Abstract
Introduction
Previous fluoroscopic studies compared total knee arthroplasty (TKA) kinematics to normal knees. It was our hypothesis that comparing TKA directly to its non-replaced controlateral knee may provide more realistic kinematics information. Using fluoroscopic analysis, we aimed to compare knee flexion angles, femoral roll-back, patellar tracking and internal and external rotation of the tibia.
Material and methods
15 patients (12 women and 3 men) with a mean age of 71.8 years (SD=7.4) operated by the same surgeon were included in this fluoroscopic study. For each patient at a minimum one year after mobile-bearing TKA, kinematics of the TKA was compared to the controlateral knee during three standardized activities: weight-bearing deep-knee bend, stair climbing and walking. A history of trauma, pain, instability or infection on the non-replaced knee was an exclusion criteria. A CT-scan of the non-replaced knee was performed for each patient to obtain a 3-D model of the knee. The Knee Osteoarthitis Outcome Score (KOOS) was also recorded.
Results
Active flexion was significantly higher in the TKA group with a weight-bearing flexion averaging 103.4° and a passive flexion 133°, and respectively 96.4° and 135° for the contro-lateral knee. Twelve TKA patients out of 15 showed a higher flexion than their contro-lateral knee. The extension was also singificantly higher in the TKA group than in their contro-lateral knee (−4.8° versus −1.8) (p=0.0095). The axial rotation was significantly higher in the non-replaced knees than in the TKA group with respectively 18.7 ° versus 8.9° (p=0.0005). The position of the femorotibial contact point during the arc of flexion was significantly more posterior for the non-replaced knees compared to the TKA. The tracking of the patella showed significantly less lateral tilt for the TKA. KOOS scores were comprised between 70 and 100 but none of the patient did consider the replaced knee as a forgotten knee.
Discussion and conclusion
The results of our study demonstrated that TKA may restore the arc of flexion with a better patellar tracking even if kinematics parameters of TKA are not directly comparable to the contro-lateral knees. This kinematics differences may explain why despite very good specific quality of life and functional score, none of the patient considered his/her replaced knee as a forgotten knee.
