Background: The floating shoulder (ipsilateral fractures of the clavicular shaft and the scapular neck) is thought to be an unstable injury pattern requiring operative stabilization in most instances. This recommendation has been made with little biomechanical data to support it. The purpose of this study was to determine the osseous and ligamentous contributions to the stability of experimentally created scapular neck fractures in a cadaver model.
Methods: Standardized scapular neck fractures were made in twelve fresh-frozen human cadaveric shoulders. Each specimen was mounted in a specially designed testing apparatus and secured to a standard materials testing device. In group 1 (six shoulders), resistance to medial displacement was determined following sequential creation of an ipsilateral clavicular fracture, coracoacromial ligament disruption, and acromioclavicular capsular disruption. In group 2 (six shoulders), resistance to medial displacement was determined following sequential sectioning of the coracoacromial and coracoclavicular ligaments.
Results: The average measured force for all specimens (groups 1 and 2) after scapular neck fracture was 183 ± 3.3 N (range, 166 to 203 N). The addition of a clavicular fracture (group 1) resulted in an average measured force of 128 ± 10.5 N (range, 83 to 153 N), which corresponds to only a 30% loss of stability. Subsequent sectioning of the coracoacromial and acromioclavicular capsular ligaments yielded an average force of 126 ± 9.1 N (range, 114 to 144 N), a 31% loss of stability, and 0 N, a complete loss of stability, respectively. Sectioning of the coracoacromial and coracoclavicular ligaments after scapular neck fracture (group 2) resulted in an average force of 103 ± 8.4 N (range, 89 to 118 N), a 44% loss of stability, and 0 N, a complete loss of stability, respectively.
Conclusions: Ipsilateral fractures of the scapular neck and the clavicular shaft do not produce a floating shoulder without additional disruption of the coracoacromial and acromioclavicular capsular ligaments. These and other unstable combined injury patterns are likely to be accompanied by substantial medial displacement of the glenoid fragment.
Clinical Relevance: Operative stabilization of ipsilateral fractures of the scapular neck and the clavicular shaft may not be necessary in the absence of concomitant injury to the coracoacromial and acromioclavicular ligaments characterized by marked medial displacement.
Gerald R. Williams Jr., MD; Penn Orthopaedic Institute, 1 Cupp Pavilion, Presbyterian Hospital, 39th and Market Streets, Philadelphia, PA 19104
John Naranja, MD; 1608 Apple Way, Minot, ND 58701
John Klimkiewicz, MD; Department of Orthopaedic Surgery, Georgetown University, 3800 Reservoir Road N.W., Washington, DC 20007
Andrew Karduna, PhD; Department of Physical Therapy, Allegheny University Hospitals, MCP-Hahnemann School of Medicine, Broad and Vine Streets, Philadelphia, PA 19102
Joseph P. Iannotti, MD, PhD; Department of Orthopaedic Surgery, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195
Matthew Ramsey, MD; Department of Orthopaedic Surgery, University of Pennsylvania School of Medicine, 3400 Spruce Street, 2nd Floor, Silverstein Pavilion, Philadelphia, PA 19104