What Does A Knee-Jerk Test Have To Do With Ankle Sprain?
Almost everyone have this test done either in person or on television, the doctors takes out a small hammer and taps a spot just below the knee and the leg jerks forward. What does this test got anything to do with ankle sprains? The answer is stretch-reflexes.
Stretch-reflex is one of the key mechanism in proprioception; the body’s ability to sense its position in space relative to its other parts and the strength of effort in movement. In an ankle sprain, muscles that are supposed to rein in an ankle that is rotating too much inward or outward either is firing too late, slowly or not firing at all. This allows the ankle to pass the ‘zone’ where tendons and ligaments experience too much stress.
How does the body knows when ankle is going out of this ‘zone’? It lies in a muscle spindle where the muscle attaches to the tendon (which in turn attaches to bone). This muscle spindle is extremely sensitive to stretch. When stimulated, it fires the motor neurons that are attached to the same muscle to contract. This reaction is very quick, as it takes a much shorter route of going up the spinal cord and back, without going up to the brain for processing; hence the automatic nature of the reflex.
Striking the tendon just below the knee cap, the neurons stimulates these muscles spindles in the tendon/muscle, which causes the motor neurons to fire and ‘jerk’ the knee.
Injury Can Impair Proprioception
Injury can reduce the effectiveness of an athlete’s proprioception. This is something that the athlete and coach may not be fully aware of even when rehabilitation seems complete. A team from the University of Pittsburgh looked at the role of the sensorimotor system as it relates to functional stability, joint injury and muscle fatigue of the shoulder and the restoration of functional stability after shoulder injury (1). They noted that to fully restore shoulder stability, deficits in mechanical stability, proprioception and neuromuscular control are needed.
If you have read our past articles, proprioception training is a key rehabilitation element for recovery. This is so for a wide range of injuries involving the knee, shoulder and ankle.
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- Journal of Athletic Training 2000; 35(3):351-363