Camp CL, Spiker AM, Zajac JM, et al. Decreased hip internal rotation increases the risk of back and abdominal muscle injuries in professional baseball players: Analysis of 258 player-seasons. J Am Acad Orthop Surg. 2018;26:198-206. doi:10.5435/JAAOS-D-17-00223
Hip range of motion (ROM) deficits have been associated with abdominal, low back, and hamstring injuries in baseball players. There is also evidence that restricted hip ROM increases shoulder torque during throwing. There is some conflicting evidence surrounding hip ROM profiles of professional baseball players. Regardless of this controversy, it is generally accepted that the coordinated movements of the entire kinetic chain play a key role in reducing the risk of injuries in baseball players. Hip ROM is one important link in the kinetic chain.
The primary purpose of this study was to better understand the hip ROM profiles of MLB pitchers and position players. Also, the researchers sought to better understand the injury rates and impact of abdominal and back injuries on MLB players. And finally, researchers set out to determine how hip ROM is related to these injuries in all players and upper extremity injuries in pitchers.
- MLB spring training participants from one organization during the years 2010 through 2015 (n = 248 player-seasons).
- Players were excluded if they were unwilling to have their ROM measured or had any recent hip injury, surgery, or pain that precluded examination.
- Both pitchers and position players were included in the analysis of abdomen and back injuries, but only pitchers were analyzed for shoulder and elbow injuries.
Hip passive internal and external rotation (IR and ER) ROM was measured in the supine position with the hips flexed to 90 degrees. Both hips were measured. Deficits (IR, ER, and total ROM) were calculated by subtracting the ROM from the side with the lesser motion from the opposite side (which had greater motion). Players were tracked over the course of the season and had cataloged any musculoskeletal injury that resulted in at least 1 day out of play.
Players were assessed for an association of hip ROM measures with injury using multivariate logistic regression analysis with a stepwise reduction to control for other confounding variables. Variables analyzed included player age, height, weight, BMI, and all other ROM measures.
- No significant differences in any of the ROM measures between lead and trailing hips for pitchers or position players.
- IR was similar between the pitchers and position players for both the lead hip (40.9° for pitchers and 40.1° for position players; P = 0.427) and trailing hip (40.8° for pitchers and 40.6° for position players; P = 0.850).
- Pitchers demonstrated an additional 2° to 3° ER and total ROM in both the lead and trailing hips compared with position players (P < 0.05).
- No hip ROM measures were correlated with shoulder or elbow injuries.
- Increasing IR deficit (difference in IR between the two hips) by 5° demonstrated an increased risk of any abdominal or back injury in pitchers (OR, 1.40; P = 0.024), back injury in pitchers (OR, 1.60; P = 0.022), and any abdominal or back injury in position players (OR, 1.35; P = 0.026).
- Hip ROM was measured by only one examiner at one point in time.
- Only professional players were included. The findings may not be generalizable to college or youth players.
- Cause-and-effect relationships cannot be established based on the study design.
The principal finding from this study was hip internal rotation deficits were predictive of back and abdominal injuries but not shoulder or elbow injury. This suggests a side to side difference in hip IR ROM is a modifiable risk factor for an abdominal and back injury in baseball players. This is the case for both pitchers and position players. Once identified during the physical examination, corrective exercise, soft tissue techniques, and joint mobilization/manipulation can be prescribed. Further research is needed to investigate any preventative effects of such interventions.
Proper sport mechanics (hitting and pitching) and a comprehensive strength/power program targeting the hips, pelvis, and trunk are also recommended. Hip rotation is an important component of transferring energy from the lower body to the core and on to the upper extremity during throwing and hitting. Limited or asymmetric hip rotation may interrupt the coordinated movements of the kinetic chain and shift excessive stress to the trunk increasing injury risk to the abdominals and back.