Biomechanical Factors Influencing the Successful Non-operative Treatment of Rotator Cuff Tears

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Rotator cuff tears are a significant clinical problem that affect greater than 1/3 of all people over the age of 60 and can cause severe shoulder pain and loss of function. While physical therapy is commonly prescribed for the initial treatment of many rotator cuff tears, it has been found to be ineffective in as many as 25 to 50% of all cases. Since there is no "one size fits all" approach to treating rotator cuff tears, which can come in many different sizes, shapes, locations, and chronicities, it is necessary to better understand the biomechanical reasons behind the failure of physical therapy in order to reduce treatment time and costs. Therefore, the objective of this study is to use combined in vivo, cadaveric, and computational approaches to investigate the effects of physical therapy and initial tear characteristics on tear propagation and alteration of glenohumeral kinematics.

In Vivo Kinematics

Through a collaboration with Dr. Tashman in the Department of Orthopaedic surgery, we are working to collect in vivo glenohumeral joint kinematic data from rotator cuff tear patients before and after they have gone through a 12-week program of physical therapy. By calculating dynamic joint translations and acromiohumeral distance within the glenohumeral joint before and after physical therapy, the effects of physical therapy on improving joint kinematics can be investigated. This information will be combined with isometric strength data, shoulder function questionnaires, and ultrasound measures of tendon thickness and tear size taken over time during physical therapy sessions to improve our understanding of the effects of physical therapy for rotator cuff tear treatment on glenohumeral joint health. Preliminary data indicates that patient-reported outcomes and glenohumeral joint stability are improved after successful exercise therapy.

Cadaveric Testing

Extensive biomechanical testing on cadaveric human rotator cuff tendons under cyclic loading conditions is being performed in order to assess the effects of tear location and chronicity on tear propagation. Comparisons of tear location between the anterior and central supraspinatus tendon have thus far shown no significant difference in load required to reach 2 cm of propagation, though anterior tears have been found to propagate earlier than central tears, demonstrating an effect of tear location on tear propagation.

Strain measurements made using a video tracking system have helped to elucidate tear propagation based on location and direction of maximum principal strains on the tendon surface. Ongoing work on cadaveric tissue with pre-existing chronic tears is being performed to compare with surgically created "acute" tears to assess the effects of tear chronicity on tear propagation. Histological analysis is also being performed to better understand the physical effects of tissue degeneration as related to tissue mechanics.

Related Publications:

Araki D, Miller RM, Fujimaki Y, Hoshino Y, Musahl V, Debski RE. Effect of Tear Location on Propagation of Isolated Supraspinatus Tendon Tears During Increasing Levels of Cyclic Loading.J. Bone Joint Surg. Am. 2015 Feb 18; 97(4):273-278.

Miller RM, Fujimaki Y, Daisuke A, Musahl V, Debski RE. Strain Distribution due to Propagation of Tears in the Anterior Supraspinatus Tendon. J. Orthop. Res. 2014 Oct;32(10):1283-9.

Computational Modeling

Ongoing work with Dr. Maiti in the Department of Bioengineering will result in the development of a finite element model to simulate tear propagation in rotator cuff tendons for a variety of tear characteristics. A novel material model for predicting damage in biological connective tissues (i.e. tendon) will be applied to tendon geometries with tears that vary in size, shape, and location while varying material properties to approximate differences in tear chronicity due to tissue degeneration. Biomechanical testing combined with high-resolution strain maps of the bursal and articular surfaces of tendon will allow for accurate model calibration and validation.

Related Publications:

Thunes J, Miller RM, Pal S, Damle S, Debski RE, Maiti S. The Effect of Size and Location of Tears in the Supraspinatus Tendon on Potential Tear Propagation. J Biomech Eng. 2015 Aug 1;137(8). doi: 10.1115/1.4030745. Epub 2015 Jun 23.

This material was originally published on the website of the Orthopaedic Robotics Laboratory