Comparison between the unstable and the dominant ankles revealed significant differences in anterior and posterior postural sway with vision (Table 3), but no differences were observed in the medial or lateral directions. Significant differences were found without vision in medial and lateral postural sway, but no significant differences were observed in the anterior or posterior directions without vision.
No significant differences in sway between the unstable and dominant ankles mediolateral direction with vision and the anteroposterior direction without vision were observed (Table 3). The unstable ankle had significantly greater sway than the dominant ankle in the anteroposterior plane with vision and in the mediolateral plane without vision.
Comparison between the unstable and nondominant ankles presented no significant differences in the medial and lateral directions with vision and the anterior and posterior directions without vision (Table 4). Significant differences were found in the anterior and posterior planes with vision and the medial and lateral planes without vision.
There were no significant differences in mediolateral sway between the unstable and the nondominant ankles with vision and the anteroposterior sway without vision. The unstable ankle showed significantly greater sway than the nondominant ankle in the anteroposterior plane with vision and in the mediolateral plane without vision. The sway of the unstable ankle was more than 4 cm greater than both of the control group ankles in the mediolateral plane (Table 4).
In the unstable ankle, high levels of postural sway were associated with slower reaction times. Table 5 shows the positive correlations between the postural sway and reaction times of the PL and PB muscles in lateral, medial, and anterior planes ranging between r = 0.55 and r = 0.81. No significant correlations were found between posterior PS and either the PL (r = 0.086) or PB (r = 0.032). Neither the TA nor the EDL was significantly correlated with any of the PS parameters. No significant correlations were found between any of the four muscles and posterior postural sway. No significant correlations were found between stable ankle or the control group's postural sway and muscular reaction times.
Mediolateral changes represent fine postural adjustments required to maintain the body weight relative to the narrow base of support (18). When the COP is translated medially, the subtalar joint is passively everted and then actively inverted to maintain balance. This active inversion moves the COP laterally so that the line of gravity is moved medially to restore equilibrium. The converse occurs when the COP is translated laterally. When the COP is translated anteriorly, the talocrural joint is passively dorsiflexed and then actively plantarflexed to restore balance. Active plantarflexion moves the COP posteriorly so that the line of gravity is moved anteriorly to maintain equilibrium. The converse occurs when the COP is translated posteriorly.
In this study, no significant difference in single-limb postural sway with eyes open was found between the dominant and nondominant ankles of the control group. This finding was consistent with those of Tropp et al. (22), Cornwall and Murrell (1) and Rose et al. (20), who suggested that the control group's ankles were symmetrical. There was a trend, however, for anteroposterior sway to be less than mediolateral in the control group suggesting that the majority of postural sway was occurring at the subtalar joint rather than at the talocrural joint. Similarly, single-limb postural sway without vision was symmetrical between the dominant and nondominant ankles and also consistent with the findings of Rose et al. (20). Although subjects identified their limbs as dominant and nondominant, the performance of both ankles was similar. Therefore, it seems that no proprioceptive advantage exists when activities are carried out using either dominant or nondominant limbs. Perhaps differences in the performance of the dominant and nondominant ankles exist in more dynamic tests of postural control. More research is required in this area.
Depriving the control subjects of vision resulted in an increased PS of ~3 cm in both medial and lateral directions. The increase was approximately 2.5 cm in both anterior and posterior directions and was consistent with the findings of Cornwall and Murrell (1). These results support the theory that vision has a significant contribution to balance (20). No significant differences were found between the dominant and the nondominant control ankles in the mediolateral or anteroposterior sway. The mediolateral sway with vision for both control ankles was approximately 3.5 cm, compared to 2.7 cm in the anteroposterior plane, and sway with vision was approximately 35% of that without vision. Derave et al. (2) also observed large increases in single-limb PS when eyes were closed.
In this study, no significant difference in postural sway with vision was found between the FAI group's unstable and stable ankles. These results were consistent with the findings of Tropp et al. (22), Isakov and Mizrahi (9), and Rose et al. (20). This suggests that the stable and unstable ankles were using the same processes to maintain postural sway, or that the unstable ankles compensated for any existing deficits with either an increased reliability on other sensory systems or increased reliance on muscles for postural control. Forkin et al. (5) observed increased postural sway in single-limb stance with vision in ankles with a history of instability albeit using subjective analysis. Holme et al. (8) found significantly greater postural sway in ankles 6 wk after a lateral ligament sprain. There was a trend toward greater mediolateral postural sway compared with anteroposterior sway in both the ankles of the present FAI and control groups.
Several studies have found increased postural sway in ankles with a history of functional instability resulting from ankle sprain compared to healthy contralateral controls. Konradsen and Ravn (12) found significantly greater postural sway with vision in unstable ankles, and a high degree of correlation between postural sway and peroneal reaction time. Goldie et al. (6) found subjects with a history of ankle sprain to have significantly increased postural sway compared to the healthy contralateral control, with eyes open and closed, and Cornwall and Murrell (1) observed increased postural sway in the anteroposterior plane in ankles 2 yr after injury.
In the current study, the FAI group results showed that the stable contralateral joint produced greater postural sway than either of the healthy control ankles and suggests that studies using a subject's stable ankle as a control are flawed. Some studies used the stable ankle as a control and found no significant differences in postural sway between the two ankles (9,22). The assumption made that the contralateral limb had not been affected now seems questionable. If unilateral injury to one ankle does result in diminished function in both, clinical assessment, treatment, and rehabilitation strategies need to involve both unstable and stable joints.
Rehabilitation exercises to improve postural control include single-limb balancing tasks on balance boards, ankle discs, and balance pads. These exercises can be progressed by increasing the complexity of the task, making them more sports-specific, or by denying vision. Once the patient has mastered these exercises, they should undertake more dynamic drills involving acceleration, deceleration, changes of direction, jumping, and landing. These are basic athletic requirements for the majority of sports participation and will aid the patient in returning to dynamic athletic activity.
In the present study, significant differences appeared between unstable and stable joints in single-limb postural sway without vision. Postural sway in both lateral and medial directions was significantly higher in the unstable than the stable ankle. This increased sway has two possible explanations. First, greater reliance on the visual system is exposed and postural sway suffers. This explanation is not supported by the findings in trials with vision, as there were no significant differences in postural sway between the unstable and stable ankles. The second and possibly more plausible explanation is that the unstable ankles cannot make the same modifications in postural control that are possible in the stable ankle. This would support the work of Van Deun et al. (25) who found individuals with function ankle instability exhibited less variability in muscular recruitment strategies and activation patterns compared to healthy controls.
No significant differences in anteroposterior postural sway without vision were found between the two ankles. This suggests that a history of ankle sprain and functional instability has no detrimental effect on postural sway at the talocrural joint with eyes closed. It is not possible to argue that the unstable and stable ankles made the same modifications in anteroposterior postural control with eyes closed, but the functional results were the same. This finding contrasts with that of Cornwall and Murrell (1) who observed increased postural sway in the anteroposterior plane in ankles 2 yr after injury.
The present study found no significant differences in sway between the unstable and stable ankles in either the mediolateral or the anteroposterior plane with vision. The mean mediolateral sway with vision for both ankles was 3.6 cm, compared to 3.2 cm in the anteroposterior plane. Without vision, the unstable ankle mean mediolateral sway was significantly greater. Denial of vision increased the mediolateral postural sway by 10.9 cm in the unstable ankle compared to 5.5 cm in the stable ankle. When vision was denied, anteroposterior sway increased by 4.3 cm in the unstable ankle, compared to 3.6 cm in the stable ankle. The effect of denying vision is felt more greatly at the subtalar joint where the base of support is narrower.
Significant differences were found in the anteroposterior plane but not in the mediolateral plane when comparing the unstable and dominant ankles with vision. The unstable ankle produced significantly greater anterior and posterior postural sway than the dominant ankle. This is a novel finding. The movement was occurring at the talocrural joint and may have two possible explanations. First, in the unstable ankle, the musculature controlling movements in the anteroposterior plane cannot function like a healthy control limb due to either delayed muscular reaction time, reduced position sense, or diminished proprioception in the mechanoreceptors monitoring anteroposterior postural sway. Second, as a result of diminished proprioceptive control, the subject with the unstable ankle has a greater reliance on visual feedback. This visual control took the form of focusing on the wall opposite and making adjustments in the anteroposterior plane according to visual cues of imbalance.
There was no significant difference found in medial or lateral postural sway with vision between the unstable and dominant ankle. As mentioned earlier, it seems that the unstable ankle functions similarly to the stable and dominant ankles in this situation; however, it was not possible to identify whether the mechanisms used to control mediolateral postural sway were the same. The significant finding is that it seems that the unstable ankle's history of functional instability did not represent any deficit in mediolateral postural sway with eyes open and is consistent with the findings of Ross and Guskiewicz (21). These results contrast, however, with those of Konradsen and Ravn (12), who found significantly greater transverse postural sway in functionally unstable ankles with eyes open compared to healthy controls, although they did not examine anteroposterior postural sway.
In the current study, without vision, the unstable ankle had significantly greater medial and lateral postural sway than the dominant ankle but not in the anteroposterior plane. These results were similar to those seen when comparing the FAI group's unstable and stable ankles. This suggests that the unstable ankles could not make the necessary adjustments to control mediolateral postural sway. Without visual feedback the central nervous system has to adapt its method of postural control, seemingly through greater activity in the subtalar joint of the unstable ankle. The results of the comparison between the unstable and nondominant control ankles mirrored those observed between the unstable and dominant control ankles.
The mediolateral and anteroposterior sway data reflect the findings from the postural sway components. With vision, the mediolateral sway for the unstable, stable, dominant, and nondominant joints were all ~3.5 cm, and no significant differences were found between the groups. With vision, the anteroposterior sway of the unstable ankle was significantly greater than the dominant and nondominant ankles. This shows that a greater reliance on visual cues is required when balancing on the unstable ankle. There was a significant difference in the mediolateral sway without vision in the unstable ankle compared with the dominant and nondominant ankles, but not in the anteroposterior plane.
Once visual feedback was removed, greater reliance on mechanoreceptor and vestibular information occurs. If it is accepted that the ankle sprain subjects had no unidentified pathologic vestibular disorders, the difference between the unstable and other ankles lies somewhere within the mechanoreceptor-efferent loop that controls mediolateral postural sway. It seemed that questions were asked of these receptors, which could not be answered. Three explanations may explain this. First, the mechanoreceptors did not sufficiently sense the changes in tension occurring within the joint and provided proprioceptive information incorrectly, not soon enough, or not at all. Second, the afferent and efferent signals did not travel fast enough to induce a rapid efferent response. Third, the muscles could not generate the required concentric or eccentric force to control the movement.
The results from this research support the findings of Karlsson et al. (10) and Karlsson and Lansinger (11) who argued that a slower reaction time and increased postural sway in unstable ankles is due to a delay in the stretching of the mechanoreceptors in the ligaments and joint capsule, which occurs at a set fraction of ankle joint motion. For this reason, more time will elapse from the onset of the movement to muscular defense in ankles with functional instability. However, Cornwall and Murrell (1) suggested that increased postural sway is due to increased joint laxity and not deafferentation of the nerves that innervate the ligaments and joint capsule.
This study examined postural sway in the frontal and sagittal planes while presenting the medial, lateral, anterior, and posterior postural sway as separate components. Previous studies have examined mediolateral or transverse sway as one single measurement. By examining the constituent components of anteroposterior and mediolateral sway separately, it was possible to identify if any deficits within the specific components was present. Peaks of postural sway in each plane were collected, which allowed the observation of its extent at the extreme range of equilibrium.
By observing postural sway in four directions and combining plantarflexion and inversion in the simulated ankle sprain mechanism, a more precise view of the detrimental effects of delayed muscle reaction time (16) on postural sway was possible. A strong positive correlation between the reaction times of both peroneal muscles and lateral and medial postural sway was observed. These results reflect those presented by Konradsen and Ravn (12) who found a strong positive linear relationship between transverse sway and peroneal reaction time. Although their study was undertaken along similar lines, there are several differences between this current study and Konradsen and Ravn's article. Medial and lateral postural sway were combined by Konradsen and Ravn (12) and were presented as transverse sway; anteroposterior sway was not investigated.
In the current study, slow peroneal reaction times were associated with increased postural sway in three of four directions examined. The fact that both the PL and PB in the unstable ankles were found to have similar relationships may be due to the fact that they have the same functional roles, performing eversion and plantarflexion. Functioning primarily as evertors acting on the subtalar joint, the peroneal muscles contribute to the maintenance of mediolateral postural control. When the peroneal muscles act as plantarflexors in postural control, they would be called on to plantarflex the talocrural joint causing a posterior movement of the COP. Equally, and perhaps more importantly, the peroneals may be called on to eccentrically control dorsiflexion and in turn the anterior movement of the COP. In an open kinetic chain, active dorsiflexion would be carried out by the TA and EDL muscles, but in a closed kinetic chain such as single-limb stance, dorsiflexion would take the form of a more controlled eccentric movement of the plantarflexors. Any deficit in peroneal muscle function, while acting eccentrically in dorsiflexion, may allow pathological anterior postural sway to occur; however, the role of the peroneal muscles in plantarflexion may be masked by the actions of the gastrosoleus complex. Similarly, the gastrosoleus complex, which was not examined in the muscular reaction time study, may also influence the control of posterior postural sway.
No relationship between TA reaction time and any of the four postural sway components was found. This could be for two reasons. First, there is no active dorsiflexion carried out in single-limb stance because movements of the COP are controlled by eccentric muscle actions. Second, as an invertor, the reaction of the TA to a rapid inversion/plantarflexion mechanism would be different to its reaction to an eversion/dorsiflexion mechanism. In other words, the ankle sprain mechanism does not challenge the primary roles of the TA. Hence, a comparison of TA reaction time to postural sway will not elicit the relationship of the TA as an invertor to postural sway. Although it is accepted that the peroneal muscles exhibit an eversion stretch reflex to an inversion/plantarflexion mechanism, the response of TA to this same mechanism remains unclear.
No relationship was found between the EDL reaction time and any of the four postural sway components. The eccentric control of dorsiflexion has been discussed previously and as dorsiflexors the same argument remains for the EDL. No significant differences were found in reaction time for the EDL and these data are being compared with pathological postural sway data. Pathological postural sway correlates with pathological reaction time, but pathological postural sway does not correlate with normal reaction time. Perhaps this is the reason why no significant differences were found between postural sway and muscular reaction time for the stable, dominant, and nondominant ankles.
The fact that pathological postural sway in the unstable ankle correlated with delayed reaction time in the peroneal muscles, and this relationship was not found in the stable ankles, rules out suggestions of a constitutional central deficit. These neuromuscular deficits may predispose unstable ankles to recurrent sprain, causing repetitive trauma and reduced stability. Apparently whatever neuromuscular deficit exists, it exists at the local level somewhere between the ankle itself and the spinal cord. Konradsen and Ravn (12) proposed that the high degree of correlation between peroneal reaction time and transverse sway showed that single-limb stance depends primarily on the integrity of the peripheral peroneal reflex. Van Cingel et al. (24) recently supported the concept of a delayed neuromuscular response contributing to FAI. Similarly, Hertel et al. (7) suggested that deficits in postural control may be attributed to altered muscular recruitment in the muscles that act over the ankle.
A positive correlation was found between the reaction times of the PL (r = 0.56) and PB (r = 0.63) muscles and anterior postural sway. This was an interesting finding in that, to date, no such results have been presented within the literature. Lundin et al. (15) found increased anterior postural sway as a result of isokinetically fatigued plantarflexors and dorsiflexors, but no data on the association between peroneal reaction time and increased anterior postural sway have been presented. Perhaps, the peroneals in the unstable ankle cannot contribute an effective plantarflexion contraction to move the talocrural joint away from the dorsiflexed position (anterior postural sway) and back to a neutral position.
On the basis of the findings of this study, several clinical recommendations can be made. First, we encourage clinicians to consider the function of the talocrural joint and the subtalar joint when rehabilitating ankles with functional instability. The muscles that cause eversion are equally as important as those that cause dorsiflexion as both movements contribute to the dynamic defense mechanism (13). Second, once patients have become proficient in static single-limb balancing tasks, they should undertake exercises that require dynamic athletic movements such as changing direction and landing from a jump. In this way, the mechanoreceptor-efferent loop is challenged in such a way to imitate sporting activity.
These results reveal postural sway deficits in ankles with FAI, where we observed greater mediolateral sway without vision and greater anteroposterior sway with vision. The results also demonstrate a significant relationship between postural sway and both PL and PB reaction times in functionally unstable ankles. Individuals who sustain an acute ankle sprain and those with FAI require proprioceptive training, evertor strengthening and restoring muscular reaction time to rehabilitate the dynamic defense mechanism.
This study was conducted at the University of Chichester, Chichester, West Sussex.
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Keywords:©2008The American College of Sports Medicine
DOMINANCE; INJURY; LIMB; SPRAIN; VISION