Abstract
Background
A navigation system is useful tool to evaluate the intraoperative knee kinematics. Rheumatoid arthritis (RA) patients often need to have TKA operation, however, there are few TKA kinematics studies comparing RA and Osteoarthritis (OA) patients.
Objective
The purpose of this study was to evaluate intraoperative TKA kinematics, and to describe the difference of kinematics between RA and OA patients.
Materials and methods
Seventy-four patients, 86 knees were included in this study. Unilateral posterior stabilized TKAs were performed (male 14, female 72, age 70 ± 1.1 years) using navigation system. Sixty-one knees had OA and 25 had RA. Evaluation items are coronal gaps, AP translation and rotation. Coronal gaps were defined as the distance between the femoral and tibial cut surface. Medial and lateral gaps are also measured. AP translation was defined as the sagittal movement between the center of femoral and tibial condyle. Rotation was defined as axial difference of axis between femur and tibia. All items were evaluated by navigation system at every 10 degrees of knee flexion from 0 degrees of extension to 140 degrees of deep flexion.
Results
In extension range, mean medial joint gaps (RA / OA) were 22.5 / 21.6 mm at 0 degree and decreased to 17.3 /15.0mm at 40 degrees, respectively. They were significantly different at 40 degrees. Lateral joint gaps were 16.4, 15.5mm at zero degree and slightly decreased to 21.0 / 20.0 mm at 40 degrees. In flexion range, mean medial joint gaps were 17.3 / 17.2 mm, 20.9 / 21.6 mm and 34.9 / 37.3 mm at 50 / 90 mm and 140 degrees. Mean lateral joint gaps were 16.4 / 15.5 mm, 21.8 / 21.6 mm and 29.0 / 31.4 mm. Both gaps were increased as knee was bent deeply(see Figure 1).
Regarding to AP translation, femoral component was once moved 6.5 / 6.1 mm forward up to 50 degrees, then moved 25.8 / 23.5 mm backward with flexion. There was no significant difference (see Figure 2).
Rotation kinematics showed significant difference in early flexion range. Consecutive external rotation of femur was recognized in RA group, but internal rotation was occurred in OA group from 0 to 60 degrees. External rotation was recognized in both groups from 60 degrees to deep flexion (see Figure 3).
Conclusion
In this study, although joint gaps and AP translation were almost similar between RA and OA, it became clear that most significant difference was rotation movement in early range of knee flexion. It recognized opposite rotation between two groups. The limitation of this study was the situation of under anesthesia and no muscle strain were loaded during the measurement of knee kinematics. However, navigation system is available not only for the accurate implantation but also the measurement of intra operative knee kinematics.
