Chronic ankle instability alters central organization of movement.

Haas CJ, Bishop MD, Doidge D, Wikstrom EA. Am J Sports Med 2010 Apr;38(4):829-34.

Epub 2010 Feb 5. Department of Applied Physiology and Kinesiology,University of Florida, Gainesville, Florida, USA.

 This is a recycle article from our “The Gait Guys” blog archive, June 2011. This article focuses on altered proprioception. Proprioception (or kinesthesis) is our ability to orient our body or a body part in space.  Poor proprioception can result in balance and coordination difficulties as well as being a risk factor for injury. Think about people with syphillis who lose all afferent information from a joint coming in through the dorsal root ganglia, this ultimately leads to a wide based ataxic gait (due to a loss of position and tactile sense) and joint destruction (due to loss of position sense and lack of pain perception). The same consequences can occur, albeit on a smaller scale, when we have diminished proprioception from a joint or its associated muscle spindles. As you read on, keep the thought in your mind that walking or running are both actually repeated attempts at finding a stable single leg stance, one after the other. Impairment of one single leg stance will affect the involved side locally as well as the contralateral side due to accelerated or abbreviated loading responses coming off of the affected side.  Arm swing will also be altered and require compensation.

Proprioception is subserved by both cutaneous receptors in the skin (pacinian coprpuscles, Ruffini endings, etc.), joint mechanoreceptors (types I,II,III and IV) and from muscle spindles (nuclear bag and nuclear chain fibers) . It is both conscious and unconscious and travels in two pathways in the nervous system. 

Conscious proprioception arises from the peripheral mechanoreceptors in the skin and joints and travels in the dorsal column system to ultimately end in the thalamus, where the information is relayed to the cortex and cerebellum.

Unconscious proprioception arises from joint mechanoreceptors and muscle spindles and travels in the spino-cerebellar pathways to end in the midline vermis and flocculonodular lobes of the cerebellum. This unconscious information is then relayed from the cerebellum to the red nucleus to the thalamus and back to the cortex, to get integrated with the conscious proprioceptive information and then central program generators (CPG’s). We have spoken about receptors more recently in the Gait Guys podcasts, #19 & 20 and CPG’s in our previous blog post this week if you care to delve more deeply into these topics.

Information from both systems (both separate and combined; the nervous system loves redundancy) is then sent down the spinal cord to effect some response in the periphery. As you can see, there is a constant feed back loop between the proprioceptors, the cerebellum and the cerebral cortex. This is what allow us to be balanced and coordinated in our movements and actions.

Chronic ankle instability is merely a more serious form of dysfunction on the continuum of ankle pathomechanics. It refers to subjects with both coronal and saggital plane stability problems due to altered proprioception. This results in a loss of fine motor coordination of the foot (ie foot intrinsics) and a recruitment of larger motor units about the joint (peroneus longus,  flexor and extensor digitorum longus, tibialis posterior and anterior, etc) . This is equivalent to writing a letter with a pencil taped to your wrist, rather than in your fingers. 

This study looked at plantar pressure changes (actually it measured the amount of deviation in forward/backward and side to side motions, which are corrective motions by the CNS due to a loss of fine motor control). As expected, they were greater in the group with ankle instability, particularly when they led with that foot (ie the impaired foot). Thus they lacked the skill necessary to perform the task and developed another movement or recruitment pattern to compensate.

This would be an excellent example of restoring function (ie skill)  for rehab, rather than just increasing strength. If fine motor control is not mastered 1^st and you do not change the central pattern, you are carving a turnip with a chainsaw.

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