2015 ISAKOS Biennial Congress ePoster #2119

Configuration of Rotator Interval During Throwing Motion

Yuji Hiroshima, MD, Kobe, Hyogo JAPAN
Hiroaki Inui, MD, Tatsuno JAPAN
Hiroshi Tanaka, MR, Tatsuno JAPAN
Hiroki Ninomiya, MD, Tatsuno, Hyogo JAPAN
Katsuya Nobuhara, Tatsuno, Hyogo JAPAN
nobuhara hospital, tasuno, hyogo, JAPAN

FDA Status Cleared

Summary: Rotator interval is the space between the supuraspinatous and the subscapularis tendons. The objective of the study was to estimate configuration of the rotator interval during arm rotation in elevation. Ten healthy volunteers were enrolled in this study. These shoulders were imaged using MRI system and a three-dimensional gradient echo. Area of the rotator interval significantly was larger in the

Abstract:

Rotator interval is the space between the supuraspinatous and the subscapularis tendons. The space could be under stress when the arm is rotated because the tendons glide in different directions by contraction of these muscles. However, how configuration of the rotator interval changes during arm rotation has remained uncertain. The objective of the study was to estimate configuration of the rotator interval during arm rotation in elevation.

Methods

Ten volunteers (10 men) without symptoms or a history of shoulder disease were enrolled in this study. Their mean age was 26 years (range, 21–35 years). All participants provided informed consent. The present study was approved by the IRB of our hospital.
The right arm was both maximally externally and internally rotated at abduction angles of 90°in the coronal plane to the trunk. The elbow was flexed in 90°. Images of these positions were obtained using a 0.2-T MRI system. Each upper extremity was controlled by a positioning device while maintaining the same relaxed position without disturbing scapular motion. The shoulders were imaged using a three-dimensional (3D) gradient echo with 2-mm sections. The cortical bones were manually digitized and were transferred to a computer. A 3D image of each subject was generated using computer software. This software allowed anatomies to be viewed from any angle and provided instant access to 3D information.
Configuration of the rotator interval in each position was determined as area surrounded by the lines connecting the anatomical landmarks. Those lines connected the points in the shortest length along the surface of the bones without penetrating the objects.

Result
Area of the rotator interval significantly was larger in the internal rotation than that in the external rotation by 56%. The line of the superior subscapularis tendon was close to the line of anterior supraspinatous tendon in the external rotation. However, the length of the former line was longer than the latter line, indicating the subscapularis tendon was more stretched than the supraspinatous tendon.

Discussion

Rotator interval is the space between the supuraspinatous and the subscapularis tendons. Configuration of the space was not fully observed even under operation, because the space was under the coracoacromial arch with arm elevation and it in itself was covered with synovial membrane. To the best of our knowledge, the study was the first evaluating the rotator interval using three-dimensional computer generated images.
Configuration of the rotator interval changes with arm rotation. With the arm externally rotated in elevation, the subscapularis tendon would be more stretched compared to the supraspinatous tendon, indicating the rotator interval might be under stress in that external position. If the rotator interval was injured causing adhesion, smooth gliding of the subscapularis tendon to the supraspinaous tendon might be disturbed with the arm external rotation in elevation.
Closure of the rotator interval is one of the options to augment joint stability in operation for shoulder with dislocation or subluxation. However, more attention should be paid to its role to help the two tendons to smoothly glide during arm rotation.