MECHANORECEPTORS

Peripheral afferents n joints n muscle n skin

Visual receptors CNS

LEVELS OF MOTOR CONTROL Sinal reflexes

Cognitive programming

Muscle

Vestibular receptors

Brain stem balance

Figure 4: Neuromuscular control pathways

the patient and the therapist to establish the diagnosis and the tolerance of the injury to load. Dorsiflexion is often the range that is most

difficult to regain following an ankle injury, but it is also the most important in terms of function. Often full active dorsiflexion is not gained before other strength and functional activities are undertaken. This can be a mistake, as the talus is not functioning correctly through the ankle mortice, thus placing unwanted stress on the subtalar joint and surrounding joints and tissues. Emphasis on accessory as well as physiological dorsiflexion is paramount in order to reduce unwanted complications, which can occur at a later stage in the rehabilitation programme. Often these complications occur higher up the anatomical chain, such as at the knee or hip, as the body adapts to a restriction in the ankle (16).

PROPRIOCEPTION Large population studies have shown the effect of intensive proprioception training programmes on reducing the incidence of re- injuring an injured ankle (17,18). Other studies using large populations have combined the use of proprioception with other rehabilitation interventions, such as bracing, taping and strength work, and have shown good outcomes (19–21). Clearly proprioception has a place, but the understanding of the different aspects of proprioception is important in order to allow the therapist to appreciate that it is not just about placing the person on a wobble board.

Many authors have defined proprioception

as the afferent input of joint position sense – the awareness of position or movement (22). Others, however, look at it in a broader sense that includes neuromuscular control (23). Activity of a joint and muscle, whether conscious or subconscious, is a combination of multi-site sensory input, which is received, processed and distributed in order to cause effect by an intricate working relationship of the brain and spinal cord (receiving) and the central nervous system (CNS; distribution). The CNS receives input from three main subsystems (Fig. 4):

n Somatosensory n Vestibular n Visual.

This article concentrates on the somatosensory subsystem.

The contribution to proprioception from the skin receptors is minimal. A much greater contribution comes from the joint and muscle spindle receptors. Mechanoreceptors, which are situated within the ankle joint capsule, ligaments and bones, act as range-limiting inhibitors and potentially stop the joint from moving through excessive ranges by signalling the presence of noxious intense stimuli. There are two types of articular receptor: quick-adapting and slow-adapting. Quick- adapting receptors tend to fire less with continuous stimulation, while slow-adapting receptors continue to fire as the stimulus to

AN ANKLE INJURY, BUT IT IS ALSO THE MOST IMPORTANT IN TERMS OF FUNCTION

16

DORSIFLEXION IS OFTEN THE RANGE THAT IS MOST DIFFICULT TO REGAIN FOLLOWING

movement continues (24). The sensation of joint motion (kinaesthesia) is regulated by the quick-adapting adaptors, while the regulation of joint position sense is thought to be related to the slow-adapting receptors. Hence, proprioceptive rehabilitation must include movement stimuli and joint position sense. The muscle receptors provide an almost complementary neural contribution alongside the mechanoreceptors. The predominance of slow activity receptors within the skeletal muscle responds to length changes and, in harmony with the articular mechanoreceptors, can feed information to the CNS when the joint and muscle are moving, accelerating or decelerating; they also identify the ankle’s position in space. Proprioceptive deficiencies can be identified through the following tests: n Single-leg timed standing (with and without visual input), comparing injured with non- injured n As above, with a functional sport-specific movement, such as a racquet-swing or football-kicking action, while weight-bearing on the injured limb n Joint position sense – being able to reposition the ankle without the aid of visual input (25).

Proprioception exercises should start as soon as possible in order to re-educate the damaged receptors associated with the ligament injury. Any pain, swelling and reactive inflammatory markers need to be observed to ensure that the introduction of proprioception exercises, especially weight-bearing exercises, does not cause a reactive synovitis, which can delay healing.

From the understanding of the subsystems

involved in proprioception, it is important that all three levels of motor control are included in the rehabilitation programme.

sportEX medicine 2008:38(Oct):14-19