Hiroki Ninomiya

Influence of Combinations of Shoulder, Elbow and Trunk Orientation on Elbow Joint Loads in Youth Baseball Pitchers:

Objectives: Shoulder and elbow pain in youth baseball pitchers is a well-recognized phenomenon. Common problems in pitching mechanics that can lead to injury begin with stride foot contact. The purpose of this study was to address the relationships between the combinations of shoulder, elbow and trunk orientation at the instant of stride foot contact and elbow joint loads in youth baseball pitchers. Methods: A total of 143 Japanese male youth baseball pitchers participated in this study after providing written informed consents approved by the hospital’s institutional review board. The procedures to be performed were also explained to their parent(s) or legal guardian(s). Each participant was not currently injured or recovering from an injury at time of testing. For data collection of baseball pitching, a set of 14-mm spherical reflective markers was placed on the skin overlying 34 anatomical landmarks determined. Subsequently, a motion capture three-dimensional automatic digitizing system was used to collect 500-Hz from 7 charge-coupled-device synchronized cameras was set up around the regulation pitching mound in an indoor laboratory. After performing a preparation routine of stretching and warm-up pitching, each player pitch to 5 fastball pitches off the pitching mound to a catcher at the regulation distance of 16 m for youth pitchers. The best pitch thrown for a strike was chosen for kinematic and kinetic analysis. The local coordinate systems were used to calculate 3-dimesional rotation at the trunk, shoulder and elbow using the typical Eulerian sequence. Afterward, the standard inverse dynamic equation was used to estimate resultant joint forces and torques at throwing shoulder and elbow. In order to normalize data between subjects, forces and torques were expressed as percent using body weight and height. A multiple regression analysis was carried out to assess the combined effects of shoulder (external rotation, abduction and horizontal adduction), elbow (pronation and extension) and trunk (extension, contralateral tilt, rotation) orientation at SFC and the onset time of trunk rotation on elbow joint loads at SFC. The onset time of trunk rotation was defined as the event in which the magnitude of trunk rotation begins to decrease from tis maximum value. Results: The peak medial force of the elbow was significant correlated with the peak internal rotation torque of the shoulder and the peak varus torque of the elbow (Figure 1). The medial force of the elbow at SFC was significantly correlated with the peak medial force of the elbow (r = .41, p < .001). The adjusted multiple R2 value was 0.45, indicating that over 45% of the variance in the medial force of the elbow at SFC was explained by the regression equation. The standard error of estimate was 4.34. All 3 of the regression variables were significant and are shown in Table 1. Conclusion: The combinations of the greater external rotation of the shoulder, contralateral trunk tilt and elbow extension at SFC may have an indirect influence on the peak medial force on the elbow (Table 1). Then the peak elbow varus torque and shoulder internal rotation torque lead to increase as a result of these. These biomechanical data provide a scientific basis for clinicians, athletes, and coaches to establish methods to prevent pitching-related injuries and improve pitching mechanics.

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.

Analysis of throwing motion

Throwing motion needs sufficient physical strength of the shoulder and efficient coordination of the trunk and lower extremity movement. To prevent the occurrence of throwing injury, the biomechanical analysis of throwing motion it is absolutely necessary. In order to investigate quantitative understanding and evaluate each individual throwing motion being complex, the Graphical User Interface — based kinematic and kinetic analysis System (Nobuhara Hospital, Japan) was developed. 448 pitchers were measured their actions with various performance levels using a Motion Capture System. The resultant joint forces and moments in the wrist, elbow and shoulder were estimated using the inverse dynamics technique.

How is biomechanical knowledge useful for understanding shoulder disorders

Shoulder has a wide range of motion. Contact point between the glenoid and the humeral head, tension of soft tissue, and alignment of muscles connecting the bones drastically change in its range of motion. Mechanism stabilizing shoulder joint is influenced by arm positioning. Assessment of joint stability should always take arm positioning into consideration. In fact, there is a subtle instability which can only be detected when the arm is elevated. The glenoid dysplasia might be a cause for its instability. These findings can be detected only by 3D computer generated images except in some typical cases. Generally, joint stability is judged by location of the humeral head center in the glenoid. More intricate approach is necessary for some disorders. Analysis of contact area and other glenohumeral relation can clarify instability which cannot be detected through investigating location of joint center. The studies using those parameters showed that the joint is inherently unstable with the arm externally rotated at 90 degrees of elevation, and that joint positioning would be more apt to be affected from the cocking to the acceleration phase during throwing activity. We think such instability might lead to throwing disorders.

Estimation of the Optimal Shoulder Orientation from the Viewpoint of Minimal Shoulder Joint Load in 183 Adolescent Baseball Pitchers

Objectives: Adolescent baseball pitchers are prone to shoulder injury as a result of the extreme force and torque placed on the shoulder, especially tremendous joint force applies to the shoulder near ball release. In our clinical experience, shoulder pain at ball release is common complaint. Little analysis is available about the relationship between shoulder orientation and shoulder joint force at the ball release. Methods: A total of 183 adolescent baseball pitchers (14 to 18 years old) participated after providing written informed consents approved by the hospital’s institutional review board. The procedures to be performed were also explained to their parent(s). Each participant was not currently injured or recovering from an injury at time of testing.For data collection, a set of 14-mm spherical reflective markers was placed on the skin overlying 34 anatomical landmarks. Subsequently, the motion capture automatic digitizing system was used to collect 500-Hz from 7 synchronized cameras was set up around the regulation pitching mound in an indoor laboratory. After stretching and warm-up pitching, each player pitch to 5 fastball pitches. Then, the best pitch thrown for a strike was chosen for kinematic and kinetic analysis.The local coordinate systems were used to calculate 3-dimesional rotation at the shoulder using the typical Eulerian sequence. The standard inverse dynamic equation was used to estimate resultant joint force at throwing shoulder. In order to normalize data between subjects, force was expressed as percent using body weight.To estimate the optimal shoulder orientation at ball release, Rz was defined a shoulder abduction angle, which indicated zero value of shoulder superior/inferior force at ball release by linear regression analysis. Similarly-defined Ry was a shoulder horizontal adduction/abduction angle, which indicated zero value of shoulder anterior/posterior force. Afterward, 2 groups with consideration for variations of shoulder orientations at ball release were created: {A- < Rz - 5, Rz - 5 ≤ A ≤ Rz + 5, Rz + 5 < A+}, {B- < Ry - 5, Ry - 5 ≤ B ≤ Ry + 5, Ry + 5 < B+}. Because shoulder range of motion is generally measured 5 degrees intervals in the orthopaedics. Then, we employed MANOVA to investigate significant differences of averages of inferior/superior and anterior/posterior forces applied to the shoulder at ball release among 2 groups respectively. Results: Superior/inferior force was significantly correlated with shoulder abduction. Also anterior/posterior force was strongly correlated with shoulder horizontal adduction/abduction (Table1). The average superior force at A- and the average inferior force at A+ were significantly greater than that at A. Also, the average anterior force at B- and the average posterior force at B+ were significantly higher than at that B (Table 2). Conclusion: The optimal shoulder orientation for minimizing shoulder force at the instant of ball release was 80.6 degrees of shoulder abduction and 10.7 degrees of shoulder adduction. Excessive shoulder horizontal abduction can lead to SLAP lesion, internal impingement and any more pitching-related shoulder injuries has been published. The results of this study demonstrated that increasing amounts of shoulder horizontal abduction were shown to increase anterior force on the shoulder. Therefore, excessive shoulder horizontal abduction can be responsible for several pitching-related shoulder injuries from the viewpoint of shoulder joint load. Table 1. Correlation coefficient between shoulder orientation and shoulder force at ball release in 183 adolescent baseball pitchers. Shoulder force at ball release (%BW) Variables Anterior force Compressive force Superior force Ball release  Shoulder abduction (°) r = -.09 (P = .233) r = .07 (P = .929) r = -.66 (P < .000)  Shoulder horizontal adduction (°) r = -.85 (P < .000) r = .12 (P = .117) r = -.38 (P < .000)  Ball speed (m/s) r = .26 (P < .000) r = .60 (P < .000) r = -.07 (P = .347) Table 2. The average (±SD) of shoulder force at ball release among |A-, A, A+| and |B-, B, B+| groups Shoulder force (%BW) A-(A- < Rz - 5) A(Rz - 5 < A < Rz + 5) A+(Rz + 5 < A+) Significantdifferences Ball release  Anterior force 15.4 ± 26.4 24.0 ± 20.3 18.4 ± 23.2 NS  Compressive force 85.3 ± 17.8 90.4 ± 22.3 88.8 ± 15.6 NS  Superior force 12.3 ± 14.5 0.1 ± 15.9 -17.1 ± 15.5 P < .050 for all Shoulder force (%BW) B-(B- < Ry - 5) B(Ry -5 < B < Ry + 5) B+(Ry + 5 < B+) Significantdifferences Ball release  Anterior force 28.6 ± 17.6 0.2 ± 14.9 -25.4 ±21.9 P < .001 for all  Compressive force 89.3 ±17.2 90.9 ± 15.9 70.0 ± 24.0 P = .009 for B vs B+P = .013 for B- vs B+  Superior force -7.4 ± 16.8 -19.8 ± 18.9 -19.6 ± 20.8 P < .001 for B vs B- Note: Rz is 80.6 degrees of shoulder abduction and Ry is 10.7 of shoulder horizontal abduction. NS is not significant at the P < .05 level

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.

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.