RESEARCH REPORT POSTER DISPLAY

DOES ACROMIOCLAVICULAR JOINT STIFFNESS CAUSE DYSFUNCTION OF THE SHOULDER? Miyamoto H^1,4, Muraki T¹, Oshiro S¹, Takasaki H⁵, Fujii M¹, Hidaka E¹, Izumi T¹, Uchiyama,MD,PhD E³, Aoki,MD,PhD M²; ¹Graduate school of health science Sapporo medical university, Sapporo, Japan. ²Department of Physical Therapy,Sapporo Medical University of Health Science, Sapporo, Japan. ³Department of Anatomy Section II, Sapporo Medical University of the School of Medicine, Sapporo, Japan. ⁴Sapporo Orthopaedic Cardiovascular Hospital, Sapporo, Japan. ⁵Sapporo Shinoro Orthopaedic Clinic, Sapporo, Japan

PURPOSE: Acromioclavicular joint stiffness can occur in patients who suffer from shoulder osteoarthritis, frozen shoulder, and rotator cuff tears. However, it is unclear whether or not it causes shoulder dysfunctions such as subacromial impingement or other joint restrictions.The purpose of this study is to examine the influence of acromioclavicular joint stiffness on scapular mobility and shoulder motion. RELEVANCE: This study contributes to application of physical therapy for the treatment of shoulder pain and contracture. PARTICIPANTS: Five frozen-thawed transthoracic specimens from fresh cadavers were used. Anatomical structures of the whole spine, thoracic cage, and bilateral upper extremity were preserved in the transthoracic specimens. Specimens with rotator cuff tears, osteoarthritis, and severe shoulder contracture were excluded. METHODS: In this study, we focused on the range of shoulder flexion, abduction and upward rotation of the scapula. The transthoracic specimens were fixed in an upright position on a wooden pole jig to allow free passive movement of the arm and scapula. In order to simulate acromioclavicular joint stiffness, we used two crossing Kirschner wires for fixation of the joint. Then, we measured the maximum range of passive flexion and abduction of the shoulder pre- and post- fixation. The angle of upward rotation of the scapula was measured at 30°, 60°, 90°, 120°, and the maximum angle of shoulder flexion and abduction pre- and post-fixation. These angles were measured by an electromagnetic tracking device (3SPACE FASTRAK, Polhemus, Vermont) with six-degree-of-freedom. ANALYSIS: A paired t-test was used to examine the differences in the shoulder and scapular angles between the two conditions. The α-level of significance was set at 0.05. RESULTS: There were no significant differences in the maximum angle of shoulder flexion and abduction between the two conditions. There were no significant differences in the angle of upward rotation of the scapula during passive flexion and up to 60 degrees of shoulder abduction.However,beyond 60 degrees of shoulder abduction,acromioclavicular joint fixation resulted in a significant reduction in the scapular rotation angle (p < 0.05). CONCLUSIONS: The results of the present cadaveric study indicated that beyond 60 degrees of shoulder abduction,acromioclavicular joint stiffness can influence the angle of upward rotation of the scapula.Unchanged maximum shoulder flexion and abduction may imply abnormal compensatory movements at the glenohumeral joint. Thus, in view of the present results,it may be inferred that acromioclavicular joint stiffness may alter the kinematics of the shoulder joint complex during vocational and sports activities;consequently,it may lead to shoulder dysfunction. IMPLICATIONS: Our findings suggest that evaluation and treatment of acromioclavicular joint stiffness should be considered in patients with shoulder dysfunction. KEYWORDS: Acromioclavicular joint, kinematics, shoulder. FUNDING ACKNOWLEDGEMENTS: No grants or outside funding were received in support of this research. CONTACT: hitosimiyamoto@yahoo.co.jp

ETHICS COMMITTEE: Institutional Review Borad of Sapporo Medical University