Purpose: This study aimed to investigate: 1) whether muscle spindle function (a major contributor to proprioception) is abnormal in individuals with knee OA, and 2) if joint repositioning accuracy is affected at other lower and upper limb joints. Although evidence of proprioceptive impairments associated with knee OA is somewhat equivocal, many studies indicated impaired proprioceptive acuity at the knee and at other joints in individuals with knee OA. However, there has been little investigation of the underlying causes of the proprioceptive impairments. Muscle spindle activity provides one of the most important contributions to perception of joint position and movement, and the central processing of muscle spindle afferent input is integral to optimal proprioception. Muscle spindle function may be compromised in individuals with knee OA given issues such as changes to quadriceps muscle mass. It is possible to probe muscle spindle function in OA by evaluating the effect of perturbing their function. Vibration (60 Hz) over muscle provides a potent perturbation and generates illusions of movement. Joint repositioning accuracy is commonly used to assess proprioceptive acuity in individuals with knee OA. It was hypothesised the effect of muscle vibration on joint repositioning accuracy in individuals with knee OA would be muted compared with a control group as a result of muscle spindle dysfunction. (Figure presented) Methods: Twenty-four individuals with moderate/severe (KL grade 3/4) right knee OA (pain score >=3/10) and 24 asymptomatic controls participated. To test the effect of muscle spindle perturbation on joint repositioning accuracy the mean relative joint repositioning error at the knee, ankle and elbow was recorded during trials with and without vibration applied to key muscles in random order. Vibration was applied to the quadriceps (knee trials), tibialis anterior (ankle) and biceps (elbow) muscles. Participants lay supine with their hips and knees flexed and supported at 90degree for all tests. Participants moved their lower leg/foot/ forearm actively to a target position determined by the tester, returned their limb to rest then moved actively to attempt to match the original target position. Vibration was applied continuously over the muscle belly during initial movement to the target position and back to rest. The difference between the target angle and the angle achieved during the matching phase was recorded. Three separate RM-ANOVAs (Group x Vibration) were conducted to determine if there were differences between the groups in repositioning accuracy at the knee, ankle and elbow in response to vibration. Results: Repositioning errors at the knee, ankle and elbow there were larger when vibration was applied to relevant muscles in both participant groups (all p<0.001) (Figure 1). Data are consistent with the prediction that perturbation to muscle spindle activity leads to the perception that the muscle was shorter (muscle shortening illusion). There was no significant interaction between group and vibration indicating the effect of vibration on the joint repositioning accuracy at the knee, ankle or elbow was similar for both participant groups. In the knee and ankle conditions there was a trend towards larger increases in inaccuracy during trials with vibration in the control group compared with the OA group (Figure 1). Conclusion: Although perturbation of muscle spindle function by vibration affected joint repositioning, this was similar for both groups, with a non-significant tendency towards an interaction between group and vibration at the knee and ankle. Our findings suggest proprioceptive impairments associated with knee OA may not be medicated by deficits in muscle spindle function.
Shanahan, C. J., Hodges, P. W., Farrell, M. J., Bennell, K. L., & Wrigley, T. V. (2012). The role of muscle spindles in proprioceptive acuity at the knee, ankle and elbow in individuals with knee osteoarthritis. Osteoarthritis and Cartilage, 20, S248–S249. https://doi.org/10.1016/j.joca.2012.02.414