Coronoid Fractures

Introduction

Fractures of the coronoid process of the ulna occur on the injury spectrum of complex elbow instability (see Chapter 36 ). Thus, associated bone and ligament injuries are the rule with coronoid fractures, and many of the topics contained herein overlap with those in Chapters 36 and 49 . When the coronoid is fractured, the complexity of both surgical decision making and operative treatment is increased. Therefore, this chapter focuses on when and how to treat these challenging injuries.

Epidemiology

Coronoid process fractures are uncommon. In a North American urban population, the incidence of coronoid fracture was estimated at 7.5 per 100,000 persons per year. In Edinburgh, the incidence of proximal ulna fractures was reported to be 15 per 100,000, with coronoid fracture occurring in 14%. In France, coronoid fractures occurred in 20% of proximal ulna fractures presenting to five trauma centers. Most coronoid fractures (73%) occur with other bony and soft tissue injuries. Although coronoid fracture may be commonly thought to occur in younger patients with high-energy injuries, the importance of coronoid fragility fractures in the elderly population after a fall from a standing height should not be overlooked.

Classification

Coronoid fractures have been classified by the systems of Regan and Morrey, O'Driscoll, and Adams. This topic is well covered in Chapter 36 . The advent of computed tomography (CT) imaging has allowed expansion of the original Regan–Morrey classification to include more complex fracture patterns ( Fig. 43.1 ). The system described by O'Driscoll is considerably more complex and describes oblique fracture patterns with several variations. This complexity may contribute to its only moderate intra- and interobserver reliability. Adams has demonstrated a strong correlation to treatment and outcome with the classic Regan–Morrey classification, justifying retaining this as a basis of further classification. Our preferred classification system is that of Adams et al. Five fracture types were observed in a series of 100 coronoid fractures characterized by 2D and 3D CT scans without consideration of other classification systems. Advantages of this system include the following:

• 1

  Recognition of the importance of both transverse and oblique fracture types

• 2

  Inclusion of the “mid-transverse” type, which is the predominant coronoid fracture morphology in terrible triad injuries

• 3

  Inclusion of the previously unclassified anterolateral oblique fracture morphology

• 4

  High intra- and interobserver reliability

In the modified Regan–Morrey classification system, oblique fractures (Type IV) are defined by involvement of either the radial (lesser sigmoid) notch (anterolateral) or sublime tubercle (anteromedial) but not both. These are termed Type IV-L and IV-M , respectively. If both structures are involved, a basilar transverse fracture is present (Type III). For the remaining transverse types, a tip fracture must be ≤3 mm in height (Type I), while a “mid-transverse” fracture must be <51% of the coronoid height (Type II).

Several authors have investigated the association between coronoid fracture patterns and different injury mechanisms. General patterns that are noteworthy include:

• 1

  Transverse morphology is most common with terrible triad injuries, with average 35% involvement of the height of the coronoid.

• 2

  Basal coronoid fractures are associated with anterior and posterior transolecranon fracture dislocations.

• 3

  Oblique anteromedial fractures are classically described as isolated bony injuries with lateral collateral ligament (LCL) disruption and are associated with varus–posteromedial rotatory instability. However, other clinical series have shown that the anteromedial fracture morphology can occur with atypical injury patterns (i.e., “terrible triad,” transolecranon fracture), and many have associated medial collateral ligament (MCL) injury.

Evaluation

Subtle injuries are very difficult to accurately identify or characterize. If a coronoid fracture is seen or suspected on plain radiographs, we obtain a CT scan with 3D reconstruction ( Fig. 43.2 ). Stress imaging may be performed, usually with anesthesia, when deciding whether the fragment needs be fixed or whether it can be ignored.

Treatment

Principles

When contemplating coronoid fracture treatment, three key issues must be addressed.

First, is operative treatment of the coronoid necessary to achieve sufficient elbow stability to allow early range of motion? Both clinical experience and biomechanical data have demonstrated that fixation is often necessary to achieve this goal.

Second, is operative treatment of the coronoid necessary to prevent posttraumatic arthrosis? O'Driscoll et al. have proposed that anteromedial coronoid fractures will often result in the rapid development of posttraumatic ulnohumeral arthrosis from point loading of the medial trochlear articular surface at the fracture site. For this reason, current expert opinion generally favors a more aggressive approach to operative fixation of anteromedial coronoid fractures. However, we have observed early arthrosis to have occurred just months after such an injury, suggesting chondrolysis from the impact may be playing a role, possibly even the dominant role in some of these injuries ( Fig. 43.3 ).

Third, do the risks of operative fixation of the coronoid outweigh the potential benefits mentioned previously? For some coronoid fractures, a separate medial approach or skin flap is required to access the fracture, which increases the risk of soft tissue complications. The added dissection appears to increase the risk of heterotopic ossification. A medial exposure also puts the ulnar nerve at risk for complications.

Finally, addressing the coronoid oftentimes requires a significantly increased operative time. Surgeons should account for the potential costs of internal fixation and consider the possibility of over treatment of coronoid fracture.