single surgeon using a subvastus approach and the same posterior cruciate ligament substituting type (PS type) of prosthesis (Genesis II™ total knee system, Smith & Nephew, Memphis, TN). The proximal tibia osteotomy and the distal femur osteotomy were set on the navigation system perpendicular to the mechanical axis in the coronal plane with 3° tibial posterior inclination in the sagittal plane. The coronal plane ligament imbalance was corrected until the gap imbalance was fewer than 2 mm. This gap balance was checked using a ligament balancer (Smith & Nephew) at 80 N in medial and lateral compartment of the knee. The navigation system was used to measure the flexion gap with the CAS ligament balancer (Depuy, Warsaw, IN, USA) at 90° knee flexion. The amount of external rotation on femoral osteotomy was adjusted by the navigation system with a balanced gap technique. The patella was resurfaced and a lateral release was not performed. Tibial A-P axis of the tibial tray was placed parallel to Akagi9s line. We measured each kinematics pattern immediately after capsule incision (preoperative knee kinematics) and after implantation (postoperative knee kinematics) in TKA. Subjects were divided into two groups based on kinematics patterns: a medial pivot group (group M) and a non-medial pivot group (group N). A chi-square test was used for statistical analysis. P values less than 0.05 were considered significant. Results There were 19 knees in group M and 19 knees in group N at preoperative knee kinematics measurement. Nineteen knees in group M at preoperation resulted in 14 knees in group M and five knees in group N at postoperative knee kinematics measurement. On the other hand in group N at preoperation resulted in 2 knees in group M and 17 knees in group N at postoperative kinematics. Preoperative knee kinematics significantly correlated with postoperative knee kinematics (P Discussion and Conclusion In conclusion, this study revealed that a precise bone cut assisted by a navigation system and a modified gap technique could not improve the knee kinematics pattern in most cases. Further technical improvement or a new implant design is required to correct preoperative abnormal knee kinematics in TKA.