Impaired varus-valgus proprioception and neuromuscular stabilization in medial knee osteoarthritis

Abstract

Impaired proprioception and poor muscular stabilization in the frontal plane may lead to knee instability during functional activities, a common complaint in persons with knee osteoarthritis (KOA). Understanding these frontal plane neuromechanical properties in KOA will help elucidate the factors contributing to knee instability and aid in the development of targeted intervention strategies. The objectives of the study were to compare knee varus-valgus proprioception, isometric muscle strength, and active muscular contribution to stability between persons with medial KOA and healthy controls. We evaluated knee frontal plane neuromechanical parameters in 14 participants with medial KOA and 14 age- and gender-matched controls, using a joint driving device (JDD) with a customized motor and a 6-axis force sensor. Analysis of covariance with BMI as a covariate was used to test the differences in varus-valgus neuromechanical parameters between these two groups. The KOA group had impaired varus proprioception acuity (1.08±0.59° vs. 0.69±0.49°, p<0.05), decreased normalized varus muscle strength (1.31±0.75% vs. 1.79±0.84% body weight, p<0.05), a trend toward decreased valgus strength (1.29±0.67% vs. 1.88±0.99%, p=0.054), and impaired ability to actively stabilize the knee in the frontal plane during external perturbation (4.67±2.86 vs. 8.26±5.95 Nm/degree, p<0.05). The knee frontal plane sensorimotor control system is compromised in persons with medial KOA. Our findings suggest varus-valgus control deficits in both the afferent input (proprioceptive acuity) and muscular effectors (muscle strength and capacity to stabilize the joint).

Keywords: Instability; Knee osteoarthritis; Proprioception; Varus–valgus motion.

Conflict of interest statement

Conflict of interest statement

None.

© 2013 Published by Elsevier Ltd.

Figures

Fig. 1

Schematic representation of the experimental setup. Several stabilization methods were employed to minimize limb rotation during testing. First, the lower third of tibia, ankle joint, and the rear part of the foot were cast with fiberglass tape and placed within two aluminum half-rings with adjustable blunt screws to form a tight coupling between the cast and the rings. The cast-rings assembly was mounted onto one end of an aluminum beam located beneath the leg. Second, the femoral condyles of the tested knee were clamped from the medial and lateral sides and supported from below. Two threaded rods connecting the medial and lateral pieces of the knee clamp and wing nuts at both sides of the rods were tightened to press the femoral condyles from medial and lateral sides. Third, the left and right hips were blocked by a pair of hip clamps, which were moved medially through two screw mechanisms to press against the greater trochanters and prevented the hips from moving to the left or right side.

Fig. 2

A typical torque-angle curve from 6 cycles of knee frontal plane angular motion. The horizontal axis represents knee varus-valgus angle, where (+) direction is valgus. The vertical axis represents knee varus-valgus torque, where (+) direction is valgus. The varus-valgus angular stiffness was calculated as the slope within 2 degrees of varus-valgus motion, 1 degree in each direction.

Fig. 3

Proprioceptive acuity in varus and valgus directions. OA group had impaired proprioception acuity in the varus direction (1.08 ± 0.59° vs. 0.69 ± 0.49°, p < 0.05). There was no difference in valgus proprioceptive acuity between these two groups (0.83 ± 0.47° vs. 0.70 ± 0.49°, p > 0.05).

Fig. 4

Change of knee varus-valgus torque-angle curves from without (in blue) to with (in red) active muscular contribution to v-v stiffness. Valgus direction is (+). Comparison was made between an osteoarthritic knee and an age-, gender-matched control knee in both 8 and 12 torque limit conditions. Both knees improved varus-valgus stiffness with active muscular contraction, but the OA knee had considerably smaller slope change.

Fig. 5

Active neuromuscular contribution to v-v stiffness. The vertical axis is change of angular stiffness from without to with active muscular stabilization. At 12 Nm torque limit, OA participants increased their knee frontal plane stiffness by 4.67 ± 2.86 Nm/degree vs. by 8.26 ± 5.95 in controls, p < 0.05. At 8 Nm torque limit, OA participants had a change of 3.11 ± 2.26 Nm/degree vs. 7.26 ± 5.05 in the control group, p < 0.05.