Compensation strategy of shoulder synergist muscles is not stereotypical in patients with rotator cuff repair.

Rotator cuff tear is a common shoulder injury that causes shoulder dysfunction and pain. Although surgical repair is the primary treatment for rotator cuff tear, it is well recognized that impaired force exertion of muscles connecting to the involved tendon and subsequent complemental change in the force exertion of synergist muscles persist even after repair. This study aimed to identify the compensation strategy of shoulder abductors by examining how synergist muscles respond to supraspinatus (SSP) muscle force deficit in patients with rotator cuff repair. Muscle shear modulus, an index of muscle force, was assessed for SSP, infraspinatus, upper trapezius, and middle deltoid muscles in repaired and contralateral control shoulders of 15 patients with unilateral tendon repair of the SSP muscle using ultrasound shear wave elastography while the patients passively or actively held their arm in shoulder abduction. In the repaired shoulder, the shear modulus of the SSP muscle declined, whereas that of other synergist muscles did not differ relative to that of the control. To find the association between the affected SSP and each of the synergist muscles, a regression analysis was used to assess the shear moduli at the population level. However, no association was observed between them. At the individual level, there was a tendency of variation among patients with regard to a specific muscle whose shear modulus complementarily increased. These results suggest that the compensation strategy for SSP muscle force deficit varies among individuals, being nonstereotypical in patients with rotator cuff injury.

Mechanical characteristic of supraspinatus muscle changes independent of its size and intramuscular fat in patient with rotator cuff repair.

PURPOSE: This study aimed i) to investigate the mechanical, morphological, and compositional characteristics of the supraspinatus muscle after rotator cuff repair by using ultrasound shear wave elastography (SWE) and B-mode imaging, and ii) to determine whether the morphological or compositional characteristics are associated with the mechanical characteristic of the supraspinatus during contraction. METHODS: Using SWE and B-mode imaging, active and passive shear moduli, muscle thickness, and echo intensity of the supraspinatus were measured from the repaired and contralateral control shoulders of 22 patients with rotator cuff repair. The shear modulus, muscle thickness, and echo intensity were compared between the repaired and control shoulders. The association between the active shear modulus and the other variables was determined. RESULTS: While the active and passive shear moduli were lower in the repaired shoulder compared to the control, the muscle thickness and echo intensity did not vary between them. Interestingly, the passive shear modulus was positively correlated with the active shear modulus only in the control shoulder. CONCLUSION: The mechanical characteristic of supraspinatus remains impaired, even without degenerative changes in the morphological and compositional characteristics after rotator cuff repair. Furthermore, the association between contractile and elastic characteristics in the supraspinatus was deteriorated in control shoulder.

Agreement in rotator cuff muscles measurement between ultrasonography and magnetic resonance imaging.

Background/objective: It is important to assess the atrophy of the rotator cuff to better understand shoulder function and pain. Previously, magnetic resonance imaging has been used for the evaluation of atrophy of rotator cuff muscles, which is time consuming. Therefore, a measurement tool requiring little time and easy accessibility is clinically desirable to be used frequently in rehabilitation. Recently, rotator cuff muscles have been evaluated using ultrasonography. However, little is known about the agreement of evaluation in rotator cuff muscles between magnetic resonance imaging and ultrasonography. The purpose of this study was to demonstrate the agreement between the muscle thickness measurements of supraspinatus, infraspinatus, and teres minor muscles by ultrasonography and the cross-sectional area measured by magnetic resonance imaging in the patient with rotator cuff tears. Methods: A total of 47 patients with rotator cuff tears were enrolled. There were the 37 small tears, four medium tears, and six large tears, and the involved rotator cuff muscles were the supraspinatus in 37 shoulders, and the supraspinatus and infraspinatus in 10 shoulders. The measuring variables were muscle thickness and cross-sectional area of supraspinatus, infraspinatus, and teres minor muscles by using magnetic resonance imaging. Further, the muscle thickness of the rotator cuff were assessed using ultrasonography. A single regression model was used for demonstrating the agreement between the cross-sectional area measurement by magnetic resonance imaging and the muscle thickness measured using ultrasonography and magnetic resonance imaging of rotator cuff muscles. Additionally, the Bland-Altman plots between magnetic resonance imaging and ultrasonography was analyzed. Results: The cross-sectional area were correlated with the muscle thickness measurement of rotator cuff muscles by magnetic resonance imaging, significantly (supraspinatus: r = 0.84, infraspinatus: ρ = 0.63, teres minor: ρ = 0.61, all p < 0.001). There were significant agreements between the cross-sectional area measured by magnetic resonance imaging and muscle thickness measured by ultrasonography (supraspinatus: r = 0.80, infraspinatus: ρ = 0.78, teres minor: ρ = 0.74, all p < 0.001). Bland-Altman plots revealed significant correlations between the average and the difference of the two measurements in supraspinatus (r = 0.36, p = 0.012), infraspinatus (r = 0.38, p < 0.001), and teres minor (r = 0.42, p < 0.001). These results clarified the proportional bias between MRI and US. Conclusion: This study showed that, similar to magnetic resonance imaging, ultrasonography is a useful tool for assessing muscle atrophy of supraspinatus, infraspinatus, and teres minor muscles.

Does Margin Convergence Reverse Pseudoparalysis in Patients with Irreparable Rotator Cuff Tears?

BACKGROUND: Margin convergence has been shown to restore muscle tension in a cadaveric model of a rotator cuff tear. However, the clinical utility of this technique remains uncertain for patients with pseudoparalysis caused by an irreparable rotator cuff tear. QUESTIONS/PURPOSES: (1) For patients with massive irreparable rotator cuff tears, in what proportion of patients does margin convergence reverse pseudoparalysis? (2) In patients with massive irreparable rotator cuff tears, does margin convergence improve American Shoulder and Elbow Surgeons (ASES) scores? (3) What is the survivorship free from MRI evidence of retear after margin convergence? METHODS: Between 2000 and 2015, we treated 203 patients for pseudoparalysis with a rotator cuff tear. Pseudoparalysis was defined as active elevation less than 90° with no stiffness, which a physical therapist evaluated in the sitting position using a goniometer after subacromial injection of 10 cc lidocaine to eliminate pain. Of those, we considered patients who underwent at least 3 weeks of unsuccessful nonoperative treatment in our hospital as potentially eligible. Twenty-one percent (43 of 203) who either improved or were lost to follow-up within 3 weeks of nonoperative treatment were excluded. A further 12% (25 of 203) were excluded because of cervical palsy, axillary nerve palsy after dislocation or subluxation, and development of severe shoulder stiffness (passive shoulder elevation < 90°). Repair was the first-line treatment, but if tears were considered irreparable with the torn tendon unable to reach the original footprint after mobilizing the cuff during surgery, margin convergence was used. When margin convergence failed, the procedure was converted to hemiarthroplasty using a small humeral head to help complete the repair. Therefore, 21% (42 of 203) of patients treated with regular repair (18% [36 of 203]) or hemiarthroplasty (3% [6 of 203]) were excluded. That left 93 patients eligible for consideration. Of those, 13 patients were lost before the minimum study follow-up of 2 years or had incomplete datasets, and 86% (80 of 93) were analyzed (49 men and 31 women; mean age 68 ± 9 years; mean follow-up 26 ± 4 months). Seventy-six percent (61 of 80) were not evaluated in the last 5 years. We considered reversal of pseudoparalysis as our primary study outcome of interest; we defined this as greater than 90° active forward elevation; physical therapists in care measured this in the sitting position by using goniometers. Clinical outcomes were evaluated based on the ASES score from chart review, active ROM in the shoulder measured by the physical therapists, and the 8-month Kaplan-Meier survivorship free from MRI evidence of retear graded by the first author. RESULTS: Pseudoparalysis was reversed in 93% (74 of 80) patients, and improvement in ASES scores was observed at the final follow-up (preoperative 22 ± 10 to postoperative 62 ± 21, mean difference 40 [95% CI 35 to 45]; p < 0.01). The 8-month Kaplan-Meier survivorship free from MRI evidence of retear after surgery was 72% (95% CI 63% to 81%). There were no differences in clinical scores between patients with and without retears (intact ASES 64 ± 24, re-tear ASES 59 ± 10, mean difference 6 [95% CI -5 to 16]; p = 0.27). CONCLUSION: Margin convergence can be a good option for treating patients with pseudoparalysis and irreparable rotator cuff tears despite the relatively high retear rates. The proportion of pseudoparalysis reversal was lower in patients with three-tendon involvement. Further studies will be needed to define the appropriate procedure in this group. LEVEL OF EVIDENCE: Level IV, therapeutic study.

Fibrosis in the rotator interval associated with articular vs. bursal side partial-thickness rotator cuff tears.

BACKGROUND: The pathogenesis of articular- and bursal-sided partial-thickness rotator cuff tears (PTRCTs) is considered to be different, and associated lesions with PTRCTs need to be examined. METHODS: The current study consisted of 76 shoulders of 73 patients (27 men, 46 women, 64.0 ± 8.3 years old) who underwent mini-open repair after conversion to full-thickness tears for either articular side (group A; n = 56) or bursal side (group B; n = 20) PTRCT with at least a 2-year follow-up. Clinical outcomes and their images were compared between the groups. Plain radiographs were used with the arm passively elevated in maximum elevation to assess restriction of glenohumeral motion. RESULTS: The retear rate was not significantly different between the groups. Both groups showed significant improvement in functional scores at the final follow-up. Patients in group A showed a higher incidence of preoperative fibrosis in the rotator interval (69.6% vs. 35.0%, respectively; P = .006) and a lower incidence of an acromial spur (7.1% vs. 35.0%, respectively; P = .008) compared with group B. Plain radiographs with arm elevation showed restriction of glenohumeral movement in 49 of 76 shoulders (64.5%) preoperatively, including 36 of the 46 shoulders with fibrosis and 13 of the other 30 shoulders. CONCLUSION: Both articular- and bursal-sided PTRCTs showed significant functional improvements after surgery. The articular-sided tears had a lower incidence of an acromial spur, but had a higher incidence of fibrosis in the rotator interval, which led to a limitation in glenohumeral motion.

Comparison of shoulder muscle strength, cross-sectional area, acromiohumeral distance, and thickness of the supraspinatus tendon between symptomatic and asymptomatic patients with rotator cuff tears.

BACKGROUND: The purpose of this study was to demonstrate the differences in shoulder muscle strength, cross-sectional area of the rotator cuff muscles, acromiohumeral distance, and supraspinatus tendon thickness between symptomatic and asymptomatic patients with rotator cuff tears. METHODS: Thirty-two symptomatic patients and 23 asymptomatic patients with rotator cuff tears participated in this study. Data of the patients with any type of tear and supraspinatus tear were analyzed. We evaluated the isometric torque, cross-sectional area of the rotator cuff muscles, supraspinatus tendon thickness, acromiohumeral distance, range of motion, and Western Ontario Rotator Cuff Index. RESULTS: Asymptomatic patients showed greater isometric torque of shoulder abduction and internal rotation than symptomatic patients with any type of tear (P ≤ .01). Asymptomatic patients also demonstrated greater cross-sectional area of the supraspinatus (P < .01); however, there was no significant difference in the cross-sectional area of the other cuff muscles. There was also no significant difference in the supraspinatus tendon thickness (P = .10). The acromiohumeral distance at 90° of shoulder abduction was larger (P = .04) in asymptomatic patients. Additionally, similar tendencies were observed in the results of patients with supraspinatus tears, except for the isometric torque of shoulder external rotation. This torque was greater (P < .01) in asymptomatic patients. CONCLUSION: Asymptomatic patients showed greater shoulder range of motion, muscle strength of shoulder abduction and internal rotation, small occupation ratio of supraspinatus tendon thickness as a percentage of acromiohumeral distance, and large cross-sectional area of supraspinatus.

Modified Putti-Platt procedure for recurrent anterior shoulder instability.

PURPOSE: The classic Putti-Platt technique was modified by suturing the lateral subscapularis tendon to the capsule instead of the anterior glenoid edge. We report the clinical results of a modified Putti-Platt procedure in patients with traumatic anterior shoulder instability. METHODS: The study reports results in 434 patients (450 shoulders) with traumatic anterior shoulder instability. The patients comprised 322 men and 122 women with a mean age of 22 years. Clinical results were evaluated by the Rowe score, Japan Shoulder Society Shoulder Instability Score (JSS-SIS); recurrence of instability, instability severity index score (ISIS), restriction of external rotation, return to sports activities, and osteoarthritis on plain radiographs and MRI were examined. RESULTS: The mean Rowe score improved from 26 to 90 points, and the mean JSS-SIS improved from 51 to 88 points. Altogether, 419 patients (97%) had no recurrence at a minimum of two years of follow-up, even though the study included 87 patients with an ISIS of ≥ 7 points. External rotation was limited at 6 months, and 33 of 228 patients (14%) could not return to the same level of sports activities. Among 44 patients at the follow-up extending to ten to 27 years, external rotation was still limited but no plain radiography showed osteoarthritis more than stage 2. CONCLUSION: This modified Putti-Platt procedure was not appropriate for throwing athletes but could be a surgical option for patients with high risk of recurrence.

Stride-Phase Kinematic Parameters That Predict Peak Elbow Varus Torque.

BACKGROUND: During baseball pitching, a high amount of elbow varus torque in the arm cocking-to-acceleration phase is thought to be a biomechanical risk factor for medial elbow pain and injury. The biomechanics of the stride phase may provide preparation for the arm cocking-to-acceleration phase that follows it. PURPOSE: To determine the kinematic parameters that predict peak elbow varus torque during the stride phase of pitching. STUDY DESIGN: Descriptive laboratory study. METHODS: Participants were 107 high school baseball pitchers (age range, 15-18 years) without shoulder or elbow problems. Whole-body kinematics and kinetics during fastball pitching were analyzed using 3-dimensional measurements from 36 retroreflective markers. A total of 26 kinematic parameters of the upper and lower limbs during the stride phase leading up to the stride foot contact were extracted for multiple regression analysis to assess their combined effect on the magnitude of peak elbow varus torque. RESULTS: Increased wrist extension, elbow pronation, knee flexion on the leading leg, knee extension on the trailing leg at stride foot contact, and upward displacement of the body's center of mass in the stride phase were significantly correlated with decreased peak elbow varus torque (all P < .05). Moreover, 38% of the variance in peak elbow varus torque was explained by a combination of these 5 significant kinematic variables (P < .001). CONCLUSION: We found that 5 kinematic parameters during the stride phase and the combination of these parameters were associated with peak elbow varus torque. The stride phase provides biomechanical preparation for pitching and plays a key role in peak elbow varus torque in subsequent pitching phases. CLINICAL RELEVANCE: The present data can be used to screen pitching mechanics with motion capture assessment to reduce peak elbow varus torque. Decreased peak elbow varus torque is expected to reduce the risk of elbow medial pain and injury.

Biomechanical Differences Between Japanese and American Professional Baseball Pitchers.

BACKGROUND: Although baseball injuries are common in both Japan and the United States, the majority of pitching injuries in Japanese players occur at the shoulder, whereas most pitching injuries in American players occur at the elbow. A biomechanical comparison between Japanese and American pitchers may help to identify the different injury mechanisms. HYPOTHESIS: Japanese pitchers produce greater shoulder kinetics whereas American pitchers generate greater elbow kinetics. Also, kinematic differences will be found between the 2 groups, including longer stride and greater lead knee flexion for Japanese pitchers. STUDY DESIGN: Descriptive laboratory study. METHODS: Biomechanical data for 19 Japanese professional baseball pitchers and an age-matched group of 19 American professional baseball pitchers were collected by use of a 3-dimensional, automated, high-speed optical motion capture system. Anthropometric, kinetic, and kinematic data for both groups were compared by use of t tests (P < .05). RESULTS: American pitchers were taller and heavier and generated greater ball velocity (38.1 ± 1.6 vs 34.7 ± 1.1 m/s; P < .001) than their Japanese counterparts. Most elbow and shoulder kinetic parameters, including elbow varus torque (99 ± 17 vs 86 ± 17 N·m; P = .018), were greater for American pitchers. However, when normalized by bodyweight and height, shoulder horizontal adduction torque was greater for Japanese pitchers (6.8% ± 1.0% vs 5.8% ± 1.1%; P = .005). Japanese pitchers had longer stride (86% ± 5% vs 82% ± 6% of height; P = .023), greater shoulder abduction at ball release (101° ± 8° vs 94° ± 9°; P = .014), and greater knee flexion after ball release (39° ± 18° vs 28° ± 14°; P = .039). Japanese pitchers also demonstrated greater shoulder internal rotation velocity, elbow flexion, and elbow extension velocity. CONCLUSION: Greater elbow varus torque may predispose American pitchers to greater risk of elbow injury. Japanese pitchers may have increased risk of shoulder injury due to greater normalized horizontal adduction torque and greater abduction angle. Japanese pitchers may be able to reduce their shoulder torque and risk of injury by shortening their stride, reducing their lead knee flexion, and decreasing their throwing arm abduction. CLINICAL RELEVANCE: Understanding anthropometric, kinetic, and kinematic differences between pitchers from the 2 countries may be of value to clinicians and coaches working to maximize performance of the pitchers while minimizing the risk of injury.

Comparison of scapular upward rotation during arm elevation in the scapular plane in healthy volunteers and patients with rotator cuff tears pre- and post-surgery.

BACKGROUND: Function loss caused by rotator cuff tears alters the scapular orientation, however, few prior studies have reported on scapular movements after rotator cuff repair. The purpose was to determine the scapular orientations before and after rotator cuff repair. METHODS: We recruited 14 healthy controls, 10 small and six massive rotator cuff tear in patients. The scapular upward rotation during arm elevation was analyzed using fluoroscopic imaging. FINDINGS: Before surgery, both rotator cuff groups demonstrated greater scapular upward rotation compared to healthy controls. Two months postoperation, the analyses showed significant differences between the patients with small rotator cuff tears and healthy controls at arm elevations of 90°, and between patients with both rotator cuff tear groups and healthy controls at arm elevations of 120°. At five months post-operation, significant differences still existed between the healthy controls and both rotator cuff groups. In regard to the temporal effects in the patients with small rotator cuff tears, the scapular upward rotation decreased significantly over time (2-5 months postoperation) at arm elevations of 120°. We did not identify a main effect owing to time in the patients with massive rotator cuff tears. INTERPRETATION: In patients with small rotator cuff tears, scapular upward rotation was reduced over the period of 2-5 months postoperation, however, the patients with massive rotator cuff tears showed greater scapular upward rotation throughout the experimental period. The results suggested that the execution of the rehabilitation program should consider that the tear size could affect scapular motion.

The kinematics of 1-on-1 rugby tackling: a study using 3-dimensional motion analysis.

BACKGROUND: Although past studies using video analysis indicated that the arm tackle and head-in-front shoulder tackle are possible risks for shoulder dislocation, the underlying mechanisms of tackling-related shoulder dislocation have not been sufficiently investigated. This study aimed to analyze the kinematic aspects of these tackling motions in 1-on-1 tackles in an experimental setting using a 3-dimensional motion-capture system. METHODS: A total of 65 one-on-one tackles were recorded using a marker-based, automatic, digitizing motion-capture system. A documented tackle was classified into 1 of 3 types, which was decided based on the first point of contact on the ball carrier and the head position at the time of impact: shoulder tackle (reference tackle), arm tackle, and head-in-front tackle. The orientations of the head, trunk, and shoulder at impact were calculated and statistically compared with each other. RESULTS: The distribution of tackles recorded in this study was as follows: 38 shoulder, 23 arm, and 4 head-in-front tackles. In comparison with the shoulder tackle as a reference, shoulder abduction on the side of impact was higher in both the arm and head-in-front tackles, while shoulder external rotation was lower in the head-in-front tackles. In the latter type of tackle, significant decreases in neck extension and ipsilateral neck rotation were also indicated. CONCLUSION: The kinematics in both the arm tackle and the head-in-front tackle is significantly different from that in the shoulder tackle and may represent a distinct risk factor for shoulder dislocation.

Estimation of Shoulder Behavior From the Viewpoint of Minimized Shoulder Joint Load Among Adolescent Baseball Pitchers.

BACKGROUND: During pitching, an overloaded joint reaction force exerted on the shoulder and excessive shoulder horizontal abduction at ball release are considered risk factors causing anterior shoulder pain for young baseball pitchers. Hypothesis/Purpose: The first aim was to examine the relationship between shoulder horizontal abduction position and force on the shoulder at ball release. The second was to identify the relative rotational position of the shoulder and the range of shoulder motion at ball release that minimize force on the shoulder. It was hypothesized that the amount of force on the shoulder would be exacerbated by excessive shoulder horizontal abduction. STUDY DESIGN: Descriptive laboratory study. METHODS: Participants were 183 adolescent baseball pitchers (mean ± SD age, 15.5 ± 1.2 years) without shoulder/elbow problems. Each pitcher threw 5 fastballs to a catcher behind a home plate. The kinematics and kinetics of the throwing shoulder during fastball pitching were calculated with 3-dimensional measurements from 36 reflective markers. In data analysis, the correlations were calculated between the relative rotational positions of the shoulder (abduction, horizontal adduction-abduction) and the forces on the shoulder (anterior-posterior, proximal, and superior-inferior) at ball release. Subsequently, the specific rotational position and range of motion of the shoulder at ball release that minimized forces on the shoulder were determined. RESULTS: Statistically significant correlations were identified between the magnitude of superior-inferior force on the shoulder and shoulder abduction position ( R2 = 0.44, P < .001) as well as between the magnitude of anterior-posterior force on the shoulder and shoulder horizontal adduction-abduction position ( R2 = 0.72, P < .001). Minimal anterior-posterior and superior-inferior forces were obtained with a combination of 80.6° of shoulder abduction and 10.7° of shoulder horizontal adduction. Any deviation >5° from this position significantly increased the anterior-posterior and superior-inferior forces on the shoulder. CONCLUSION: Increasing shoulder horizontal abduction position significantly increased the magnitude of anterior force on the shoulder at ball release. The combination of 80.6° of shoulder abduction and 10.7° of horizontal shoulder adduction minimized the shear forces on the shoulder at this point. CLINICAL RELEVANCE: The present data can be useful for screening pitching technique to prevent shoulder pain and injury with motion capture assessment.

Kinematics of Rugby Tackling: A Pilot Study With 3-dimensional Motion Analysis.

BACKGROUND: Although improper tackling technique in rugby can affect the outcome of the tackle and lead to head, neck, and shoulder injuries, the effects of the height of the tackle or the side of the leading leg at the time of impact have not been investigated. Hypothesis/Purpose: The purpose was to characterize the trunk orientation at impact during various tackles. It was hypothesized that 3-dimensional motion analysis would be able to capture the critical kinematic differences in the 4 types of tackles studied. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 66 tackles on a tackle bag were recorded among 13 elite rugby players. Four types of tackles were evaluated: the normal shoulder tackle, in which the tackler's dominant shoulder made impact while the leading foot was on the same side as that shoulder; the low tackle, in which the tackler targeted the lower portion of the tackle bag; the opposite-leg tackle, in which the tackler's leading leg was on the opposite side as the shoulder making impact; and the low and opposite-leg tackle, which was a combination of the previous 2 types of tackles. The orientation of the trunk at impact was calculated, and 2-way repeated-measures analyses of variance were used to compare the characteristics of these tackles. RESULTS: Trunk inclination at impact was lower in the low tackle than in the normal tackle ( P < .01), regardless of the side of the leading leg. Trunk bending to the side of the impacted shoulder was lower in the opposite-leg tackle ( P < .01), and these findings were more significant in the normal-height tackles ( P < .01). Trunk rotation to the side of the impacted shoulder was lower in the opposite-leg tackles ( P < .01) and more significant in the lower-height tackles ( P = .03). CONCLUSION: The 3-dimensional motion capture system was effective in investigating the kinematics of rugby tackling. The kinematics in the low and opposite-leg tackles were significantly different from those in the normal shoulder tackle, which may affect tackle performance and the possible risk of contact injury. CLINICAL RELEVANCE: When a rugby coach provides tackling instructions to players, it is advantageous to have information about the kinematics of different types of tackles.

Translational movement within the glenohumeral joint at different rotation velocities as seen by cine MRI.

BACKGROUND: The glenohumeral joint is subjected to opposing forces when the direction of shoulder motion is changed, accelerating and decelerating to make the movements. The influence of motion velocity or acceleration on translation of the humeral head has not been evaluated although direction and distance of humeral head translation has been analyzed in real time in normal shoulders. We hypothesized that, in a normal shoulder, the humeral head does not deviate significantly or suddenly during active shoulder rotation regardless of motion velocity. The purpose of this study was to clarify normal intraarticular kinematics of humeral head position and translation during axial shoulder rotation with the arm by the side of the body at different rotational velocities using cine magnetic resonance imaging (MRI). METHODS: Both shoulders of ten healthy adults (mean age group between 27.80 ± 6.05 years) were used in this study. Prior to MRI scan, dynamic glenohumeral stability was confirmed by physical examination. The glenohumeral joint was scanned during active shoulder rotation at three angular velocities (low, medium and high velocities), with the arm by the side of the body by real-time cine MRI while recording with the help of a video camera. Translation of the humeral head and rotation angles on MR imaging and video camera were measured to match shoulder rotational positions. RESULTS: There were no statistical differences of the humeral head position and translation among three rotation velocities (p > 0.05). Translation of the humeral head was distributed from 1.44 ± 2.45 mm anteriorly to 0.65 ± 1.84 mm posteriorly at low velocity, from 0.74 ± 1.92 mm anteriorly to 0.75 ± 2.17 mm posteriorly at medium velocity, and from 2.62 ± 2.19 anteriorly to 1.17 ± 1.44 mm posteriorly at high velocity. CONCLUSIONS: Translation of the humeral head was shown to undergo no significant change throughout the ranges of internal and external rotation, or among different rotational velocities in dynamic stability of the glenohumeral joint.

Three-dimensional kinematic analysis of throwing motion focusing on pelvic rotation at stride foot contact.

BACKGROUND: Because the throwing motion can be considered a kinetic chain, pelvic and trunk motion should be included in the analysis. Early pelvic rotation during the throwing sequence has been reported to be a factor leading to overloading of the shoulder and the elbow. A large pelvic rotation angle at the stride foot contact (SFC) was thought to indicate early pelvic opening. This study examined the kinematic features in each motion segment associated with increased pelvic rotation at SFC in pitchers of various ages and competition levels. MATERIALS AND METHODS: The study included 324 pitchers with various age/competition levels. Throwing motion was analyzed using an infrared-type motion capture system. In the assessment, pelvic rotation angle at SFC was adopted as a parameter for the timing of pelvic opening. Statistical analyses were performed for correlation between pelvic rotation and kinematic variables of other motion segments at the instant of SFC as well as the difference in kinematics between the groups of different levels. RESULTS: Most of the kinematic results were not significantly different among the 4 groups with different levels. The increase in the pelvic opening angle at SFC was significantly correlated with increased trunk bend to the nonthrowing arm side and decreased hip flexion angle on the throwing arm side. DISCUSSION AND CONCLUSION: Early pelvic rotation in the throwing motion sequence, as manifested by increased pelvic rotation at SFC, was correlated with changes in kinematic parameters at other motion segments such as increased trunk tilt and decreased hip flexion.

Characteristics and Clinical Outcomes in Overhead Sports Athletes after Rotator Cuff Repair.

Rotator cuff tears in young overhead sports athletes are rare. The pathomechanism causing rotator cuff tears in young overhead athletes is different from that in aged patients. The purpose of this study was to investigate rotator cuff tear characteristics in young overhead sports athletes to reveal the pathomechanism causing these injuries. This study included 25 overhead sports athletes less than 30 years old with atraumatic rotator cuff tears necessitating repair. Rotator cuff tear characteristics were evaluated intraoperatively, including rotator cuff tear shape and injured rotator cuff tendon. Clinical outcome measures were assessed before surgery and at the final follow-up. In this study, 22 patients reported minimal to no shoulder pain and returned to sports without significant complaints at last follow-up. The isolated infraspinatus tendon was most often injured; the incidence rate of the tear at this site was 32% (8 cases). In the deceleration phase of overhead motion, the eccentric contraction force of the ISP (infraspinatus) tendon peaks and the increased load leads to injury at the ISP tendon. The pathomechanism of rotator cuff injuries in young overhead athletes might be not only internal or subacromial impingement, but also these mechanisms.

Assessment of the restriction of arm elevation after intramedullary fixation for proximal humeral fractures.

BACKGROUND: Nail protrusion is suspected as a reason for the restriction of arm elevation after antegrade nailing of proximal humeral fractures, although assessment of the restriction of the glenohumeral joint during arm elevation has been insufficient. METHODS: In this retrospective study, 30 shoulders with proximal humeral fractures in 29 cases were treated with Polarus short nails (Acumed, Beaverton, OR, USA). At a mean final follow-up of 14 months, clinical outcomes, bony union, alignment including retroversion of the head and entry points of the nails were evaluated. The ability of a subject to achieve maximum elevation above the zero position was also evaluated. RESULTS: Constant and Japanese Shoulder Association scores were a mean (SD) of 54 (12) and 71 (8.9) points, respectively. Even though all cases achieved bony union without mal-alignment of the head and greater tuberosity height or protrusion of the nail at its entry point, only six subjects could achieve maximum elevation above the zero position. CONCLUSIONS: Based on these findings, treatment of proximal humeral fractures with an antegrade humeral nail inserted from the top of the humeral head results in restricted arm elevation, even in patients without nail protrusion or fragment malalignment.

Rotator Interval Lesion and Damaged Subscapularis Tendon Repair in a High School Baseball Player.

In 2013, a 16-year-old baseball pitcher visited Nobuhara Hospital complaining of shoulder pain and limited range of motion in his throwing shoulder. High signal intensity in the rotator interval (RI) area (ball sign), injured subscapularis tendon, and damage to both the superior and middle glenohumeral ligaments were identified using magnetic resonance imaging (MRI). Repair of the RI lesion and partially damaged subscapularis tendon was performed in this pitcher. During surgery, an opened RI and dropping of the subscapularis tendon were observed. The RI was closed in a 90° externally rotated and abducted position. To reconfirm the exact repaired state of the patient, arthroscopic examination was performed from behind. However, suture points were not visible in the >30° externally rotated position, which indicates that the RI could not be correctly repaired with the arthroscopic procedure. One year after surgery, the patient obtained full function of the shoulder and returned to play at a national convention. Surgical repair of the RI lesion should be performed in exactly the correct position of the upper extremity.

Increased horizontal shoulder abduction is associated with an increase in shoulder joint load in baseball pitching.

BACKGROUND: Soft tissues of the shoulder undergoes substantial stresses due to humeral head movement, and this may contribute to throwing shoulder injuries in baseball pitchers. Prevention and management of throwing shoulder injuries critically rely on reduction of shear force at the shoulder joint. However, the amount and direction of the force applied to the shoulder during the throwing motion have not been clarified. The purpose of this study was to analyze forces applied to the shoulder during a baseball pitch. METHODS: We performed biomechanical analysis of 213 baseball pitchers of various ages and skill levels. Throwing motion was analyzed with a 3-dimensional motion capture system. The Euler angle sequence was adopted to describe angular values of the upper arm relative to the trunk for shoulder rotation, and inverse dynamics was used to estimate the resultant joint forces at the shoulder. RESULTS: There was a significant relation between horizontal abduction/adduction angle and resultant anterior/posterior force at the point of maximum external rotation (MER) (r = -0.63, P < .01), whereby increased horizontal abduction was associated with increased resultant anterior force. There was a significant but weak correlation between abduction/adduction angle and superior/inferior force at MER (r = 0.24, P < .01). Comparison among the groups with variable ages and skill levels showed larger horizontal abduction and smaller external rotation angles at MER in the adult amateur player group, whereas normalized compression force and internal rotation torque values at MER were smaller in the junior high school- and elementary school-aged groups. DISCUSSION: These results suggest that excessive horizontal abduction at MER increases anterior shear force in the shoulder and may lead to shoulder injuries. Focusing on reducing horizontal abduction at MER in the throwing motion may be key to preventing and managing shoulder injuries in baseball pitchers.

Glenohumeral relationships at different angles of abduction.

PURPOSE: The objective of this study was to clarify the relationships among anatomical landmarks of the glenohumeral joint at different angles of abduction. METHODS: Fifteen volunteers (ten men, five women; mean age 29 years) were enrolled in this study. Images of externally and internally rotated positions at 45°, 90°, and 135° of abduction in the plane 30° anterior to the trunk were taken using an open magnetic resonance imaging system. Landmarks including the glenoidal long axis with its center, bicipital groove, center of the head, and humeral shaft axis were determined. Using a line set on the surface of the head in the plane parallel to the humeral axis (including the head center and bicipital groove with its parallel and perpendicular lines), the glenoid location and rotational relationships were investigated in each position. RESULTS: The average angles of axial rotation were 48° ± 27° at 45º of abduction, 71° ± 20° at 90° of abduction, and 40° ± 27° at 135° of abduction. The trajectories of the glenoid center primarily extended over the anterior portion of the humeral head at 45° of abduction and over the posterior portion at 90° of abduction, while those at 135° of abduction were localized on a small upper portion of the head. CONCLUSIONS: The glenohumeral relationships demonstrated that arm abduction might influence shoulder function through its effects on the portion of the humeral surface in contact with the glenoid during rotation and the resultant changes in the glenohumeral relationships.