Rod A. Harter

Validity and Reliability of Limits-of-Stability Testing: A Comparison of 2 Postural Stability Evaluation Devices

CONTEXT A lack of published comparisons between measures from commercially available computerized posturography devices and the outcome measures used to define the limits of stability (LOS) makes meaningful interpretation of dynamic postural stability measures difficult. OBJECTIVES To compare postural stability measures between and within devices to establish concurrent and construct validity and to determine test-retest reliability for LOS measures generated by the NeuroCom Smart Balance Master and the Biodex Balance System. DESIGN Cross-sectional study. SETTING Controlled research laboratory. PATIENTS OR OTHER PARTICIPANTS A total of 23 healthy participants with no vestibular or visual disabilities or lower limb impairments. INTERVENTION(S) The LOS were assessed during 2 laboratory test sessions 1 week apart. MAIN OUTCOME MEASURE(S) Three NeuroCom LOS variables (directional control, endpoint excursion, and movement velocity) and 2 Biodex LOS variables (directional control, test duration). RESULTS Test-retest reliability ranged from high to low across the 5 LOS measures (intraclass correlation coefficient [2,k] = 0.82 to 0.48). Pearson correlations revealed 4 significant relationships (P < .05) between and within the 2 computerized posturography devices (r = 0.42 to -0.65). CONCLUSIONS Based on the wide range of intraclass correlation values we observed for the NeuroCom measures, clinicians and researchers alike should establish the reliability of LOS testing for their own clinics and laboratories. The low to moderate reliability outcomes observed for the Biodex measures were not of sufficient magnitude for us to recommend using the LOS measures from this system as the gold standard. The moderate Pearson interclass correlations we observed suggest that the Biodex and NeuroCom postural stability systems provided unique information. In this study of healthy participants, the concurrent and construct validity of the Biodex and NeuroCom LOS tests were not definitively established. We recommend that this study be repeated with a clinical population to further explore the matter.

The Interrelationships Among Sex Hormone Concentrations, Motoneuron Excitability, and Anterior Tibial Displacement in Women and Men

CONTEXT Sex hormone fluctuations have been implicated as a contributing factor to the high rates of noncontact injury to the anterior cruciate ligament in females. OBJECTIVE To determine the strength of the relationships among variables of sex hormone concentrations, motoneuron excitability, and anterior tibial displacement (ATD) in women and men and to determine if these relationships differ between the sexes. DESIGN Cohort study. SETTING Sports medicine laboratory. PATIENTS OR OTHER PARTICIPANTS Twenty-eight regularly menstruating women (age = 22.4 +/- 3.4 years) and 15 men (age = 22.3 +/- 3.7 years) participated in the study. INTERVENTION(S) Fluctuations in sex hormones were determined for the participants. Female participants were tested every other day of their menstrual cycles, whereas male participants were tested every fourth day during the 28-day period. MAIN OUTCOME MEASURE(S) We measured Hoffmann reflexes (maximum Hoffmann reflex [H(max)] to maximum M-wave [M(max)] ratio in the soleus), ATD under a 134-N load, and saliva concentrations of estrogen and progesterone. The independent variable was sex. Pearson product moment correlation coefficients were calculated for each participant by pairing measurements made on the same day. Two-tailed independent-samples t tests were used to determine the difference between the male and female correlations for each variable. RESULTS Over the course of the study, the relationships between H(max)ratioM(max) and estrogen, H(max)ratioM(max) and progesterone, ATD and estrogen, and ATD and progesterone were not different between the sexes. However, the relationship between ATD and progesterone was different between the sexes (P = .036). CONCLUSIONS The observed correlations did not support our hypothesis that the relationships between sex hormone levels and reflex activity or between sex hormone levels and ATD would be different for women compared with men. If sex hormone concentrations significantly contribute to anterior cruciate ligament ruptures because of changes in laxity or in motoneuron excitability, their mechanism of action is likely multifactorial and complex.

Shoulder joint position sense after thermal, open, and arthroscopic capsulorrhaphy for recurrent anterior instability.

Identifying the optimal surgical treatment for recurrent, anterior glenohumeral instability remains a challenge. Our purpose was to compare shoulder joint position sense among open, arthroscopic, and thermal capsulorrhaphy patients after repair of recurrent anterior instability and to compare these patients to healthy, control subjects. Sixty-seven adults (45 post-surgical patients, 22 controls) volunteered to participate in the study. We evaluated both the surgically repaired and contralateral shoulders of 45 capsulorrhaphy patients (28 men, 17 women) and compared their results with the normal bilateral shoulders of 22 age-matched controls (11 men, 11 women). Accuracy of joint position sense was quantified via passive reproduction of target positions set at 60% and 90% of each subjects maximum passive external rotation (ER(max)). We observed no significant differences in joint position sense between the repaired shoulders and the contralateral normal shoulders of all groups of capsulorrhaphy patients. Open and thermal capsulorrhaphy patients demonstrated significantly better (P </= .05) repaired-limb joint position sense (5.4 degrees +/- 3.3 degrees and 5.6 degrees +/- 3.3 degrees , respectively) than arthroscopic patients (9.2 degrees +/- 3.7 degrees ) and control subjects (8.1 degrees +/- 4.0 degrees ). These results indicate that joint position sense was similar in the repaired shoulders and uninjured shoulders of each group of capsulorrhaphy patients. The mechanism responsible for heightened position sense in open and thermal capsulorrhaphy patients is unknown, but may result from capsular retensioning and muscular scarring. The long-term implications of this outcome deserve further attention.

Intersession Reliability of Hoffmann Reflex Gain and Presynaptic Inhibition in the Human Soleus Muscle

UNLABELLED Hayes BT, Hicks-Little CA, Harter RA, Widrick JJ, Hoffman MA. Intersession reliability of Hoffmann reflex gain and presynaptic inhibition in the human soleus muscle. OBJECTIVE To determine the day-to-day reliability of Hoffmann reflex (H-reflex) gain and presynaptic inhibition of spinal reflexes in the human soleus muscle. DESIGN Controlled trial. SETTING Research laboratory. PARTICIPANTS Volunteers (N=30; mean +/- SD age, 23.4+/-3.9y; height, 175.64+/-10.87cm; mass, 84.50+/-24.18kg) with no history of lower extremity pathology and/or injury participated. INTERVENTIONS Subjects lay prone with the head, shoulders, arms, and hips supported in a static position by a massage body pillow and the ankle positioned at 90 degrees . Recording electrodes were placed over the soleus and tibialis anterior muscle bellies, and the stimulating electrodes were positioned over the tibial nerve in the popliteal space and the common peroneal nerve near the fibular head. MAIN OUTCOME MEASURES The H-reflex and motor wave recruitment curves were then measured and recorded. Presynaptic inhibition was also assessed in the soleus muscle, and a conditioning stimulation of the common peroneal nerve (1 x motor threshold = motor threshold) was used prior to soleus H-reflex measurement. Two testing sessions took place between 2 and 7 days, and each session occurred at the same time of day. RESULTS Assessments of H-reflex gain and presynaptic inhibition yielded test-retest reliability of R equal to . 95 and .91, respectively. CONCLUSIONS Measures of presynaptic inhibition and H-reflex gain (H slope/M slope) in the human soleus muscle are consistent and reliable day to day.