Introduction
External moment that affects knee joint can be divided to the knee adduction moment (KAM), the flexion moment (KFM), and the rotation moment (KRM). Previous study regarding knee osteoarthritis (OA) reported that among these three components of the total knee joint moment (TJM), the peak KAM and KFM has been related to OA progression, and that the dominance in 1st peak TJM shifted from KFM to KAM with OA progression. High tibial osteotomy (HTO) is a surgical treatment option for medial compartment OA, correcting varus limb alignment to valgus. Recent biomechanical study reported that HTO reduce the KAM. However, the influence of HTO on each component of the knee moment remains unknown. The purpose of the present study was to clarify the change of relative contributions of each moment components to TJM before and after HTO.
Methods
Institutional review board approval of ethical committee and informed written consent was obtained for this study. Fifty-five patients (55 knees) who underwent Medial open-wedge (MOW) HTO performed by single surgeon at our hospital and gait analysis before and 1 year after surgery between February 2016 to October 2019 were enrolled in this study. There were 25 men and 29 women with a mean age of 58.2 ± 6.1 years at the time of surgery. Clinical evaluation was performed using the visual analogue scale (VAS) for pain (0-10 [worst pain]), and the functional knee score (Japanese Knee Osteoarthritis Measurement (JKOM) score, 25-125 [worst]). All patients were assessed while walking at a self-selected speed using an optical motion capture system; subsequently, six degrees of freedom knee joint kinematics were calculated using the Point Cluster Technique. Three moment components at the knee joint were calculated by using inverse dynamics. Moreover, total joint moment (TJM: TJM = v(KAM2+ KFM2 + KRM2)) and relative contributions of each moment components at the knee (%KAM = KAM2/TJM2*100, %KFM = KFM2/TJM2*100, %KRM = KRM2/TJM2*100) at maximum reaction force data were measured. Paired t-test was performed for statistical analysis between pre and postoperative results. Statistical differences were considered significant for values of p<0.05.
Results
The VAS and JKOM score improved from 52 to 12, and 58.2 to 36.2 respectively. The KAM decreased significantly throughout the stance phase (P < 0.001), but no significance was observed in KFM (Figure 1). The TJM decreased significantly postoperatively at 1st and 2nd peak (P <0.001). The preoperative relative contributions of KAM, KFM and KRM to TJM at 1st peak were 47.7%, 50.9% and 1.3%, respectively, and postoperative contribution rate were16.2%, 79.21% and 5.1%, respectively. Although there was no significant difference in TJM before and after HTO, the relative contribution of KAM significantly decreased (P <0.001) and that of KFM increased (P < 0.001) (Figure 2).
Discussion And Conclusion
The results revealed that the first peak of KAM decreased significantly after MOWHTO, indicating that MOWHTO reduced total stress to medial knee compartment in stance phase. This study also presented the transition from a KAM to a KFM dominance postoperatively. These results indicated that the correction of coronal alignment after MOWHTO changed gait kinematics three-dimensionally and dynamically, and the function of the quadriceps, which is an antagonist of the external flexion moment, was improved by the increase of the flexion moment. In conclusion, our results suggest that alignment correction by MOWHTO resulted in not only the pain relief but an improvement of the knee joint function by the conversion of KAM to KFM.