Dynamic postural control but not mechanical stability differs among those with and without chronic ankle instability.

The purpose of this investigation was to compare dynamic postural control and mechanical ankle stability among patients with and without chronic ankle instability (CAI) and controls. Seventy-two subjects were divided equally into three groups: uninjured controls, people with previous ankle injury but without CAI, and people with CAI. Subjects completed a single-leg hop-stabilization task, and then had an anterior drawer test and lateral ankle radiograph performed bilaterally. The dynamic postural stability index was calculated from the ground reaction forces of the single-leg hop-stabilization task. Ankle joint stiffness (N/m) was measured with an instrumented arthrometer during the anterior drawer test, and fibula position was assessed from the radiographic image. Patients with previous ankle injuries but without CAI demonstrated higher frontal plane dynamic postural stability scores than both the uninjured control and CAI groups (P<0.01). Patients with and without CAI had significantly higher sagittal plane dynamic postural stability scores (P<0.01) and increased ankle joint stiffness (P=0.045) relative to the control group. The increased frontal plane dynamic postural control may represent a component of a coping mechanism that limits recurrent sprains and the development of CAI. Mechanical stability alterations are speculated to result from the initial ankle trauma.

Failed jump landing trials: deficits in neuromuscular control.

The purpose of this investigation was to compare neuromuscular control variables during successful and failed jump landings in multiple directions (sagittal, diagonal, and lateral). All data were collected during a single leg hop stabilization maneuver, which required subjects to stand 70 cm from the center of a force plate, jump off both legs, touch a designated marker placed at a height equivalent to 50% of their maximum vertical jump, and land on a single leg for all directions. Twenty-six subjects [10 males (22+/-3.9 years of age, 70.9+/-7.6 kg, and 176.8+/-0.5 cm) and 16 females (20.6+/-0.5 years of age, 65.6+/-9.1 kg, and 166.4+/-5.9 cm)] volunteered to participate in this investigation. Muscle activation times, average preparatory, and reactive electromyographic (EMG) amplitudes were calculated for the vastus medialis, semi-membranosis, lateral gastrocnemius, and tibialis anterior. EMG data revealed that successful jump landing trials had earlier activation times and higher preparatory and reactive EMG amplitudes. There was no difference for EMG activation times or amplitudes among directions. The results indicate neuromuscular control differences between successful and failed trials because of earlier muscle onset and greater amplitude. The results also suggest that in a healthy population, the direction of the jump protocol will not affect lower extremity EMG characteristics.

Shoulder proprioception in baseball pitchers.

We examined proprioceptive differences between the dominant and nondominant shoulders of 21 collegiate baseball pitchers without a history of shoulder instability or surgery. A proprioceptive testing device was used to measure kinesthesia and joint position sense. Joint position sense was significantly (P =.05) more accurate in the nondominant shoulder than in the dominant shoulder when starting at 75% of maximal external rotation and moving into internal rotation. There were no significant differences for proprioception in the other measured positions or with kinesthesia testing. Six pitchers with recent shoulder pain had a significant (P =.04) kinesthetic deficit in the symptomatic dominant shoulder compared with the asymptomatic shoulder, as measured in neutral rotation moving into internal rotation. The net effect of training, exercise-induced laxity, and increased external rotation in baseball pitchers does not affect proprioception, although shoulder pain, possibly due to rotator cuff inflammation or tendinitis, is associated with reduced kinesthetic sensation.

In vivo quantification of capsular end-point in the nonimpaired glenohumeral joint using an instrumented measurement system.

STUDY DESIGN: Single-group factorial. OBJECTIVES: Quantify glenohumeral joint translations as a function of force using an instrumented measurement system. Our first specific aim was to compare the magnitude of force (N) required to reach capsular end-point between the anterior, posterior, and inferior directions. Our second specific aim was to compare the magnitude of translation (mm) at capsular end-point between the anterior, posterior, and inferior directions. BACKGROUND: Manual force-displacement techniques are subjective in nature, and the clinician must rely on "feel" to determine capsular end-point. Several investigators have attempted to utilize more objective measures at the glenohumeral joint, however none have quantified the force or displacements necessary to achieve a true capsular end-point. METHODS AND MEASURES: An arthrometric technique was used to measure anterior, posterior, and inferior glenohumeral translations in 20 nonimpaired shoulders (11 women and 9 men with a mean age of 20.9 +/- 3.6 years). RESULTS: The magnitude of applied force required to reach capsular end-point was significantly different between directions of translations. Anterior-directed translations required a significantly greater magnitude of applied force to reach capsular end-point than inferior-directed translations. The magnitude of translation was not significantly different between directions at capsular end-point. CONCLUSIONS: Applied forces in the range of 181 to 203 N are necessary to reach capsular end-point in subjects with nonimpaired shoulders. Anterior translation required significantly higher forces (203.1 +/- 13.1 N) to reach capsular end-point than inferior translation (181.4 +/- 31.9 N).

Instrumented measurement of glenohumeral joint laxity and its relationship to passive range of motion and generalized joint laxity.

The purpose of this study was to objectively characterize in vivo glenohumeral joint laxity using an instrumented shoulder arthrometer. Secondary objectives were to examine the relationship of glenohumeral joint laxity with passive range of motion and generalized joint laxity. Fifty-one recreational athletes with no history of shoulder injury or long-term participation in overhead sports participated in this study. Anterior and posterior laxity data were obtained at displacement forces of 67, 89, 111, and 134 N. Bilateral passive shoulder range of motion measures were obtained, and a modified Beighton Mobility Score was used to quantify generalized joint laxity. There were no significant differences in glenohumeral joint laxity between the right and left shoulders (P values = 0.14 to 0.73). No significant differences in laxity were seen between directions (F(1,400) = 1.35, P = 0.25). However, significant differences were observed between force levels (F(3,400) = 27.17, P < 0.0001). No moderate or stronger correlations between laxity, passive range of motion, and generalized joint laxity were seen. These data confirm the presence of a wide spectrum of symmetric laxity in subjects that fails to correlate strongly with passive range of motion or generalized joint laxity.

Instrumented measurement of glenohumeral joint laxity: reliability and normative data.

This study assessed shoulder laxity using an instrumented arthrometer. We compared anterior and posterior translations at various force levels to determine the reliability of our measurement technique and to provide normative data in healthy shoulders. Fifty shoulders were assessed for glenohumeral joint laxity in two directions (anterior and posterior) and at four force levels (67, 89, 111, and 134 N). The dependent measure was joint displacement. Laxity values were widely, yet normally, distributed in our group of healthy shoulders. Intraclass correlation coefficients revealed excellent between-trial reliability (0.92) and fair between-session (0.73) and between-examiner (0.74) reliability. The average standard error of measurement between trials (0.56 mm), sessions (1.5 mm), and examiners (1.7 mm) demonstrated an unprecedentedly high degree of precision for quantifying glenohumeral joint laxity. Paired t tests revealed no significant laxity differences between sides (P>0.05), indicating bilateral symmetry. A 2 (direction) x 4 (force) analysis of variance revealed significant differences in laxity between directions (P<0.0001) and force levels (P<0.0001). Our results show that our instrumented technique for quantifying glenohumeral joint laxity is precise and reproducible. Posterior translation was significantly greater than anterior, and a significant increase in translation was observed between increasing levels of force.

Patterns of glenohumeral joint laxity and stiffness in healthy men and women.

PURPOSE: The purpose of this study was to identify gender-related differences in glenohumeral (GH) joint laxity, stiffness, and generalized joint hypermobility in healthy men and women. METHODS: Fifty-one healthy men and women were tested for generalized joint hypermobility, and anterior-posterior (AP) joint laxity and stiffness using a single-group factorial design. RESULTS: Women exhibited significantly more anterior joint laxity (men 8.3 +/- 2.2 mm vs women 11.4 +/- 2.8 mm, P < 0.001) and less anterior joint stiffness (men 20.5 +/- 5.0 N x mm(-1) vs women 16.3 +/- 4.2 N x mm(-1), P < 0.01) than men. Men had significantly more posterior joint laxity than anterior (Ant 8.3 +/- 2.2 mm vs Post 9.6 +/- 2.9 mm; P < 0.001), and women also had significantly less anterior joint stiffness than posterior [Ant 16.3 +/- 4.2 N x mm(-1) vs Post 22.1 +/- 6.9 N x mm(-1); P < 0.01], Women also demonstrated significantly more generalized joint hypermobility than men (men 1.0 +/- 1.7 vs women 2.9 +/- 2.1; P = 0.02). CONCLUSIONS: Our findings may indicate a possible increased risk for instability in women, especially those participating in sports that require repetitive overhead-throwing motion. Future investigations should seek to determine the contribution of increased GH joint laxity and decreased joint stiffness to various injury states and examine these variables in other populations such as overhead-throwing athletes.

The importance of gender on myokinetic deficits before and after microinjury.

PURPOSE: The purpose of this study was to determine the importance of gender on myokinetic deficits before and after muscle microinjury. METHODS: A repeated measures design assessed selected muscle force production characteristics in 20 male and 25 female volunteers. Peak force production (PFP) and the peak rate of force production (PRFP) were assessed before and over a 4-d period after an induced muscle microinjury. RESULTS: ANOVA revealed statistically significant mean (+/-SD) differences between men and women for PFP and PRFP (P < 0.0001). Both genders demonstrated significant between-day differences for PFP (P < 0.016), whereas only men demonstrated significant between-day differences for PRFP (P < 0.016). CONCLUSIONS: Our results reveal that muscle force generating capabilities of physically active men exceed that of women both before and after microinjury. Myokinetic deficits were most pronounced acutely, between 24 and 48 h postinjury, followed by a near complete recovery at day 4 (96 h postinjury). Both genders suffered acute and residual deficits for PFP, whereas only men showed significant acute deficits for PRFP. We recommend that athletes, both male and female, refrain from strenuous exercise at least 48 h postinjury, or until force-generating capabilities normalize. More research needs to be conducted to substantiate these findings.

Proprioception in the posterior cruciate ligament deficient knee.

This study was undertaken to evaluate knee proprioception in patients with isolated unilateral posterior cruciate ligament (PCL) injuries. Eighteen subjects with isolated PCL tears were studied 1-234 months after injury. The threshold to detect passive motion (TTDPM) was used to evaluate kinesthesia and the ability to passively reproduce passive positioning (RPP) to test joint position sense. Two starting positions were tested in all knees: 45 degrees (middle range) and 110 degrees (end range) to evaluate knee proprioception when the PCL is under different amounts of tension. TTDPM and RPP were tested as the knee moved into flexion and extension from both starting positions. A statistically significant reduction in TTDPM was identified in PCL-injured knees tested from the 45 degrees starting position, moving into flexion and extension. RPP was statistically better in the PCL-deficient knee as tested from 110 degrees moving into flexion and extension. No difference was identified in the TTDPM starting at 110 degrees or in RPP with the presented angle at 45 degrees moving into flexion or extension. These subtle but statistically significant findings suggest that proprioceptive mechanoreceptors may play a clinical role in PCL-intact and PCL-deficient patients. Further, it appears that kinesthesia and joint position sense may function through different mechanisms.

Comparison of performance-based and patient-reported measures of function in anterior-cruciate-ligament-deficient individuals.

There is a dearth of reliable and valid instrumentation that measures disability following injury and/or surgery of the knee joint that is responsive to clinically significant changes over time. The purpose of this investigation was to determine whether performance-based or patient-reported measures of function are more effective in estimating disability in individuals with an anterior-cruciate-ligament (ACL)-deficient knee. Subjective rating of knee function was used as the criterion measure for disability, and selected performance-based and patient-reported measures were used as estimation variables. Twenty-nine individuals with an ACL-deficient knee participated in this investigation. Step-wise regression analysis revealed that the Cincinnati Knee Scale, Lysholm Knee Scale, and hop index were the most effective estimates of disability. The results demonstrate that patient-reported measures are more related to the patient's level of disability in individuals with an ACL-deficient knee. More research is necessary to substantiate these findings.

Flexible magnets are not effective in decreasing pain perception and recovery time after muscle microinjury.

OBJECTIVE: To assess the therapeutic effects of flexible magnets on pain perception, intramuscular swelling, range of motion, and muscular strength in individuals with a muscle microinjury. DESIGN AND SETTING: This experiment was a single-blind, placebo study using a repeated-measures design. Subjects performed an intense exercise protocol to induce a muscle microinjury. After pretreatment measurements were recorded, subjects were randomly assigned to an experimental (magnet), placebo (imitation magnet), or control (no magnet) group. Posttreatment measurements were repeated at 24, 48, and 72 hours. SUBJECTS: Forty-five healthy subjects participated in the study. MEASUREMENTS: Subjects were measured repeatedly for pain perception, upper arm girth, range of motion, and static force production. Four separate univariate analyses of variances were used to reveal statistically significant mean (+/-SD) differences between variables over time. Interaction effects were analyzed using Scheffe post hoc analysis. RESULTS: Analysis of variance revealed no statistically significant (P > .05) mean differences between conditions for any dependent pretreatment and posttreatment measurements. No significant interaction effects were demonstrated between conditions and times. CONCLUSIONS: No significant therapeutic effects on pain control and muscular dysfunction were observed in subjects wearing flexible magnets.

The effects of joint position and direction of joint motion on proprioceptive sensibility in anterior cruciate ligament-deficient athletes.

We studied a group of anterior cruciate ligament-deficient athletes to identify whether joint position and direction of joint motion have a significant effect on proprioception. Twenty-nine anterior cruciate ligament-deficient athletes were tested for their threshold to detect passive motion at both 15 degrees and 45 degrees moving into the directions of both flexion and extension. The single-legged hop test was used to identify function in the deficient limb. Results demonstrated statistically significant deficits in threshold to detect passive motion for the deficient limb at 15 degrees moving into extension. For the deficient limb, threshold to detect passive motion was significantly more sensitive moving into extension than flexion at a starting angle of 15 degrees; at a starting angle of 15 degrees moving into extension threshold was significantly more sensitive than at a starting angle of 45 degrees moving into extension. We conclude that in deficient limbs proprioception is significantly more sensitive in the end ranges of knee extension (15 degrees) and is significantly more sensitive moving into the direction of extension. To effectively restore reflex stabilization of the lower limb we recommend a rehabilitation program emphasizing performance-based, weightbearing, closed kinetic chain exercise for the muscle groups that act on the knee joint.

Knee joint proprioception: a comparison between female intercollegiate gymnasts and controls.

The role of proprioception as a protective mechanism has gained interest in recent years. From the clinical standpoint, several studies have dealt with ways to enhance proprioception following surgery and during rehabilitation. If kinesthesia (ability to detect passive motion) can be enhanced as a consequence of long-term athletic training, such training must be included as a part of the rehabilitation process to protect the patient from reinjury. Consequently, the purpose of this study was to compare the kinesthetic knee pattern between trained gymnasts and healthy nongymnasts. The proprioception testing device (PTD) was used to evaluate knee kinesthesia. From 45 degrees of flexion, the knee was passively extended with the PTD. The device was stopped by the subject when this passive motion was detected. Fifteen healthy college-age female gymnasts (mean age 19.3 years) and 30 normal volunteers (mean age 20.7 years) comprised our study sample. A one-way analysis of variance (ANOVA) was used to compare the mean values of the dominant gymnastic knee to the dominant knee in the control group. Results revealed statistically significant mean differences between the trained gymnastic group and the untrained control group (F1.34(.95) = 7.17, P = 0.011). The results of this study suggest that extensive training has a positive influence on knee kinesthesia in addition to increasing muscle tone. According to the findings of this and other studies, highly trained athletes possess enhanced neurosensory pathways which are speculated to develop as a result of long-term athletic training. Although definite conclusions cannot be made from our investigation, prospective studies can determine the true role of athletic training in proprioceptive patterns.

Proprioception of the shoulder joint in healthy, unstable, and surgically repaired shoulders.

Shoulder proprioception was measured in 90 subjects who were assigned to three experimental groups: group 1 (n = 40), healthy college-age subjects; group 2 (n = 30), patients with anterior instability; and group 3 (n = 20), patients who have had surgical reconstruction. Kinesthesia and joint position sense were measured with a specially designed proprioception testing device. The results revealed no significant differences in proprioception between dominant and nondominont shoulders in group 1 for any test condition. Significant differences (p < 0.05) were revealed between the unstable and uninvolved shoulder for both kinesthesia and joint position sense in group 2. No significant mean differences were revealed between the surgical and contralaterol shoulder in group 3 under any test condition. This series of studies provides evidence that proprioceptive deficits caused by partial deafferentiation result when copsuloligomentous structures are damaged. Reconstructive surgery appears to restore some of these proprioception characteristics.

Muscular and functional performance characteristics of individuals wearing prophylactic knee braces.

The efficacy of prophylactic knee bracing has been refuted with regard to reducing the incidence and/or severity of injuries to the knee joint. This is thought to be a result of the prophylactic knee brace's ineffectiveness in protecting the knee joint from valgus loads. Furthermore, discrepancies exist regarding the prophylactic knee brace's detrimental effect on functional performance. The purpose of this study was to measure the effect of the prophylactic knee brace on selected isokinetic muscular characteristics and forward sprint speed. Twenty physically active, healthy, male college students with no prior history of brace use participated in this study. The subjects were randomly tested both with and without the prophylactic knee brace worn on various performance parameters. The dependent measures assessed included peak torque (PT) and torque acceleration energy (TAE) at 60 and 240 degrees /s. A 40-yard forward sprint was selected to assess sprint speed. A paired t-test analysis revealed mean values which were significantly less for PT at 60 degrees /s (p < .05), 240 degrees /s (p < .01), and TAE at 240 degrees /s (p < .05) with the prophylactic knee brace applied during knee extension. Analysis also revealed slower times for sprint speed (p < .01), while the subjects were wearing the prophylactic knee brace. Muscular strength (PT) and power (TAE) scores were not correlated (p > .05) with sprint speed. This study suggests that wearing the prophylactic knee brace may consequently inhibit muscular and functional performance of the athlete, but that specific population has yet to be studied.