Current treatments for chronic ankle instability (CAI) may be ineffective in reducing its development and recurrence. To help address this issue, the authors have proposed a new treatment paradigm based on a theoretical model of CAI as an organismic constraint on the sensorimotor system.
By Patrick O. McKeon, PhD, ATC, CSCS, and Erik A. Wikstrom, PhD, ATC, FACSM
Ankle sprains are the most common injuries associated with physical activity and athletic participation,1,2 accounting for approximately 60% of all injuries that occur during interscholastic and intercollegiate sports.1-5 Medical costs for ankle sprains have been estimated to be approximately $4 billion annually.6,7 Thus ankle sprains, while often viewed as mild injuries, represent a significant public health problem7,8 and a major healthcare burden.
Further, about 30% of those who suffer a first time ankle sprain develop chronic ankle instability (CAI); some have reported this number to be as high as 75%.9-11 This means at least one out of every three individuals who sprain an ankle will go on to suffer residual symptoms indefinitely. Indeed, the residual symptoms that define CAI significantly alter an individual’s health and function by causing them to become less active over time. CAI is also a major contributing factor in the development of post-traumatic ankle osteoarthritis,12 for which there are no effective conservative treatments.
It is apparent, based on the information presented above, that CAI presents a major obstacle affecting the maintenance of regular physical activity for Americans and the prevention of post-traumatic ankle osteoarthritis. Further, high recurrence rates,9-11 incidence of post-traumatic ankle osteoarthritis,12 and consequent healthcare burdens6,7 clearly indicate that current treatments for CAI may be ineffective in reducing its development and recurrence. To help address this issue, we have proposed a new treatment paradigm based on a theoretical model of CAI as an organismic constraint on the sensorimotor system.
The theoretical model
The human body is a system capable of accomplishing movement goals in a variety of ways.13 The dynamic nature of this system (ie, its ability to adapt to changing demands) is often described by what is referred to as the dynamic systems theory of motor control. According to this theory, the organization of the sensorimotor system is constrained, or shaped, by the interaction of organismic, task, and environmental constraints (see Figure 1).13,14 The theory states that the sensorimotor system develops and changes strategies (ie, self-organizes) based on its current state and on interactions with the environment as they relate to a particular movement goal.14 Thus, a healthy sensorimotor system can accomplish a movement goal in a variety of ways even if changes in the task, environment, or both occur. Increasing numbers of possible solutions (ie, degrees of freedom) translate to an enhanced ability to successfully accomplish the movement goal and cope with change.
CAI can be viewed as an organismic constraint, potentially because the damaged mechanoreceptors in the lateral ligaments cannot be used for movement solution development, thus reducing the functional variability and ability of the sensorimotor system to accomplish movement goals.15 This constraint has been proposed to increase the risk of recurrent injury.14 Injury epidemiological evidence supports this framework in that the primary risk factor for an ankle sprain is a previous history of the same injury.16 Further, poor sensorimotor control is also a risk factor for ankle injury.17
The hallmark of CAI is self-reported disability in combination with experiences of the ankle giving way during functional activities.18 Those with CAI have also demonstrated alterations in both sensory and motor aspects of sensorimotor control, including plantar sensation threshold deficits,21 increased joint position sense errors,22 decreased dorsiflexion range of motion,21, 22 impaired muscle reaction time,23 decreased balance,24 and gait and landing alterations.25-29 Thus, it appears that there is a continuum of disability (see Figure 2) associated with sensorimotor control that modulates self-reported activity limitations and participation restrictions experienced by those with CAI.15,30
To gain understanding into this continuum, research is needed to elucidate the link among constraints, sensorimotor control, and injury risk.
While the exact neurophysiologic mechanism of CAI remains unknown, it has been hypothesized that damaged structures from the ankle sprain relay absent or inappropriate afferent information to the central nervous system (ie, sensory dysfunction).31 In healthy individuals, organization of movement solutions arises from the abundance of degrees of freedom from both sensory and motor sources.13 As a movement is executed, sensory information “tunes” motor output, and actual movement itself serves to “tune” sensory input. If a source of sensory input is impaired, as in the condition of CAI, the sensorimotor system dynamically reprioritizes other inputs available to compensate for the loss of information,32 as we have previously shown.33,34 We have evidence to support this hypothesis;21,27, 35-41 that this dysfunction limits an individual’s ability to self-organize (ie, cope with changes in the environment or with increased activity demands) due to an inability to appropriately modulate movement based on information from internal and external sources (see Figure 3). The consequence is a reduction in the total degrees of freedom available from sensory inputs to detect and cope with change.
It may be that the motor issues related to CAI—including poor balance, gait alterations, and episodes of giving way—are related to sensory deficits. This is consistent with the original hypothesis of Freeman et al,31 who suggested the recurrent instability that those with CAI experience was due to deafferentation of the lateral ankle ligaments as a consequence of injury. This loss of afferent information was then thought to manifest as the diminished ability to balance on one leg and as self-reported episodes of instability. Therefore, the constraints experienced by those with CAI may be related to alterations in the sensory degrees of freedom available to the sensorimotor system for tuning motor output.
The paradigm shift
Traditionally, rehabilitation strategies for CAI have focused solely on motor impairments within the sensorimotor system, with little attention paid to the role of sensory inputs in the regulation of function. We hypothesize that, due to the CAI-related disruption of sensory information, the sensorimotor system is more reliant on other sources of somatosensory input (ie, plantar cutaneous receptors, muscle spindles, posterior ankle articular receptors) available to tune movement.33 From a dynamic systems perspective, targeting and manipulating sensory information sources will have a very beneficial effect on rehabilitation outcomes in those with CAI.42 Targeting sources of sensory information will allow the patient to optimize movement patterns to cope with changing conditions—a marked limitation of existing treatment paradigms that target only motor impairments. Investigating the effect of therapeutic interventions that address this sensory phenomenon may offer individuals with CAI the opportunity to better self-organize (ie, compensate) for the loss of sensory information from damaged structures and resolve motor impairments.
Manual therapies, such as ankle joint mobilizations, plantar massage, and stretching, are hypothesized to target specific sensory inputs such that CAI-associated dysfunction will improve through enhanced afferent and global function (see Figure 4). Targeting certain sensory pathways to improve the quality and quantity of sensory information provided to the sensorimotor system may enhance the output on the motor side of the system. This has led us to the development of a new treatment paradigm for CAI known as sensory-targeted ankle rehabilitation strategies (STARS). In this paradigm, we have explored the effects of ankle joint mobilizations, plantar massage, and triceps surae stretching on patient-, clinician-, and laboratory-based outcome measures that are representative of sensorimotor function and disability in those with CAI. The outcome of this research has potential to generate a paradigm shift for treatment strategies in this population.
STARS interventions and initial evidence
The STARS interventions include ankle joint mobilization, plantar massage, and triceps surae strengthening. (See Table 1 for images and additional descriptions of each modality.)
Ankle joint mobilization. In the STARS paradigm, we and others have begun using anterior-to-posterior Maitland grade III joint mobilizations. As an example, we are using a treatment period of five minutes to stimulate the surrounding ankle capsuloligamentous receptors. Each treatment consists of two sets of joint mobilizations, two minutes each, in which one-second grade III oscillations are performed, with one minute of rest between sets. While the parameters might vary with regard to number of oscillations, patient positioning, and number of treatments, ankle joint mobilizations consistently improve ankle joint range of motion,43,44 as well as postural control and self-reported function,43 in patients with CAI. A recent systematic review has also demonstrated improvements in patient-, clinician-, and laboratory-based outcomes with greater effectiveness with multiple treatments compared with single treatments in those with a history of ankle sprains.45
Plantar massage. The plantar cutaneous receptors play an important role in the maintenance of postural control and those with CAI may rely more heavily on their information. To capitalize on this source of information, we built a protocol in which patients receive five minutes of foot massage, which combines effleurage and petrissage techniques, on the plantar surface of the foot. Similar to joint mobilizations, we have used two two-minute sets of plantar massage with one minute of rest in between each set. Previously, a similar protocol demonstrated that those with CAI experienced improved postural control after undergoing a single treatment session.46 Similar results have also been shown in the elderly, a patient population that also has organismic constraints.47
Triceps surae stretching. Research also suggests the muscle spindles within the gastrocnemius-soleus complex (triceps surae) are important for maintenance of postural control.48,49 Using the STARS paradigm, it would be possible to use this treatment modality to improve outcomes associated with a history of ankle sprains. In our study, we used a protocol of two sets of heel cord (calf) stretching. Each set consisted of three 30-second stretches, with 10 seconds of rest between stretches and one minute between sets. While little research has been done on the effectiveness of stretching in those with CAI, a recent systematic review demonstrated that stretching was an effective modality for improving dorsiflexion range of motion in those with a history of ankle sprains.50
To date, a number of studies from several different labs have demonstrated the effectiveness of different sensory-targeted ankle rehabilitation strategies on a variety of patient-, clinician-, and laboratory-based outcomes.51 However, no investigation has systematically compared different STARS interventions against each other on a wide range of outcome measures. Thus, the purpose of our investigation was to determine the effectiveness of STARS for facilitating immediate and prolonged improvements in subjective and objective outcome measures of clinical disablement and sensorimotor dysfunction in those with CAI. More information about this study (NIAMS 5R03AR061561) can be found at clinicaltrials.gov. Specific outcome measures for the STARS project included the changes due to each STARS on the Foot and Ankle Ability Measure52 and self-reported episodes of giving way, the weight-bearing lunge test,43 the single-limb balance test,53 time-to-boundary measures of single limb balance,34,36 gait initiation,54,55 and plantar cutaneous sensitivity.56
Future research and clinical implications
There are several important clinical questions that will need to be answered regardless of the existing literature and our own results. As a result, future research is needed to determine the dosage needed to optimally improve subjective and objective sensorimotor outcomes in patients with CAI. Similarly, while STARS treatment has been associated with improvement in a number of outcomes, there remain an even larger number of possible variables that may better illustrate how STARS results in improved function for those with CAI. Most important, in the age of personalized medicine, future research is needed to establish predictive criteria that would allow a clinician to select the most effective intervention or interventions for those with CAI based on a simple initial evaluation. Lastly, the existing knowledge and our results will begin to form a framework for the systematic investigation of combination therapies for patients with CAI, such as combining STARS with more traditional motor-focused interventions such as balance training.
Clinical take-home points:
- The sensorimotor system relies on both sensory and motor sources to tune its behavior in the presence of changing task and environmental demands.
- Damaged or limited sensory information may result in a more constrained sensorimotor system.
- By targeting certain sensory pathways through manual therapy interventions, it may be possible to provide the sensorimotor system greater freedom to cope with change and enhance functional performance in those with CAI.
- The STARS interventions are delivered across a five-minute treatment session six times over the course of two weeks. These low-cost treatment strategies can be implemented in any healthcare setting with little to no equipment needed.
Patrick O. McKeon, PhD, ATC, CSCS, is the clinical education coordinator within the Athletic Training Education Program at Ithaca College in New York. Erik A. Wikstrom, PhD, ATC, FACSM, is an associate professor within the Department of Kinesiology at the University of North Carolina at Charlotte.
Disclosure: This study was supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases, grant #5R03AR061561.
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