The purpose of this study was to evaluate the scapular stability function using a 3D scan during the preseason and its relationship to the incidence of throwing shoulder and elbow injuries (throwing injuries).
Twenty-nine college baseball pitchers without shoulder and elbow joint pain during pitching at the time of measurement were included in the study. Scapular stability function was measured using a 3D scan (Go! SCAN SPARK) in the preseason. The measurement postures were scapula plane elevation, elbow full flexion, and the palm on the backside of the head, as well as the posture with elbow extension resistance from that position. The scapular upward/downward rotation angle (ST angle) relative to the trunk was calculated for each posture. ST angle was calculated using the Euler angle according to ISB recommendation, and the ST angle alteration between two postures was used as the analysis variable. All calculations were performed using Python 3.9.19. The incidence of throwing injuries was examined for six months from the preseason measurement. Statistical analysis was performed using the Mann–Whitney U test for the ST angle alteration between injured and non-injured players, ROC curves to calculate cutoff values of ST angle alteration that predicted the incidence, and Odds ratios (ORs) and profile likelihood 95% CIs were calculated based on the cutoff values.
Five of the 29 pitchers reported throwing injuries during the 6-month follow-up period. ST angle alteration was significantly difference between injured and non-injured players (7.2±4.4, 0.9±5.8 degree upward rotation, respectively). The cutoff value for predicting the occurrence of throwing injuries was 6.42 degrees upward rotation of ST angle alteration (AUC=0.77). Nine pitchers indicated a larger upward rotation than that cutoff value and were divided into the larger UR group. Twenty players indicated a smaller upward rotation than the cutoff value or rotated in a downward direction; they were divided into the lower UR group. Furthermore, the incidence of throwing injuries was significantly higher for the larger UR group, and the odds ratio, 95% CIs were 15.2, 1.36-167.99.
The larger ST angle upward rotation during the resistance to elbow extension at the scapular plane elevation indicated dysfunction of scapular stabilizing. This dysfunction might induce improper glenohumeral joint configuration during the pitching motion. The evaluation of scapulothoracic stabilizing function using 3D scans in the preseason can use the risk assessment of developing throwing injuries.
Conventional evaluation of scapulothoracic joint function is often used in qualitative assessments, and its reliability has been cited as a limitation. The 3D scan can assess the three-dimensional rotation and can be applied to clinical situations. It is considered to be a new evaluation method for scapulothoracic joint function. Moreover, the scapular stabilizing function was shown to be a critical focusing point for the risk assessment of throwing injury.
scapulothoracic joint
evaluation
