The effects of joint damage on muscle function, proprioception and rehabilitation.

SUMMARY. The paper summarizes a series of studies investigating reduced quadriceps femoris activation and its effect on rehabilitation of patients with traumatic and arthritic knee damage. It incorporates findings from related research fields and speculates on the physiological causes of reduced voluntary activation following joint damage and its clinical implications. Arthrogenic reduction in voluntary activation is the inability to maximally activate muscles acting across damaged joints. This phenomenon may cause muscle weakness by preventing complete activation of the muscle and if prolonged may result in muscle fibre atrophy, and may possibly impede rehabilitation. In patients with anterior cruciate ligament (ACL) deficient knees the reduction in quadriceps femoris activation was related to the amount of joint damage sustained and caused some quadriceps femoris weakness. Patients with isolated ACL ruptures had a small reduction of quadriceps femoris activation that did not impede conservative rehabilitation. However, patients with ACL ruptures and associated joint damage had a large reduction in activation and responded poorly to rehabilitation. Operative stabilization of ACL-deficient limbs may increase activation and improve efficacy of rehabilitation. Quadriceps femoris activation was also reduced in patients with mild knee osteoarthritis, who responded well to rehabilitation. Following joint damage, abnormal articular afferent information may decrease alpha-motoneurone excitability, reducing voluntary quadriceps femoris activation. If joint damage is extensive the resulting large reduction in activation may prevent the threshold for stimulation of muscle hypertrophy from being reached, which impedes rehabilitation. Abnormal articular afferent information may also decrease gamma-motoneurone excitability causing proprioceptive deficits. Rehabilitation which increases alpha-motoneurone excitability may also increase gamma-motoneurone excitability, improving proprioception. Copyright 1997 Harcourt Publishers Ltd.