Proprioception in anterior cruciate ligament deficient knees and its relevance in anterior cruciate ligament reconstruction

Injury to the anterior cruciate ligament (ACL) not only causes mechanical instability but also leads to a functional deficit in the form of diminished proprioception of the knee joint. "Functional" recovery is often incomplete even after "anatomic" arthroscopic ACL reconstruction, as some patients with a clinically satisfactory repair and good ligament tension continue to complain of a feeling of instability and giving way, although the knee does not sublux on clinical testing. Factors that may play a role could be proprioceptive elements, as the intact ACL has been shown to have significant receptors. Significant data have come to light demonstrating proprioceptive differences between normal and injured knees, and often between injured and reconstructed knees. ACL remnants have been shown to have proprioceptive fibers that could enhance functional recovery if they adhere to or grow into the reconstructed ligament. Conventionally the torn remnants are shaved off from the knee before graft insertion; modern surgical techniques, with remnant sparing methods have shown better outcomes and functional recovery, and this could be an avenue for future research and development. This article analyzes and reviews our understanding of the sensory element of ACL deficiency, with specific reference to proprioception as an important component of functional knee stability. The types of mechanoreceptors, their distribution and presence in ACL remnants is reviewed, and suggestions are made to minimize soft tissue shaving during ACL reconstruction to ensure a better functional outcome in the reconstructed knee.

Impact of enhanced sensory input on treadmill step frequency: infants born with myelomeningocele

PURPOSE

To determine the effect of enhanced sensory input on the step frequency of infants with myelomeningocele (MMC) when supported on a motorized treadmill.

METHODS

Twenty-seven infants aged 2 to 10 months with MMC lesions at, or caudal to, L1 participated. We supported infants upright on the treadmill for 2 sets of 6 trials, each 30 seconds long. Enhanced sensory inputs within each set were presented in random order and included baseline, visual flow, unloading, weights, Velcro, and friction.

RESULTS

Overall friction and visual flow significantly increased step rate, particularly for the older subjects. Friction and Velcro increased stance-phase duration. Enhanced sensory input had minimal effect on leg activity when infants were not stepping.

CONCLUSIONS

: Increased friction via Dycem and enhancing visual flow via a checkerboard pattern on the treadmill belt appear to be more effective than the traditional smooth black belt surface for eliciting stepping patterns in infants with MMC.

Multi-sensory weights depend on contextual noise in reference frame transformations

During reach planning, we integrate multiple senses to estimate the location of the hand and the target, which is used to generate a movement. Visual and proprioceptive information are combined to determine the location of the hand. The goal of this study was to investigate whether multi-sensory integration is affected by extraretinal signals, such as head roll. It is believed that a coordinate matching transformation is required before vision and proprioception can be combined because proprioceptive and visual sensory reference frames do not generally align. This transformation utilizes extraretinal signals about current head roll position, i.e., to rotate proprioceptive signals into visual coordinates. Since head roll is an estimated sensory signal with noise, this head roll dependency of the reference frame transformation should introduce additional noise to the transformed signal, reducing its reliability and thus its weight in the multi-sensory integration. To investigate the role of noisy reference frame transformations on multi-sensory weighting, we developed a novel probabilistic (Bayesian) multi-sensory integration model (based on Sober and Sabes, 2003) that included explicit (noisy) reference frame transformations. We then performed a reaching experiment to test the model's predictions. To test for head roll dependent multi-sensory integration, we introduced conflicts between viewed and actual hand position and measured reach errors. Reach analysis revealed that eccentric head roll orientations led to an increase of movement variability, consistent with our model. We further found that the weighting of vision and proprioception depended on head roll, which we interpret as being a result of signal dependant noise. Thus, the brain has online knowledge of the statistics of its internal sensory representations. In summary, we show that sensory reliability is used in a context-dependent way to adjust multi-sensory integration weights for reaching.

Beyond dreams: do sleep-related movements contribute to brain development?

Conventional wisdom has long held that the twitches of sleeping infants and adults are by-products of a dreaming brain. With the discovery of active (or REM) sleep in the 1950s and the recognition soon thereafter that active sleep is characterized by inhibition of motor outflow, researchers elaborated on conventional wisdom and concluded that sleep-related twitches are epiphenomena that result from incomplete blockade of dream-related cortical activity. This view persists despite the fact that twitching is unaffected in infants and adults when the cortex is disconnected from the brainstem. In 1966, Roffwarg and colleagues introduced the ontogenetic hypothesis, which addressed the preponderance of active sleep in early infancy. This hypothesis posited that the brainstem mechanisms that produce active sleep provide direct ascending stimulation to the forebrain and descending stimulation to the musculature, thereby promoting brain and neuromuscular development. However, this hypothesis and the subsequent work that tested it did not directly address the developmental significance of twitching or sensory feedback as a contributor to activity-dependent development. Here I review recent findings that have inspired an elaboration of the ontogenetic hypothesis. Specifically, in addition to direct brainstem activation of cortex during active sleep, sensory feedback arising from limb twitches produces discrete and substantial activation of somatosensory cortex and, beyond that, of hippocampus. Delineating how twitching during active sleep contributes to the establishment, refinement, and maintenance of neural circuits may aid our understanding of the early developmental events that make sensorimotor integration possible. In addition, twitches may prove to be sensitive and powerful tools for assessing somatosensory function in humans across the lifespan as well as functional recovery in individuals with injuries or conditions that affect sensorimotor function.

Visual, motor and attentional influences on proprioceptive contributions to perception of hand path rectilinearity during reaching

We examined how proprioceptive contributions to perception of hand path straightness are influenced by visual, motor and attentional sources of performance variability during horizontal planar reaching. Subjects held the handle of a robot that constrained goal-directed movements of the hand to the paths of controlled curvature. Subjects attempted to detect the presence of hand path curvature during both active (subject driven) and passive (robot driven) movements that either required active muscle force production or not. Subjects were less able to discriminate curved from straight paths when actively reaching for a target versus when the robot moved their hand through the same curved paths. This effect was especially evident during robot-driven movements requiring concurrent activation of lengthening but not shortening muscles. Subjects were less likely to report curvature and were more variable in reporting when movements appeared straight in a novel "visual channel" condition previously shown to block adaptive updating of motor commands in response to deviations from a straight-line hand path. Similarly, compromised performance was obtained when subjects simultaneously performed a distracting secondary task (key pressing with the contralateral hand). The effects compounded when these last two treatments were combined. It is concluded that environmental, intrinsic and attentional factors all impact the ability to detect deviations from a rectilinear hand path during goal-directed movement by decreasing proprioceptive contributions to limb state estimation. In contrast, response variability increased only in experimental conditions thought to impose additional attentional demands on the observer. Implications of these results for perception and other sensorimotor behaviors are discussed.

Elbow joint position sense after neuromuscular training with handheld vibration

CONTEXT

Clinicians use neuromuscular control exercises to enhance joint position sense (JPS); however, because standardizing such exercises is difficult, validations of their use are limited.

OBJECTIVE

To evaluate the acute effects of a neuromuscular training exercise with a handheld vibrating dumbbell on elbow JPS acuity.

DESIGN

Crossover study.

SETTING

University athletic training research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Thirty-one healthy, college-aged volunteers (16 men, 15 women, age = 23 + or - 3 years, height = 173 + or - 8 cm, mass = 76 + or - 14 kg).

INTERVENTION(S)

We measured and trained elbow JPS using an electromagnetic tracking device that provided auditory and visual biofeedback. For JPS testing, participants held a dumbbell and actively identified the target elbow flexion angle (90 degrees ) using the software-generated biofeedback, followed by 3 repositioning trials without feedback. Each neuromuscular training protocol included 3 exercises during which participants held a 2.55-kg dumbbell vibrating at 15, 5, or 0 Hz and used software-generated biofeedback to locate and maintain the target elbow flexion angle for 15 seconds.

MAIN OUTCOME MEASURE(S)

We calculated absolute (accuracy) and variable (variability) errors using the differences between target and reproduced angles.

RESULTS

Training protocols using 15-Hz vibration enhanced accuracy and decreased variability of elbow JPS (P < or = .005), whereas 5-Hz vibration did not affect accuracy (F(1,61) = 2.625, P = .100) but did decrease variability (F(1,61) = 7.250, P = .009). The control condition and 0-Hz training protocol had no effect on accuracy or variability (P > or = .200).

CONCLUSIONS

Our results suggest these neuromuscular control exercises, which included low-magnitude, low-frequency handheld vibration, may enhance elbow JPS. Future researchers should examine vibration of various durations and frequencies, should include injured participants and functional multijoint and multiplanar measures, and should examine long-term effects of training protocols on JPS and injury.

The architecture of the connective tissue in the musculoskeletal system-an often overlooked functional parameter as to proprioception in the locomotor apparatus

The architecture of the connective tissue, including structures such as fasciae, sheaths, and membranes, is more important for understanding functional meaning than is more traditional anatomy, whose anatomical dissection method neglects and denies the continuity of the connective tissue as integrating matrix of the body.

The connective tissue anatomy and architecture exhibits two functional tendencies that are present in all areas of the body in different ways and relationships. In body cavities, the “disconnecting” quality of shaping space enables mobility; between organs and body parts, the “connecting” dimension enables functional mechanical interactions. In the musculoskeletal system, those two features of the connective tissue are also present. They cannot be found by the usual analytic dissection procedures. An architectural description is necessary.

This article uses such a methodologic approach and gives such a description for the lateral elbow region. The result is an alternative architectural view of the anatomic substrate involved in the transmission and conveyance of forces over synovial joints. An architectural description of the muscular and connective tissue organized in series with each other to enable the transmission of forces over these dynamic entities is more appropriate than is the classical concept of “passive” force-guiding structures such as ligaments organized in parallel to actively force-transmitting structures such as muscles with tendons.

The discrimination between so-called joint receptors and muscle receptors is an artificial distinction when function is considered. Mechanoreceptors, also the so-called muscle receptors, are arranged in the context of force circumstances—that is, of the architecture of muscle and connective tissue rather than of the classical anatomic structures such as muscle, capsules, and ligaments. In the lateral cubital region of the rat, a spectrum of mechanosensitive substrate occurs at the transitional areas between regular dense connective tissue layers and the muscle fascicles organized in series with them. This substrate exhibits features of type and location of the mechanosensitive nerve terminals that usually are considered characteristic for “joint receptors” as well as for “muscle receptors.”

The receptors for proprioception are concentrated in those areas where tensile stresses are conveyed over the elbow joint. Structures cannot be divided into either joint receptors or muscle receptors when muscular and collagenous connective tissue structures function in series to maintain joint integrity and stability. In vivo, those connective tissue structures are strained during movements of the skeletal parts, those movements in turn being induced and led by tension in muscular tissue. In principle, because of the architecture, receptors can also be stimulated by changes in muscle tension without skeletal movement, or by skeletal movement without change in muscle tension. A mutual relationship exists between structure (and function) of the mechanoreceptors and the architecture of the muscular and regular dense connective tissue. Both are instrumental in the coding of proprioceptive information to the central nervous system.

Ultrastructural and molecular biologic comparison of classic proprioceptors and palisade endings in sheep extraocular muscles

PURPOSE

To analyze and compare the structural and molecular features of classic proprioceptors like muscle spindles and Golgi tendon organs (GTOs) and putative proprioceptors (palisade endings) in sheep extraocular muscle (EOMs).

METHODS

The EOMs of four sheep were analyzed. Frozen sections or wholemount preparations of the samples were immunohistochemically labeled and analyzed by confocal laser scanning microscopy. Triple labeling with different combinations of antibodies against neurofilament, synaptophysin, and choline acetyltransferase (ChAT), as well as alpha-bungarotoxin and phalloidin, was performed. Microscopic anatomy of the nerve end organs was analyzed by transmission electron microscopy.

RESULTS

The microscopic anatomy demonstrated that muscle spindles and GTOs had a perineural capsule and palisade endings a connective tissue capsule. Sensory nerve terminals in muscle spindles and GTOs contained only a few vesicles, whereas palisade nerve terminals were full of clear vesicles. Likewise, motor terminals in the muscle spindles' polar regions were full of clear vesicles. Immunohistochemistry showed that sensory nerve fibers as well as their sensory nerve terminals in muscle spindles and GTOs were ChAT-negative. Palisade endings were supplied by ChAT-positive nerve fibers, and the palisade complexes including palisade nerve terminals were also ChAT-immunoreactive. Motor terminals in muscle spindles were ChAT and alpha-bungarotoxin positive.

CONCLUSIONS

The present study demonstrated in sheep EOMs that palisade endings are innervated by cholinergic axons exhibiting characteristics typical of motoneurons, whereas muscle spindles (except the polar regions) and GTOs are supplied by noncholinergic axons. These results raise the question of whether palisade endings are candidates for proprioceptors in EOMs.

Joint-position sense and kinesthesia in cerebral palsy

OBJECTIVES

To examine joint-position sense and kinesthesia in all extremities in participants with diplegic or hemiplegic cerebral palsy (CP).

DESIGN

Survey of joint-position sense and kinesthesia differences between aged-matched controls and 2 groups with CP.

SETTING

University movement assessment laboratory.

PARTICIPANTS

Population-based sample of participants with CP, diplegia (n=21), hemiplegia (n=17), and age-matched volunteers (n=21) without neurologic disease.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Joint-position sense and kinesthesia were measured in the transverse plane (forearm pronation/supination and hip internal/external rotation) using a custom-built device. For joint-position sense, participants actively rotated the tested limb to align the distal end with 10 target positions first with the limb and targets visible to assess their ability to perform the task motorically. The task was then repeated with vision of the limb occluded, with targets remaining visible. Joint-position sense error was determined by the magnitude and direction of the rotation errors for each limb in the vision and no vision conditions. Kinesthesia was evaluated by the ability to detect passive limb rotation without vision.

RESULTS

No group differences were detected in the vision condition. Indicative of joint-position sense deficits, a significant increase in errors was found in the no vision condition in all limbs except the dominant upper limb for both groups with CP. Joint-position sense errors were systematically biased toward the direction of internal rotation. Kinesthesia deficits were evident on the nondominant upper limb in diplegia and hemiplegia, and bilaterally in the lower limbs in hemiplegia. In hemiplegia, joint-position sense and kinesthesia deficits were noted on the dominant limbs, but were significantly worse on the nondominant limbs.

CONCLUSIONS

These results indicate that people with CP have proprioception deficits in all limbs.

Evaluating the center of gravity of dislocations in soccer players with and without reconstruction of the anterior cruciate ligament using a balance platform

OBJECTIVE

The objective of this study was to compare the dislocation of the center of gravity and postural balance in sedentary and recreational soccer players with and without anterior cruciate ligament (ACL) reconstruction using the Biodex Balance System (BBS).

METHOD

Sixty-four subjects were divided into three groups: a) soccer players who were post- anterior cruciate ligament reconstruction; b) soccer players with no anterior cruciate ligament injuries; and c) sedentary subjects. The subjects were submitted to functional stability tests using the Biodex Balance System. The instability protocols used were level eight (more stable) and level two (less stable). Three stability indexes were calculated: the anteroposterior stability index, the mediolateral stability index, and the general stability index.

RESULTS

Postural balance (dislocation) on the reconstructed side of the athletes was worse than on the side that had not undergone reconstruction. The postural balance of the sedentary group was dislocated less on both sides than the reconstructed knees of the athletes without anterior cruciate ligament injuries. There were no differences in postural balance with relation to left/right dominance for the uninjured athletes and the sedentary individuals.

CONCLUSION

The dislocation of the center of gravity and change in postural balance in sedentary individuals and on the operated limb of Surgery Group are less marked than in the soccer players from the Non Surgery Group and on the non-operated limbs. The dislocation of the center of gravity and the change in postural balance from the operated limb of the soccer players is less marked than in their non-operated limbs.

Position-specific deficit of joint position sense in ankles with chronic functional instability

The present study was aimed to test a hypothesis that individuals with functional ankle instability (FAI) underestimate the joint angle at greater plantarflexion and inversion. Seventeen males with unilateral FAI and 17 controls (males without FAI) consented for participation in this IRB-approved, case-control study. Using a passive reproduction test, we assessed ankle joint position sense (JPS) for test positions between 30 and -10 degrees plantarflexion with an inclement of 10 degrees with or without 20° inversion at each plantarflexion angle. The constant error (CE) was defined as the value obtained by subtracting the true angle of a test position from the corresponding perceived angle. At plantarflexed and inverted test positions, the CE values were smaller in negative with greater in the FAI group than in the control group. That is, in the FAI group, the FAI group underestimated the true plantarflexion angle at combined 30° plantarflexion and 20° inversion. We conclude that the ankle with FAI underestimate the amount of plantarflexion, which increases the chance of reaching greater planterflexion and inversion than patients' intention at high risk situations of spraining such as landing. Key pointsJoint position sense (JPS) of the ankle with functional ankle instability was investigated utilizing a passive reproduction test.The FAI group demonstrated greater error of the joint position than the control group only when the ankle was positioned at combined inversion and plantarflexion.The FAI group underestimated plantarflexion angle when the ankle was placed at combined inversion and plantarflexion.

Persons with recurrent low back pain exhibit a rigid postural control strategy

Persons with recurrent low back pain (LBP) have been observed to have altered proprioceptive postural control. These patients seem to adopt a body and trunk stiffening strategy and rely more on ankle proprioception to control their posture during quiet upright standing. The aim of this study is to determine the effect of changing postural condition (stable and unstable support surface) on postural stability and proprioceptive postural control strategy in persons with recurrent LBP. Postural sway characteristics of 21 persons with recurrent LBP and 24 healthy individuals were evaluated in upright posture with or without standing on "foam" for the conditions as follows: (1) control (no vibration); (2) vibration of the triceps surae muscles; (3) paraspinal muscle vibration; (4) vibration of the tibialis anterior muscles. Vision was occluded in all conditions except for one control trial. All trials lasted 60 s. Vibration (60 Hz, 0.5 mm), as a potent stimulus for muscle spindles, was initiated 15 s after the start of the trial for a duration of 15 s. Persons with recurrent LBP showed significantly different postural control strategies favoring ankle muscle proprioceptive control (ratio closer to 1) instead of paraspinal muscle proprioceptive control (ratio closer to 0) for both standing without foam (ratio ankle muscle/paraspinal muscle control = 0.83) (P < 0.0001) and on foam (ratio ankle muscle/paraspinal muscle control = 0.87; P < 0.0001) compared to healthy individuals (0.67 and 0.46, respectively). It is concluded that young persons with recurrent LBP seem to use the same proprioceptive postural control strategy even in conditions when this ankle strategy is not the most appropriate such as standing on an unstable support surface. The adopted proprioceptive postural control strategy might be effective in simple conditions, however, when used in all postural conditions this could be a mechanism to undue spinal loading, pain and recurrences.

Balance deficits in recreational athletes with chronic ankle instability

CONTEXT

Deficits in static and dynamic stability during single-leg stance have been noted in individuals with chronic ankle instability (CAI), but few investigators have tested subjects for subtle deficits in dynamic balance. Subtle deficits in dynamic balance during a double-leg stance may reveal changes in the sensorimotor system because of CAI.

OBJECTIVE

To use a standardized tibial nerve stimulation as a perturbation to test for dynamic balance deficits between a group of recreational athletes with CAI and a group of recreational athletes with stable ankles.

DESIGN

Case-control study.

SETTING

Laboratory.

PATIENTS OR OTHER PARTICIPANTS

Twenty recreational athletes with CAI and 20 recreational athletes with stable ankles.

INTERVENTION(S)

Balance deficits were assessed for each subject during static and dynamic trials.

MAIN OUTCOME MEASURE(S)

Time to stabilization and center-of-pressure excursion path length, velocity, and area from ground reaction forces during double-leg stance were collected through a forceplate. We used an accelerometer to measure tibial acceleration. Data were collected during static stance and during a bilateral perturbation using maximal motor neuron recruitment elicited by electric stimulation of the tibial nerve.

RESULTS

Only time to stabilization in the anterior-posterior direction was significantly different between groups ( P = .04), with the CAI group taking longer to return to a stable range of ground reaction forces. We found no other differences in stability measures between the groups.

CONCLUSIONS

Dynamic balance in double-leg stance as measured by time to stabilization appears to be affected in individuals with CAI. Deficits in the response to external perturbation may indicate subtle central sensorimotor changes.

Intra-articular anesthesia and knee muscle response

BACKGROUND

Many receptors located within the intra-articular knee structures contribute to the neuromuscular responses of the knee. The purpose was to compare the automatic postural response induced by a perturbation at the foot before and after an intra-articular injection of a local anesthetic (bupivicaine), after a saline (sham) injection, and after no intra-articular injection (control) in the knee.

METHODS

Muscle onset latencies and automatic response magnitudes for the vastus medialis, vastus lateralis, biceps femoris, medial hamstrings, tibialis anterior, and gastrocnemius were measured using electromyography (EMG) when anteriorly directed perturbations were applied to the feet of 30 subjects. All subjects then received a lidocaine skin injection followed by: an intra-articular bupivicaine injection (treatment group); an intra-articular saline injection (sham group); or no injection (control group), depending on their randomized group assignment. The perturbation tests were then repeated.

FINDINGS

Muscle onset latencies and automatic response magnitudes did not change as a result of the intra-articular injections. Latencies were significantly greater for the vastus medialis and vastus lateralis when compared to the medial hamstrings, biceps femoris and tibialis anterior (P<0.001). Automatic response magnitudes for the tibialis anterior were significantly greater than those of the hamstrings, which were greater than those of the quadriceps (P<0.001).

INTERPRETATION

There were no differences in muscle response when anteriorly directed perturbations were applied to the foot with or without an injection of local anesthetic in the knee. Intra-articular receptors were either unaffected by the anesthetic or the extra-articular receptors or receptors of the other joints were able to compensate for their loss.

Comparison of static and dynamic balance in female collegiate soccer, basketball, and gymnastics athletes

CONTEXT

How athletes from different sports perform on balance tests is not well understood. When prescribing balance exercises to athletes in different sports, it may be important to recognize performance variations.

OBJECTIVE

To compare static and dynamic balance among collegiate athletes competing or training in soccer, basketball, and gymnastics.

DESIGN

A quasi-experimental, between-groups design. Independent variables included limb (dominant and nondominant) and sport played.

SETTING

A university athletic training facility.

PATIENTS OR OTHER PARTICIPANTS

Thirty-four female volunteers who competed in National Collegiate Athletic Association Division I soccer (n = 11), basketball (n = 11), or gymnastics (n = 12).

INTERVENTION(S)

To assess static balance, participants performed 3 stance variations (double leg, single leg, and tandem leg) on 2 surfaces (stiff and compliant). For assessment of dynamic balance, participants performed multidirectional maximal single-leg reaches from a unilateral base of support.

MAIN OUTCOME MEASURE(S)

Errors from the Balance Error Scoring System and normalized leg reach distances from the Star Excursion Balance Test were used to assess static and dynamic balance, respectively.

RESULTS

Balance Error Scoring System error scores for the gymnastics group were 55% lower than for the basketball group (P = .01), and Star Excursion Balance Test scores were 7% higher in the soccer group than the basketball group (P = .04).

CONCLUSIONS

Gymnasts and soccer players did not differ in terms of static and dynamic balance. In contrast, basketball players displayed inferior static balance compared with gymnasts and inferior dynamic balance compared with soccer players.

Functional fatigue and upper extremity sensorimotor system acuity in baseball athletes

CONTEXT

The sensorimotor system controls the balance between upper extremity stability and mobility during athletic performance. Research indicates that fatigue hampers sensorimotor system function; however, few investigators have studied functional fatigue or multijoint, multiplanar measures.

OBJECTIVE

To examine the effect of functional fatigue on upper extremity position reproduction in overhead throwing athletes.

DESIGN

Single-session, repeated-measures design.

SETTING

University musculoskeletal laboratory.

PATIENTS OR OTHER PARTICIPANTS

Sixteen healthy collegiate baseball players (age = 21.0 +/- 1.6 years, height = 175.8 +/- 10.2 cm, mass = 82.8 +/- 4.3 kg).

INTERVENTION(S)

Subjects threw a baseball from a single knee with maximum velocity (every 5 seconds) and rated their level of upper extremity exertion after every 20 throws. Subjects stopped after reporting above level 14 on the Borg scale and began posttests immediately.

MAIN OUTCOME MEASURE(S)

We measured active multijoint reproduction of 2 positions: arm cock and ball release. Dependent variables were absolute and variable error for 10 joint motions: scapulothoracic internal-external rotation, upward rotation, and posterior tilt; glenohumeral internal-external rotation, horizontal abduction-adduction, and flexion-extension; elbow pronation-supination and flexion-extension; and wrist ulnar-radial deviation and flexion-extension. We calculated acuity for each joint and the entire upper extremity using 3-dimensional variable error.

RESULTS

Fatigue occurred after an average of 62 +/- 28 throws and increased 3-dimensional variable error scores (ie, decreased acuity) of the entire upper extremity and all joints in both positions (P < .05) except for the wrist in arm cock. Fatigue increased errors (ranging from 0.6 degrees to 2.3 degrees ) at arm cock for scapulothoracic internal-external rotation, upward rotation, and posterior tilt; glenohumeral internal-external rotation and flexion-extension; elbow flexion-extension; and wrist ulnar-radial deviation and at ball release for scapulothoracic internal-external rotation and upward rotation, glenohumeral horizontal abduction-adduction, elbow pronation-supination, and wrist ulnar-radial deviation and flexion-extension (P < .05).

CONCLUSIONS

Functional fatigue affects the acuity of the entire upper extremity, each individual joint, and multiple joint motions in overhead throwers. Clinicians should consider the deleterious effects of upper extremity fatigue when designing injury prevention and rehabilitation programs and should incorporate multijoint and multiplanar endurance exercises. Compromised neuromuscular control of the scapulohumeral relationship may hold pathologic implications for this population as well.

Low-load eversion force sense, self-reported ankle instability, and frequency of giving way

CONTEXT

Functional ankle instability has been attributed to proprioceptive loss. However, in previous studies of proprioception,authors have not investigated the ability to sense force at the ankle. Additionally, previous investigators have viewed functional ankle instability as either a present or absent condition,rather than a continuum.

OBJECTIVE

To determine the relationship of ankle giving-way frequency and perceived ankle instability to ankle eversion force sense.

DESIGN

Cohort design.

SETTING

Sports medicine research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Twenty individuals (5 men,15 women) with a history of unilateral ankle instability.

INTERVENTION(S)

We tested subjects with 2 loads: 10% and 30% of maximal voluntary isometric contraction.

MAIN OUTCOME MEASURE(S)

We measured eversion force sense by calculating absolute, constant, and variable errors from a 3-trial force-matching procedure. Furthermore, subjects reported their frequency of giving way in units of times per day,week, or month, and these data were extrapolated to estimate annual giving-way frequency. Finally, subjects answers to 6 questions about ankle stability during typical daily or sports activities were summed to create a perceived ankle instability index.

RESULTS

Significant relationships were found for only the 10% maximal voluntary isometric contraction. For absolute error,a positive relationship existed between the number of self reported episodes of giving way and eversion force sense for both ipsilateral (r .58) and contralateral (r .49) testing of the injured ankle. Constant error was correlated with giving way(r = -.56) for ipsilateral testing of the injured ankle. The ankle instability index was also positively correlated with eversion force sense absolute error (r .51) for ipsilateral testing only.

CONCLUSIONS

Our results suggest that subjects with ankle instability had difficulty replicating eversion forces. Specifically,larger errors were related to both self-reported giving-way episodes and perceived ankle instability.

Relative impact of radiographic osteoarthritis and pain on quadriceps strength, proprioception, static postural sway and lower limb function

OBJECTIVE

To investigate the relative impact of radiographic osteoarthritis (ROA) and current knee pain on lower limb physical function, quadriceps strength, knee joint proprioception, and postural sway.

METHODS

Using a 2x2 factorial design, 142 community derived subjects aged over 45 were divided into four subgroups based on the presence or absence of ROA (Kellgren & Lawrence>grade 2) and knee pain (as assessed by NHANES questions and a 100 mm visual analogue scale). Maximum isometric contraction of the quadriceps, knee joint proprioceptive acuity, static postural sway, and WOMAC index (both whole and function subscale) were assessed in all subjects.

RESULTS

Compared with normal subjects, reported disability was greater for all other subgroups (p<0.01). Subjects with both ROA and knee pain reported the greatest disability, and those with knee pain only had greater disability than those with ROA only. Quadriceps weakness was observed in all groups compared with normal subjects (p<0.01), though they were no significant intergroup differences. Subjects with knee pain had a greater sway area than those without (p<0.05) but the presence of ROA was not associated with increased postural sway. No differences in proprioceptive acuity were observed between groups.

CONCLUSIONS

The presence of knee pain has a negative association with quadriceps strength, postural sway, and disability compared with ROA. However, the presence of pain-free ROA has a significant negative influence on relative quadriceps strength and reported disability.

Acute muscle stretching and shoulder position sense

CONTEXT

Stretching is common among athletes as a potential method for injury prevention. Stretching-induced changes in the muscle spindle properties are a suggested mechanism, which may imply reduced proprioception after stretching; however, little is known of this association.

OBJECTIVE

To evaluate whether acute stretching of the shoulder muscles affects position sense.

DESIGN

A crossover design with subjects randomized to 3 groups.

SETTING

A university human research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Nine male (age = 24 +/- 3 years) and 9 female (age = 21 +/- 2 years) healthy volunteers.

INTERVENTION(S)

Stretching of shoulder (1) agonists or (2) antagonists or (3) nonstretching control.

MAIN OUTCOME MEASURE(S)

We determined position sense acuity of the right shoulder before and after the interventions by having subjects attempt to reproduce arm positions of 15 degrees and 30 degrees (shoulder adduction) while starting at 45 degrees to the sagittal plane. The outcome variables were response variability (variable error) and overall accuracy (absolute error).

RESULTS

The relative change in variable error (ie, variable error after/variable error before) was not significantly different between the interventions ( P = .38). Similarly, no change in absolute error was found ( P = .76). Furthermore, no differences were noted regarding test sequence or the interaction of intervention x sequence for either variable error ( P = .73 and .53, respectively) or absolute error ( P = .71 and .67, respectively).

CONCLUSIONS

We found no effect on shoulder position sense after an acute bout of stretching of either agonist or antagonist shoulder muscles.

Functional multijoint position reproduction acuity in overhead-throwing athletes

CONTEXT

Baseball players rely on the sensorimotor system to uphold the balance between upper extremity stability and mobility while maintaining athletic performance. However, few researchers have studied functional multijoint measures of sensorimotor acuity in overhead-throwing athletes.

OBJECTIVE

To compare sensorimotor acuity between 2 high-demand functional positions and among planes of motion within individual joints and to describe a novel method of measuring sensorimotor function.

DESIGN

Single-session, repeated-measures design.

SETTING

University musculoskeletal research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Twenty-one National Collegiate Athletic Association Division I baseball players (age = 20.8 +/- 1.5 years, height = 181.3 +/- 5.1 cm, mass = 87.8 +/- 9.1 kg) with no history of upper extremity injury or central nervous system disorder.

MAIN OUTCOME MEASURE(S)

We measured active multijoint position reproduction acuity in multiple planes using an electromagnetic tracking device. Subjects reproduced 2 positions: arm cock and ball release. We calculated absolute and variable error for individual motions at the scapulothoracic, glenohumeral, elbow, and wrist joints and calculated overall joint acuity with 3-dimensional variable error.

RESULTS

Acuity was significantly better in the arm-cock position compared with ball release at the scapulothoracic and glenohumeral joints. We observed significant differences among planes of motion within the scapulothoracic and glenohumeral joints at ball release. Scapulothoracic internal rotation and glenohumeral horizontal abduction and rotation displayed less acuity than other motions.

CONCLUSIONS

We established the reliability of a functional measure of upper extremity sensorimotor system acuity in baseball players. Using this technique, we observed differences in acuity between 2 test positions and among planes of motion within the glenohumeral and scapulothoracic joints. Clinicians may consider these differences when designing and implementing sensorimotor system training. Our error scores are similar in magnitude to those reported using single-joint and single-plane measures. However, 3-dimensional, multijoint measures allow practical, unconstrained test positions and offer additional insight into the upper extremity as a functional unit.

Spatiotemporal mapping of cortical activity accompanying voluntary movements using an event-related beamforming approach

We describe a novel spatial filtering approach to the localization of cortical activity accompanying voluntary movements. The synthetic aperture magnetometry (SAM) minimum-variance beamformer algorithm was used to compute spatial filters three-dimensionally over the entire brain from single trial neuromagnetic recordings of subjects performing self-paced index finger movements. Images of instantaneous source power ("event-related SAM") computed at selected latencies revealed activation of multiple cortical motor areas prior to and following left and right index finger movements in individual subjects, even in the presence of low-frequency noise (e.g., eye movements). A slow premovement motor field (MF) reaching maximal amplitude approximately 50 ms prior to movement onset was localized to the hand area of contralateral precentral gyrus, followed by activity in the contralateral postcentral gyrus at 40 ms, corresponding to the first movement-evoked field (MEFI). A novel finding was a second activation of the precentral gyrus at a latency of approximately 150 ms, corresponding to the second movement-evoked field (MEFII). Group averaging of spatially normalized images indicated additional premovement activity in the ipsilateral precentral gyrus and the left inferior parietal cortex for both left and right finger movements. Weaker activations were also observed in bilateral premotor areas and the supplementary motor area. These results show that event-related beamforming provides a robust method for studying complex patterns of time-locked cortical activity accompanying voluntary movements, and offers a new approach for the localization of multiple cortical sources derived from neuromagnetic recordings in single subject and group data.

Proposed mechanisms and treatment strategies for motion sickness disorder: a case series

OBJECTIVE

To present an overview of symptomatic motion sickness disorder and to propose allopathic and chiropractic approaches for treatment.

CLINICAL FEATURES

Three representative cases are presented involving patients with motion sickness. All 3 patients had suffered from this condition throughout their lives. A discussion of the hypothesis of sensory conflict as a causative factor in cases of motion sickness is offered.

INTERVENTION AND OUTCOME

Following methods founded in applied kinesiology and using spinal and cranial manipulative treatment, the patients were able to travel long distances without nausea, sickness, or dizziness. The evaluation of these patients' responses to treatment was determined by the doctor's observation, the patients' subjective description of symptoms while riding in a motor vehicle, a visual analog scale for neck and associated pain, and applied kinesiology chiropractic physical assessment tools.

CONCLUSION

Further studies into chiropractic manipulative treatments for sensory conflict and proprioceptive dysfunctions associated with the problem of motion sickness are indicated. The hypothesis of sensory conflict as the cause of motion sickness should be explored more fully by other chiropractic physicians and researchers.

The influence of external loads on movement precision during active shoulder internal rotation movements as measured by 3 indices of accuracy

CONTEXT

Using constant, variable, and absolute error to measure movement accuracy might provide a more complete description of joint position sense than any of these values alone.

OBJECTIVE

To determine the effect of loaded movements and type of feedback on shoulder joint position sense and movement velocity.

DESIGN

Applied study with repeated measures comparing type of feedback and the presence of a load.

SETTING

Laboratory.

PATIENTS OR OTHER PARTICIPANTS

Twenty healthy subjects (age = 27.2 +/- 3.3 years, height = 173.2 +/- 18.1 cm, mass = 70.8 +/- 14.5 kg) were seated with their arms in a custom shoulder wheel.

INTERVENTION(S)

Subjects internally rotated 27 degrees in the plane of the scapula, with either visual feedback provided by a video monitor or proprioceptive feedback provided by prior passive positioning, to a target at 48 degrees of external rotation. Subjects performed the internal rotation movements with video feedback and proprioceptive feedback and with and without load (5% of body weight).

MAIN OUTCOME MEASURE(S)

High-speed motion analysis recorded peak rotational velocity and accuracy. Constant, variable, and absolute error for joint position sense was calculated from the final position.

RESULTS

Unloaded movements demonstrated significantly greater variable error than for loaded movements (2.0 +/- 0.7 degrees and 1.5 +/- 0.4 degrees, respectively) (P < .05), but there were no differences in constant or absolute error. Peak velocity was greater for movements with proprioceptive feedback (45.6 +/- 2.9 degrees/s) than visual feedback (39.1 +/- 2.1 degrees/s) and for unloaded (47.8 +/- 3.6 degrees/s) than loaded (36.9 +/- 1.0 degrees/s) movements (P < .05).

CONCLUSIONS

Shoulder joint position sense demonstrated greater variable error unloaded versus loaded movements. Both visual feedback and additional loads decreased peak rotational velocity.

A multi-station proprioceptive exercise program in patients with bilateral knee osteoarthrosis: functional capacity, pain and sensoriomotor function. A randomized controlled trial

We investigated the effects of a multi-station proprioceptive exercise program on functional capacity, perceived knee pain, and sensoriomotor function. Twenty-two patients (aged 41-75 years) with grade 2-3 bilateral knee osteoarthrosis were randomly assigned to two groups: treatment (TR; n = 12) and non-treatment (NONTR; n = 10). TR performed 11 different balance/coordination and proprioception exercises, twice a week for 6 weeks. Functional capacity and perceived knee pain during rest and physical activity was measured. Also knee position sense, kinaesthesia, postural control, isometric and isokinetic knee strength (at 60, 120 and 180°·s(-1)) measures were taken at baseline and after 6 weeks of training. There was no significant difference in any of the tested variables between TR and NONTR before the intervention period. In TR perceived knee pain during daily activities and functional tests was lessened following the exercise program (p < 0.05). Perceived knee pain was also lower in TR vs. NONTR after training (p < 0.05). The time for rising from a chair, stair climbing and descending improved in TR (p < 0.05) and these values were faster compared with NONTR after training (p < 0.05). Joint position sense (degrees) for active and passive tests and for weight bearing tests improved in TR (p < 0.05) and the values were lower compared with NONTR after training (p < 0.05). Postural control ('eyes closed') also improved for single leg and tandem tests in TR (p < 0.01) and these values were higher compared with NONTR after training. The isometric quadriceps strength of TR improved (p < 0.05) but the values were not significantly different compared with NONTR after training. There was no change in isokinetic strength for TR and NONTR after the training period. The results suggest that using a multi-station proprioceptive exercise program it is possible to improve postural control, functional capacity and decrease perceived knee pain in patients with bilateral knee osteoarthrosis. Key PointsIt is possible to improve postural control, functional capacity and decrease perceived knee pain in patients with bilateral knee osteoarthrosis with a pure proprioceptive/ balance exercise program used in the present study.The exercise regime used in the present study was as effective as previous studies, but of much shorter duration and utilized unsophisticated, inexpensive equipment which is available in most physiotherapy departments.Therefore, the incorporation of this exercise program into clinical practice is readily feasible.

Sustained muscle activity minimally influences dynamic position sense of the ankle

STUDY DESIGN

Cross-sectional study.

OBJECTIVE

The purpose of this study was to determine if a sustained fatiguing contraction of the dorsiflexor muscles alters the dynamic position sense (proprioception) and the associated central nervous system processing time of information from the ankle.

BACKGROUND

Ankle injury has been hypothesized to be related to altered proprioception as a consequence of fatiguing exercise. Previous reports assessing proprioception include tests of motor performance (balance and limb repositioning) or tests of a joint under static conditions. This study used a novel experimental approach to test the effects of exercise on the somatosensory system of the ankle.

METHODS AND MEASURES

Nineteen healthy subjects were tested on their ability to extend the metacarpophalangeal joint of their left index finger when their left ankle was passively plantar flexed (0 degrees-40 degrees, 10 velocities) through a predetermined target angle (20 degrees). Testing occurred before and after a fatiguing contraction of the dorsiflexor muscles.

RESULTS

Subjects accurately indicated the ankle target angle up to ankle velocities of 70 degrees/s (300 ms) both before and after the sustained fatiguing contraction. At velocities above 70 degrees/s all subjects could no longer scale to accurately indicate the target angle with the index finger and consequently overshot the target. The central nervous system processing time was estimated to be approximately 85 milliseconds before and after the sustained contraction.

CONCLUSIONS

These results indicate that a sustained activity of the dorsiflexion muscles of the ankle minimally affects dynamic position sense and the ability to process dynamic position sense information. Understanding the impact of exercise on sensory system processing will be integral to establishing the scientific basis for rehabilitation programs that purport to train proprioception.

Effects of Pronated and Supinated Foot Postures on Static and Dynamic Postural Stability

Context: The foot is the most distal segment in the lower extremity chain and represents a relatively small base of support on which the body maintains balance (particularly in single-leg stance). Although it seems reasonable that even minor biomechanical alterations in the support surface may influence postural-control strategies, the implications of a hypermobile or hypomobile foot on balance have received little attention to date.Objective: To determine if supinated and pronated foot types influence measures of static and dynamic balance.Design: Participants were assigned to 1 of 3 groups depending on foot type, as defined by navicular-drop measures: pronated (>/=10 mm), neutral (5-9 mm), or supinated (</=4 mm). Measures of static and dynamic balance were obtained for each participant and compared across groups.Setting: Sports medicine and athletic training research laboratory.Patients or Other Participants: Sixteen individuals with pronated (navicular drop = 13.0 +/- 3.7 mm), neutral (navicular drop = 6.2 +/- 1.1 mm), or supinated (navicular drop = 2.2 +/- 1.7 mm) foot postures volunteered to participate in the study.Main Outcome Measure(s): We used the Chattecx Balance System to measure center of balance, stability index, and postural sway during static single-limb stance under eyes-open and eyes-closed conditions. Center of balance was defined as the point on the foot at which the body weight was equally distributed between the medial-lateral and anterior-posterior quadrants and was recorded in centimeters. Stability index was defined as the mean deviation in sway around the center of balance. Postural sway was expressed as the maximum sway distance recorded (cm) in the medial-lateral and anterior-posterior directions. The Star Excursion Balance Test was used to measure dynamic balance, which was reported as the reach distance (cm) in each of the 8 directions tested. The average of 3 trials of each measure was calculated and normalized to the subject's height.Results: We found no difference in center of balance or postural sway as a function of foot type. The stability index was greater in pronators than in supinators, but neither group was different from those with neutral foot types. Dynamic reach differed among groups but only in some directions. Generally, pronators reached farther in the anterior and anterior medial directions and supinators reached farther in the posterior and posterio-lateral directions. In the lateral direction, supinators reached farther than pronators but not farther than neutrals.Conclusions: Our results suggest that postural stability is affected by foot type under both static and dynamic conditions. These differences appear to be related to structural differences as opposed to differences in peripheral input. These effects should be considered when clinicians use such balance measures to assess injury deficits and recovery.

Reliability of Joint Position Sense and Force-Reproduction Measures During Internal and External Rotation of the Shoulder

OBJECTIVE: To determine the reliability of 2 common measures of proprioception. DESIGN AND SETTING: Joint position sense (JPS) and force reproduction (FR) were measured in the dominant shoulder using internal-rotation (IR) and external-rotation (ER) target angles on 2 consecutive days. SUBJECTS: Thirty-one healthy subjects (age = 22.0 +/- 2.8 years, height = 171.8 +/- 9.2 cm, mass = 69.5 +/- 15.9 kg) who did not regularly compete in overhand sports volunteered to participate in the study. MEASUREMENTS: Error scores were calculated at 2 target angles by averaging the absolute difference of 3 trials of JPS and FR. Reliability was determined by comparing the error scores obtained on 2 consecutive days. RESULTS: The inclinometer was found to be a reliable instrument as both intertester (.999) and intratester (.999) intraclass correlation coefficients were high. The JPS and FR measurements were also found to be reliable, with intraclass correlation coefficients ranging from.978 to.984. No differences were observed between trials for either measure. CONCLUSIONS: The inclinometer was a reliable instrument and can provide an affordable and accurate measure of range of motion and JPS. Both JPS and FR were also reliable measures of proprioception in the shoulder. Further research is needed to identify the specific mechanism of proprioception during these tasks.

Movement speed effects on limb position drift

Previous research has shown that even when limb position drifts considerably during continuous blind performance, the topological and metrical properties of generated hand paths remain remarkably invariant. We tested two possible accounts of this intriguing effect. According to one hypothesis, position drift is due to degradation of limb-position information. This hypothesis predicted that drift of static hand positions at movement reversals should not depend on movement speed. According to the other hypothesis, position drift is due to degradation of movement information. This hypothesis predicted that drift of static hand positions at movement reversals should vary with movement speed. We tested these two hypotheses by varying the required movement speed when normal human adults performed back-and-forth manual positioning movements in the absence of visual feedback. Movement distance and direction were well preserved even though hand positions between movements drifted considerably. In accord with the movement error hypothesis, but not in accord with the position hypothesis, the rate at which hand positions drifted depended on movement speed. The data are consistent with the idea that hand position, which defines the origin of the trajectory control coordinate system, and movement trajectory are controlled by distinct neural mechanisms.

Spike width reduction modifies the dynamics of short-term depression at a central synapse in the locust

Short-term synaptic depression is an important component of computation within neural networks, but little is known of its contribution to information processing during synaptically generated spike trains. We analyzed short-term synaptic depression at a synapse between two identified motoneurons innervating the hind leg of the locust: the FETi-FlTi synapse (fast extensor tibiae-flexor tibiae). Brief electrical stimulation of a single hind leg proprioceptor, the lump receptor (LR), led to prolonged sequences of spikes in FETi, similar in number and frequency to those during natural kicking movements. Depression at the FETi-FlTi synapse during LR-evoked spike bursts was compared quantitatively to that during antidromic spike trains evoked by electrical stimulation of FETi in the extensor tibiae muscle, and by modeling. The magnitude of the short-term depression was significantly greater during LR-evoked spike trains. On the basis of the model parameters required to fit the depression, the FETi-FlTi synapse is predominantly used for transmitting the timing of the onset of FETi spiking rather than its spike rate. During LR-evoked spike trains, there was a rapid reduction in presynaptic spike width that did not occur during antidromic spike trains under physiological calcium concentrations. This produced a concomitant reduction in the amplitude of the FlTi EPSP, suggesting that it contributed to the differences between the two stimulation regimes. Differences in the short-term depression between synaptically evoked and antidromic spike trains emphasize that the properties of synaptic information transfer are dependent on the in vivo conditions at the synapse and may not be reproduced by in vitro spike trains.

Multisensory integration during motor planning

When planning goal-directed reaches, subjects must estimate the position of the arm by integrating visual and proprioceptive signals from the sensory periphery. These integrated position estimates are required at two stages of motor planning: first to determine the desired movement vector, and second to transform the movement vector into a joint-based motor command. We quantified the contributions of each sensory modality to the position estimate formed at each planning stage. Subjects made reaches in a virtual reality environment in which vision and proprioception were dissociated by shifting the location of visual feedback. The relative weighting of vision and proprioception at each stage was then determined using computational models of feedforward motor control. We found that the position estimate used for movement vector planning relies mostly on visual input, whereas the estimate used to compute the joint-based motor command relies more on proprioceptive signals. This suggests that when estimating the position of the arm, the brain selects different combinations of sensory input based on the computation in which the resulting estimate will be used.

Reposition sense of lumbar curvature with flexed and asymmetric lifting postures

STUDY DESIGN

Reposition sense of lumbar curvature was assessed as a function of trunk flexion, trunk asymmetry, and target lumbar curvature using a repeated-measures design and an active-active proprioception paradigm.

OBJECTIVE

The objectives of the research were to measure the ability of the subjects to sense and control the lumbar curvature in different lifting postures and to see if error in the lumbar curvature would increase in high-risk postures.

SUMMARY OF BACKGROUND DATA

The risk of low back disorders (LBDs) is related to trunk posture, with greater risk reported in flexed and asymmetric trunk positions. Spinal posture, including trunk position and lumbar lordosis, influences spinal stability. Hence, the ability to accurately sense and control spinal curvature may be an important factor in the control of LBD risk.

METHODS

Eleven subjects were trained to assume specified lumbar curvatures using visual feedback. The ability of the subjects to reproduce this curvature without feedback was then assessed. This procedure was repeated for different trunk postures, including flexion and asymmetry, and with different target lumbar curvatures.

RESULTS

These measurements demonstrated reposition error was increased in flexed trunk positions but was unchanged with trunk asymmetry. This increase in reposition error with flexion was diminished when the target posture and lumbar curvature were highly flexed and kyphotic.

CONCLUSIONS

This research suggests that it may be difficult to control spinal curvature in flexed positions, leading to an increased risk of injury. For jobs in which flexed working postures are unavoidable, therefore, it is important to minimize potentially unstable events such as slipping or shifting loads to avoid injury.

The Effect of a Neoprene Shoulder Stabilizer on Active Joint-Reposition Sense in Subjects With Stable and Unstable Shoulders

OBJECTIVE: To compare the effects of shoulder bracing on active joint-reposition sense in subjects with stable and unstable shoulders. DESIGN AND SETTING: Two subject groups, with stable and unstable shoulders, participated in an active joint-reposition test of the shoulder under braced and unbraced conditions. SUBJECTS: Forty subjects (22 men, 18 women; age = 21.85 +/- 3.12 years; height = 173.97 +/- 10.08 cm; weight = 71.27 +/- 11.68 kg) were recruited to participate in this study. Twenty Division I athletes were referred to us for shoulder instability, which was subsequently confirmed with clinical assessment. The remaining 20 subjects were recruited from a similar student population and assessed as having stable shoulders. MEASUREMENTS: Each subject's ability to perceive joint position sense in space was tested by actively reproducing 3 preset angles (10 degrees from full external rotation, 30 degrees of external rotation, and 30 degrees of internal rotation) with and without a shoulder brace. Full, active external-rotation range of motion was assessed before active joint-reposition sense testing. RESULTS: While wearing the shoulder brace, the group with unstable shoulders demonstrated significant improvement in the accuracy of active joint repositioning at 10 degrees from full external rotation in comparison with the stable group. Furthermore, those with unstable shoulders demonstrated significantly less full external rotation than did those with stable shoulders, and the brace reduced full external rotation only for those with stable shoulders. CONCLUSIONS: Our findings suggest that shoulder active joint-reposition sense in subjects with unstable shoulders can be improved at close to maximal external rotation by wearing a shoulder brace. This effect does not appear to be related to restriction of shoulder external rotation.

Sensorimotor system measurement techniques

OBJECTIVE

To provide an overview of currently available sensorimotor assessment techniques.

DATA SOURCES

We drew information from an extensive review of the scientific literature conducted in the areas of proprioception, neuromuscular control, and motor control measurement. Literature searches were conducted using MEDLINE for the years 1965 to 1999 with the key words proprioception, somatosensory evoked potentials, nerve conduction testing, electromyography, muscle dynamometry, isometric, isokinetic, kinetic, kinematic, posture, equilibrium, balance, stiffness, neuromuscular, sensorimotor, and measurement. Additional sources were collected using the reference lists of identified articles.

DATA SYNTHESIS

Sensorimotor measurement techniques are discussed with reference to the underlying physiologic mechanisms, influential factors and locations of the variable within the system, clinical research questions, limitations of the measurement technique, and directions for future research.

CONCLUSIONS/RECOMMENDATIONS

The complex interactions and relationships among the individual components of the sensorimotor system make measuring and analyzing specific characteristics and functions difficult. Additionally, the specific assessment techniques used to measure a variable can influence attained results. Optimizing the application of sensorimotor research to clinical settings can, therefore, be best accomplished through the use of common nomenclature to describe underlying physiologic mechanisms and specific measurement techniques.

The sensorimotor system, part I: the physiologic basis of functional joint stability

OBJECTIVE

To define the nomenclature and physiologic mechanisms responsible for functional joint stability.

DATA SOURCES

Information was drawn from an extensive MEDLINE search of the scientific literature conducted in the areas of proprioception, neuromuscular control, and mechanisms of functional joint stability for the years 1970 through 1999. An emphasis was placed on defining pertinent nomenclature based on the original references.

DATA SYNTHESIS

Afferent proprioceptive input is conveyed to all levels of the central nervous system. They serve fundamental roles in optimal motor control and sensorimotor control over functional joint stability.

CONCLUSIONS/APPLICATIONS

Sensorimotor control over the dynamic restraints is a complex process that involves components traditionally associated with motor control. Recognizing and understanding the complexities involved will facilitate the continued development and institution of management strategies based on scientific rationales.

Factors Contributing to Chronic Ankle Instability: Kinesthesia and Joint Position Sense

OBJECTIVE: To present a comprehensive review of the influence of altered kinesthesia and joint position sense on chronic ankle instability and to present a model connecting deficits in ankle position sense with the increased risk of sustaining lateral ankle sprains. DATA SOURCES: I searched MEDLINE for the years 1966-2001 using the key words ankle and kinesthesia or position sense and books on proprioception. DATA SYNTHESIS: Study findings suggest a risk for unprovoked lateral ankle sprains when the lateral border of the foot accidentally catches the ground surface during the late swing phase of normal locomotion. In normal situations, the lateral border of the foot clears the ground by only 5 mm, and a small increase in ankle-position error may substantially increase the risk of a collision. Findings of affected kinesthesia and joint position sense in subjects with chronically unstable ankles dominate over studies showing nonsignificant results, but the answer is far from clear. CONCLUSIONS/RECOMMENDATIONS: Changes in joint position sense and kinesthesia of a magnitude found in subjects with chronically unstable ankles can lead to an increased risk of sustaining lateral ankle sprains. Results from a small number of studies suggest that balance and coordination training can restore the increased uncertainty of joint positioning to normal levels.

Peroneal Reaction Times and Eversion Motor Response in Healthy and Unstable Ankles

OBJECTIVE: To measure and compare latency, electromechanical delay, and speed of motor response of the peroneus longus muscle in a large sample of subjects with healthy or unstable ankles. DESIGN AND SETTING: Subjects with healthy or unstable ankles underwent identical test procedures consisting of 6 consecutive, sudden 50 degrees ankle-inversion movements in the standing position with full weight on the tested leg. Latency, first and second decelerations, and total inversion time were monitored. In a separate setting, electromechanical delay was measured during a voluntary ankle eversion. SUBJECTS: We tested 81 subjects (27 males, 54 females) with healthy ankles or unilateral or bilateral ankle instability: 40 individuals with 48 unstable ankles (18 males, 22 females; age range, 18 to 23 years), and 41 individuals with 46 healthy ankles (9 males, 32 females; age range 15 to 29 years). MEASUREMENTS: Using surface electromyography, the latency of the peroneus longus muscle was measured during sudden inversion. Simultaneously, using accelerometry, first and second decelerations were measured. Separately, the electromechanical delay was measured using electromyography and accelerometry. RESULTS: The time of the first deceleration was significantly shorter in subjects with unstable ankles (25.5 milliseconds versus 28.4 milliseconds for those with healthy ankles). The latency, total inversion time, second deceleration time, and electromechanical delay were not shown to be significantly different between healthy and unstable ankles. CONCLUSIONS: The significantly shorter first deceleration during sudden inversion in the standing position in subjects with unstable ankles compared with subjects with healthy ankles is explained by less control of inversion speed in the first phase of the sudden inversion in unstable ankles. Our study does not confirm the results of the systematic literature search showing a longer latency in subjects with unstable ankles.

Kinesthesia Is Not Affected by Functional Ankle Instability Status

OBJECTIVE: To determine whether subjects with functional ankle instability suffered kinesthetic deficits in the injured ankle compared with the healthy ankle and to examine the effect of prophylactic ankle bracing on kinesthesia in uninjured and functionally unstable ankles. DESIGN AND SETTING: We tested subjects over 4 consecutive days in a climate-controlled athletic training/sports medicine laboratory setting. A single-group time-series design enabled all subjects to serve as their own controls. A different bracing condition was tested on each of those occasions. SUBJECTS: Sixteen subjects (8 men, 8 women; age = 21.6 +/- 1.7 years; mass = 73.5 +/- 15.0 kg; height = 172.9 +/- 8.8 cm) with unilateral functional ankle instability participated in this study. MEASUREMENTS: Kinesthetic threshold-to-detection of passive motion (TTDPM) measurements were obtained during passive inversion and eversion movements (0.5 degrees.s(-1)) under 4 different bracing or taping conditions (unbraced, Swede-O Ankle Lok, Aircast Air-Stirrup, and tape). RESULTS: We analyzed the data using a 3-factor analysis of variance with repeated measures on the ankle and motion factors. Threshold-to-detection of passive motion scores in the unbraced condition were significantly better than the TTDPM scores in any of the other 3 test conditions. No significant differences were seen in TTDPM scores between the 2 ankles under any of the 4 conditions. CONCLUSIONS: Threshold-to-detection of passive motion scores did not differ in uninjured ankles and those with functional instability; however, bracing with either the Ankle Lok or Air-Stirrup decreased the ability to detect passive motion when compared with the no-tape (unbraced) condition. Further research is needed to determine the exact contributions of taping and bracing on ankle joint kinesthesia.

Chronic Ankle Instability Does Not Affect Lower Extremity Functional Performance

OBJECTIVE: To determine if functional performance is impaired in individuals with self-reported chronic ankle instability. DESIGN AND SETTING: We used a between-groups design to assess 3 functional variables. All data were collected at a Division III college and a military academy. Before testing, all subjects performed a 5-minute warm-up, followed by a series of stretches for the lower extremity muscles. Subjects then performed cocontraction, shuttle run, and agility hop tests in a counterbalanced fashion. Three trials for each functional test were completed and averaged for analysis. SUBJECTS: Twenty men with a history of at least 1 significant ankle sprain and episodes of at least 1 repeated ankle injury or feelings of instability or "giving way" were compared with 20 men with no prior history of ankle injury. Subjects were matched by age, height, weight, and activity level. MEASUREMENTS: Time to completion was measured in seconds for the cocontraction and the shuttle run tests. The agility hop test was measured on an error point scale. RESULTS: Using 3 separate, independent, 2-tailed t tests, we found no significant difference between groups for the cocontraction (P =.452), shuttle run (P =.680), or agility hop (P =.902) tests. CONCLUSIONS: Chronic ankle instability is a subjectively reported phenomenon defined as the tendency to "give way" during normal activity. Although athletes commonly complain of subjective symptoms associated with chronic ankle instability, our findings suggest that these symptoms do not negatively influence actual functional performance. Future researchers should evaluate other, more demanding functional-performance tests to further substantiate these findings.

Rehabilitation of the Ankle After Acute Sprain or Chronic Instability

OBJECTIVE: To outline rehabilitation concepts that are applicable to acute and chronic injury of the ankle, to provide evidence for current techniques used in the rehabilitation of the ankle, and to describe a functional rehabilitation program that progresses from basic to advanced, while taking into consideration empirical data from the literature and clinical practice. BACKGROUND: Important considerations in the rehabilitation of ankle injuries include controlling the acute inflammatory process, regaining full ankle range of motion, increasing muscle strength and power, and improving proprioceptive abilities. These goals can be achieved through various modalities, flexibility exercises, and progressive strength- and balance-training exercises. In this article, we discuss the deleterious effects of ankle injury on ankle-joint proprioception and muscular strength and how these variables can be quantifiably measured to follow progress through a rehabilitation program. Evidence to support the effectiveness of applying orthotics and ankle braces during the acute and subacute phases of ankle rehabilitation is provided, along with recommendations for functional rehabilitation of ankle injuries, including a structured progression of exercises. RECOMMENDATIONS: Early functional rehabilitation of the ankle should include range-of-motion exercises and isometric and isotonic strength-training exercises. In the intermediate stage of rehabilitation, a progression of proprioception-training exercises should be incorporated. Advanced rehabilitation should focus on sport-specific activities to prepare the athlete for return to competition. Although it is important to individualize each rehabilitation program, this well-structured template for ankle rehabilitation can be adapted as needed.

The role of the sensorimotor system in the athletic shoulder

OBJECTIVE

To discuss the role of the sensorimotor system as it relates to functional stability, joint injury, and muscle fatigue of the athletic shoulder and to provide clinicians with the necessary tools for restoring functional stability to the athletic shoulder after injury.

DATA SOURCES

We searched MEDLINE, SPORT Discus, and CINAHL from 1965 through 1999 using the key words "proprioception," "neuromuscular control," "shoulder rehabilitation," and "shoulder stability."

DATA SYNTHESIS

Shoulder functional stability results from an interaction between static and dynamic stabilizers at the shoulder. This interaction is mediated by the sensorimotor system. After joint injury or fatigue, proprioceptive deficits have been demonstrated, and neuromuscular control has been altered. To restore stability after injury, deficits in both mechanical stability and proprioception and neuromuscular control must be addressed. A functional rehabilitation program addressing awareness of proprioception, restoration of dynamic stability, facilitation of preparatory and reactive muscle activation, and implementation of functional activities is vital for returning an athlete to competition.

CONCLUSIONS/RECOMMENDATIONS

After capsuloligamentous injury to the shoulder joint, decreased proprioceptive input to the central nervous system results in decreased neuromuscular control. The compounding effects of mechanical instability and neuromuscular deficits create an unstable shoulder joint. Clinicians should not only address the mechanical instability that results from joint injury but also implement both traditional and functional rehabilitation to return an athlete to competition.

Effects of muscular fatigue on knee joint laxity and neuromuscular characteristics of male and female athletes

OBJECTIVE

To elucidate the effects of muscular fatigue on knee joint laxity and the neuromuscular characteristics of male and female athletes. We were particularly interested in determining whether such effects would be more pronounced in female athletes than in males participating in the same sport.

DESIGN AND SETTING

Subjects were assessed on 4 dependent variables during a rested and an isokinetically induced muscular fatigue state. We ensured that posttesting measurements were obtained in the fatigued state by testing only 2 dependent variables after each exercise bout.

SUBJECTS

We recruited male (n = 17) and female (n = 17) subjects from a population of healthy collegiate basketball and soccer players.

MEASUREMENTS

MEASURED DEPENDENT VARIABLES WERE AS FOLLOWS: anterior tibial translation, kinesthesia determined by assessing the threshold to detection of passive motion moving into knee flexion and extension; lower extremity balance ability quantified through a stability index value; and the electromyography-measured muscle activity of 6 knee-stabilizing muscles.

RESULTS

In response to muscular fatigue, subjects demonstrated an overall decrease in the ability to detect joint motion moving into the direction of extension, an increase in the onset of contraction time for the medial hamstring and lateral gastrocnemius muscles, and an increase in the first contraction area of the vastus medialis and vastus lateralis muscles. Additionally, the increase in area of the vastus lateralis was greater for the males compared with the females.

CONCLUSIONS

Our results suggest that both male and female athletes exhibit decrements in proprioceptive ability and alterations in muscular activity subsequent to muscular fatigue.

Examination of balance measures produced by the biodex stability system

OBJECTIVE

Our purpose was to establish normal patterns and relationships of stability using the Biodex Stability System.

DESIGN AND SETTING

The design of this study used both nonexperimental and quasi-experimental methods. All testing was performed in a university sports medicine laboratory.

SUBJECTS

Nineteen healthy subjects (8 males, 11 females, age = 24.4 +/- 4.2 years; wt = 70.5 +/- 20 kg; ht = 171.2 +/- 11.7 cm) with no history of lower extremity injury participated in this study.

MEASUREMENTS

For data analysis, the medial/lateral stability index (MLSI), anterior/posterior stability index (APSI), overall stability index (OSI), and time-in-balance scores were recorded.

RESULTS

Multiple regression revealed that APSI and MLSI significantly contributed to the OSI, with the APSI accounting for 95% of the OSI variance. Additionally, the percentage of time spent between 0 degrees and 5 degrees from level was significantly greater than the time spent between 6 degrees and 10 degrees , 11 degrees and 15 degrees , and 16 degrees and 20 degrees . Furthermore, the percentage of time spent between 6 degrees and 10 degrees was significantly greater than the time spent between 16 degrees and 20 degrees .

CONCLUSIONS

These data suggest that uninjured individuals spent the majority of the time balanced within 0 degrees to 5 degrees from level and progressively less time at greater angles. Additionally, the data suggest that the OSI is very closely related to the APSI and receives a relatively small contribution from the MLSI. Because of this small contribution, if the clinician is interested in both anterior-posterior and medial-lateral motions, it may be best to use the MLSI and APSI separately rather than the OSI.

Effects of strength training on strength development and joint position sense in functionally unstable ankles

OBJECTIVE

To examine the effects of ankle-strengthening exercises on joint position sense and strength development in subjects with functionally unstable ankles.

DESIGN AND SETTING

Subjects were randomly assigned to a training or control group. The training group participated in a 6-week strength-training protocol using rubber tubing 3 times a week throughout the training period. The control group did not participate in the strength-training protocol.

SUBJECTS

Twenty healthy college students (10 females, 10 males, age = 20.6 +/- 2.23 years; ht = 176.40 +/- 7.14 cm; wt = 74.18 +/- 10.17 kg) with a history of functional ankle instability volunteered to participate in this study.

MEASUREMENTS

We pretested and posttested dorsiflexor and evertor isometric strength with a handheld dynamometer and collected joint position sense (JPS) data at 20 degrees for inversion and plantar flexion and at 10 degrees for eversion and dorsiflexion.

RESULTS

Statistical tests for strength and JPS revealed significant group-by-time interactions for dorsiflexion strength, eversion strength, inversion JPS, and plantar flexion JPS. Simple main-effects testing revealed improvements in training group strength and JPS at posttesting. There were no significant effects for eversion JPS, but the group main effect for dorsiflexion JPS was significant, with the experimental group having better scores than the control group.

CONCLUSIONS

Ankle-strengthening exercises improved strength, inversion JPS, dorsiflexion JPS, and plantar flexion JPS in subjects with functionally unstable ankles.

Open and closed kinetic chain exercises improve shoulder joint reposition sense equally in healthy subjects

OBJECTIVE

To compare the effects of open and closed kinetic chain exercise on shoulder joint reposition sense.

DESIGN AND SETTING

Subjects with no previous upper extremity injury participated in a 6-week exercise program consisting of 3 sessions per week.

SUBJECTS

Thirty-nine healthy male military cadets: 13 each in the open, closed, and control groups.

MEASUREMENTS

Each subject was pretested and posttested for both active and passive joint reposition sense at 30 degrees external rotation, 30 degrees internal rotation, and 10 degrees from full external rotation.

RESULTS

The open and closed kinetic chain groups de- creased in reposition sense error scores in comparison with the control group, but no difference was found between the 2 training groups.

CONCLUSION

Our findings suggest that shoulder joint reposition sense can be enhanced with training in healthy subjects. Also, open and closed kinetic chain exercises appear to be equally effective in improving shoulder joint reposition sense.

Anthropometric and performance measures for high school basketball players

OBJECTIVE

To determine possible anthropometric and performance sex differences in a population of high school basketball players.

DESIGN AND SETTING

Measurements were collected during the first week of basketball practice before the 1995-1996 season. Varsity basketball players from 4 high schools were tested on a battery of measures chosen to detect possible anthropometric and performance sex differences.

SUBJECTS

Fifty-four female and sixty-one male subjects, from varsity basketball teams at high schools enrolled in the athletic training outreach program at the University of Wisconsin Hospital Sports Medicine Center in Madison, WI, volunteered to take part in this study.

MEASUREMENTS

We took anthropometric measurements on each of the 115 subjects. These included height, weight, body composition, ankle range of motion, and medial longitudinal arch type in weightbearing. Performance measures included the vertical jump, 22.86-m (25-yd) shuttle run, 18.29-m (20-yd) sprint, and single-limb balance time.

RESULTS

We compared anthropometric and performance characteristics using a 2-sample t test. The only exception to this was for medial longitudinal arch type, where the 2 groups were compared using a 2-tailed Fisher's exact test. The male subjects were significantly taller and heavier, while the females had a significantly higher percentage of body fat. There were no significant differences found for ankle plantar flexion and dorsiflexion, but the females had significantly more inversion and eversion range of motion. Analysis of medial longitudinal arch type found females to have a higher percentage of pronated arches and males to have a higher percentage of supinated arches. Performance testing revealed that the males were able to jump significantly higher and run the 22.86-m (25-yard) shuttle run and 18.29-m (20-yard) sprint significantly faster than the female subjects. There was no significant difference between the groups for single-limb balance time.

CONCLUSIONS

We found significant anthropometric and performance sex differences in a cohort of high school basketball players. Further study of these measures is necessary to determine if these differences can predict the risk for ankle injuries in this particular population.

The effects of selected ankle appliances on postural control

OBJECTIVE

Although ankle braces supposedly protect the ankle by providing mechanical support of the joint and enhancing proprioceptive input, their proprioceptive effects are unclear. Measuring the center of pressure during posture provides a reasonably well-controlled evaluation of proprioceptive input at the ankle. We, therefore, compared the changes in the center of pressure resulting from wearing ankle braces and wearing no brace (control).

DESIGN AND SETTING

Center-of-pressure variables were measured during a one-legged modified Romberg test with six variations. The six test conditions systematically altered the three sensory modalities that control posture: visual input, vestibular input, and proprioceptive input. Subjects performed three 16-second trials of each Romberg variation for each brace condition.

SUBJECTS

Twenty-four male volunteers (age = 18 to 26 yr) with no history of ankle injuries in the past 5 years and no difficulty with balance.

MEASUREMENTS

Center of pressure, transmitted through the bottom of the foot, was monitored during each trial and transformed into total distance traveled, anterior-posterior (AP) position, and medial-lateral (ML) position.

RESULTS

Average AP and ML center-of-pressure positions were increased only during brace wearing when all sensory modalities were functioning normally (control condition). Total center-of-pressure distance was the same for all three brace conditions.

CONCLUSIONS

Our results do not support or refute the concept that bracing enhances proprioception. The fact that subjects relocated their center of pressure only during the control condition is perplexing. If braces were to enhance proprioception, one would expect to see lower average ML and average AP center-of-pressure values when comparing the braced with the unbraced conditions. Alternatively, the relocated position may represent a more stable position resulting from enhanced proprioception.

Effect of unilateral functional instability of the ankle on postural sway and inversion and eversion strength

OBJECTIVE

The purpose of this study was to determine if individuals with unilateral functional ankle instability had decreased ability to maintain postural sway, as well as decreased isokinetic eccentric strength of ankle evertors and invertors.

DESIGN AND SETTING

SUBJECTS WITH NO PREVIOUS HISTORY OF ANKLE INJURY WERE COMPARED WITH SUBJECTS WITH FUNCTIONAL ANKLE INSTABILITY ON THE FOLLOWING TESTS: isokinetic eccentric inversion and eversion strength and measures of single-limb postural sway.

SUBJECTS

EIGHTEEN SUBJECTS PARTICIPATED IN THIS STUDY: 9 subjects in the functional instability (FI) group (age = 22.89 +/- 3.18 yr, ht = 181 +/- 6.0 cm, wt = 80.25 +/- 12.2 kg) and 9 noninjured (NI) controls (age = 26.22 +/- 2.34 yr, ht = 170 +/- 10.0 cm, wt = 65.08 +/- 12.03 kg).

MEASUREMENTS

Subjects performed postural sway assessment on a balance system under static and dynamic conditions. Ankle inversion and eversion eccentric strength were evaluated at 90 degrees /sec using an isokinetic dynamometer. Additionally, we assessed the degree of mechanical instability in the FI group with a series of stress radiographs.

RESULTS

No significant differences in single-limb postural sway measures or in eversion strength between limbs in the FI group or between groups were found. A significant group-by-limb interaction was present in inversion peak torque; however, post hoc testing revealed the only difference to be between the dominant and nondominant limbs of the NI group.

CONCLUSIONS

Postural sway and inversion and eversion eccentric peak torque are not affected by functional instability of the ankle. Alternate methods of postural sway assessment and ankle strength measurement are discussed as possible areas for future study.

Proprioceptive neuromuscular facilitation techniques in sports medicine: a reassessment

OBJECTIVE

The purpose of this survey was for comparison with a similar 1981 survey to determine if proprioceptive neuromuscular facilitation (PNF) techniques are being implemented in the same manner today.

DESIGN AND SETTING

The survey was made available at the 1993 NATA Clinical Symposium.

SUBJECTS

The subjects were 131 athletic trainers representing all major national athletic conferences who attended the 1993 NATA Clinical Symposium and who stated that they used PNF exercise in their practice.

MEASUREMENTS

The survey consisted of 15 questions dealing with academic preparation, years of practice, scope and method of preparation in PNF, application of nine PNF techniques to various joints and regions of the body, and the most successful use of PNF techniques.

RESULTS

PNF techniques are most frequently applied during rehabilitation of the knee, shoulder, and hip, similar to 1981 except that the use of these techniques during ankle rehabilitation has increased. In both studies, the most frequently used techniques were contract-relax and hold-relax. Two techniques not surveyed in 1981, contract-relax-contract and hold-relax-contract, are becoming techniques of choice for elbow, wrist, hip, and knee rehabilitation. The use of PNF techniques in the muscle re-education phase of rehabilitation is an application identified in this survey not cited by athletic trainers in the 1981 survey.

CONCLUSIONS

Proprioceptive and kinesthetic deficits are known to occur after certain types of injuries, and the use of PNF techniques to correct these problems is a natural application A contemporary trend in exercise rehabilitation is multiplanar exercises, which are typified by PNF techniques.

Neurotrophin-3 administration attenuates deficits of pyridoxine-induced large-fiber sensory neuropathy

Chronic treatment of adult rats for 2-3 weeks with high doses of pyridoxine (vitamin B6) produced a profound proprioceptive loss, similar to that found in humans overdosed with this vitamin or treated with the chemotherapeutic agent cisplatin. Pyridoxine toxicity was manifest as deficits in simple and precise locomotion and sensory nerve function and as degeneration of large-diameter/large-fiber spinal sensory neurons. As assessed quantitatively in a beam-walking task and by EMG recording of H waves evoked by peripheral nerve stimulation, coadministration of the neurotrophic factor neurotrophin-3 (NT-3; 5-20 mg . kg-1 . d-1, s.c.) during chronic pyridoxine treatment largely attenuated the behavioral and electrophysiological sequelae associated with pyridoxine toxicity. Furthermore, NT-3 administration prevented degeneration of sensory fibers in the dorsal column of the spinal cord. These data are consistent with the evidence that NT-3 is a target-derived neurotrophic factor for muscle sensory afferents and suggest that pharmacological doses of NT-3 may be beneficial in the treatment of large-fiber sensory neuropathies.

Proprioceptive control of interjoint coordination

This paper reviews a series of experiments comparing intact controls with functionally deafferented patients to determine the role of proprioception in controlling dynamic interactions between limb segments during movement. We examine the control of hand path in a planar movement-reversal task and in a familiar three-dimensional gesture with similar biomechanical characteristics. In the planar task subjects had to move their hand out and back along a series of straight-line segments in the horizontal plane without visual feedback. The lengths and directions of the target line segments were chosen to require different amounts of shoulder motion while requiring the same elbow excursion. In controls, hand paths were, as required, straight with sharp bends at the outermost point. In patients, however, distinctive errors appeared at movement reversals, consisting of widened hand paths resulting from desynchronization in the reversals of elbow and shoulder motions. These errors reflected an inability to program elbow muscle contractions in accord with interaction torques produced at the elbow by variations in acceleration of the shoulder. The reversal errors were substantially reduced after patients had practiced for a few trials while visually monitoring movements of their arm. The improvement was not limited to the direction where they had practiced with vision, but also extended to other directions in which the elbow torques were different. This suggests that practice with vision of the arm served to improve the general rules that subjects used to plan movement, rather than simply improving the performance of a specific response. Similar to their performance on the planar task, the patients made errors in interjoint coordination during unconstrained three-dimensional gestures with movement reversals. We conclude (i) that both the planning and the learning of movement required an internal model of the dynamic properties of the limb that takes account of interaction torques acting at different joints; (ii) that this internal model is normally established and updated using proprioceptive information; but (iii) that when proprioception is lacking, vision of the limb in motion partially substitutes for proprioception.