The Superior Shoulder Suspensory Complex, Floating Shoulder Injuries, and Other Segmental Injuries to the Shoulder Girdle

Introduction

Segmental injury patterns about the shoulder have earned the name “floating shoulder” and “double disruptions” of the shoulder suspensory complex because they frequently consist of two radiographically distinct skeletal and/or ligamentous injuries about the shoulder girdle. The cumulative instability from two colocalized injuries has made this injury pattern difficult to conceptualize, and its clinical significance and optimal treatment remain controversial. The goal of this chapter is to provide a basis for understanding (1) the pathoanatomy and injury stratification of this injury pattern, (2) the rationale for available treatment options, and (3) the outcomes scoring systems used most frequently in the relevant primary literature. The surgical techniques for management of the various injuries at the clavicle and scapula that comprise the individual aspects of these double disruptions are described elsewhere in this book, and so have been excluded from this chapter in favor of an increased focus on pathoanatomy, indications, and outcomes when these multiple injuries simultaneously befall the same shoulder.

The term “floating” in orthopedic surgery is used to describe segmental injury patterns where skeletal injury has occurred above and below a joint. It is a commonly held belief that the loss of bony stability both above and below an articulation generates a cumulative instability that is more clinically disabling than the maximum instability caused by either of its component injury patterns as considered in isolation. In these cases, a risk-benefit assessment of surgical intervention at each individual injury may not justify surgical fixation, but the combination of the two injuries may. Many orthopedic surgeons advocate for partial or complete surgical stabilization of such injuries as a result of this cumulative instability.

The concept of the superior shoulder suspensory complex (SSSC) was first described by Ganz and Noesberger in 1975 in their work Treatment of Scapular Fractures , but did not gain the formal title of “floating shoulder” until discussed by Herscovici and coauthors in 1992. The idea ties together the interconnected ring of bony and ligamentous structures about the glenohumeral joint and is perhaps articulated best by Goss shortly following its formal identification. The bony structures of the coracoid, distal clavicle, acromion, and superior aspect of the glenoid are connected into a bony-ligamentous ring by the coracoclavicular (CC), coracoacromial (CA), and acromioclavicular (AC) ligaments which help create a stable platform for the glenohumeral joint This platform is supported away from the chest wall by the clavicular shaft (superior strut) and the scapular body/glenoid neck (inferior strut). In the context of glenoid neck fractures, the ligamentous interconnections of the CC, CA, and AC ligaments generate redundant stability around the glenoid platform, in which the stabilizing structures must be fully dissociated from all aspects of the superior struts (including both the anterior strut of the clavicle and the posterior strut of the acromion and spine) before clinically significant instability occurs, as depicted in Fig. 17.1 .

At the time of the writing of this chapter, there is insufficient evidence to indicate that any constellation of bony injuries about the shoulder girdle will benefit from surgical management if no single component of that constellation warrants surgical correction when considered in isolation. In other words, double disruptions of the SSSC (of which “floating shoulder” injuries are a subset) are not necessarily greater than the sum of their parts. Similarly, no specific fixation tactic can currently be recommended as superior to any other based on limited outcomes data, such as fixation of the clavicle, scapula, or both. There is, however, growing consensus that treatment options should be considered with a goal of restoring scapular anatomy to within debated acceptable limits, with specific attention to glenopolar angle (GPA), as it is likely that this parameter correlates with shoulder function after injury. An understanding of the redundant stability provided by the SSSC will help tailor fixation and rehabilitation strategies to each individual patients’ injury. An example of this is the indirect reduction and stabilization of scapular neck fractures which may be achievable using only fixation of associated clavicle fractures.

Anatomy and Pathoanatomy—Historical Evolution of an Injury Definition

The purpose of this section is to define floating shoulder injuries and characterize which fracture patterns may experience redundant stability from the SSSC.

The term “floating shoulder” was originally used to describe the combination of a scapular neck and ipsilateral midshaft clavicle fracture. These authors asserted that isolated fractures of the clavicle OR scapula both do well when treated conservatively, but that fractures of both the clavicle AND scapula do not, due to an assumed inherent instability. Their choice of “floating shoulder” as the name for this injury constellation is confusing, as the term “shoulder” usually refers to the glenohumeral joint. One would imagine that the term floating shoulder would refer to a floating glenohumeral joint, and other authors have noted this term is a misnomer and should best be applied to a glenoid neck fracture with ipsilateral humeral neck fracture. In the case of floating shoulder as described initially and in the vast majority of the published literature, however, there is no injury distal to the glenohumeral articulation, and so with this in mind it may be easier to conceptualize the idea of cumulative glenoid instability as being caused by a floating AC joint.

The original description was followed shortly by a theoretical description of the SSSC by Goss et al. in 1993. The work was not focused on the concept of the floating shoulder specifically, but instead proposed a theoretical, conceptual framework for shoulder stability meant to facilitate understanding and treatment of complex and segmental injuries in the shoulder. Most importantly, it proposed how the shoulder architecture, when conceptualized as an osseoligamentous superior ring held by superior and inferior struts, may help guide treatment. For example, the redundancy of the superior and inferior struts means that if either the clavicle or scapular body/glenoid neck is disrupted in isolation, theoretically the other strut can provide stability. Similarly, as a ring structure, it is proposed that if a single aspect of the SSSC is disrupted, the remainder of the ring can impart stability (see Fig. 17.1 ).

In 2001 Williams et al. provided biomechanical evidence supporting the concept of the SSSC’s redundant stability. This cadaver-based biomechanical study involving serial sectioning of components of the SSSC showed that in the context of a glenoid neck fracture, gross instability occurred only after complete dissociation of the coracoid from its surrounding stabilizers, including all ligamentous attachments to the acromion and clavicle. It was only after indirect dissociation of the glenoid from the acromion, which is acting as a superior/posterior strut, through combinatorial ligamentous sectioning of the AC, CA, and CC ligaments (in addition to the superior and inferior struts through simulated fracture), that true instability was achieved (see Fig. 17.2 ). These and other authors make special note that ligamentous injury, while not directly visualized on plain films, can be inferred based on displacement on plain films. ^, This biomechanical work implies the existence of a third, redundant, posterior strut: the acromion, although the authors do not specifically define it as such. Additional studies have speculated about the role acromial fracture may play in destabilizing this third strut, and if this should therefore be included in the concept of “floating shoulder.”

Based on these studies we are left with a model for shoulder stability in the context of segmental disruption as appears in Fig. 17.1 . Due to the redundant stability of the SSSC, glenoid fractures at the surgical neck with intact ligamentous connections between the coracoid and acromion or clavicle are stable even in the context of a clavicle fracture as the glenoid platform is suspended from the acromial posterior strut ( Fig. 17.2 ). Conversely, glenoid fractures at the surgical neck with ruptured connections between the coracoid and the acromion/clavicle complex will be unstable regardless of a fracture at either one. In general, large displacements (including medialization ) have been interpreted as markers for ligamentous instability, though this is unproven at this point as no studies cataloging magnetic resonance imaging (MRI) findings in floating shoulder injuries have been performed.

Floating shoulder injuries are a subset of double disruptions of the SSSC in which a scapular neck fracture is one site of disruption. The second disruption can be at a number of locations, including fracture of the clavicle, acromion, or rupture of the AC, CA, or CC ligaments. It is important to note that the two concepts of cumulative instability (floating shoulder) and redundant stabilization (SSSC) overlap most importantly in the case of scapular neck fractures with a superior exit point MEDIAL to the coracoid process (also called “surgical neck” fractures ). In these cases, the SSSC may impart stability to the glenoid through the coracoid process and its ligamentous association with the clavicle and acromion ( Figs. 17.1 and 17.2 ).

Special attention must be paid to the character of the surgical neck fracture, because there are a variety of scapular fracture patterns that are frequently included under the heading of floating shoulder injuries, but which are expected to behave differently based on redundant stabilization through the SSSC (see Fig. 17.3 ). For example, fractures of the anatomic glenoid neck (with superior exit points LATERAL to the coracoid process) maintain no ligamentous connection to the SSSC and therefore do not benefit from its redundant stabilization. Similarly, fractures extending into the articular surface may cause loss of humeral containment or may have significant articular incongruence. The outcomes for these fractures are likely to be driven by different factors than scapular neck–associated floating shoulders and therefore will have distinct operative indications outside those associated with floating shoulder. The idea that there is an interaction between the SSSC and floating shoulder injuries that may direct treatment modalities and affect outcomes, however, requires one to limit this interpretation to surgical neck fractures only.

Quantifying Injury Severity and Outcomes in Floating Shoulder Injuries

Classification Systems and Injury Stratification

Isolated fractures of the scapular articular surface, glenoid anatomic neck, coracoid process, and body have all been discussed separately in this book and in multiple other resources. A variety of different classification systems exist for describing the nature and severity of scapular injuries. ^, The term “floating shoulder” was first used by Herscovici et al. in 1992, defined as a scapular neck and ipsilateral midshaft clavicle fracture. In much of the current literature, however, the term has come to be more loosely interpreted within the context of the term “floating” and now includes a variety of segmental skeletal disruptions around the shoulder girdle ( Fig. 17.4A ). There is no widely used classification system for these combined injuries, however. Recent literature has attempted to develop a system based on displacement and stability (as determined by radiographic findings), but has not been widely adopted in subsequent reports.

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