Acromioclavicular dislocation associated with scapular fractures – pathoanatomy of the injury

Summary

Introduction: No detailed study dealing with an injury to the AC joint in combination with scapular fractures has been published to date. The aim of this study is to describe pathoanatomy of these injuries.

Methods: In a series of 519 scapular fractures in adult patients from the period of 2002−2020 we identified a total of 20 (3.9%) cases associated with AC dislocation. The group comprised 17 men and 3 women with the mean age of 49 years (range, 21−78). Radiographs of the shoulder joint followed by CT examination, including 3D reconstructions, were performed in all patients. This documentation allowed assessment of the scapular fracture pattern and type of injury to the AC joint.

Results: AC dislocation was associated with a simple scapular fracture in 15 cases (7 fractures of the coracoid base, 4 fractures of the acromion or the lateral spine, 2 fractures of the scapular body, 1 fracture of the superior and 1 fracture of the inferior glenoid). In 5 cases AC dislocation accompanied multiple or complex scapular fractures (once a combination of a coracoid fracture and a fracture of the lateral scapular spine, once a combination of a fracture of the superior glenoid and of the acromion, 2 cases of a complex intraarticular fracture and 1 case of scapulothoracic dissociation).

Conclusion: AC dislocation is relatively infrequent injury accompanying scapular fractures. It is most commonly associated with fractures of coracoid, acromion/lateral spine or superior glenoid. No case of AC dislocation was recorded in a fracture of the scapular neck.

Keywords:

fracture – scapular – acromioclavicular dislocation – pathoanatomy

INTRODUCTION

The incidence of acromioclavicular (AC) dislocation associated with scapular fractures is reported to be between 3% and 6% [1–3]. Probably the first case of AC dislocation combined with a scapular fracture, more specifically with separation of the coracoid, was discussed by Gurtl [4] in 1864. A more detailed study of this issue was published by Ehalt [5] in 1934. Since then, numerous cases of AC dislocation combined with scapular fractures, mainly those of the coracoid, but also with other scapular fracture patterns, have been described in the form of case reports [6-20]. However, no detailed study dealing with an injury to the AC joint in combination with scapular fractures has been published to date. The aim of this study is to describe pathoanatomy of these injuries.

METHODS

Material: In a series of 519 scapular fractures in adult patients from the period of 2002−2020 we identified a total of 20 (3.9%) cases associated with AC dislocation. The group comprised 17 men and 3 women with the mean age of 49 years (range, 21−78). The mean age of men was 48 years, that of women 61 years. The right side was involved in 8 cases, the left side in 12 cases. All the patients in the group were skeletally mature, with an acute injury to the AC joint and an acute scapular fracture.

Method: Radiographs of the shoulder joint followed by CT examination, including 3D reconstructions, were performed in all the patients. This documentation allowed assessment of the scapular fracture pattern and the type of injury to the AC joint.

Evaluation: The following parameters were examined:

- the scapular fracture pattern classified according to Bartoníček et al. [21],

- incidence rate of AC dislocation of the given type of the scapular injury,

- type of AC dislocation according to the Rockwood classification [22],

- the type of injury to the coracoclavicular junction.

RESULTS

Type of injury to the scapula: AC dislocation was recorded in fractures of the processes (coracoid, acromion), scapular body, glenoid, in complex fractures and scapulothoracic dissociation (STD).

AC dislocation was associated with a simple scapular fracture in 15 cases, i.e. 7 fractures of the coracoid base, 4 fractures of the acromion or the lateral spine, 2 fractures of the scapular body, 1 fracture of the superior and 1 fracture of the inferior glenoid (Fig. 1).

In 5 cases AC dislocation accompanied multiple or complex scapular fractures, i.e. once a combination of a coracoid fracture and a fracture of the lateral scapular spine, once a combination of a fracture of the superior glenoid and of the acromion, 2 cases of a complex intraarticular fracture (Fig. 2) and 1 case of STD.

AC dislocation was most frequently combined with fractures of the processes (14 cases), no case of AC dislocation was recorded in fractures of the scapular neck (Tab. 1).

Relative incidence of AC dislocation in individual types and subtypes of scapular fractures is shown in Tab. 2 and 3.

Types of AC dislocation: Rockwood type III was recorded in 12 cases, type IV in 5 cases, including 1 case combined also with dislocation of the SC joint, type V in 2 cases (Fig. 3); and in 1 case of STD there occurred only distraction of the AC joint (Fig. 4).

Type III was associated with a fracture of the coracoid base in 5 cases, with a scapular body fracture in 2 cases, a complex intraarticular fracture in 2 cases, a comminuted fracture of the coracoid and the lateral spine in 1 case, a fracture of the inferior glenoid in 1 case and a fracture of the superior glenoid and acromion in 1 case. Type IV was recorded in 4 cases in combination with a fracture of the acromion or the lateral spine and in 1 case in association with a fracture of the coracoid base. Type V was identified in 1 case in a fracture of the coracoid base and in 1 case in a fracture of the superior glenoid with a concomitant rupture of the coracoclavicular ligament.

Type of injury to the coracoclavicular junction: Rupture of the coracoclavicular ligament was identified in 7 cases, causing ligamentous instability, combined with a fracture of the acromion or the lateral spine in 4 cases, a fracture of the scapular body in 2 cases (Fig. 5) and a fracture of the inferior glenoid in 1 case (Fig. 6).

In 11 cases the coracoclavicular ligament remained intact; however, separation of the coracoid or the superior glenoid resulted in osseous instability (Fig. 1): 7 cases were an isolated extraarticular fracture of the coracoid base, 1 case a comminuted fracture of the coracoid associated with a fracture of the lateral spine, 1 case a combination of a fracture of the superior glenoid and the acromion. In 2 complex intraarticular fractures AC instability was caused by separation of the superior glenoid.

In 2 cases there occurred combined osseous-ligamentous instability, including 1 case of rupture of the coracoclavicular ligament and fracture of the superior glenoid (Fig. 7) and 1 case rupture of the coracoclavicular ligament and fracture of the coracoid base as part of STD.

Overall, rupture of the coracoclavicular ligament occurred in 9 cases, separation of the coracoid in 9 cases and fracture of the superior glenoid in 4 cases.

DISCUSSION

To date, injuries to the AC joint have been mentioned only marginally in larger studies of scapular fractures [1−3,16,17,19]; more details can be found only in individual case reports [6−15,18,20]. Thus our study is the first to deal with this issue in detail. Analysis has shown that AC dislocation is a relatively infrequent complication of scapular fractures, with the incidence of less than 4%. AC dislocation accompanies most often fractures of the processes of the scapula (coracoid, acromion or the lateral scapular spine) or fractures of the superior glenoid, either isolated or occurring as part of complex intraarticular fractures of the scapula.

Fractures of the coracoid and the superior glenoid disrupt integrity of the coracoclavicular junction and are a direct cause of AC dislocation. This finding is in case of a fracture of the coracoid base important also from the viewpoint of treatment, because reduction and internal fixation of the coracoid stabilizes also AC dislocation. And, vice versa, reduction and stabilization of AC dislocation may lead to indirect reduction and healing of the coracoid fracture. Fractures of the superior glenoid should be assessed in terms of displacement and on this basis preferable treatment, i.e., open reduction and internal fixation or a mere reduction and stabilization of the AC joint, should be used.

An interesting finding in our cohort was combined osseous-ligamentous instability resulting from disruption of the coracoclavicular junction at two levels. Such a lesion has not been reported in the literature, yet.

CONCLUSION

AC dislocation is a relatively infrequent injury accompanying scapular fractures. It is most commonly associated with fractures of the coracoid, acromion/ lateral spine or superior glenoid. No case of AC dislocation was recorded in fractures of the scapular neck. The coracoclavicular junction is more often affected by osseous instability caused by fracture of the coracoid base or the superior glenoid than by ligamentous instability resulting from rupture of the coracoclavicular ligament. Combined osseous-ligamentous instability is rare.

Conflict of interests

The authors declare that they have not conflict of interest in connection with this paper and that the article has not been published in any other journal, except congress abstracts and clinical guidelines.

MUDr. Tomáš Strnad

Klinika ortopedie 1. LF UK UVN – FVN Praha

e-mail: tomas.strnad@uvn.cz

ORCID: 0000-0001-5021-1031