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H. Miyamoto1,2, K. Watanabe3, N. Iida4, T. Taniguchi5, K. Hirota5, K. Negishi5, M. Fujimiya2
1Sendai Seiyo Gakuin College, Division of Physical Therapy, Department of Rehabilitation Science, Sendai, Japan, 2Sapporo Medical University, 2nd Department of Anatomy, School of Medicine, Sapporo, Japan, 3Sapporo Medical University, 2nd Division of Physical Therapy, School of Health Sciences, Sapporo, Japan, 4Sapporo Medical University Hospital, Department of Rehabilitation, Sapporo, Japan, 5Sapporo Medical University, Graduate School of Health Sciences, Sapporo, Japan
Background: The prevalence of partial rotator cuff tear, which is a form of shoulder dysfunction, increases with aging. In order to develop an exercise therapy that is effective as a conservative treatment, it is essential to quantitatively understand the mechanical stress exerted on the remaining part of the tendon in partial tears and to examine the associated risk. However, safe load limits have not yet been clarified.
Purpose: We created a partial rotator cuff tear model using fresh-frozen cadavers to quantitatively measure the strain on the tendon due to continuous increase in tension on the supraspinatus tendon and compared values between non-tear and surface-tear tendons.
Methods: Eight fresh-frozen shoulder specimens from eight cadavers were utilized. The shoulders were fixed at an angle ranging from -10° to 30° on the scapular plane, and the tensile load on the shoulder joint was increased from 0 to 120N. For non-tear supraspinatus tendons, a strain gauge was installed in the deep layer of the supraspinatus tendon, and then the surface layer was cut and the deep layer measured again.
Results: Significant increases in the strain on the deep layer of the supraspinatus tendon were observed with increases in the tensile force on the supraspinatus tendon. At all scapula elevation angles, the strain on the deep layer of the supraspinatus tendon increased in the surface-tear group in comparison to the non-tear group. Strain under the maximum tensile force of 120 N was 5.33% (surface-tear) vs. 2.68% (non-tear) at a scapular plane elevation of 30°, 4.36% vs. 1.72% at 20°, 2.91% vs. 1.16% at 10°, 2.54% vs. 0.72% at 0°, and 2.51% vs. 0.20% at -10°.
Conclusion(s): In our previous study, we reported that the strain on the surface layer of the supraspinatus tendon at a scapular plane elevation from -10° to 0° was significantly larger than the values obtained from 10° to 30°. However, when measuring deep layer strain, we observed the strain on the supraspinatus tendon at a scapular plane elevation from 30° to 10° was significantly larger than that from 0° to -10°. In the surface-tear group of this study, the strain on the deep layer of the supraspinatus tendon; i.e., the remaining tendon, was increased at all angles of scapular plane elevation compared to the non-tear group. This strain was greater at a scapular plane elevation of 30° and 20°. Supraspinatus tendons with tears in the tendon surface layer had more than twice as much tensile force on its deep layer. Based on these findings, care and attention should be paid to the amount of load applied and shoulder positioning during rehabilitation.
Implications: The biomechanical properties of the supraspinatus tendon differed between the surface-tear and non-tear state. Surface tears in the supraspinatus tendon increase the risk to the tendon due to the transfer of increased tensile forces to the deep layer. This finding can be applied to the provision of safer and more effective shoulder physical therapy in clinical and sports settings for patients with known or suspected surface tendon tears.
Funding, acknowledgements: This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Keywords: surface tear, supraspinatus tendon, fresh-frozen cadaver
Topic: Musculoskeletal: upper limb
Did this work require ethics approval? Yes
Institution: Sendai Seiyo Gakuin College, Sapporo Medical University
Committee: The Institutional Research Ethics Committee
Ethics number: 0202, 29-2-30
All authors, affiliations and abstracts have been published as submitted.
