THE RELATIONSHIP BETWEEN SCAPULAR POSITION AND GLENOHUMERAL RANGE OF MOTION IN HIGH SCHOOL BASEBALL PLAYERS

T. Higuchi¹, Y. Kanazawa², M. Matsuo³, S. Yokoyama⁴

¹Osaka University of Human Sciences, Department of Physical Therapy, Shojaku, Japan, ²Hokuriku University, Faculty of Health and Medical Sciences, Kanazawa, Japan, ³Nishi Kyushu University, Faculty of Rehabilitation Sciences, Kanzaki, Japan, ⁴Kyoto Tachibana University, Department of Physical Therapy, Kyoto, Japan

Background: Glenohumeral internal rotation deficit (GIRD) has been thought to be a cause of throwing injuries in baseball players. Past research using cadavers indicated that scapular position from further internal rotation is associated with the restriction of glenohumeral rotational range of motion (ROM) because of the occurrence of internal impingement. However, to the best of our knowledge, the relationship between internal/external scapular position of rotation and glenohumeral rotational ROM in baseball players remains unclear.

Purpose: The purpose of this study was to investigate the relationship between scapular position of rotation and glenohumeral rotational ROM in Japanese high school baseball players.

Methods: Sixty male high school baseball players were included in this study. Participants’ age, height, weight, duration of playing baseball, and presence or absence and severity of throwing-related shoulder or elbow pain were asked before measurements. Internal/external scapular position was defined as the scapula index. For the measurement of the scapula index, the distance between the sternal notch to coracoid process (SN-CP) and the posterolateral corner of the acromion to thoracic spine at the same level (PLA-TS) was measured using a tape measure. Then, the scapula index was calculated with the equation as follows. Scapula index = (SN-CP / PLA-TS) ×100. A higher value on the scapula index indicates the scapula is at a further position of external rotation. The scapula index was measured on the participant’s arm at rest and in an elevated position. For the measurement of the glenohumeral ROM, the participant was instructed to lay in the supine position with their shoulder abducted and the elbow positioned at 90 degrees. One examiner rotated the participant’s glenohumeral joint internally and externally, and the other examiner measured the ROM using a digital inclinometer.

Results: Twenty-eight participants (46.7%) had throwing-related pain. The scapula index was lower on the dominant side compared to the non-dominant side both at rest and in an elevated positions. There is a significantly positive correlation between the scapula index at an elevated position and the external glenohumeral rotation ROM. There was no significant correlation between the scapula index at rest position and the ROM, the scapula index at an elevated position and the glenohumeral internal rotation ROM, and the scapula index at both rest and in an elevated position and the glenohumeral ROM on the non-dominant side.

Conclusions: The results of this study indicate that the external scapular rotation during arm elevation was restricted to the dominant side for high school baseball players. Additionally, a scapular position from further internal rotation of the arm at an elevated position may be a cause of the GIRD.

Implications: The scapular position from further internal rotation could be a cause of the GIRD, and some interventions increasing the external rotation of the scapular position, such as the strength of the scapular retractor muscles or stretching the pectoralis minor muscles, may improve shoulder functions and reduce the incidence of throwing injuries.

Funding acknowledgements: This study was unfunded.

Keywords:
Baseball
Scapular position
Range of motion

Topics:
Sport & sports injuries
Musculoskeletal: upper limb
Musculoskeletal

Did this work require ethics approval? Yes

Institution: Kyoto Tachibana University

Committee: The Ethics Committee of Kyoto Tachibana University

Ethics number: 45031