The Journal of Bone and Joint Surgery (American) 83:1182-1187 (2001)
© 2001 The Journal of Bone and Joint Surgery, Inc.
The Floating Shoulder: A Biomechanical Basis for Classification and Management
Gerald R. Williams, Jr, MD,
John Naranja, MD,
John Klimkiewicz, MD,
Andrew Karduna, PhD,
Joseph P. Iannotti, MD, PhD and
Matthew Ramsey, MD
Investigation performed at the Shoulder and Elbow Service, Department
of Orthopaedic Surgery, University of Pennsylvania School of Medicine,
Philadelphia, Pennsylvania
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
No benefits in any form have been received or will be received from
a commercial party related directly or indirectly to the subject
of this article. No funds were received in support of this study.
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.

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