The floating shoulder: A biomechanical basis for classification and management

Background: The floating shoulder (ipsilateral fractures of the clavicular shaft and the scapular neck) is thought to be an unstable injury pattern re quiring 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 st ability of experimentally created scapular neck fractures in a cadaver mode l. Methods: Standardized scapular neck fractures were made in twelve fresh-fro zen human cadaveric shoulders. Each specimen was mounted in a specially des igned testing apparatus and secured to a standard materials testing device. In group 1 (six shoulders), resistance to medial displacement was determin ed following sequential creation of an ipsilateral clavicular fracture, cor acoacromial ligament disruption, and acromioclavicular capsular disruption. In group 2 (six shoulders), resistance to medial displacement was determin ed following sequential sectioning of the coracoacromial and coracoclavicul ar ligaments. Results: The average measured force for all specimens (groups 1 and 2) afte r scapular neck fracture was 183 +/- 3.3 N (range, 166 to 203 N). The addit ion of a clavicular fracture (group 1) resulted in an average measured forc e of 128 +/- 10.5 N (range, 83 to 153 N), which corresponds to only a 30% l oss of stability. Subsequent sectioning of the coracoacromial and acromiocl avicular capsular ligaments yielded an average force of 126 +/- 9.1 N (rang e, 114 to 144 N), a 31% loss of stability, and 0 N, a complete loss of stab ility, respectively. Sectioning of the coracoacromial and coracoclavicular ligaments after scapular neck fracture (group 2) resulted in an average for ce 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 t he coracoacromial and acromioclavicular capsular ligaments. These and other unstable combined injury patterns are likely to be accompanied by substant ial 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 acromiociavicular ligament s characterized by marked medial displacement.