The ankle sprain is probably the single most common injury in sports.1 Of this injury classification, the inversion sprain is the most common type with more than 85% of all ankle sprains occurring to the lateral ligaments.2 The surrounding musculature and the associated neural structures may be affected. A number of studies have demonstrated that if left unresolved, these deficits will lead to chronic instability, which may affect future athletic performance and put the athlete at greater risk for reinjury.2-5
Freeman and colleagues originally proposed the term functional instability (FI) to designate the disability to which patients refer when they say that their foot tends to give way.6 These researchers also attempted to differentiate this phenomenon from mechanical instability (MI), which they designated as instability with an anatomic etiology. This distinction is important because Freeman wrote that FI followed about 40% of injuries to the lateral ligaments of the ankle and that this FI was caused by a deafferentiation of neural inputs originating from the ankle.6 Additionally, he suggested that the joint deafferentiation may be permanent and result in impaired reflex stabilization of the leg muscles during sudden passive displacement of the ankle.
When these concepts are applied to current clinical practice, it becomes evident that it is up to the clinician to devise and implement a rehabilitation program to address these deficits. A successful rehabilitation program following an ankle sprain must take into account these factors: An understanding of the structure and function of this physiologic joint, its associated receptors, and their involvement with the locomotor system; restoration and improvement of the athlete’s functional ability without reinjury; and specific exercise training to meet demands placed on the body as a whole and to allow return to full participation in the chosen endeavor.7
Previous rehabilitation programs for the ankle have emphasized protection of ligamentous structures while increasing the available range of motion and then strengthening the supportive musculature. However, until recently, the importance of addressing balance and proprioception may have been neglected.8,9
When originally introduced by Sherrington, the term proprioception was defined to include all neural inputs originating from the joints, muscles, tendons, and associated deep tissue.10 When these structures are subjected to mechanical deformation, action potentials are conducted to the central nervous system (CNS), where the information can influence muscular response and position sense. The integration of afferent neural input to the CNS contributes to the body’s ability to maintain postural stability.9 The basic units where these action potentials originate are the joint receptors, which are stimulated by mechanical forces associated with soft tissue elongation, relaxation, compression, and fluid tension.11 Wyke described and categorized these receptors by a variety of different characteristics.12
Type I receptors behave as low-threshold, slowly adapting mechanoreceptors responding to changing mechanical stresses. These receptors are active in every position of the joint, even when it’s immobile. The rate of discharge from these receptors changes whenever the joint is moved. Type II receptors behave as low-threshold, rapidly adapting mechanoreceptors. They are entirely inactive in immobile joints and become active for brief periods only at the onset of movement, signaling joint acceleration. Type III receptors behave as high-threshold (translating to the more intense stimulus necessary to activate these receptors), slowly adapting mechanoreceptors that, again, are completely inactive in immobile joints and become active only at the extremes of joint motion. Finally, type IV receptors are inactive in normal circumstances, but they become active when subjected to marked mechanical deformation or tension, or in response to direct mechanical or chemical irritation. An understanding of these receptor types is important because it emphasizes the point that a well-formulated rehabilitation program must address all components of motion. For example, it is necessary to address speed and acceleration or end-range motion and mid-range motion so none of the receptor types are neglected.
During a traumatic inversion sprain of the ankle, a number of factors can cause damage to the neural components. Thus one of the ingredients of a successful rehabilitation program following an inversion sprain of the ankle should be an effort to address or attempt to compensate for these neural deficits. This portion of the rehabilitation can be divided into four elements, each with specific goals as well as areas of emphasis.
By establishing a baseline for balance and proprioceptive activities, the clinician is able to document progress and determine when the athlete is ready to advance along the functional progression. A clinically applicable drill is the Romberg position. This test can be made an objective measure of balance and proprioception by having the athlete stand unilaterally on the affected side so the therapist can assess the patient’s ability to hold this position. A comparison can then be made to the uninvolved side. A similar test that is significantly more objective is instrumented stabilometry. This method uses a force plate to measure the displacement of a patient’s center of pressure while in a standing stationary position. Kinzey and Armstrong13 illustrated a more functional exam when they described the star-excursion test.13 In this test they proposed to measure dynamic balance, which they described as the ability to maintain single-leg stance while manipulating the other leg.
Range of motion is progressed during this phase, within a protected stress level, by using the balance board. In an effort to control the intensity of this activity the athlete begins in the seated position (Figure 2). Varying the size of the sphere over which the balance board travels can also control the motion. The clinician should be aware that with an inversion sprain, unrestricted lateral motion might increase the athlete’s complaints and be detrimental to his or her progress. A towel placed under the lateral side of the balance board is a simple way to limit excursion in this direction. Attention should also be paid to the volume of any activity done during this phase. Volume is roughly calculated by multiplying the number of repetitions for any given exercise by the amount of resistance. Thus, earlier on, the athlete begins with four sets of 10 repetitions each of dorsiflexion and plantar flexion, inversion and eversion, and, finally, circumduction. As the athlete progresses, the clinician must remember that the structures he or she is trying to affect are postural in nature. Emphasis should be on endurance: In other words, working toward sets of 30 or more repetitions is quite appropriate.
Strength gains are also an important component of enhancing proprioception. Newton17 noted how proprioceptive input to the spinal cord from muscle receptors might compensate for joint afference. Resistance activities during this protection phase are best performed nonweight-bearing. By applying the resistance manually, clinicians are better able to adapt their resistance to achieve a maximal level without eliciting pain or risking an unanticipated movement into a harmful part of the range (Figure 3).
As the athlete progresses further into rehabilitation, use of the balance board becomes more intense. The athlete now performs this activity in a standing position and can be challenged by trying it with the eyes open and then closed to manipulate the effect of visual input (Figure 5). Strength activities can also be done in closed kinetic chain. One such activity is terminal knee extensions performed while standing on the involved limb, as external resistance is applied from a posterior to anterior direction behind the knee (Figure 6). The athlete then performs unilateral partial squats while maintaining balance. This activity elicits response in both the quadriceps muscle and the triceps surae muscle group, and also requires maintaining balance during a dynamic activity.
During the later stages of phase III of the athlete’s rehabilitation, he or she begins dynamic balance and proprioceptive activities. The balance board can again be used by having the athlete balance on the affected limb and “play catch” with the clinician (Figure 7). The intensity of this activity can be varied. For example, medicine balls of varying weights and sizes can be used. The clinician can throw to a variety of locations, requiring a shift in the center of gravity and instantaneous adjustment of balance from the athlete. Other activities include low- to medium-level plyometric activities. For example, the athlete can perform two-foot ankle hopping, progress to side ankle hops, and finally to barrier jumps.11 The ultimate goal during this stage is to regain all the rudimentary skills necessary to return to sport.
In the case of a basketball player, the clinician could begin the final phase with multidirectional activities. For example, when introducing on-court activities, the athlete could begin with a defensive slide right on one baseline, then backpedal down the sideline, do a defensive slide left along the far baseline and, finally, sprint down the last sideline. As long as this series could be carried out with little to no difficulty and with no exacerbation of symptoms, the area in which this activity is performed could progressively decrease: The athlete would next perform the drill using just the half court area and then just the key, requiring the athlete to change direction more quickly. In another activity the athlete could perform the zigzag defensive slide drill, during which the patient, as a defensive player, would guard an offensive player who would simulate bringing the ball up the court. At designated spots the offensive player would change directions and the defensive player would have to respond accordingly. Again, this activity could be progressed by having the offensive player change directions unannounced, requiring an instantaneous change of direction by the defensive player. Finally, before returning an athlete to competition, he or she should be able to perform in game situations during practice without any indication of injury.
Jeffrey K. Kawaguchi, PT, ATC, is assistant athletic trainer at the University of Virginia in Charlottesville.
References
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