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Introduction Ulnar nerve instability (UNI) is a common cause of ulnar neuropathy. The relationship between UNI and medial elbow instability has not yet been investigated in baseball pitchers. We investigated the association between UNI and the degree of ulnar collateral ligamentous laxity in high school baseball pitchers. Methods We examined 172 local high school baseball pitchers. A clinical examination assessed pitchers' physical condition during the winter off-season from 2021 to 2023. Ultrasound examinations were conducted on the medial joint gap of both sides of the pitchers during valgus stress and non-stress conditions. The participants were divided into three groups based on the ultrasonographic findings of UNI: no instability (type N), subluxation (type S), and dislocation (type D). For the pitching side, we assessed the relationship between the type of UNI and medial elbow instability and other clinical and physical findings, including ulnar nerve symptoms, grip strength, and key pinch strength. Results The prevalence of UNI on the throwing side was 62% (subluxation, 32%; dislocation, 30%) and 60% (subluxation, 26%; dislocation, 34%) on the non-throwing side. Regarding the rates according to the three types of UNI, there was no significant difference between the pitching and non-pitching sides. There was a significant difference in the distance between the medial joint gap under stress and non-stress conditions, with 0.59 mm on the throwing side and 0.36 mm on the non-throwing side; however, no significant difference was found in the degree of ulnar collateral ligamentous laxity when comparing each type of UNI on the throwing side. Conclusion In this study of 172 high school baseball pitchers, UNI occurred on the throwing side in 62% of subjects (32% subluxation, 30% dislocation) and on the non-throwing side in 60% of subjects (26% subluxation, 34% dislocation). There was no significant difference in the rates of the three types of UNI between the pitching and non-pitching sides. Additionally, there was no association between UNI type and the presence or absence of ulnar nerve symptoms. The medial joint gap distance under both stress and non-stress conditions was significantly larger on the throwing side compared to the non-throwing side. However, no significant association was found between the different types of UNI and the degree of ulnar collateral ligamentous laxity on the throwing side in this population.

Background: Differences in shoulder range of motion (ROM), shoulder muscle strength, and humeral torsion between left- and right-handed high school baseball pitchers remain poorly characterized. Hypothesis: Similar differences in shoulder ROM, strength, and humeral torsion between right-handed pitchers (RHPs) and left-handed pitchers (LHPs) observed in professionals will also be present in high school pitchers, with potential variations due to developmental stages. Study Design: Cross-sectional study; Level of evidence, 3. Methods: The authors included 921 high school baseball pitchers (706 RHPs and 215 LHPs) and evaluated their age, height, weight, body mass index, baseball experience, shoulder ROM, and muscle strength. Humeral torsion was measured in 211 RHPs and 57 LHPs. The Mann-Whitney U test was performed to determine the differences between the RHPs and LHPs and between the dominant and nondominant sides in each group. Pearson correlation analysis was performed to test the relationship between humeral torsion and shoulder ROM. Logistic regression analysis was conducted to determine the independent factors associated with LHP. Results: LHPs exhibited increased nondominant external rotation (ER) (103.1° vs 100.0°; P = .004), dominant horizontal adduction (HA) (23.0° vs 19.6°; P = .015), and side-to-side ratio in prone internal rotation (PIR) strength (107.6% vs 98.3%; P < .001) compared with RHPs. Additionally, LHPs were shorter (171.4 vs 172.9 cm; P = .002) with lower side-to-side differences in ER (5.7° vs 8.9°; P < .001) and HA (–6.5° vs −11.3°; P < .001), dominant prone ER (PER) strength (15.4 vs 16.8 kgf; P = .040), side-to-side ratio in PER strength (93.1% vs 103.7%; P < .001), and side-to-side differences in humeral torsion (5.8° vs 9.9°; P = .011) compared with RHPs. After adjusting for confounding factors, a smaller side-to-side ratio in PER strength (P < .001; OR, 0.911) and larger side-to-side ratio in PIR strength (P < .001; OR, 1.031) were independent factors associated with being an LHP. Conclusion: LHPs have a decreased side-to-side ratio in PER strength and increased side-to-side ratio in PIR strength compared with RHPs. These findings suggest that shoulder-related biomechanical differences between right- and left-handed pitchers are evident in high school athletes.

This study investigated biomechanical differences between right-handed (RHPs) and left-handed (LHPs) youth baseball players by analyzing shoulder and elbow range of motion (ROM), muscle strength, and humeral torsion. Side-to-side asymmetries were also examined to identify potential handedness-related adaptations. This cross-sectional study included 2008 youth baseball players (1829 RHPs and 179 LHPs) aged 9-13 years; female players were excluded because of their small number, and only male participants were analyzed. Shoulder and elbow ROM, muscle strength, and humeral torsion were evaluated, with humeral torsion data collected from 1024 measurements (946 RHPs, 78 LHPs). Group differences were analyzed using the Mann-Whitney U and Wilcoxon Signed-Rank tests. Logistic regression analysis identified independent factors associated with being an LHP, while Pearson correlation analyses explored the relationships between humeral torsion and external/internal rotation. LHPs exhibited significantly larger nondominant shoulder external rotation ( < 0.001), dominant internal rotation ( = 0.003), dominant shoulder horizontal adduction ( = 0.007), dominant elbow flexion ( = 0.006), and side-to-side prone internal rotation strength ratio ( < 0.001). LHPs also showed smaller dominant shoulder external rotation ( = 0.012), nondominant shoulder internal rotation ( = 0.001), nondominant horizontal adduction ( = 0.037), dominant prone external rotation strength ( = 0.002), and humeral torsion ( = 0.031). Humeral torsion differences correlated with external rotation in LHPs (r = 0.236) and internal rotation in RHPs (r = -0.153). Predictors of left-handedness included lower dominant shoulder external rotation (OR = 0.937) and higher dominant elbow flexion (OR = 1.410). This study provides novel insights into the normal functional characteristics of LHPs, an area that has been relatively underexplored. These findings serve as a basis for future studies on risk assessment, injury prevention, and performance optimization in youth baseball players.

Background: Left-handed baseball pitchers exhibit unique throwing biomechanics, yet the risk factors for shoulder and elbow injuries in this population remain unclear. Purpose: To prospectively investigate preseason risk factors for shoulder and elbow injuries in left-handed high school baseball pitchers. Study Design: Cohort study; Level of evidence, 2. Methods: A total of 160 left-handed high school baseball pitchers were enrolled. Preseason evaluations included age, height, weight, shoulder muscle strength, and range of motion of the shoulder and elbow. Participants completed a self-recorded questionnaire on shoulder and elbow pain and associated pitching limitations during the subsequent season. Participants were categorized into the noninjured or injured group. The Mann-Whitney U test, chi-square test, logistic regression analysis, and receiver operating characteristic curve analysis were used to identify injury risk factors and cutoff values for shoulder and elbow injuries. Results: Shoulder and elbow injuries occurred in 27 participants (16.9%). The injured group had significantly greater abduction–external rotation (ABER) in the dominant shoulder (114.8°± 11.9° vs 107.5°± 13.0°; P = .008) and a greater total arc of the dominant shoulder (166.4°± 25.1° vs 156.0°± 23.4°; P = .039). Logistic regression analysis showed that ABER in the dominant shoulder was an independent risk factor for injuries (P = .031; OR, 1.04). Receiver operating characteristic curve analysis determined that an ABER ≥109° predicted injury (P = .017). Pitchers with ABER ≥109° had a 3.3 times higher incidence of injury than those with ABER <109° (P = .005). Conclusion: Increased shoulder ABER was significantly associated with shoulder and elbow injuries among left-handed high school baseball pitchers. Pitchers with ABER ≥109° are at higher risk.

Background: The Functional Movement Screen (FMS) is used to evaluate fundamental movement patterns in patients. It is unknown whether the FMS can be used as a predictive tool for the occurrence of pitching injuries in baseball players. Purpose: To prospectively investigate the relationship between shoulder and elbow injuries and individual components of the FMS during the preseason in high school baseball pitchers and determine which components of the FMS can be used as screening tools to predict shoulder and elbow injuries. Study Design: Cohort study; Level of evidence, 2. Methods: Eligible participants comprised 133 male high school baseball pitchers aged 15 to 17 years who underwent a preseason medical examination in 2017. Included participants were right-handed pitchers who had been involved in preseason practices without restrictions in baseball activities. The physical examination included assessments of background factors, bilateral shoulder and elbow range of motion, and grip and shoulder strength as well as the FMS. A shoulder or elbow injury was defined as any condition causing the inability to pitch for ≥8 days. Injuries occurring in the season immediately after the preseason medical examination were recorded. Logistic regression analysis was performed to identify risk factors associated with an injury. Results: Overall, 90 high school baseball pitchers were enrolled in this study. The incidence of injuries was 22.2%. A comparison of FMS scores revealed significantly higher values for shoulder mobility on both sides (dominant side: P = .025; nondominant side: P = .034) and lower values for rotary stability on the dominant side (P < .001) in the injured versus noninjured group. Logistic regression analysis identified poor rotary stability on the dominant side as a significant independent risk factor for baseball injuries (odds ratio, 5.30; P = .009). Conclusion: In right-handed high school baseball pitchers, a low FMS score for rotary stability on the dominant side during the preseason was a significant independent risk factor for injuries in the following season. The FMS score for rotary stability may be used as a predictive tool for the occurrence of pitching injuries in high school baseball pitchers.

Background/Objectives: Non-invasive evaluations of muscle elasticity and tone are crucial in musculoskeletal medicine. Shear wave elastography (SWE) provides quantitative assessments of muscle elasticity, whereas train-of-four (TOF) monitoring measures muscle tone during neuromuscular blockades. This study investigated the relationship between muscle elasticity and tone during anesthesia induction using continuous SWE (C-SWE) and TOF monitoring. Methods: Fifteen patients who underwent general anesthesia with rocuronium were recruited. The muscle elasticity of the vastus lateralis was assessed using C-SWE, and muscle tone was evaluated using TOF monitoring. Measurements were taken at two time points: before rocuronium administration and during complete muscle relaxation, confirmed by the TOF ratio (TOF = 0). Statistical analyses were performed using paired t-tests and correlation analyses. Results: Data from 11 patients were analyzed. The mean shear wave velocity (SWV) decreased significantly from 5.0 ± 0.4 m/s before rocuronium administration to 3.1 ± 0.3 m/s during complete relaxation (p < 0.0001). A significant negative correlation was observed between the baseline SWV and the degree of reduction in the SWV (r = −0.728, p = 0.011). No significant correlations were found between SWV and demographic factors such as age, sex, height, or body mass index. Conclusions: C-SWE and TOF monitoring are reliable and sensitive methods for evaluating muscle elasticity and tone during general anesthesia. This study highlights the interplay between muscle tone and elasticity, suggesting that muscles with a higher baseline tone exhibit a greater reduction in elasticity after relaxation. These findings have implications for improving intraoperative muscle function assessments and advancing the application of C-SWE in clinical practice.

Background/Objectives: The repetitive overhead throwing of baseball stresses the posterior shoulder, including the rotator cuff and capsule, causing stiffness, tissue thickening, and dysfunction. Previous studies on collegiate baseball players have linked these changes to glenohumeral internal rotation deficits, pain, and injuries. However, these studies primarily used acoustic radiation force impulse-based shear wave elastography (SWE), which has limitations, including tissue heating and lack of portability. The acute effects of pitching on infraspinatus (ISP) muscle elasticity in high school pitchers remain unclear. Therefore, this study aimed to evaluate the acute impact of pitching on ISP muscle elasticity in high school baseball pitchers using continuous SWE (C-SWE), which is a safer and more portable method. The relationship between ISP muscle elasticity and pitching load was also examined. Methods: ISP muscle shear wave velocity (SWV), shoulder range of motion, and strength were evaluated in high school baseball pitchers. The participants were categorized into pitching and non-pitching groups based on whether they pitched with full effort on the day of their medical checkup. C-SWE was used to assess ISP muscle elasticity. Results: The pitching group had considerably higher ISP muscle SWV on the dominant side than the non-pitching group (p = 0.008). A significant positive correlation was observed between pitch and ISP muscle SWV (r = 0.467, p = 0.003). Conclusions: Repetitive pitching acutely increases ISP muscle stiffness in high school pitchers, contributing to posterior shoulder tightness. C-SWE is a safe and practical method for assessing tissue elasticity and developing injury prevention strategies.

The histological and genetic changes associated with significant tendon-to-bone differences after extracorporeal shockwave therapy (ESWT) remain unknown. This controlled laboratory study investigated the histological and genetic changes induced by ESWT in the rotator cuff. Left supraspinatus tendon ruptures were induced in 22 retired male Wistar rats. Three weeks later, rotator cuff repair was performed. One week post-repair, the rats were randomly assigned into either the ESWT or control group, with 11 rats per group. Compared with the control group, the ratio of cellularity was significantly lower, while that of collagen fiber orientation was significantly higher in the ESWT group. The number of blood vessels and the total histological scores were not significantly different between the two groups. Real-time polymerase chain reaction analysis revealed significantly higher messenger RNA (mRNA) expressions of CCN2 and SCX in the ESWT group than in the control group. No statistically significant differences in mRNA expression were found between the SOX9 and Tnmd. ESWT induces histological changes and increases the mRNA expressions of CCN2 and SCX in the repair of chronic rotator cuff tears in rats. These findings highlight the potential of ESWT to promote histological and molecular changes associated with tendon-to-bone healing.