Kathleen A. Swanik

A bilateral comparison of posterior capsule thickness and its correlation with glenohumeral range of motion and scapular upward rotation in collegiate baseball players

HYPOTHESIS We hypothesized that posterior capsule thickness (PCT) would be greater on the dominant arm compared to the non-dominant arm. We also hypothesized that PCT would negatively correlate with glenohumeral internal rotation and scapular upward rotation. In addition, PCT would positively correlate with glenohumeral external rotation. However, currently PCT has not been measured nor have correlations been identified to exist with glenohumeral and scapular motion. Therefore, the purpose of the study was to determine if the posterior capsule was hypertrophied on the dominant arm and to identify if relationships exist with glenohumeral internal rotation (IR), external rotation (ER), and scapular upward rotation (SUR). MATERIALS AND METHODS PCT was measured using a 10-MHz transducer. Glenohumeral IR and ER was measured supine using a digital inclinometer. SUR was measure at 0°, 60°, 90°, and 120° of glenohumeral abduction using a modified digital inclinometer. RESULTS PCT was greater on the dominant compared with the nondominant arm (P = .001). A negative correlation was found between PCT and IR (-0.498, P = .0001). A positive correlation was found between PCT and ER (0.450, P = .002) and between PCT and SUR at 60°, 90°, and 120° of glenohumeral abduction (0.388, P = .006; 0.327, P = .023; 0.304, P = .036, respectively). DISCUSSION This in vivo study demonstrated a hypertrophied posterior capsule and its association with GIRD, ER, and SUR. These observations suggest that PCT does occur on the throwing arm of baseball players and is linked with glenohumeral and scapular alterations. CONCLUSIONS This methodology could be used as a noninvasive screening evaluation for overhead athletes to identify those who may be at risk for shoulder injuries due to excessive capsular thickening.

High-Risk Drinking Characteristics in Collegiate Athletes

Objective: The authors aimed to further describe the relationship of alcohol use by college athletes to variables, such as sport participation, time of year, and level of competition. Participants: There were 720 participants from Divisions I, II, and III who participated in either a team sport or an individual sport. Methods: The authors measured characteristics of alcohol use by college athletes at 9 colleges and universities. Results: Participants reported a high rate of consuming 5 or more drinks per occasion in the past 2 weeks. There were greater percentages of team sport athletes reporting this behavior than athletes of individual sports, and there were significant differences according to level of competition. Conclusions: The college athletes in this study reported high-risk alcohol use at percentages much higher than previously reported. The findings and practical application of the results are discussed.

Glenohumeral rotation and scapular position adaptations after a single high school female sports season.

CONTEXT Anterior instability and impingement are common in overhead athletes and have been associated with decreases in internal rotation (IR) and increases in external rotation (ER) motion. However, the chronology and the effect of different female sports on these conditions have yet to be determined. OBJECTIVE To measure glenohumeral IR and ER rotation, total range of motion, and scapular position in female overhead athletes over a single competitive season. DESIGN Multiple group pretest-posttest study. SETTING High school. PATIENTS OR OTHER PARTICIPANTS Thirty-six female overhead athletes (age = 15.29 +/- 1.18 years, height = 164.16 +/- 7.14 cm, mass = 58.24 +/- 9.54 kg) with no history of shoulder or elbow surgery participating in high school swimming, volleyball, or tennis. INTERVENTION(S) Participants were measured for all dependent variables at preseason and postseason. MAIN OUTCOME MEASURE(S) Participants were measured for glenohumeral IR and ER with the scapula stabilized. Total glenohumeral range of motion was calculated as the sum of IR and ER. Scapular upward rotation was measured at 0 degrees , 60 degrees , 90 degrees , and 120 degrees of glenohumeral abduction in the scapular plane, and scapular protraction was measured at 0 degrees , 45 degrees (hands on hips), and 90 degrees of glenohumeral abduction. RESULTS Internal rotation decreased from preseason to postseason (P = .012). Swimmers had less IR than both volleyball and tennis players (P = .001). External rotation also decreased in the swimmers (P = .001). Overall, preseason to postseason total motion decreased for athletes participating in swimming (P = .001) and tennis (P = .019). For all participants, preseason to postseason scapular protraction at 45 degrees glenohumeral abduction decreased (P = .007). CONCLUSIONS Female overhead athletes demonstrated decreases in IR after only one competitive season. Clinically, our results indicate that overhead athletes should be monitored for motion changes throughout their competitive seasons.

Neuromuscular dynamic restraint in women with anterior cruciate ligament injuries.

The purpose of this study was to identify neuromuscular characteristics related to dynamic restraint in the knee. Observing compensatory changes to these characteristics in women with anterior cruciate ligament injuries provides important information for understanding functional knee stability, injury prevention, and performance. Twelve female subjects with anterior cruciate ligament injuries and 17 female control subjects participated in this study to assess electromyographic activity during landing from a hop and knee perturbation; hamstring muscle stiffness and flexibility; and isokinetic strength. Females with anterior cruciate ligament deficiencies had significantly increased preparatory muscle activity in the lateral hamstring before landing, but no differences in reactive muscle activity during landing or reflex latency after joint perturbation. Females with anterior cruciate ligament deficiencies had significantly less hamstring muscle stiffness and flexibility, but also had greater peak torque and torque development for knee flexion. Lower Lysholm scores were observed in females with anterior cruciate ligament deficiencies but no difference was found in functional performance of the single leg hop test. These neuromuscular characteristics provide a foundation for future research investigating injury prevention and rehabilitation techniques that maximize dynamic restraint through stiffness regulation and the timing of specific muscle activation strategies.

Gender comparisons of dynamic restraint and motor skill in children.

Objectives:To assess differences in neuromuscular dynamic restraint between high-skilled and low-skilled prepubescent girls and boys. To determine the contribution of sport experience and physical characteristics to motor skill. Subjects:Nineteen girls and 17 boys (8.89-9.40 y) participated. Intervention:Isometric hamstring and quadriceps muscle strength was assessed. Subjects performed 3 landing trials for measurement of preparatory EMG and vertical leg stiffness. Motor skill was assessed through analysis of 12 fundamental tasks. Sport experience was reported as hours per week and total years in organized and nonorganized activity. Outcome Measures:Dynamic restraint variables of isometric strength, preparatory EMG activity, and vertical leg stiffness were measured between groups. The contributions of time in sport, type of sport, and physical characteristics on skill were analyzed. Results:No significant gender or skill differences were found in quadriceps strength (P = 0.73), hamstring strength (P = 0.96), hamstring-to-quadriceps ratio (P = 0.71), or vertical leg stiffness (P = 0.38). Low-skilled children exhibited significantly greater (47.8%) preparatory hamstring-quadriceps coactivation than high-skilled subjects (P = 0.03). Participation in organized and nonorganized sport accounted for 29% of the variance in motor skill. Conclusions:Neuromuscular differences between genders were not observed, but dynamic restraint EMG measures differed between skill levels. The factors predisposing females to noncontact injuries may develop prepuberty to postpuberty from a combination of variables. Greater coactivation in the low-skilled group appears consistent with immature feedforward neuromuscular control strategies. These unrefined motor skills are less economical, may compromise dynamic restraint, and appear partially determined by sport experience.

Humeral retroversion and its association with posterior capsule thickness in collegiate baseball players

HYPOTHESIS AND BACKGROUND Baseball players commonly present with decreases in internal rotation (IR) and concurrent increases in external rotation (ER) motion. Several glenohumeral (GH) adaptations have been theorized to cause these changes in motion, including humeral retroversion (HR) and posterior capsule thickness (PCT). However, limited data exist examining the inter-relationship between HR and PCT. Therefore, the purpose of this study was to measure HR, GH IR and ER rotation, and PCT. MATERIALS AND METHODS HR and PCT were measured with an ultrasound system (Sonosite Titan; Sonosite, Bothell, WA, USA), and GH IR and ER were measured with a digital inclinometer. RESULTS The dominant arm had significantly more HR (15.6°, P = .0001) than the nondominant arm. Pearson correlation coefficients showed a significant negative relationship between HR and GH IR (-0.472, P = .001) and a significant positive relationship between HR and GH ER (0.295, P = .042). A significant positive correlation was also found between HR and PCT (0.427, P = .003). DISCUSSION This was the first study to identify a relationship between HR and PCT in addition to GH IR and ER. The identification of these multiple correlations appears to suggest that the loss of IR caused by HR may be placing additional stress on the posterior capsule during the deceleration phase of the throw, thereby causing a fibroblastic healing response. CONCLUSIONS HR has previously been identified as a positive adaptation because of the increase in ER without anterior capsule attenuation. However, this study suggests that HR may be contributing to the negative adaptation of PCT.

An Electromyographic Assessment of the “Bear Hug”: An Examination for the Evaluation of the Subscapularis Muscle

PURPOSE The lift-off and belly-press tests are common tests for evaluation of the subscapularis. We compared these tests with the recently developed bear-hug test by assessing electromyographic (EMG) activity of the shoulder internal rotators during examination. METHODS Twenty-one healthy male volunteers (mean age, 22.95 +/- 3.71 years; mean weight, 73.48 +/- 6.93 kg; mean height, 68.76 +/- 2.26 cm) with no previous history of shoulder surgery or injury participated in the study. Fine-wire and surface EMG activity of the glenohumeral joint internal rotators (i.e., upper and lower subscapularis, pectoralis major, and latissimus dorsi) was recorded while 5 subscapularis tests were being performed (bear hug at 0 degrees, 45 degrees, and 90 degrees; lift off; and belly press). Peak EMG values were normalized to the maximum voluntary isometric contraction (MVIC) for each muscle. A 4 (muscle) x 5 (test) analysis of variance with repeated measures on test was used to analyze peak EMG activity (percentage of maximum voluntary isometric contraction). Follow-up univariate analysis of variance and Tukey post hoc analyses were performed for each of the 5 tests. RESULTS The bear-hug test performed at 45 degrees of shoulder flexion showed significantly greater peak EMG activity in the upper subscapularis (107.64% +/- 63.52%) and lower subscapularis (85.75% +/- 64.69%) compared with the pectoralis major (41.43% +/- 25.42%) and latissimus dorsi (20.32% +/- 15.70%) (P < .05). The bear-hug test performed at 90 degrees of shoulder flexion showed significantly greater peak EMG activity in the lower subscapularis (166.0% +/- 132.71%) compared with the upper subscapularis (97.23% +/- 70.78%), pectoralis major (50.63% +/- 29.60%), and latissimus dorsi (17.56% +/- 13.64%) (P < .05). The belly-press test showed significantly greater peak EMG activity in the upper subscapularis (77.88% +/- 53.23%) and lower subscapularis (71.82% +/- 46.49%) compared with the pectoralis major (18.49% +/- 14.85%) and latissimus dorsi (34.85% +/- 27.73%) (P < .05). CONCLUSIONS The bear-hug examination performed at 45 degrees of shoulder flexion and the belly-press test may be valuable diagnostic tools in the clinical evaluation of the upper subscapularis muscle. In addition, the bear-hug test at 90 degrees of shoulder flexion may be a valuable diagnostic tool in assessing the clinical function of the lower subscapularis. CLINICAL RELEVANCE The bear-hug examination performed at specific degrees of shoulder flexion may be a valuable way to assess the function of the subscapularis muscle.

Stiffness Regulation and Muscle-Recruitment Strategies of the Shoulder in Response to External Rotation Perturbations

BACKGROUND The complex interactions between capsuloligamentous structures and muscle-recruitment strategies that maintain glenohumeral stability remain unclear. The purposes of the present study were to determine whether stiffness regulation and muscle-activation strategies differed under varying joint positions and levels of contraction in the shoulder and to determine the relationship between generalized joint laxity, glenohumeral joint laxity, and joint stiffness. METHODS Forty healthy, physically active subjects with a mean age (and standard deviation) of 25.2 +/- 4.6 years, a mean height of 174.7 +/- 6.7 cm, and a mean mass of 73.1 +/- 13.8 kg were tested. Shoulder stiffness and the activation of muscles (including the rotator cuff and the anterior deltoid) were measured at two levels of internal rotation torque (0% and 50% of maximum) and two joint positions (0 degrees and 90% of maximum external rotation) before and after a 5 degrees external rotation perturbation. Generalized laxity and glenohumeral joint laxity (in the anterior, posterior, and inferior directions) were also assessed. RESULTS Stiffness was 77% greater at 50% of maximum internal rotation torque than at 0% of maximum internal rotation torque (p < 0.001) but was not significantly different between joint positions (p = 0.73). From 0% to 50% of maximum internal rotation torque, preparatory and reactive recruitment of the subscapularis increased significantly more (p < 0.05) than those of the other muscles. Also, subscapularis preparatory activity was 36% greater in 0 degrees of external rotation than in 90% of maximum external rotation (p < 0.01). Generalized joint laxity (as indicated by a score of >/=4) was present in 20% of the subjects. Glenohumeral joint laxity (as indicated by a grade of >/=2) was present in the anterior, posterior, and inferior directions in 13%, 15%, and 15% of the subjects, respectively. No correlation existed between passive stiffness and generalized or glenohumeral laxity (r = -0.12 to 0.29; p = 0.08 to 0.48). CONCLUSIONS Moderate levels of muscle contraction can significantly increase glenohumeral joint stiffness and stability. Preactivation of the subscapularis appears to be the primary dynamic stabilizer with the arm in 0 degrees of external rotation. However, with the arm in 90% of maximum external rotation (the apprehension position), less subscapularis activity is observed and the maintenance of stability may shift toward other musculoskeletal structures because joint stiffness does not change. A relationship between generalized joint laxity, glenohumeral laxity, and stiffness was not observed in healthy subjects.

Neuromuscular and stiffness adaptations in division I collegiate baseball players

To compare bi-lateral shoulder EMG, active and short range glenohumeral stiffness, and examine its correlation to posterior capsule thickness (PCT) in collegiate baseball players. Surface and fine wire EMG was recorded on shoulder and scapular musculature during stiffness testing. Posterior capsule thickness was assessed separately using a diagnostic ultrasound. Serratus anterior EMG area and peak on the dominant arm was significantly greater compared to the non-dominant arm. The dominant arm had significantly greater active and short range glenohumeral stiffness compared to the non-dominant arm. Active glenohumeral stiffness was significantly correlated with PCT, however short range glenohumeral stiffness was not significantly correlated with PCT. Healthy collegiate baseball players present with adaptations of their stiffness regulation strategies. There were also correlations between stiffness and morphologic changes. Our results support the theory that PCT has an impact on the energy absorption capabilities of the shoulder during the deceleration phase of throwing. It also seems that tightening of the series elastic component within the posterior rotator cuff may be causing the increase in short range stiffness on the dominant arm.

Concurrent Validity of the Anterior Drawer Test and an Arthrometer in Evaluating Ankle Laxity

This study focused on the concurrent validity and reliability of an ankle arthrometer and clinical tests of ankle laxity. A posttest-only control group design was used to compare anterior-posterior (AP) displacement in participants with clinically graded laxity (mechanical instability) and a control group. Forty-four individuals with no recent ankle sprains participated in this study. An ankle arthrometer measured AP displacement, and one investigator clinically graded the anterior drawer test. Pearson correlations were significant (r = 0.48, P , .05) between the anterior drawer and arthrometer measurements of AP displacement. Independent t tests revealed significantly greater AP displacement (P , .05) in mechanically unstable ankles on the anterior drawer test. The intraclass correlation coefficients [2,1] for arthrometer AP displacement ranged from 0.44 to 0.87, with reliability decreasing as the laxity grade increased. The ankle arthrometer is a reliable measure of AP laxity and has concurrent validity with a standardized clinical grading system in differentiating levels of joint laxity. A