Glenohumeral Rotation Research Articles

Scapular Summit 2009, July 16, 2009, Lexington, Kentucky

This was the third research meeting focused on scapular function and dysfunction, following similar meetings in 2003 and 2006. The purpose of this meeting, hosted by the Shoulder Center of Kentucky, was to continue to examine the biomechanical and clinical factors thought to be associated with the role of the scapula in shoulder function and dysfunction. Since the last Summit, much more information has been created in this area, and it was thought that enough progress had been made that an organized overview of current knowledge could provide some consensus statements to guide further research and provide assessment and treatment guidelines. A call for abstracts was extended to researchers with proven interest and published research on the scapula. The meeting was organized around 3 primary categories of information: scapular kinematics and dysfunction, clinical evaluation of the scapula, and interventions. The last session of the meeting involved development of consensus statements for each category. This document represents the current state of knowledge concerning the aspects of scapular function and dysfunction discussed at the Summit. It is expected that, as more knowledge is developed, the gaps will be filled in and a clearer understanding of the roles of the scapula in shoulder function will emerge. This issue includes the consensus statements and abstracts from the Summit.

The Acute Effects of Sleeper Stretches on Shoulder Range of Motion

The deceleration phase of the throwing motion creates large distraction forces at the shoulder, which may result in posterior shoulder tightness and ensuing alterations in shoulder range of motion (ROM) and may result in an increased risk of shoulder injury. Researchers have hypothesized that various stretching options increase this motion, but few data on the effectiveness of treating such tightness are available. To evaluate the acute effects of "sleeper stretches" on shoulder ROM. Descriptive with repeated measures. Biomechanics laboratory and 2 separate collegiate athletic training facilities. Thirty-three National Collegiate Athletic Association Division I baseball players (15 pitchers, 18 position players; age = 19.8 +/- 1.3 years, height = 184.7 +/- 6.4 cm, mass = 84.8 +/- 7.7 kg) and 33 physically active male college students (age = 20.1 +/- 0.6 years, height = 179.6 +/- 6.6 cm, mass = 83.4 +/- 11.3 kg) who reported no recent participation (within 5 years) in overhead athletic activities. Range-of-motion measurements of the dominant shoulder were assessed before and after completion of 3 sets of 30-second passive sleeper stretches among the baseball players. The ROM measurements in the nonthrower group were taken using identical methods as those in the baseball group, but this group did not perform any stretch or movement between measurements. Internal and external glenohumeral rotation ROM and posterior shoulder motion (glenohumeral horizontal adduction). In the baseball group, posterior shoulder tightness, internal rotation ROM, and external rotation ROM were -3.5 degrees +/- 7.7 degrees , 43.8 degrees +/- 9.5 degrees , and 118.6 degrees +/- 10.9 degrees , respectively, before the stretches and were -1.2 degrees +/- 8.8 degrees , 46.9 degrees +/- 9.8 degrees , and 119.2 degrees +/- 11.0 degrees , respectively, after the stretches. These data revealed increases in posterior shoulder motion (P = .01, effect size = 0.30) and in internal shoulder rotation (P = .003, effect size = 0.32) after application of the stretches. No other differences were observed in the baseball group, and no differences were noted in the nonthrower group. Based on our results, the sleeper stretches produced a statistically significant acute increase in posterior shoulder flexibility. However, this change in motion may not be clinically significant.

A survey of glenohumeral joint rotational range and non-specific shoulder pain in elite cricketers

Objectives To determine if a glenohumeral joint internal rotation range of motion difference (IRD) and external rotation difference (ERD) exists between dominant and non-dominant shoulders of cricketers as demonstrated in other overhead sports, and, if present, to establish if differences exist between cricketers with and without a history of gradual onset non-specific shoulder pain. Design An observational study. Setting Non-clinical, at national cricket indoor training venues. Participants One hundred and nine elite male and female cricketers (11–35 years), representing 97% of the England and Wales national and West of England regional Under 13 teams, consented. The final number included for data analysis was 133. Main outcome measures Data relating to playing position, cricket exposure, shoulder pain and demographic details collected using a questionnaire. Passive isolated glenohumeral rotation measured in 90° shoulder abduction using an inclinometer. Results Cricketers who regularly bowl or throw overarm had significantly less internal (−7.9°, p<0.001) and greater external (8.6°, p<0.001) dominant to non-dominant glenohumeral rotation. Wicket-keepers had tendencies for smaller differences that were still statistically significant [mean IRD −5.9° ( p<0.001); ERD 5.0° ( p=0.002)]. Cricketers who experienced shoulder pain demonstrated a significantly greater IRD [mean 3.2° ( p=0.032)] than those who did not. Conclusions The results of this study support measurement of passive glenohumeral joint rotation during musculoskeletal profiling and indicate that a possible link between increased IRD and non-specific shoulder pain warrants further investigation.

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

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. 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. 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). 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. The bear-hug examination performed at specific degrees of shoulder flexion may be a valuable way to assess the function of the subscapularis muscle.

Elective shoulder arthroplasty in patients older than ninety years of age

This study examined the outcome of elective shoulder arthroplasty for glenohumeral osteoarthritis or rotator cuff arthropathy in patients aged older than 90 years. The study included 7 shoulders in 6 patients with an average age of 93 years 5 months, (range, 91 years 0 months to 97 years 4 months). Average follow-up was 2.2 years, (range, 1-4 years). Preoperative range of motion, Simple Shoulder Test (SST) scores, and Medical Outcomes Study Short-Form 36-Item Health Survey (SF-36) scores were obtained and compared with postoperative values at 3 and 6 months and yearly thereafter. Average forward elevation improved from 87 degrees to 137 degrees (P < .00001), and external rotation to the side improved from 0 degrees to 50 degrees (P < .0001). The SST scores improved from a preoperative average of 2.0 to 6.1 at 3 months (P < .0001), 6.9 at 6 months (P < .0001), 8.0 at 1 year (P < .00001), and 7.4 at 2 years (P < .0001). Significant improvements occurred in 6 of 8 SF-36 domains: Mental Health (P < .05), Vitality (P < .01), Role limitations due to emotional problems (P < .05), Social Function (P < .001), Role limitations due to physical health (P < .001), and Comfort (P < .00001). No patient had worse pain or function postoperatively. These data suggest that elective shoulder arthroplasty can be performed in patients 90 years of age and older, providing excellent pain relief, improved functional outcome, and enhanced general health status.

Simulated Type II Superior Labral Anterior Posterior Lesions Do Not Alter the Path of Glenohumeral Articulation

Background Previous studies have demonstrated increased glenohumeral translations with simulated type II superior labral anterior posterior lesions, which may explain the sensation of instability in the overhead-throwing athlete. It is unknown whether this amount of increased translation alters glenohumeral kinematics. Purpose To determine whether type II superior labral anterior posterior lesions significantly alter glenohumeral kinematics as defined by path of glenohumeral articulation in a simulated cadaveric model of the throwing shoulder. Study Design Controlled laboratory study. Methods Six cadaveric shoulders were tested for glenohumeral rotational range of motion and translation using a custom shoulder testing system and the Microscribe 3DLX. The path of glenohumeral articulation was measured by calculating the humeral head center with respect to the glenoid articular surface at maximal internal rotation, 30°, 60°, 90°, and maximal external rotation. Data were recorded for vented intact shoulders, shoulders with arthroscopically created type II superior labral anterior posterior lesions, and shoulders with arthroscopically repaired superior labral anterior posterior lesions. Results A subtle but significant increase in external rotation (2.7°) was seen after creating a type II lesion. Small increases in glenohumeral translation were found in the anterior (0.9 mm) and inferior (0.9 mm) directions with application of a 15-N force in the superior labral anterior posterior group. Increases in glenohumeral rotation and translation were restored to the intact state after repair of the lesion. No significant differences were found in the path of glenohumeral articulation for the superior labral anterior posterior condition compared with the intact shoulder. Conclusion The small amounts of increased external rotation and translation found with arthroscopically created type II superior labral anterior posterior lesions do not significantly affect glenohumeral kinematics in this passive motion model as quantified by the path of glenohumeral articulation. Clinical Relevance Findings suggest that in the absence of pain or mechanical symptoms, type II superior labral anterior posterior lesions that do not significantly involve the superior and middle glenohumeral ligaments may not need surgical repair.

Use of the reverse shoulder prosthesis for the treatment of failed hemiarthroplasty in patients with glenohumeral arthritis and rotator cuff deficiency

Use of the reverse shoulder prosthesis for the treatment of failed hemiarthroplasty in patients with glenohumeral arthritis and rotator cuff deficiency

Conventional Shoulder Arthroplasty in the Athlete

Humeral head replacement and total shoulder arthroplasty are successful procedures for improving pain and function for patients with glenohumeral arthritis and intact rotator cuff. Shoulder replacement is becoming more commonplace in younger patients and in an elderly population, with increasing numbers participating in sports. Therefore, many patients have greater expectations of postoperative function, including return to athletics. Before surgery, it is important to counsel the patient regarding the types of activities that are safe and those that are not recommended. Patient expectations can also be managed by evaluating the preoperative level of function and the cause of the glenohumeral arthritis. In general, patients with greater athletic aptitude before surgery will have an easier time returning to sports. Postoperatively, the rehabilitation program is designed to first restore range of motion and improve function in activities of daily living. At 3 months postoperatively, the rehabilitation program becomes more individualized for each patient and sports-specific training is allowed. Performing lesser tuberosity osteotomy when repairing the subscapularis might allow for more reliable healing and greater function after surgery. Ultimately, patient satisfaction with the outcome of shoulder replacement is dependent on a combination of preoperative expectations for athletic participation after surgery and postoperative subjective assessment of symptoms and function.

Relationship of glenohumeral elevation and 3-dimensional scapular kinematics with disability in patients with shoulder disorders

To determine variables among glenohumeral elevation and 3-dimensional scapular rotations that are related to shoulder function as assessed by the Disability of the Arm, Shoulder and Hand-Disability/Symptom (DASH-D/S) scale. Prospective, cross-sectional study. Eighty-eight patients with shoulder pain and limited range of motion were included. Each patient performed 2 full active range of motion activities, forward flexion and abduction, and 2 activities of daily living, combing hair and simulating washing the back. Glenohumeral elevation and scapular rotations were measured by the Polhemus Fastrak electromagnetic system. On multiple regression analysis, glenohumeral elevation in combing hair and scapular lateral rotation in both abduction and simulating washing the back were the best predictors of shoulder function and explained 39.7% of the variance of the DASH-D/S score. These findings support the classical rehabilitation of the shoulder based on glenohumeral elevation and suggest the importance of attention paid to scapular lateral rotation.

Kinematic evaluation of the Hawkins and Neer sign

To study the kinematics of the glenohumeral joint during the testing of the Neer and Hawkins signs, we used dynamic radiostereometry. Eighteen patients with impingement syndrome (Neer stage 2) and eleven controls were included. During testing of the Neer sign, there was no significant difference in humeral rotation and translation between patients and controls. During testing of the Hawkins sign, the center of the humeral head was positioned more laterally and superiorly in controls than in patients. The maximum amount of abduction, either relative glenohumeral rotation or as absolute rotation, was not influenced by the presence of impingement symptoms. Absence of kinematic abnormalities during the Neer maneuver and changed humeral translation in the Hawkins position suggest that the latter test is a more sensitive diagnostic tool. Our findings do not support that abnormal passive shoulder motions precede development of impingement syndrome.

Humeral Head Retroversion in Competitive Baseball Players and Its Relationship to Glenohumeral Rotation Range of Motion

Prospective case series. To determine if an osseous component in the form of increased humeral head retroversion may contribute to observed differences in the amount of rotation between the throwing and nonthrowing shoulders of competitive baseball players. Differences in side-to-side shoulder rotation range of motion (ROM) are seen in throwing athletes. In the past, these differences have been attributed to adaptive changes to the surrounding soft tissue structures, including attenuation of the anteroinferior capsule and ligaments, and tightening of the posterior capsule. Recent studies, however, suggest that a possible osseous adaptation in the form of increased humeral head retroversion may be the cause of this side-to-side ROM difference. bilateral computed tomography (CT) scans to determine the angle of humeral head version. Maximal shoulder internal and external rotation ROM at 90 degrees abduction were measured both passively and actively for both shoulders. Players had statistically significant (P<.001) side-to-side difference in humeral head version, with an average of 10.60 greater retroversion in their throwing arm compared to their nonthrowing arm. A significant side-to-side difference was not observed in the control group (average difference, 2.30; P = .197). Greater humeral head retroversion was associated with greater external rotation ROM and lesser internal rotation ROM in the throwing arm of the throwers. Our results indicated that highly competitive baseball players do have greater humeral head retroversion in their dominant arm, which can partially explain the observed differences in side-to-side shoulder rotation ROM.

Adolescent Baseball Pitching Technique

Document the biomechanics of the pitching motion to help provide insight about the etiology of common injuries seen in adolescent baseball pitchers. Kinematic and kinetic data for the upper and lower extremities, thorax, and pelvis were collected from 24 adolescent pitchers, using modern three-dimensional computerized motion-analysis techniques. Original information regarding forearm and wrist motion was reported in this study and were consistent with expected motions for the fastball pitch. Average excursion of motion was: pronation/supination 63 +/- 15 degrees, wrist flexion/extension 44 +/- 14 degrees, and ulnar/radial deviation 12 +/- 4 degrees. Explosive forearm motion occurred between ball release (BR) and maximal glenohumeral internal rotation (GH-MIR) with a peak pronation velocity of 2051 +/- 646 degrees.s(-1). The majority of internal/external and abduction/adduction shoulder motion was attributed to the glenohumeral motion. Internal glenohumeral rotation range of motion was 125 +/- 13 degrees and mean peak internal glenohumeral rotation velocity was 3343 +/- 453 degrees.s(-1). Thorax and pelvic motion peak velocities and accelerations occurred before the peak elbow varus moment, which occurred at 59% of the pitch cycle (PC). The peak shoulder, elbow, and wrist velocities and accelerations occurred after the peak elbow varus moment. The pelvis squared to the plate at 51 +/- 10% PC and the thorax at 59 +/- 7% PC with maximal glenohumeral external rotation (GH-MER) at 65% PC and BR at 78 +/- 3% PC. The data collected in this study were consistent with the literature, with the exception of joint velocities and moments, which were lower than those in one published study. We have established the kinematic and kinetic parameters of the adolescent baseball pitch. These measured parameters and the differences between adolescent pitchers and their adult counterparts can be used to examine and help determine the causes of the rapid increase in adolescent pitching injuries.

Arthroscopic Versus Open Rotator Interval Closure: Biomechanical Evaluation of Stability and Motion

The purposes of this study were to investigate the differences between open and arthroscopic closure of the rotator interval (RI) on glenohumeral translation and range of motion. We also sought to determine if the addition of either an open or arthroscopic RI closure increases stability of the shoulder. Fourteen fresh-frozen (10 paired) cadaveric shoulder specimens were mounted in a custom testing apparatus, and glenohumeral translation and rotation were obtained by using an optoelectric tracking system (Optotrak Certus; Northern Digital, Ontario, Canada). Specimens were randomly allocated to either open (n = 7) or arthroscopic (n = 7) plication of the RI. The following were measured first with an intact and vented specimen and subsequently after an RI closure using either open or arthroscopic techniques: (1) range of motion in neutral and 90 degrees abduction; (2) anterior and posterior translation at neutral rotation; (3) anterior translation at 90 degrees abduction with external rotation; and (4) posterior translation at 90 degrees flexion with internal rotation. Posterior stability was not improved from the intact state by either open (1.0-mm change) or arthroscopic (0.1-mm change) repair. The sulcus stability was improved in the open group (5.7 mm to 2.9 mm, P = .028), but not arthroscopically (5.1 to 4.1 mm, P = .499). Neutral anterior stability was improved after open repair (7.2 to 2.6 mm, P = .018), but not arthroscopically (2.3 to 2.4 mm, P = 0.5). However, anterior stability in external rotation (ER) at 90 degrees abduction was improved in the arthroscopic repair group (5.5 to 3.1 mm, P = .006). The mean loss of ER in neutral was greater in the open group (40.8 degrees) versus the arthroscopic group (24.4 degrees, P = .0038). The arthroscopic group showed an 11.7 degrees loss of ER in 90 degree abduction (P = .018) versus the open group loss of 4.8 degrees. There were no significant differences in loss of IR in either neutral or 90 degree abduction. Posterior stability was not improved by either open or arthroscopic rotator interval repair, and sulcus stability only improved with the open technique. Anterior stability in neutral was improved after open repair and in the arthroscopic repair group with the arm abducted. There was a large loss of external rotation with both techniques. This study suggests that arthroscopic RI closure adds little to the overall posterior and inferior stability of the shoulder joint, although anterior stability may be improved. There is a potentially large loss of external rotation after either repair method.

Use of the reverse shoulder prosthesis for the treatment of failed hemiarthroplasty in patients with glenohumeral arthritis and rotator cuff deficiency

We report the use of the reverse shoulder prosthesis in the revision of a failed shoulder hemiarthroplasty in 19 shoulders in 18 patients (7 men, 11 women) with severe pain and loss of function. The primary procedure had been undertaken for glenohumeral arthritis associated with severe rotator cuff deficiency. Statistically significant improvements were seen in pain and functional outcome. After a mean follow-up of 44 months (24 to 89), mean forward flexion improved by 26.4 degrees and mean abduction improved by 35 degrees . There were six prosthesis-related complications in six shoulders (32%), five of which had severe bone loss of the glenoid, proximal humerus or both. Three shoulders (16%) had non-prosthesis related complications. The use of the reverse shoulder prosthesis provides improvement in pain and function for patients with failure of a hemiarthroplasty for glenohumeral arthritis and rotator cuff deficiency. However, high rates of complications were associated with glenoid and proximal humeral bone loss.

The three-dimensional motions of glenohumeral joint under semi-loaded condition during arm abduction using vertically open MRI

Magnetic resonance imaging is an accurate non-invasive tool for visualizing muscles, tendons, and bones. It also provides 3D coordinate values. The purpose of the present study was to visualize and quantify the 3D positions of the glenohumeral joint during isometric abduction of the arm using vertically open magnetic resonance imaging. We examined 14 shoulders of seven healthy volunteers. Magnetic resonance images were obtained in a seated position and in seven static positions of the arm from 0 degrees to maximum abduction using vertically open magnetic resonance imaging. 3D surface models were created and 3D movements of each bone in the glenohumeral joint were calculated using a computer algorithm. We analyzed the translation and contact pattern of the glenohumeral joint. In supero-inferior direction, the humeral head translated slight inferiorly from +1.9 (SD 1.0) mm at 0 degrees to +0.8 (SD 1.8) mm at the maximum abduction. In antero-posterior direction, the humeral head translated anteriorly from 0 degrees to 90 degrees (mean +2.4, SD 2.6 mm) and posteriorly from 90 degrees to 150 degrees of abduction (mean -1.4, SD 2.7 mm). Furthermore, the humeral head had a unique contact patterns with the glenoid; the contact part of the humeral head with the glenoid changed from the central part to the posterior in the midrange of abduction. The humeral head showed a small translation in the antero-posterior direction between 90 degrees and 150 degrees of abduction. In addition, the posterior part of the humeral head contacted the glenoid in this range of abduction. These findings of motion patterns in asymptomatic subjects will be necessary when comparing the kinematics with pathologic condition such as the glenohumeral instability and rotator cuff tear.

Quantitative Assessment of Glenohumeral Translation after Anterior Shoulder Dislocation and Subsequent Arthroscopic Bankart Repair

Background During the past decade, developments in arthroscopic technology have made arthroscopic repair of labral lesions feasible. However, results with the use of the transglenoid suture technique, or with the use of bioabsorbable tacks, have remained variable in the literature, and the recurrence rates are still inferior to those of open Bankart repair. Hypothesis Arthroscopic Bankart repair with suture anchors can re-create translational and rotational range of motion of the intact glenohumeral joint, and the number of preoperative dislocations has an influence on the result. Study Design Controlled laboratory study. Materials Twelve cadaveric shoulders were tested in a robot-assisted shoulder simulator. Anterior and posterior translation and external rotation were measured for intact, dislocated (shoulders were randomly selected to 1 of 3 groups, which were dislocated 1, 3, or 7 times), and repaired conditions at 0° and 90° of glenohumeral elevation. Results After shoulder dislocation, a significant increase was found in translation and rotation, confirming the creation of a traumatic shoulder instability model. Further testing of the specimen revealed that translational and rotational ranges of motion were reduced by arthroscopic Bankart repair at both testing positions. External rotation was decreased significantly at 0° and 90° of abduction. No significant differences were found between the 3 dislocation groups. Conclusion The results demonstrate a sufficient biomechanical performance of arthroscopic Bankart repair using suture anchors in a traumatic anterior shoulder instability model. With the numbers available, no relationship was found between the number of dislocations and the postoperative result concerning translational or rotational motion. Clinical Relevance Glenohumeral translation and rotation after arthroscopic Bankart repair with use of suture anchors approached near normal values, confirming the clinical success of this technique.

Path of Glenohumeral Articulation Throughout the Rotational Range of Motion in a Thrower's Shoulder Model

Background Overhead-throwing athletes have increased external and diminished internal glenohumeral rotation that may alter glenohumeral kinematics. Purpose To quantify the kinematic changes present in a cadaveric model of a thrower's shoulder. Study Design Controlled laboratory study. Methods In 8 fresh-frozen cadaveric shoulders, the rotator cuff and overlying muscles were removed, and the glenohumeral capsule, coracoacromial ligament, and coracohumeral ligament were left intact. The scapula was fixed, and the humerus was placed in 90° of shoulder abduction in a 6 degrees of freedom testing device. A compressive force of 44 N was applied. A thrower's shoulder model was created, and sequential conditions were examined: intact, after anterior stretching, and after the addition of posterior-inferior capsular plication. Kinematic measurements were obtained through a complete range of glenohumeral rotation. Results Glenohumeral external rotation increased 16%, from 149° to 173° (P <. 001), after stretching in external rotation and remained increased by 11% to 166° (P <. 001) after posterior-inferior capsular plication. With the addition of the posterior-inferior capsular plication, internal rotation averaged 7°, which was not significantly different from the intact state (11°, P =. 55) or the stretched state (16°, P =. 07). The total glenohumeral rotation after stretching followed by posterior-inferior capsular plication did not differ significantly from intact state (P =. 25). At maximum external rotation, the humeral head apex was shifted posteriorly in the stretched (P =. 003) and plicated (P <. 001) states compared with the intact state. The humeral head apex was posteriorly displaced at 135° and 150° of external rotation compared with the intact condition (P =. 039 and. 049, respectively). In maximum internal rotation, anterior stretching had no significant effect on the humeral head apex position. However, after posterior-inferior capsular plication, the humeral head apex was significantly shifted inferiorly (P =. 005) and anteriorly (P =. 03) in maximum internal rotation compared with the intact state. Conclusion Significant changes in glenohumeral motion occur in this model during the simulated late-cocking and follow through phases of throwing. In this model, posterior capsular tightness alters the humeral head position most profoundly during the deceleration and follow-through phases of throwing.

The Effect of Glenohumeral Rotation on Scapular Upward Rotation in Different Positions of Scapular-Plane Elevation

Context:Glenohumeral and scapular upward rotation are important factors in functional upper extremity motion.Objectives:To determine how different amounts of glenohumeral rotation (internal, external, and neutral) affect scapular upward rotation.Design:Controlled laboratory study. Independent variables were the amounts of internal, external, and neutral glenohumeral rotation. The dependent variable was the amount of scapular upward rotation.Setting:Research laboratory.Participants:40 subjects who were right-hand dominant, sedentary, and age 16 to 35 years.Main Outcome Measures:An inclinometer assessed scapular upward rotation with the 3 different positions of glenohumeral rotation in each 0°, 30°, 60°, and 90° of humeral elevation in the scapular plane.Results:Scapular upward rotation tended to increase with glenohumeral internal and external rotation, compared with neutral rotation in each degree of humeral elevation. This trend was seen on both right and left sides.Conclusions:Scapular upward rotation at different levels of humeral elevation in the scapular plane was affected by the positions of glenohumeral rotation.

Variability in isometric force and moment generating capacity of glenohumeral external rotator muscles

Muscles which cause glenohumeral external rotation possess varying ability for generating force and moment due to differences in muscle architecture, moment arm, and the interaction of these two factors. This study's purpose was to determine a complete dataset of muscle-tendon parameters for predicting the moment generating capacity and force-length dependence for external rotation of infraspinatus, supraspinatus and teres minor muscles. Muscle fascicle length, sarcomere length, pennation angle, and muscle volume were measured for sub-regions of infraspinatus and supraspinatus, and teres minor from 10 glenohumeral specimens. Tendon excursion was measured for glenohumeral rotation. From these parameter measurements, optimal fascicle length, physiological cross-sectional area, muscle force-length dependence, and maximum isometric moment generating capacity were calculated. Substantial differences were found for optimal muscle length, physiologic cross-sectional area, and tendon length for the 10 specimens of this study. Muscle sub-region had a significant effect on the force-length relationship for infraspinatus (P<0.001), but was not significant for supraspinatus (P=0.49). For infraspinatus and supraspinatus, maximum isometric rotation moment capacity was greater at 10 degrees versus 60 degrees abduction (P<0.001). Maximum isometric rotation moment capacity for the teres minor was greater at 10 degrees versus 60 degrees abduction (P<0.01). Sub-regions demonstrated significant differences in isometric moment capacity (P<0.001). Functional capabilities of these muscles depend on muscle architecture and moment arm as well as their combined effects. The results allow for development of stochastic and deterministic models of glenohumeral external rotation strength which can be used for prediction of muscle forces and joint moments.

Comparison between geometric and functional method for the estimation of the glenohumeral rotation center

comparison between geometric and functional method for the estimation of the glenohumeral rotation center