Analysis of the three-dimensional scapular kinematics and associated scapular muscle activity during scapular muscle exercises.

OBJECTIVE: To compare scapular kinematics and muscle activity among various scapular muscle exercises. DESIGN: A cross-sectional study. SETTING: A university research laboratory. PARTICIPANTS: Eighteen healthy men participated in this study. MAIN OUTCOME MEASURES: Three-dimensional scapular kinematics was measured with an electromagnetic motion capture system. Activities of the upper trapezius (UT), lower trapezius (LT), and serratus anterior (SA) were measured by using surface electromyography (EMG). In addition, the ratio of LT to the UT (LT/UT) and SA to the UT (SA/UT) was calculated. A repeated one-way analysis of variance and Shaffer's post-hoc analysis were used to detect the differences in each outcome during five exercises. RESULTS: The scapula was rotated upwardly during all exercises except push-up plus. The LT/UT ratio during side-lying external rotation and side-lying flexion were significantly higher than that for scapular plane elevation (P < .05), although the highest activity of the lower trapezius was produced during scapular plane elevation. The activities of the serratus anterior and SA/UT ratio during horizontal adducted elevation and push-up plus were significantly higher than that during scapular plane elevation (P < .05). CONCLUSION: Horizontal adducted elevation might be more appropriate for increasing scapular upward rotation with high serratus anterior activity and SA/UT ratio than push-up plus.

Prevalence of impaired foot function in baseball players with and without disabled throwing shoulder/elbow: a case-control study.

Prevalence of impaired foot function among baseball players with and without a disabled throwing shoulder/elbow was investigated. The study included 138 male players. Players who had previously complained of shoulder/elbow pain during throwing motion were defined as the players with a history, and those who experienced shoulder/elbow pain during the examination were defined as having the injury. Foot function was evaluated by foot "rock paper scissors" movements and floating toes. Their prevalence was assessed and the relationships between players with and without the injuries were statistically analyzed. The prevalence of players with a history and injury was 27% and 7%, respectively. The prevalence of impaired foot function on the non-throwing side among players with injury was significantly higher than those without (60% vs. 28%, P < 0.001) and higher tendency on the throwing side than those without (60% vs. 32%). Regarding floating toes, players with a relevant history showed a significantly higher prevalence on the throwing side than those without (49% vs 28%, P < 0.001) and higher tendency on the non-throwing side than those without (49% vs 32%). Players with disabled throwing shoulder/elbow have a significantly higher prevalence of impaired foot function and floating toes than players without it.

Non-operative management of shoulder osteoarthritis: Current concepts.

Glenohumeral osteoarthritis (OA) is one of the most common causes of shoulder pain. Conservative treatment options include physical therapy, pharmacological therapy, and biological therapy. Patients with glenohumeral OA present shoulder pain and decreased shoulder range of motion (ROM). Abnormal scapular motion is also seen in patients as adaptation to the restricted glenohumeral motion. Physical therapy is performed to (1) decrease pain, (2) increase shoulder ROM, and (3) protect the glenohumeral joint. To decrease pain, it should be assessed whether the pain appears at rest or during shoulder motion. Physical therapy may be effective for motion pain rather than rest pain. To increase shoulder ROM, the soft tissues responsible for the ROM loss need to be identified and targeted for intervention. To protect the glenohumeral joint, rotator cuff strengthening exercises are recommended. Administration of pharmacological agents is the major part next to physical therapy in the conservative treatment. The main aim of pharmacological treatment is the reduction of pain and diminution of inflammation in the joint. To achieve this aim, non-steroidal anti-inflammatory drugs are recommended as first-line therapy. Additionally, the supplementation of oral vitamin C and vitamin D can help to slow down cartilage degeneration. Depending on the individual comorbidities and contraindications, sufficient medication with good pain reduction is thus possible for each patient. This interrupts the chronic inflammatory state in the joint and, in turn, enables pain-free physical therapy. Biologics such as platelet-rich plasma, bone marrow aspirate concentrate, and mesenchymal stem cells have gathered increased attention. Good clinical outcomes have been reported, but we need to be aware that these options are helpful in decreasing shoulder pain but neither stopping the progression nor improving OA. Further evidence of biologics needs to be obtained to determine their effectiveness. In athletes, a combined approach of activity modification and physical therapy can be effective. Oral medications can provide patients with transient pain relief. Intra-articular corticosteroid injection, which provides longer-term effects, must be used cautiously in athletes. There is mixed evidence for the efficacy of hyaluronic acid injections. There is still limited evidence regarding the use of biologics.

Effect of shoulder immobilization position and activities of daily living on the stiffness of the repaired supraspinatus tendon.

BACKGROUND: Although tension on the supraspinatus tendon may be increased by wearing an abduction brace in an improper position or activities of daily living with the operated arm in the brace, the amount of tension has not been objectively evaluated. METHODS: Eighteen patients who underwent arthroscopic rotator cuff repair were enrolled. The stiffness of the repaired supraspinatus tendon was measured with ultrasound elastography to estimate the tension on the repaired tendon. Measurements were performed in 5 immobilization positions (0°, 30°, and 45° of arm elevation in the scapular plane; 30° of arm elevation in the scapular plane+60° (horizontal adduction) and -60° (horizontal abduction)) and 3 static positions simulating drinking, brushing teeth, and dressing. FINDINGS: Stiffness at 30° of scapular plane elevation was lower than 0° of scapular plane elevation (P = 0.034), 30° of elevation in the scapular plane+60° (P < 0.001), and -60° (P < 0.001). There was no significant difference in the stiffness between 30° and 45° of scapular plane elevation (P = 1.000). The stiffness was the greatest at 30° of elevation in the scapular plane-60° among the 5 immobilization positions. The stiffnesses at drinking and brushing teeth were greater than 30° of scapular plane elevation (P < 0.001). INTERPRETATION: Immobilization with the arm ≥30° of elevation in the scapular plane may be an optimal position for minimizing stiffness or tension on the repaired tendon. Drinking and brushing teeth may need to be performed using the non-operated arm to protect the repaired tendon.

Physical functions, to be or not to be a risk factor for osteochondritis dissecans of the humeral capitellum?

Background: Physical risk factors for osteochondritis dissecans (OCD) of the humeral capitellum in young baseball players have not been fully elucidated. We aimed to identify the risk factors for capitellar OCD in baseball players aged 8-14 years. Methods: Between December 2018 and December 2019, young baseball players were recruited from 8 regional baseball leagues. Ultrasonography and physical assessments were performed preseason and at the end of the study period. Bilateral passive ranges of motion (ROM) of horizontal adduction of the shoulders, internal rotation (IR) of the hips, and the thoracic kyphosis angle were measured. 1-year follow-ups were scheduled to determine the occurrence of OCD. Players with OCD were categorized into an OCD group; those without OCD and any elbow pain for one year were categorized into a non-injured group. The players' baseline data (age, sex, position in baseball, and Rohrer's Index) were analyzed using univariate analyses. Their physical parameters were analyzed using two-way analysis of variance with repeated measures to investigate OCD-related risk factors. Results: In total, 3651 baseball players attended the 1-year follow-up. Of these, 71 (1.9%) players had OCD of the humeral capitellum. In the OCD group, a significant association was found at baseline and at the end of the study period between a higher Rohrer index at the baseline and a smaller hip IR ROM on the nondominant side. Conclusions: Loss of hip IR ROM on the nondominant side is a newly discovered risk factor related to physical function in the development of OCD.

Prevalence of disabled throwing shoulder and its shoulder function among youth football goalkeepers.

Aim: Although the football goalkeepers are overhead athletes, no studies have reported the prevalence of disabled throwing shoulder (DTS) and the shoulder function. Thus, this study aimed to investigate the prevalence of DTS among youth football goalkeepers and to determine the relationship among their shoulder functions. Methods: Youth football goalkeepers, who participated in a pre-participation medical examination were included in the study. The questionnaire was handed out before the examination to determine the players' age, dominant hand, and shoulder pain history. If the player had a history of shoulder pain during ball throwing motion in the past, they were defined as goalkeepers with DTS. Physical examination of scapular positioning, scapular retraction and rotator cuff muscle strength, and ultrasonographic evaluation were performed. Results: Six goalkeepers (16%) had a history of DTS among the 38 male youth football goalkeepers. The presence of scapular malpositioning, limitation of scapular retraction, and decrease in rotator cuff strength was significantly higher in goalkeepers with DTS than in those without DTS (p = 0.03, p < 0.001, p < 0.001, respectively). Three goalkeepers with DTS revealed ultrasonographic findings. Conclusion: The prevalence of DTS among youth football goalkeepers was 16%. All these players had scapular malpositioning and limitation of scapular retraction. Scapular malpositioning and limitation of scapular retraction may be related to the DTS in youth football goalkeepers. Level of evidence: Level IV.

Increased external rotation related to the soft tissues is associated with pathologic internal impingement in high-school baseball players.

BACKGROUND: Changes in soft-tissue structures such as anterior laxity and posterior tightness are thought to contribute to the development of pathologic internal impingement in baseball players. Although side-to-side differences in shoulder rotational range of motion (ROM) is commonly used in clinical practice to quantify the soft-tissue changes, the ROM does not accurately reflect the soft-tissue changes because the ROM is affected not only by the soft tissues, but also by the bone. Increased retroversion of the humeral head is often observed in the dominant shoulder of throwing athletes. The purpose of this study was to determine the relationship between the soft-tissue-related (STR) ROM and pathologic internal impingement in baseball players. METHODS: Bilateral humeral retroversion and ranges of glenohumeral external rotation (ER) and internal rotation (IR) were investigated in 81 high-school baseball players. The players were divided into two groups: the internal impingement group (19 players) and the control group (62 players). Humeral retroversion was measured using the ultrasound-assisted technique to assess the bone-related ER and IR. The STR ER and IR were defined as subtracting the amount of humeral retroversion from the measured ER and IR. RESULTS: The side-to-side difference (throwing shoulder - nonthrowing shoulder) in humeral retroversion showed no significant difference between the internal impingement group (6° ± 10°) and control group (11° ± 11°) (P = .064). The side-to-side difference in STR ER was significantly greater in the internal impingement group (12° ± 12°) than that in the control group (1° ± 14°) (P = .002). No significant difference was observed in the side-to-side difference in STR IR between the internal impingement group (-7° ± 16°) and control group (-5° ± 15°) (P = .696). Pathologic internal impingement was significantly associated with the side-to-side difference of STR ER (odds ratio, 1.06 for increase of 1°; 95% confidence interval, 1.02-1.11; P = .008). CONCLUSION: In high-school baseball players, the increased STR ER in the throwing shoulder may be associated with pathologic internal impingement. An increase of 10° in side-to-side difference in STR ER would increase the risk of pathologic internal impingement by 1.8 times.

Changes in shoulder muscle activities and glenohumeral motion after rotator cuff repair: an assessment using ultrasound real-time tissue elastography.

BACKGROUND: Although rotator cuff repair is performed to restore the function of the rotator cuff muscles and glenohumeral (GH) joint motion, little has been known regarding the recovery process. The purpose of this study was (1) to investigate changes over time in activities of the supraspinatus and deltoid muscles assessed by ultrasound real-time tissue elastography (RTE) after rotator cuff repair and (2) to determine contributions of the activities of these muscles to the GH joint motion. METHODS: Twenty patients after rotator cuff repair and 13 control participants were enrolled in this study. Elasticity of the supraspinatus and middle deltoid muscles were measured at rest and 30° of humerothoracic elevation in the scapular plane (scaption) by using RTE. The elasticity at 30° of scaption was normalized to that at rest in each muscle to quantify their muscle activities. In addition, the supraspinatus-to-middle deltoid (SSP/MD) ratio for the normalized elasticity was calculated. The GH elevation angle was measured with a digital inclinometer, which was calculated by subtracting the scapular upward rotation angle from 30° of scaption. For patients after rotator cuff repair, all measurements were performed at 6 weeks, 8 weeks, 3 months, and 6 months after surgery. Rotator cuff integrity was examined with magnetic resonance imaging at 6 months after surgery. RESULTS: Fifteen of 20 patients who remained intact at 6 months after surgery completed this study. The supraspinatus activity at 6 weeks was significantly smaller than that at 3 months (P = .006) and 6 months (P = .010). There was no significant difference in the supraspinatus activity between the patients at 3 months and the control participants (P = .586). The middle deltoid activity at 6 weeks was significantly greater than that at 6 months (P = .003). There was positive correlation between GH elevation angle and the activity of the supraspinatus relative to the deltoid at 6 weeks (r = 0.75, P = .001) and 8 weeks (r = 0.53, P = .041). CONCLUSION: The supraspinatus activity increased from 6 weeks to 3 months after surgery. The supraspinatus activity at 3 months after surgery was the same level as that in healthy individuals. On the other hand, the deltoid activity decreased from 6 weeks to 6 months after surgery. The increase in activity of the supraspinatus relative to the deltoid was likely to be related to the increase in GH elevation during postoperative at 8 weeks.

Differences in scapular motion and parascapular muscle activities among patients with symptomatic and asymptomatic rotator cuff tears, and healthy individuals.

BACKGROUND: Altered scapular motion is thought to be one of the factors associated with the development of symptomatic rotator cuff tears. However, the differences in kinematics and muscle activities of scapular upward/downward rotation between patients with symptomatic and asymptomatic tears are unclear. The purpose of this study was to compare the differences in kinematics and muscle activities of scapular rotation among patients with symptomatic and asymptomatic tears, and healthy individuals. METHODS: Twenty-three patients with rotator cuff tears and 9 healthy individuals (healthy group) participated in this study. Based on a visual analog scale (VAS, 0-100 mm), the patients were divided into symptomatic (13 patients; VAS ≥20 mm) and asymptomatic (10 patients; VAS <20 mm) groups. Scapular upward rotation was measured with a digital inclinometer. Elasticities of the upper trapezius, levator scapulae, and rhomboid major were assessed by using ultrasound real-time tissue elastography to quantify their muscle activities. All measurements were performed at 0°, 60°, 90°, and 120° of active arm elevation in the scapular plane. RESULTS: Scapular upward rotation was significantly less in the symptomatic group (9.4° ± 5.6°) compared with the asymptomatic group (15.7° ± 6.0°; P = .022) at 90° of arm elevation. The activity of the levator scapulae was significantly higher in the symptomatic group compared with the asymptomatic and healthy groups (P = .013 and P = .005, respectively) at 90° of arm elevation. The activity of the upper trapezius was significantly higher in the symptomatic group compared with the healthy group (P = .015) at 120° of arm elevation. CONCLUSION: Patients with symptomatic rotator cuff tears showed less scapular upward rotation and higher activity of the levator scapulae at 90° of arm elevation compared to patients with asymptomatic rotator cuff tears.

The Influence of Pitch Velocity on Medial Elbow Pain and Medial Epicondyle Abnormality Among Youth Baseball Players.

BACKGROUND: Pitch velocity is associated with elbow injuries among skillful baseball players. However, the relationship between pitch velocity and throwing elbow injuries among youth players has not yet been clarified. PURPOSE: To investigate the influence of pitch velocity on medial elbow pain and medial epicondyle abnormality among youth baseball players. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: The participants consisted of 256 elementary school players (mean age, 11 ± 1 years; range, 9-12 years). The medial aspect of the elbow was evaluated using ultrasound imaging. A questionnaire was used to investigate past or present pain in the elbow, background of the players (age, height, body mass index, and years of baseball experience), and playing environment (number of days of practice in a week, experience as a pitcher, and cryotherapy of the shoulder and elbow after practice). Positioning of the scapula, range of motion in shoulder internal/external rotations and hip internal rotation, angle of the straight-leg raise, and heel-to-buttock distance were measured. The pitch velocity was recorded using a pitch velocity radar gun. The relationship between these variables and the presence of medial epicondyle abnormality, as well as past or present elbow pain, were statistically analyzed. RESULTS: A medial epicondyle abnormality was observed in 130 players (51%), elbow pain in the past in 65 players (25%), and elbow pain during the examination in 14 players (5%). Sixty-nine players (27%) experienced elbow pain either in the past or during examination. Abnormality of the medial epicondyle had a relationship with the pitch velocity (odds ratio [OR], 1.1 for increase of 1 km/h; 95% CI, 1.1-1.2; P < .0001) and the number of practice days in a week (OR, 1.8 for increase of the practice days; 95% CI, 1.4-2.5; P < .0001). Pitch velocity was also significantly related with past pain, present pain, and past and/or present pain of the elbow (OR [km/h], 1.1, 1.1, 1.1; 95% CI, 1.0-1.1, 1.0-1.2, 1.1-1.2; P < .0001, P = .002, P < .0001, respectively). CONCLUSION: Pitch velocity was significantly associated with abnormality of the medial epicondyle and elbow pain. A 10-km/h increase in pitch velocity would increase the risk of medial epicondyle abnormality and medial elbow pain by 3 times.

The differences in sagittal plane whole-body angular momentum during gait between patients with hemiparesis and healthy people.

Regulation of whole-body angular momentum (WBAM) is essential for maintaining dynamic balance during gait. Patients with hemiparesis frequently fall toward the anterior direction; however, whether this is due to impaired WBAM control in the sagittal plane during gait remains unknown. The present study aimed to investigate the differences in WBAM in the sagittal plane during gait between patients with hemiparesis and healthy individuals. Thirty-three chronic stroke patients with hemiparesis and twenty-two age- and gender-matched healthy controls walked along a 7-m walkway while gait data were recorded using a motion analysis system and force plates. WBAM and joint moment were calculated in the sagittal plane during each gait cycle. The range of WBAM in the sagittal plane in the second half of the paretic gait cycle was significantly larger than that in the first and second halves of the right gait cycle in the controls (P = 0.015 and P = 0.011). Furthermore, multiple regression analysis revealed the slower walking speed (P < 0.001) and larger knee extension moment on the non-paretic side (P = 0.003) contributed to the larger range of WBAM in the sagittal plane in the second half of the paretic gait cycle. Our findings suggest that dynamic stability in the sagittal plane is impaired in the second half of the paretic gait cycle. In addition, the large knee extension moment on the non-paretic side might play a role in the dynamic instability in the sagittal plane during gait in patients with hemiparesis.

Influence of thoracic posture on scapulothoracic and glenohumeral motions during eccentric shoulder external rotation.

BACKGROUND: Throwing injuries to the shoulder joint often occur during shoulder external rotation. An appropriate combination of thoracic, scapular, and humeral motion during throwing is important to prevent such injuries, but it is unclear how thoracic posture contributes to shoulder motion during throwing. RESEARCH QUESTION: The purpose of this study, therefore, was to clarify the influence of thoracic posture on scapulothoracic and glenohumeral motion during shoulder external rotation. METHODS: Eccentric external rotation at 90° of shoulder abduction in thoracic flexion and extension postures was performed by 15 asymptomatic participants. Three-dimensional scapulothoracic and glenohumeral movements were measured with an electromagnetic tracking device at 75°, 80°, 85°, and maximum shoulder external rotation. The thoracic angle and maximum shoulder external rotation in absolute coordination were measured with a three-dimensional motion capture system. RESULTS: The results showed that scapular posterior tilting and external rotation in the thoracic extension posture were significantly greater than those in the flexion posture (p < 0.05). Glenohumeral horizontal extension was significantly less in the thoracic extension posture than in the flexion posture (p < 0.05), whereas maximum shoulder external rotation was significantly greater (p < 0.01). Thus, thoracic extension increased scapulothoracic posterior tilting and external rotation and reduced glenohumeral horizontal extension during shoulder external rotation, as well as increasing maximum shoulder external rotation. SIGNIFICANCE: These findings suggest that thoracic extension may contribute to reduction of mechanical demand in the glenohumeral joint during throwing, potentially reducing shoulder injuries.

Regulation of quasi-joint stiffness by combination of activation of ankle muscles in midstances during gait in patients with hemiparesis.

BACKGROUND: The regulation of ankle joint stiffness by combination of activation of plantarflexor and dorsiflexor during gait has not been investigated in patients with hemiparesis. The objective of the present study was to examine the relationship between combination of activation of ankle muscles and quasi-joint stiffness (QJS) during the stance phase of gait. METHODS: The activation of the medial head of the gastrocnemius (MG), soleus, and tibialis anterior, gait parameters were collected from 19 patients with hemiparesis due to stroke and from 12 healthy controls using a three-dimensional motion analysis system. The indexes of reciprocal activation and coactivation were calculated from the ratio of plantarflexor to dorsiflexor activation and magnitude of coactivation (MC), which is computed by multiplying an index of simultaneous activation of ankle muscles by plantarflexor activation. RESULTS: QJS was significantly correlated with MC of MG on the paretic side, whereas it correlated with the ratio of MG (r = 0.63, p < 0.05) in healthy controls and the ratio of MG (r = 0.67, p < 0.05) and soleus (r = 0.61, p < 0.05) on the non-paretic side in midstance. Furthermore, QJS on the paretic side was lower than that on the non-paretic side and in healthy controls (p < 0.05). SIGNIFICANCE: Our findings support that the regulation of QJS in midstance by reciprocal activation is altered on the paretic side, whereas it may be regulated by reciprocal activation and enhanced by relatively high activity of plantarflexor on the non-paretic side and in healthy controls.

Contact pressure of the coracoacromial arch in shoulders with joint contracture: A cadaveric study.

BACKGROUNDS: There have been many reports describing that the capsular fibrosis of the shoulder joint is the main cause of frozen shoulder, whereas others reported the significance of subacromial impingement as an etiological factor. The purpose of this study was to investigate the contact pressure between the coracoacromial arch and the rotator cuff tendons to clarify the contact phenomenon in shoulders with joint contracture. METHODS: Fourteen fresh-frozen cadaveric shoulders were used. Specimens were divided into two groups: normal group (8 shoulders, definition: more than 61° of flexion and abduction and more than 21° of external rotation) and joint contracture group (6 shoulders, definition: less than 60° of flexion and abduction and less than 20° of external rotation). Contact pressure and area beneath the coracoacromial arch were measured by a flexible force sensor during flexion, abduction, internal and external rotation in adduction and abduction, extension and horizontal extension motions. RESULTS: The peak contact pressure under the acromion was observed at 90° in flexion and abduction in the normal group, whereas that in the contracture group was observed at 30° in flexion (P = 0.037) and at 30° in abduction (P = 0.041). Contact pressure in the contracture group was significantly higher than that in the normal group at 20° and 30° of abduction (P = 0.043, P = 0.041, respectively). There were no significant differences of contact pressure during other motions. Although no significant differences of contact pressure beneath the coracoacromial ligament were observed, contact area significantly increased in extension and horizontal extension motion. CONCLUSION: The contact between the acromion and the rotator cuff was observed in lower angles of flexion and abduction in shoulders with contracture than in those without. When treating patients with shoulder contracture, we need to perform rehabilitation taking such an abnormal movement into consideration.

Age-Related Changes in Morphology and Function of Scapular Muscles in Asymptomatic People.

BACKGROUND: Aging is a contributing factor to rotator cuff tears. Dysfunction of the scapular muscles can be a potential cause of rotator cuff tears. Although aging can contribute to dysfunction of the scapular muscles and subsequently result in rotator cuff tears, the effects of aging on scapular muscles are unclear. OBJECTIVE: To determine changes in sizes and electromyographic activities of the scapular muscles with age in asymptomatic subjects. DESIGN: Cross-sectional study. PATIENTS: Fifty-four asymptomatic subjects without shoulder pain and dysfunction (18 male and 36 female) were recruited for this study. Subjects consisted of 19 people aged 20-39 years (young adult group, 27.2 ± 5.2 years), 17 people aged 40-59 years (middle age group, 49.9 ± 6.6 years), and 18 people aged 60-79 years (elderly group, 68.0 ± 7.1 years). METHODS: Using ultrasonography, we measured the muscle thickness of the trapezius (upper and lower portions), serratus anterior, and middle deltoid muscles during rest with the subject in a sitting position. Activities of the same muscles were measured with surface electromyography during shoulder elevation in the scapular plane up to 120°. The electromyographic data were analyzed at ranges 0°-30°, 30°-60°, and 60°-90°. Analysis of variance and Bonferroni multiple comparisons were used for statistical analysis. RESULTS: Muscle thickness of the lower trapezius in the elderly group was decreased significantly compared with that in the young adult group (95% confidence interval -0.40, 2.24; P < .001) and middle age group (95% confidence interval -0.34, 1.89; P = .012). There were no significant differences in muscle activity and activity ratio between groups. CONCLUSION: In scapular muscles, muscle thickness of the lower trapezius significantly decreased with aging, although there were no decreases in muscle thicknesses of the other muscles between different age groups. For the functional change, aging may not affect the scapular muscle activities and balance of the activities between the deltoid and scapular muscles. LEVEL OF EVIDENCE: IV.

Differences in humeral retroversion in dominant and nondominant sides of young baseball players.

BACKGROUND: The relationship between the disabled throwing shoulder and humeral retroversion has recently attracted a great deal of attention. However, none of the previous studies clarified when the side-to-side difference of humeral retroversion in young baseball players would start. This study aimed to clarify when the difference of humeral retroversion in the dominant and nondominant sides appeared in baseball players. METHODS: The bicipital-forearm angle in bilateral shoulders of 172 elementary school baseball players was measured by ultrasound. The bicipital-forearm angle was defined as an angle between the perpendicular line to the bicipital groove and the ulnar long axis with the elbow flexed at 90°. The correlation between the bicipital-forearm angle and the grade and the difference of the bicipital-forearm angle between the dominant and nondominant sides were analyzed. RESULTS: In the nondominant shoulders, the bicipital-forearm angle increased with the grade in school (r = 0.32, P < .0001), but this was not observed in the dominant shoulders. In the fourth to sixth graders, the bicipital-forearm angles were significantly smaller in the dominant shoulders than in the nondominant shoulders. CONCLUSION: Our findings indicated that humeral retroversion decreased with age in the nonthrowing side but not in the throwing side and that the side-to-side difference of humeral retroversion in the baseball players became obvious from the fourth grade. We assume that the repetitive throwing motion restricts the physiologic humeral derotation process and the difference became apparent from the fourth grade when the growth spurt begins in boys.

The effect of scapular position on subacromial contact behavior: a cadaver study.

BACKGROUND: Patients with subacromial impingement were reported to show abnormal scapular positions during shoulder elevation. However, the relationship between the scapular positions and subacromial impingement is unclear. The purpose of this study was to biomechanically determine the effect of scapular position on subacromial contact behavior by using fresh frozen cadavers. METHODS: The peak contact pressure on the coracoacromial arch was measured with a flexible tactile force sensor in 9 fresh frozen cadaver shoulders. The measurement was performed during passive glenohumeral elevation in the scapular plane ranging from 30° to 75°. The scapular downward and internal rotations and anterior tilt were simulated by tilting the scapula in 5° increments up to 20°. The measurement was also performed with combination of scapular downward and internal rotations and anterior tilt positions. RESULTS: The peak contact pressure decreased linearly with anterior tilt, and a significant difference between neutral scapular position (1.06 ± 0.89 MPa) and anterior tilt by 20° (0.46 ± 0.18 MPa) was observed (P < .05). However, the scapular positioning in the other directions did not change the peak contact pressure significantly. Furthermore, any combination of abnormal scapular positions did not affect peak contact pressure significantly. CONCLUSION: Scapular anterior tilt decreased peak contact pressure during passive shoulder elevation. In addition, scapular downward and internal rotations had little effect on peak contact pressure. The abnormal scapular motion reported in previous studies might not be directly related to symptoms caused by subacromial impingement.

Transosseous-equivalent repair with and without medial row suture tying: a cadaveric study of infraspinatus tendon strain measurement.

BACKGROUND: How the use of the transosseous-equivalent (TOE) technique effects the stress concentration in repaired rotator cuff tendon is unknown. This study was conducted to determine the strain between the intact rotator cuff tendon and the tendon repaired using the TOE technique with and without medial row suture tying. MATERIALS AND METHODS: Strain of the infraspinatus tendon from 10 fresh-frozen cadavers was measured at the (A) tendon insertion, (B) tendon footprint, (C) tendon of the medial suture level, and (D) musculotendinous junction of the tendon. The strain was measured during 2 cycles of internal and external rotations while applying 4 different loads to the infraspinatus. After the intact tendon was evaluated, an artificially created tear of the infraspinatus was repaired using the TOE technique. Medial row sutures were tied in 5 shoulders (T group) and untied in the rest (UT group). The strains at 4 sites were compared between the intact and the TOE-repaired tendon and between the T and UT groups. RESULTS: The strain was significantly reduced at site B in the repaired tendon in the T and UT groups compared with the intact tendon for all loads (P < .05). At site C, the strain increased for all loads in the T group compared with the intact tendon (P < .05). CONCLUSION: The strain of the tendon over the footprint area was significantly smaller than the intact tendon when repaired with the TOE technique. The strain at the medial suture level was significantly greater when the medial sutures were tied compared with those untied.

Changes in stiffness of the dorsal scapular muscles before and after computer work: a comparison between individuals with and without neck and shoulder complaints.

PURPOSE: The aim of this study was to compare the stiffness of the dorsal scapular muscles before and after computer work between individuals with and without neck and shoulder complaints. METHODS: Thirty subjects were divided into patient (n = 18) and control (n = 12) groups. The stiffness of the upper trapezius, levator scapulae, and rhomboid major was measured using ultrasound elastography before and after a 30-min typing task. The strain ratio of the muscle to an acoustic coupler was calculated (a lower strain ratio value indicates greater muscle stiffness). RESULTS: At baseline, the strain ratio of the upper trapezius in the patient group (3.762 ± 1.679) (mean ± SD) was significantly lower than that of the control group (7.763 ± 5.921) (p = 0.041). No significant change in the strain ratio of the upper trapezius after the typing task was observed in the patient group (4.158 ± 3.465) (p = 0.549). A significant decrease in the strain ratio of the levator scapulae after the typing task was observed in the patient group (before: 9.006 ± 7.079, after: 5.718 ± 2.847) (p = 0.022), whereas there was no significant change in the control group (p = 0.436). CONCLUSIONS: The increase in stiffness of the upper trapezius is an objective finding and may be a persistently altered condition in individuals with neck and shoulder complaints. The patterns of change in stiffness of the levator scapulae are different between individuals with and without neck and shoulder complaints.

Does Scapular Motion Regress with Aging and is It Restricted in Patients with Idiopathic Frozen Shoulder?

PURPOSES: It has been reported that the amount of posterior tilt and upward rotation in scapular motions decreases with aging. The purposes of the current study were to investigate age related scapular motion regression and scapular restriction in patients with idiopathic frozen shoulder (IFS). METHODS: The groups were recruited as follows: two groups of 50 asymptomatic subjects aged in their twenties and fifties, and 56 patients with IFS. We passively moved the scapula toward 8 directions: elevation/depression; upward/downward rotation; external/internal rotation; and anterior/posterior tilt. The grading of scapular motion was ranged from 0 to 3 (3, normal; and 0, severe restriction) and the score for each direction and the total aggregated score for all directions were calculated. RESULTS: Scapular restriction was present in 3 subjects (6%) in the normal 20s group, 10 (14%) in the 50s group, and 51 (91%) in the IFS group. The total score between the normal 20s and 50s groups did not show statistical difference; however, greater significance was present between the normal 50s group and the IFS group (p < 0.01). There was statistical significance in depression (p < 0.01), downward rotation (p < 0.01), and posterior tilt (p < 0.01) among the 3 groups. CONCLUSION: Depression, downward rotation, and posterior tilt substantially regress with aging. Scapular motions towards depression, downward rotation, external rotation, and posterior tilt are severely restricted in the IFS group.