Sakata J, Nakamura E, Suzuki T, et al. Throwing injuries in youth baseball players: Can a prevention program help? Am J Sports Med. 2019;47(11):2709-2716. doi:10.1177/0363546519861378
Shoulder and elbow injuries are becoming increasingly common in youth baseball players. Injury prevention programs should target known modifiable risk factors. These risk factors include elbow extension range of motion deficit, posterior shoulder tightness, decreased shoulder and hip rotational ROM, rotator cuff weakness, scapular dysfunction, rounded shoulder posture, and impairments in single leg balance.
The purpose of this study was to investigate the effectiveness of a prevention program on the incidence of throwing-related arm injuries in youth baseball players.
- Youth baseball players (n = 237) ages 9 to 11 years
- From 16 competitive teams in Japan
Research participants were randomized to an intervention group and a control group. The intervention group performed the injury prevention program at least once weekly as part of their warm-up. The control group performed their usual warm-up procedures. The injury prevention program was termed the modified Yokohama Baseball–9 (mYKB-9). The nine exercises addressed impairments in shoulder mobility, elbow mobility, trunk mobility, hip mobility, and single leg balance. Participants were provided with baseball diaries for recording of the number of times that they completed the mYKB-9 per week.
Over a 12-month period, each participant was examined by a medical doctor every 4 months. This included a clinical examination of the shoulder and elbow as well as ultrasonography of the elbow. Participants recorded the number of practices and games played as well as any episodes of elbow and/or shoulder pain in their baseball diaries. An elbow injury was defined as pain during throwing associated with abnormal findings on clinical examination or ultrasonography. A shoulder injury was defined as pain during throwing with abnormal findings on clinical examination. An athlete exposure (AE) was defined as 1 athlete participating in 1 practice or game, where he or she is at risk of sustaining an injury to the elbow or shoulder.
Ball speed during pitching was used as a performance- related measure (pre- and post-intervention). Variables of physical function (passive range of motion of the elbow, shoulder and hip, dynamic balance, and thoracic kyphosis angle) were assessed by a physical therapist during the pre- and post-intervention periods.
- The overall incidence of shoulder and/or elbow injuries was 1.7 per 1000 AEs in the intervention group and 3.1 per 1000 AEs in the control group.
- The incidence of elbow injury in the intervention and control groups was 1.2 per 1000 AEs and 2.1 per 1000 AEs, respectively.
- The incidence of shoulder injury in the intervention and control groups was 0.6 per 1000 AEs and 1.2 per 1000 AEs, respectively.
- Regression analysis showed a statistically significant reduction in the incidence of shoulder and/or elbow injury in the intervention group as compared with the control group (Hazard Ratio, 1.940; 95% CI, 1.175-3.205; P = .010).
- Improvements in ball speed favored the intervention group (6.4 vs. 4.1 km/hr, P = .010).
- Physical function variables were significantly different in favor of the intervention group: shoulder horizontal adduction PROM deficits (P = .03), thoracic kyphosis angle (P<.05), and IR ROM of the non-dominant hip (P = .015).
- Blinding of research participants and physical therapists was not preserved.
- All youth baseball players were included – position players and pitchers, boys and girls.
The risk of throwing-related arm injuries was 48.5% lower in the intervention group as compared with the control group. The reduction in injury risk was also associated with increased ball speed and improvements in hip mobility, shoulder mobility, and thoracic kyphosis. These findings suggest a comprehensive impairment-based injury prevention program can be effective in youth baseball players. This randomized controlled trial is the highest level of evidence which supports the role of injury prevention programs in baseball players.
A 73.4% compliance rate was reported in the intervention group. Injury incidence was similar when athletes performed the program once or twice per week. Also, the program was said to take only approximately 10 minutes to complete. No expensive equipment is necessary. This makes the mYKB-9 program a very practical option for coaches and players to include as part of a pre-practice or pre-game warm-up.
The specific exercises utilized can be adapted to meet the individual needs of the athlete. Pre-season clinical examinations performed by a trainer, physical therapist, or physician can easily identify the known risk factors. An individualized corrective exercise plan can then be prescribed and utilized as part of the athlete’s warm-up routine. Periodic reassessments during the season are beneficial in case adjustments need to be made.