Abstract
Background
Patient satisfaction after total knee arthroplasty (TKA) has been lower than after a similar procedure, total hip arthroplasty. Poor subjective outcomes after TKA may be partially explained by abnormal kinematics patterns after TKA. The purpose of this study was to analyse rotational kinematics patterns in knees that had undergone posterior stabilized (PS)-TKA, and to clarify the relationships between rotational kinematics patterns and patient satisfaction, as well as between rotational kinematics patterns and knee function.
Materials & Methods
A total of 49 osteoarthritis knees after primary PS-TKA (NexGen LPS-Flex fixed bearing knee system) were included in this study; deformed valgus, severe flexion contractures, and highly unstable knees were excluded. We used a computer navigation system and measured knee kinematics after each surgery was completed. A single investigator gently applied a manual range of motion from full extension to flexion. The angle of the internal rotation of the tibia was measured automatically at 0º, 30º, 45º, 60º, and 90º, along with maximum extension and flexion. We categorized the post-operative rotational kinematics patterns for individual cases, focusing on the initial knee flexion from 0–30º. Type A corresponded to an increased internal rotation angle of the tibia during the initial knee flexion (screw home-like movement). Type B corresponded to an increased external or an unchanged rotation angle of the tibia. We examined the range of motion (ROM) at 6 months after surgery and assessed the 2011 Knee Society Score (2011 KSS) at ≥1 year following surgery.
Statistical analysis. The difference between the two groups was compared using a Wilcoxon rank sum test. Analyses were performed with JMP statistical software v8.0 (SAS Institute). A p-value of <0.05 was regarded as significant.
Results
The tibia exhibited an average of 5º of internal rotation at initial knee flexion. The type A kinematics pattern achieved a better ROM and functional activity score (2011 KSS) than the type B kinematics pattern.
Discussion
Modern TKA implants have been designed to reproduce normal knee kinematics to achieve better patient satisfaction and knee function. However, few reports have described the relationship between the rotational kinematics patterns at initial knee flexion and patient satisfaction. In our study, the type A postoperative rotational kinematics pattern (screw home-like movement) had better ROM and functional activity score than the type B kinematics pattern. The movement toward the internal rotation of the tibia during initial knee flexion might be important in achieving better clinical results after PS-TKA.
