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Background:Repetitive tensile stresses from valgus torque can induce elbow injury in adolescent baseball players. Insufficient hip range of motion (ROM) can change throwing mechanics, reducing the transfer of energy from the lower to the upper extremities. Thus, hip ROM limitations may force the upper extremities to bear the burden of a strong throw. Improper pitching mechanics caused by insufficient hip ROM are thought to increase valgus torque on the elbow when throwing, increasing the risk of elbow injury.Purpose:To investigate the relationship between elbow pain and hip ROM in adolescent baseball players.Study Design:Cross-sectional study; Level of evidence, 3.Methods:A total of 122 adolescent baseball players with a mean age of 12.0 years (range, 6-14 years) participated in this study. Elbow pain, hip flexion angle, and the internal rotation angles of the hip at 0° and 90° of flexion were assessed. Participants were divided into a pain group and a normal group based on the pain assessment, and each hip angle was compared between groups using Student t tests. P values <.05 were considered statistically significant.Results:Thirty-one of 122 players had elbow pain. The hip flexion angle of the trail leg was 121.9° ± 12.3° for the normal group and 111.2° ± 11.3° for the pain group (P = .0001). The plant leg hip flexion angles were 122.0° ± 12.4° and 113.6° ± 11.3° (P = .0014) for the normal and pain groups, respectively. The internal rotation angle at 0° of hip flexion of the trail leg was 49.4° ± 12.6° and 45.6° ± 8.8° (not significant), and of the plant leg was 49.1° ± 12.5° and 48.7° ± 11.5° (not significant), for the normal and pain groups, respectively. The internal rotation of the trail leg at 90° of hip flexion was 46.9° ± 13.3° in the normal group and 36.1° ± 15.7° in the pain group (P = .0005). In the plant leg, the internal rotation angle at 90° of hip flexion was 46.9° ± 12.2° and 36.4° ± 18.1° for the normal and pain groups, respectively (P = .0013).Conclusion:Limitations to hip flexion and internal rotation at 90° of hip flexion were risk factors for elbow injury. Differences in internal rotation angles between 0° and 90° of hip flexion may be important criteria for identifying adolescent baseball players at risk of elbow pain.

It is known that free nerve endings are degenerated after application of shock waves. We therefore hypothesized that the application of shock waves to muscle induces dysfunction of neuromuscular transmission at neuromuscular junctions. We investigated changes in neuromuscular transmission in response to shock wave application. Sprague-Dawley rats were used in this study. Two thousand shock waves at an energy flux density of 0.18 mJ/mm 2 were applied to their right calf muscles. Neuromuscular junctions of gastrocnemius muscles were evaluated using rhodamine-a-bungarotoxin on the day of treatment (n ¼ 5). Amplitude and latency of compound muscle action potentials were measured on the day of treatment and 1, 2, 4, 6, and 8 weeks after treatment (n ¼ 10, each group). Degenerated acetylcholine receptors existed in all treated muscles. Although the action potential amplitude on the treated side was significantly less than on the control side from the day of treatment (25.1 AE 7.8 vs. 34.5 AE 9.1, p ¼ 0.012) to 6 weeks (27.9 AE 7.2 vs. 34.5 AE 7.2, p ¼ 0.037), there was no significant difference at 8 weeks. There was no significant difference in transmission latency between the groups. Keywords: neuromuscular junction; extracorporeal shock wave therapy; compound muscle action potential; neuromuscular transmission; acetylcholine receptor Impaired muscle coordination of limbs afflicted with central nervous system dysfunctions such as cerebral infarction, cerebral palsy, and dystonia is very common. This impairment causes severe limitations of daily living 1,2 and affects patients for their lifetime. Injection of botulinum toxin to focal muscles decreases muscle tone and is effective in improving motor function for impaired muscle coordination of limbs.3,4 For the past 20 years, treatment using botulinum toxin has gained acceptance as a popular treatment. However, the treatment using botulinum toxin has several difficulties with complications including severe allergic reaction and asthenia.3 Moreover, economic considerations inhibit many patients from undergoing this treatment because of its high cost. Recently, it has been reported that extra corporal shock wave treatment (ESWT) is able to improve function without inducing weakness in patients who suffer from spasticity and dystonia. 5,6 However, the mechanism of its clinical effect in the treatment of spasticity and dystonia has not been clarified. It is known that free nerve endings and sensory nerve fibers are degenerated after the application of shock waves.7,8 Therefore, we hypothesized that the application of shock waves to muscles induces dysfunction of neuromuscular transmission at neuromuscular junctions (NMJs). The purpose of this study was to investigate the changes in NMJs in response to ESWT to clarify its mechanism in the treatment of spasticity and dystonia. MATERIALS AND METHODSSeventy, 8-week-old male Sprague-Dawley rats (Japan SLC, Shizuoka, Japan) were used in this study. Animals were housed in an animal resources facility. Their room was mai...

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