One of the disabling sequelae of ankle inversion sprains is the tendency for sprains to recur. Because sprain of the lateral ligament of the ankle is one of the most common injuries of the musculoskeletal system (16), the problem of recurrence provides a major economic and social burden. However, the reasons for recurrence are unclear, and thus successful rehabilitation is difficult.
A common belief is that ankle inversion sprains recur because proprioception is impaired by the initial sprain (e.g., 10). Proprioception is the term used to describe a group of sensations including the sensation of movement and position of the joints and sensations related to the muscle force (11). When indicating impairment from ankle sprain, however, it is generally inferred that the sensation of movement and/or position is impaired. This hypothesis is based on the assumption that joint mechanoreceptors are disrupted by the original sprain, resulting in reduced proprioceptive information from the joint ligament and capsule, thereby predisposing the ankle to further injury (10). However, current physiological understanding suggests that three classes of afferent are responsible for providing proprioceptive signals: in addition to input from afferents arising from the ligament and joint capsule, there is also input from proprioceptive receptors located in the cutaneous and muscle tissues. Of these three classes of afferent, it is thought that muscle afferents provide the most important information at most joints in the body (e.g., 23,38), except at the fingers (7,39) and toes (2). At the distal joints, cutaneous input appears to provide information that is equal in importance to the muscle input. Joint receptors have been shown to simply duplicate information provided by these other sources, at least at the knee (4 cf. 25) and the fingers (5). It is possible, therefore, that a decrease in discharge from the joint mechanoreceptors would not incur a noticeable proprioceptive deficit.
Sprains of the lateral ligament occur when the ankle is excessively plantarflexed and inverted (3), and therefore if proprioception were pathologically impaired, it could be in either of these planes of movement. However, previous studies have not consistently found a proprioceptive deficit. In the inversion plane, no impairment was found by Gross (21) in the ability to match ankle position actively or passively, whereas Glencross and Thornton (19) found an impairment for matching some, but not all, angles. The ability to detect movement was found to be impaired by Lentell et al. (29). The one study that investigated the plantarflexion plane reported impaired ability to detect movements (14).
Although three of these four studies found some impairment, the methods used did not conform with the suggested requirements of psychophysical test procedures. Psychophysical tests have been used to measure proprioception for over a century (e.g., 5,20,23,38). These proprioceptive tests are based on the principles of psychophysics and require that, when testing thresholds, movement stimuli should be presented a large number of times because thresholds vary with time (e.g., 6,33,44). Additionally, threshold is not an “all or none” cutoff, and therefore movement stimuli of different magnitudes should be presented, a large number of times each, to determine the average location of the threshold (6,32). When determining the threshold, the criterion for consistent detection should also be clearly specified because the threshold varies with the stringency of the criterion. Finally, movement stimuli should be presented in more than one direction. If only one direction of movement is tested a forced-choice condition applies (i.e. “is it moving or not?”) whereby 50% of the movements are expected to be detected by chance. In such testing, subjects may detect a nonspecific event rather than specific proprioceptive cues (e.g., 31). However, previous studies have rarely embraced these principles rigorously. For example, when testing proprioceptive performance, Gross (21) only repeated the ankle movements twice, Lentell et al. (29) three times, and Glencross and Thornton (19) five times. Furthermore, Lentell et al. (29) tested the single movement direction of inversion. In addition, the magnitude of the movement was measured by reading from a protractor by both Lentell et al. (29) and Glencross and Thornton (19). A goniometer is probably inadequately sensitive to measure normal proprioception at the ankle (e.g., 22,38). Interestingly, Lentell et al. (29) mentioned that, although the group means were different, half the subjects with ankle inversion sprains were actually unaffected. Finally, Garn and Newton (14) also only tested one plane of movement, that of plantarflexion. Thus, the test procedures previously used suggest that the effect of recurrent ankle inversion sprain on proprioceptive acuity has not been conclusively established.
The tendency for ankle inversion sprains to recur can be prevented by the application of an orthosis to the injured ankle (e.g., 41,42). Although it is unclear how orthoses act to prevent sprains, one suggestion is that proprioception is enhanced by an external support. It is conceivable that an external support could provide cutaneous cues directly or facilitate muscle afferent input. Interestingly, the use of an air stirrup orthotic did not confer a proprioceptive advantage in any plane of ankle movement (8). However, it is more common to apply tape than a brace because it is cheaper, and the benefits appear to be similar. Taping the ankle has been shown to decrease the error in a position matching task in the plantarflexion-dorsiflexion plane in healthy subjects (40). It also appears that ankle taping decreased the error in matching inversion angles in previously injured ankles, although not to the same extent as braces (24). Because the tape is in intimate contact with the skin providing strong cutaneous proprioceptive cues, it could be expected that the ability to detect ankle movement should also improve with ankle taping. However, the effect of ankle taping on movement perception has not been assessed.
The present study was therefore designed to determine whether detection of plantarflexion and dorsiflexion movements was impaired in subjects with recurrent ankle inversion sprain when compared with a group of healthy control subjects, and whether proprioceptive acuity was improved when the ankle was taped using a common taping procedure. Proprioception was measured in the plantarflexion-dorsiflexion plane as this movement is an integral part of the spraining position.
Forty-three subjects aged between 18 and 41 yr, 25 of whom had a recurrent ankle inversion sprain, volunteered to participate in these experiments. Ankle inversion sprain was defined as recurrent if the subject had sustained at least three sprains, one of which had occurred in the past 2 yr. Subjects were excluded if they had sustained a sprain in the past 3 wk, because the inflammation and pain associated with an acute injury could distort the results. Subjects were also excluded if they had sustained a fracture, or if they suffered any neurological deficit or other injury to the leg that may interfere with proprioceptive acuity. A control group of 18 subjects were matched to the experimental group for age, height, weight, and activity level (Table 1). Subjects were excluded from the control group if they had ever sustained an ankle injury or if they had any neurological condition or other injury that may impair proprioceptive acuity.
Subjects were unaware of the experimental hypotheses and were not given feedback about their performance. The study was approved by the institution’s human ethics committee and written informed consent was gained from all subjects before data collection. The experiments were designed to test the effect on proprioceptive acuity of (i) recurrent ankle inversion sprain and (ii) taping the ankle. Performance was measured at velocities of 0.1, 0.5, and 2.5°·s−1.
In each experimental condition, dorsiflexion and plantarflexion movements were imposed about the axis of rotation of the ankles using a linear servomotor under position feedback and driven by a variable ramp generator. The test foot was supported on a metal plate with a heel rest and secured by a Velcro strap across the dorsum (Fig. 1). The axis of rotation of the apparatus was aligned with the axis of rotation of the ankle joint. Subjects could not see the leg or test apparatus, and earmuffs eliminated auditory cues. Performance was tested in two 1.5-h sessions, one session each for the taped and untaped conditions. The order of testing the taped and untaped conditions was randomized.
The test protocol was identical for both the taped and untaped conditions. Subjects sat with the knee in relaxed flexion (approximately 60°) and the foot placed on a footplate (Fig. 1). Movement was restricted to the ankle, with none occurring at the knee or toes. Initially, the ankle was positioned in the middle of its plantarflexion-dorsiflexion range of movement, usually 20° plantarflexion. Each test movement began from this initial position. Movements were imposed into either dorsiflexion or plantarflexion after a random time interval of between 2 and 10 s. Each movement was held for 3 s before reset to the initial angle to allow for reaction time at higher velocities. Responses were accepted during this hold period. Subjects were instructed to relax the leg muscles completely and to report the direction of any perceived movement when they could do so with certainty. Frequent reminders of these instructions aimed to minimize incorrect reporting of direction (false positive responses) and responses in the absence of imposed movement. Frequent rests were allowed to prevent fatigue and to assist with concentration.
The order of testing the three velocities (0.1, 0.5, and 2.5°·s−1) was randomized. At each velocity, proprioceptive performance was measured as the 70% detection level for both plantarflexion and dorsiflexion movements (e.g., 17,21,24). That is, a random mix of 10 plantarflexion and 10 dorsiflexion movements of a constant amplitude were imposed at the test joint. At each velocity, the 70% detection level was identified by adjusting the amplitude of the movement until subjects correctly reported 7 of 10 movements in each direction.
Application of tape.
Movement perception was measured using the same protocol and test velocities with the test ankle both taped and untaped. The method of taping was that commonly used by physiotherapists and athletes to prevent and treat injuries to the ankle (26). Inelastic tape was applied as a combination of ankle locks, stirrups and “figure of 6” applications (Fig. 2). The taped and untaped conditions were tested in random order.
Plantarflexion and dorsiflexion data were analyzed separately using the Mann-Whitney rank sum test (12 tests). Because there was no significant difference between the directions of movement at any velocity, data were averaged for further analysis. Comparisons were made using a repeated measures three-way ANOVA. The two within-subject factors comprised velocity (0.1, 0.5, and 2.5°·s−1) and tape (taped or untaped), and the one between subject factor was group (sprainers or controls). The significance level was set at α = 0.05. Statistical analysis was performed using SPSS 7.0.
Most subjects could perceive movements before they could identify their direction, as reported in previous studies (e.g., 23,28,38). However, because event detection may depend on nonspecific or nonproprioceptive cues, subjects were instructed to respond only when they were certain of the direction of the movement. The low rate of false positives (<4% for any subject) confirms that subjects observed this instruction. Thus, by the criteria used here, some imposed movements might not have been detected, although subjects were aware that some nonspecific event had occurred.
In all conditions, subjects perceived smaller displacements as the velocity of movement increased (ANOVA, P < 0.01), as previously reported for ankles (38) and for other joints (e.g., 23).
There was no significant difference in proprioceptive performance between the experimental and the control group at any velocity tested (P = 0.27, Fig. 3 and Table 2), and no significant interaction between velocity and group (P = 0.08). At the slowest test velocity, 0.1°·s−1, subjects could perceive movements of 0.85° ± 0.48 (mean ± SD) at the sprained ankles, and 0.68° ± 0.26 at the healthy ankles. At 0.5°·s−1, movements of 0.56° ± 0.32 were detected at the sprained ankles and of 0.41° ± 0.12 at the control ankles. At the fastest test velocity, 2.5°·s−1, movements of 0.22° ± 0.1 were perceived at the sprained ankle and 0.23° ± 0.19 at the healthy ankle.
There was no significant difference (P = 0.28) in proprioceptive performance between the taped and untaped ankles at any movement velocity for either subject group (Fig. 4). When the ankle was taped, movements of 0.7° ± 0.47 could be detected at the sprained ankle when imposed at the slowest test velocity and 0.64° ± 0.2 at the control ankles. At 0.5°·s−1, when the ankle was taped, movements of 0.59° ± 0.39 could be detected at the sprained ankle and of 0.44° ± 0.1 at the healthy ankle, and at 2.5°·s−1 movements of 0.19° ± 0.01 were detected at the sprained ankle and 0.24° ± 0.15 at the healthy ankle. There was a significant interaction between tape and velocity (P = 0.03), suggesting that, although there was no overall effect, increasing velocity of imposed movements had a different effect on the taped and untaped ankles. There were no other significant interactions.
It is widely believed that the tendency for ankle inversion sprains to recur is due to a proprioceptive deficit caused by deafferentation during the original trauma. The findings of the present study do not support this belief for movements in the dorsiflexion-plantarflexion plane. We found that there was no significant difference in the ability to perceive movements applied at three velocities (0.1°, 0.5°, and 2.5°·s−1) between subjects with recurrent sprains and a control group.
No significant difference existed between the groups for detection of movements imposed at 0.1·s−1 and 0.5°·s−1. These velocities encompass the velocity of normal body sway (9) and therefore are likely to be similar to the velocity of sway during balance tasks, such as stabilometry tests and Romberg’s test. Performance of such balance tasks has been found to be impaired in subjects with recurrent ankle inversion sprain (36,43). It was thought that this impairment was caused by a proprioceptive deficit (e.g., 10). However, the present findings suggest that proprioception is unaffected at 0.1°·s−1 and 0.5°·s−1, and therefore impaired balance is unlikely to be due to a proprioceptive deficit in the plantarflexion-dorsiflexion plane. It is possible that the poor performance during balance tasks results from other impairments, such as impaired proprioception in the inversion-eversion plane (29), decreased reaction time in the peronei (27), or from altered central motor program (17).
Of particular interest, recurrent ankle inversion sprain did not impair the ability to detect ankle movements imposed at 2.5°·s−1. Sprains would normally occur during activities requiring faster velocities than those tested here. However, it is well-known that detection of passive movements improves with increasing velocity (e.g., 31,38), and therefore proprioception may be even more acute at velocities reached during running and jumping activities. One might speculate that the lack of difference in performance at 2.5°·s−1 suggests that detection of passive movements in the plantarflexion-dorsiflexion plane is unlikely to be impaired at faster velocities.
The lack of significant difference in movement perception between the experimental and control groups is not surprising given current physiological understanding about the mechanisms underlying proprioception. Currently it is thought that, of the three classes of afferent responsible for providing proprioceptive signals, the muscle afferents play the most important role (e.g., 23,38). In contrast, the joint receptors are thought not to be essential to normal proprioceptive acuity, but instead provide signals that duplicate information received from the other classes of afferent (e.g., 4,31). The importance of muscle input at the ankle has been further substantiated by the finding that, even with the muscles relaxed, proprioceptive acuity at the ankle can be improved fivefold by altering the position of the ankle to stretch the plantarflexor muscles (38). Thus, it could be argued from the current findings that any loss of input from joint receptors due to ankle inversion sprain appears to be compensated by the muscle afferents.
The present findings relate to the ability to detect movement in the plantarflexion-dorsiflexion plane of movement. It is possible, even likely, that these findings do not generalize to either the inversion-eversion plane of movement or to other proprioceptive tasks, such as active or passive position matching. The structures probably disrupted by ankle inversion sprain are those that resist inversion rather than plantarflexion forces, such as the lateral ligament and perhaps the peroneal muscles. Such damage may therefore cause impairment only in proprioceptive tasks specific to the inversion-eversion plane of movement. Similarly, our findings on movement sense cannot be generalized to position sense. As argued by McCloskey (30), “separate lines of information can arise in muscle to signal movement and position” (p. 119), and therefore it is possible that one type of sensation may be affected, whereas the other remains intact.
The unexpected finding that taping did not improve proprioceptive acuity is inconsistent with the effect of orthoses and previous findings for position matching tasks (24,40). It was hypothesized that the tape would either provide additional cutaneous cues or may provide a general facilitation at spinal or higher levels, thereby enhancing the perception of movement signals from other proprioceptive sources (e.g., 13,37). Cutaneous afferents are known to converge with muscle afferents in primates and to modulate input at other levels of processing in the central nervous system (1,12,15,34,35). For example, digital cutaneous input modulates stretch reflexes and sense of effort (34), and cutaneous input can exert excitatory effects on some motoneurons (e.g., 35). This in turn, given the importance of muscle afferents to proprioceptive acuity, should enhance proprioceptive performance. Improved performance was not observed. One explanation for the lack of improvement might be that the ankles were taped to restrict inversion movements, and so dorsiflexion and plantarflexion movements may not have been markedly restricted. A difference in acuity may therefore have been noticed in the inversion-eversion plane. Our findings suggest that the preventative effect of taping the ankle during challenging sports activities does not arise from enhanced proprioceptive performance in the dorsiflexion-plantarflexion plane of movement.
Proprioceptive deficit has been offered as an explanation for the tendency for ankle inversion sprains to recur, and therefore “proprioceptive training” has been recommended in the treatment of ankle inversion sprain by most orthopedic and sports physiotherapy texts (e.g., 3). The present study did not find a proprioceptive deficit in dorsiflexion-plantarflexion movements at sprained ankles, nor that taping the ankle improved this measure of proprioceptive acuity.
This work was supported by the University Research Grant Scheme and the Physiotherapy Research Foundation.
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