Abstract
The external knee adduction moment is considered a surrogate measure for the medial tibiofemoral contact force and is commonly used to quantify the load reducing effect of orthopedic interventions. However, only limited and controversial data exist about the correlation between adduction moment and medial force. The objective of this study was to examine whether the adduction moment is indeed a strong predictor for the medial force by determining their correlation during gait. Instrumented knee implants with telemetric data transmission were used to measure tibiofemoral contact forces in nine subjects. Gait analyses were performed simultaneously to the joint load measurements. Skeletal kinematics, as well as the ground reaction forces and inertial parameters, were used as inputs in an inverse dynamics approach to calculate the external knee adduction moment. Linear regression analysis was used to analyze the correlation between adduction moment and medial force for the whole stance phase and separately for the early and late stance phase. Whereas only moderate correlations between adduction moment and medial force were observed throughout the whole stance phase (R2 = 0.56) and during the late stance phase (R2 = 0.51), a high correlation was observed at the early stance phase (R2 = 0.76). Furthermore, the adduction moment was highly correlated to the medial force ratio throughout the whole stance phase (R2 = 0.75). These results suggest that the adduction moment is a surrogate measure, well-suited to predicting the medial force ratio throughout the whole stance phase or medial force during the early stance phase. However, particularly during the late stance phase, moderate correlations and high inter-individual variations revealed that the predictive value of the adduction moment is limited. Further analyses are necessary to examine whether a combination of other kinematic, kinetic or neuromuscular factors may lead to a more reliable prediction of the force magnitude.
Highlights
Osteoarthritis (OA) of the knee joint is a common disease which is accompanied by pain and impaired mobility
The peak medial forces during late stance (187644%BW) were somewhat larger than those observed during early stance (176627%BW)
Whereas a first distinct peak of the external knee adduction moment (EAM) was observed in all subjects at early stance, only six subjects exhibited a clearly discernible peak at late stance (Figure 1B)
Summary
Osteoarthritis (OA) of the knee joint is a common disease which is accompanied by pain and impaired mobility. A common indirect measure of the medial tibiofemoral contact force (Fmed) is the external knee adduction moment (EAM). This moment is mainly determined by the ground reaction force and its lever arm to the knee joint center. By passing medially to the knee joint center, the force vector creates an adduction moment that is thought to increase the medial compartment load [4]. Studies have shown that the EAM is related to limb alignment [5,6,7,8], bone mineral density of the proximal tibia [6] and the progression of OA [7,9]. While there is indirect evidence that the EAM and the actual loads transferred through the medial tibiofemoral compartment are related, the quantitative relationship between EAM and Fmed is not well established
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