Effect of the neck-shaft angle on stability in the onlay type of reverse shoulder arthroplasty: a cadaveric study |
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| Institution: | 1. Department of Orthopaedic Surgery, New England Baptist Hospital, Boston, MA, USA;2. Boston Sports and Shoulder Center, Waltham, MA, USA;3. MedStar Union Memorial Hospital, Baltimore, MD, USA;1. Department of Development and Regeneration, KU Leuven, Division of orthopaedics, University Hospitals Leuven, Leuven, Belgium;2. Department of Imaging and Pathology, KU Leuven, Leuven, Belgium;3. Department of Radiology, UZ Leuven, Leuven, Belgium;1. Orthopaedic Associates of Central Texas, Austin, TX, USA;2. Southern Oregon Orthopedics, Medford, OR, USA;3. Banner Health, Phoenix, AZ, USA;4. The Cleveland Shoulder Institute, Beachwood, OH, USA;5. University of Virginia, Charlottesville, VA, USA;1. Department of Orthopaedic Surgery, University of Utah Orthopedic Center, University of Utah, Salt Lake City, Utah, USA;2. Department of Physical Therapy and Athletic Training, University of Utah, Salt Lake City, Utah, USA;1. Orthopaedics Biomechanics Laboratory, Sunnybrook Research Institute, Toronto, Ontario, Canada;2. Division of Orthopaedic Surgery, University of Toronto, Toronto, Ontario, Canada;3. Division of Orthopaedic Surgery, Sunnybrook Health Sciences Centre, Ontario, Canada;4. Division of Orthopaedics, Department of Surgery, University of Toronto, Toronto, Ontario, Canada;5. Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario, Canada |
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| Abstract: | BackgroundAlthough reverse shoulder arthroplasty (RSA) has been indicated for treating patients suffering from cuff tear arthropathy, instability is a severe complication. The relationship between the humeral neck-shaft angle and joint stability in RSA as well as the clinical effect of subscapularis tendon repair on postoperative stability after RSA remain controversial. This study is primarily aimed to investigate the relationship between humeral neck-shaft angle and stability using the onlay type of RSA with preserved shoulder girdle muscles using fresh frozen cadavers. Moreover, we aimed to investigate the effect of subscapularis tendon repair after RSA placement.MethodsAn onlay type RSA of not-lateralized glenosphere in a massive rotator cuff tear model with preserved shoulder component muscles was placed on 7 fresh frozen cadavers, and traction tests were performed to dislocate by changing the neck-shaft angle of the stem to 135°, 145°, and 155°. The anterior dislocation force (DF) was evaluated in 6 patterns as follows: 2 patterns at 30° and 60° of abduction and 3 patterns at 30° of internal rotation, in neutral rotation, and 30° of external rotation. DF was recorded at neck-shaft angles of 135°, 145°, and 155° and with and without subscapularis tendon repair.ResultsAt 30° abduction, DF was significantly higher at a neck-shaft angle of 155° regardless of the rotational position (P < .05), and at abduction 60°, there was no difference in DF according to any rotational position and any neck-shaft angle. Regardless of the neck-shaft angle, the DF was significantly higher at 60° abduction than at 30° abduction (P < .05). Furthermore, the DF was significantly higher with subscapularis tendon repair (P < .01).ConclusionOur results showed some relationship between humeral neck-shaft angle and stability in the onlay type of RSA with preserved shoulder component muscles using fresh frozen cadavers. Moreover, a neck-shaft angle of 155° showed the highest anterior DF among neck-shaft angles of 135° and 145° at 30° abduction, and there was no difference at abduction 60° among any neck-shaft angle. Furthermore, subscapularis tendon repair also contributed to anterior stability. |
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| Keywords: | Reverse total shoulder arthroplasty Stability Neck-shaft angle Biomechanics Subscapularis Onlay type |
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