Effect of Lateral Ankle Joint Anesthesia on Center of Balance, Postural Sway, and Joint Position Sense

The purpose of this study was to investigate the effects of induced anesthesia of the lateral ankle joint on proprioception as assessed in weight-bearing and nonweight-bearing conditions. Sixteen subjects were assessed under normal conditions and following an 8-cc injection of lidocaine into the anterior talofibular ligament of the ankle being tested. Center of balance and postural sway measurements were analyzed, revealing a significant lateral adjustment of center of balance during the stable tests compared to a medial adjustment during the dynamic tests under the anesthetized condition. ANOVA of postural sway scores revealed no main effect for condition (anesthesia vs. no anesthesia), but sway scores were higher during the two dynamic conditions as compared to the stable condition. ANOVA of joint position error scores revealed no main effect for condition. Findings suggest that inhibition of the joint receptor afferent fibers adversely affected joint proprioception as assessed while subjects were weight bearing but not while they were non—weight bearing. Article: Lateral ankle ligament sprains are one of the most common injuries incurred during athletics. The incidence of prolonged functional instability, or giving way of the ankle, following lateral ankle sprains has been reported to be between 31 and 35% (1, 10, 11, 17). Debate exists as to whether the functional instability is due primarily to proprioceptive deficits or mechanical instability (16, 18). Damage to joint proprioceptors has been suggested as the cause of functional instability following ligamentous injury. Freeman et al. (11) were the first to report a decrease in the frequency of functional instability following ankle sprains when coordination exercises were performed as part of rehabilitation. This finding has led to the inclusion of balance training in ankle rehabilitation programs (15). Joint proprioceptors are believed to be damaged during injury to the lateral ligaments of the ankle because the joint receptor fibers possess less tensile strength than the ligament fibers (11). Damage to the joint receptors is believed to cause joint deafferentation. This diminishes the supply of messages from the injured joint up the afferent pathway and disrupts proprioceptive function (11). * J.N. Hertel is with Virginia Military Institute, Lexington, VA. K.M. Guskiewicz is with the Department of Physical Education, Exercise and Sport Science, University of North Carolina, Chapel Hill. D.M. Kahier is with the Department of Orthopedic Surgery, University of Virginia Health Sciences Center. D.H. Perrin is with the Curry School of Education, Memorial Gymnasium, University of Virginia, Charlottesville, VA 22903. Direct correspondence to D.H. Perrin. Nerve injury has been reported to be as high as 86 and 83% for the peroneal and posterior tibial nerves, respectively, following Grade III ankle sprains (24). Several studies have shown that lateral ankle sprains have adverse effects on ankle joint position sense (12, 13) and postural sway (6, 11, 12, 17, 21, 25). Contradictory findings indicating no significant loss of joint position sense (14) or postural sway (14, 27, 28) have also been reported. In addition, lateral ankle sprains have been shown to reduce peroneal muscle reaction time to lateral perturbation of the ankle (2, 18, 19, 23). Bullock-Saxton (3) also found decreased EMG responses of the ipsilateral gluteus maximus muscle, one of the primary postural stabilizer muscles, in subjects with severe unilateral ankle sprains. Researchers in three studies (7, 9, 20) attempted to simulate joint deafferentation by injecting a local anesthetic into the ankle joint. Two studies (7, 20) found that postural sway did not increase with deafferentation of the ankle joint. Konradsen et al. (20) found that passive joint position sense decreased significantly following anesthesia. Feuerbach et al. (9) found a decreased ability to actively reposition the ankle following injection of a local anesthetic. Weight-bearing or closed kinetic chain exercises have gained popularity in the rehabilitation of lower extremity joint injuries. A closed kinetic chain exists when the terminal segment of an extremity is fixed and a predictable pattern of joint movements occurs (4). An open kinetic chain is said to exist anytime the terminal segment is not fixed. One of the purported benefits of closed kinetic chain exercise is increased proprioceptive stimulation (4, 26), although there is a lack of scientific evidence to support this claim. The purpose of this study was to determine if induced anesthesia of the lateral ankle joint affected proprioception assessed in weight-bearing and non-weightbearing conditions. Center of balance and postural sway were used as measurements of joint proprioception for the weightbearing condition, while passive joint position sense was used as a measurement of joint proprioception for the nonweight-bearing condition. MATERIALS AND METHODS Subjects Sixteen active individuals (8 males, 8 females, age = 22.6 ± 1.9 years, height = 172.1 ± 10.0 cm, weight = 69.7 ± 11.3 kg) volunteered to participate in this study. All subjects were free of previous injury to the tested lower extremity and were free of any vestibular lesions. Each subject read and signed a human consent form approved by a Medical School Human Investigation Committee. Instrumentation and Procedures Center of balance and postural sway were measured using a Chattecx Dynamic Balance System (Chattanooga Group, Hixson, TN). Passive joint position sense was measured using a KinCom isokinetic dynamometer (Chattanooga Group, Hixson, TN). Subjects reported for testing on two separate occasions. They were randomly assigned to a counterbalanced schedule, which determined if the ankle was anesthetized during the first or second testing session and whether center of balance and postural sway or joint position sense was assessed first. Randomization and counterbalancing were implemented to help control for any learning effects. The lateral aspect of the ankle was anesthetized using an 8-cc injection of 1% lidocaine, injected into the anterior talofibular ligament and lateral joint capsule. The peroneal tendons and sheaths were not injected. Anesthesia was considered sufficient 5 min following injection, at which time testing began. All injections were administered by the same orthopedic surgeon. Each subject was assessed for center of balance and postural sway during unilateral stance while barefoot, with eyes closed and arms folded across the chest. Subjects were instructed to maintain their balance under one static and two dynamic conditions. One trial was conducted from a stable platform and two trials were conducted from a moving platform, the latter testing plantar flexion/dorsiflexion and inversion/eversion movements. Three 10-s trials were performed for each of the three conditions. Mean center of balance and mean postural sway for each condition were calculated. The Chattecx Balance System measured vertical reaction forces using four force transducers placed under the medial and lateral aspects of the heel and forefoot. The angular perturbations of the device have a period of 8.33 s and are constructed as a sinusoidal from horizontal to 4° posterior tilt (dorsiflexion) and back to horizontal. The period can be varied from 0 to 8.3 s, and the subject can be tilted two additional ways: from horizontal to a plantar flexed position back to horizontal, or from 4° plantar flexion through 4° dorsiflexion and back to horizontal. The inversion/eversion condition was measured in the same manner but with the subject turned at a right angle from the plantar flexion/dorsiflexion position. Fluctuations in displacement of the center of balance reflected the amount of postural sway during the three independent platform conditions. Center of balance is defined as the center point of vertical foot pressure throughout the 10-s trial. The center of balance measurements are expressed as points on an x-axis (medial/lateral) and yaxis (anterior/posterior) grid. Postural sway, as assessed by this device, is the distance expressed in centimeters that an individual travels away from his or her mean center of balance. Mattacola and Perrin (22) investigated intertester reliability of the Chattecx Balance System during single-leg static and dynamic testing and reported intraclass correlation coefficients (and standard errors of measurement in centimeters) ranging from .41 (.21) to .90 (.06). Byl and Sinnott (5) investigated intratester and intertester reliability of the instrument and reported correlation coefficients of .92 and .90, respectively. Passive joint position sense was measured with the subject barefoot, lying supine with the knee flexed to 90° and the ankle plantar flexed 10° and in subtalar neutral. The foot was secured to a foot plate that passively inverted and everted the foot at a speed of 3° per second. The subjects were tested with their eyes closed to eliminate any visual feedback. The foot was passively moved to one of three reference angles (10° eversion, 20° and 30° inversion) from the initial neutral position. The ankle was held at the test position for 15 s and was passively moved to the end range of motion and then returned toward the start position. The ankle was again stopped at the test position for 15 s and then returned to the start position. The ankle was then returned toward the reference angle, and the subject was instructed to provide resistance to the passive movement when he or she sensed that the ankle had replicated the reference angle. This force exceeded the dynamometer's preset minimal force, thus terminating movement and providing the dynamometer with a measurement of the reproduced angle. Data were collected in degrees of error from the reference angle. Three trials for each position were performed in a counterbalanced order, and mean scores of error were determined for each posit