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Coronoid Fractures and the Terrible Triad: An Algorithm for Successful Management


Relevant Anatomy

The elbow is a complex hinge joint connecting the distal end of the humerus with the proximal ends of the radius and ulna, forming three articulations: the ulnohumeral, radiocapitellar, and proximal radioulnar joints ( Fig. 47.1 ). The primary degrees of freedom allowed by the elbow are flexion/extension and pronation/supination. Flexion/extension is accomplished through the ulnohumeral and radiocapitellar joints, while pronation/supination involves the radiocapitellar and proximal radioulnar joints of the elbow as well as the distal radioulnar joint of the wrist.

Fig. 47.1, (A) Medial side of the elbow depicting the medial collateral ligament which consists of anterior, posterior, and transverse bands. (B) Lateral side of the elbow depicting the lateral collateral ligament complex which primarily includes the lateral radial collateral ligament, lateral ulnar collateral ligament, and annular ligament.

The elbow is an inherently stable joint due to a combination of bony congruity and dynamic and static stabilizers. The ulnohumeral articulation is a highly congruous joint with the coronoid process serving as a block to posterior translation of the ulna and the olecranon serving as a block to anterior translation ( Fig. 47.2 ). The muscles crossing the elbow (triceps, anconeus, biceps, brachialis, flexor/pronator mass, common extensor origin) serve as dynamic stabilizers at the elbow. Their tone (either resting tone or active tone when bracing for an impact) holds the bony articulations of the elbow tight and congruous by resisting distraction at the joint, similar in function to the rotator cuff of the shoulder. The collateral ligaments, acting together, also resist distractive forces placed on the elbow.

Fig. 47.2, Lateral view of the elbow demonstrating the bony congruity. The coronoid process prevents posterior translation of the ulna, especially in flexion, while the olecranon process prevents anterior translation of the ulna, especially in extension. (Morrey’s The Elbow and Its Disorders 5th Edition, Morrey, Bernard; Llusa Perez, Manuel. 2018 Elsevier, figue 2-11.)

Varus/valgus stability is imparted to the elbow primarily from bony congruity and static stabilizers. The width of the elbow joint in the coronal plane, comprised of the ulnohumeral and radiocapitellar joints, provides inherent stability. The medial collateral ligament (MCL), comprised of anterior, posterior, and transverse bundles, serves to resist valgus stress, with the anterior bundle being the primary constraint ( Fig. 47.3 ). The secondary constraint to valgus stress is the radial head, which becomes the primary constraint in the setting of an MCL injury.

Fig. 47.3, Elbow stability to valgus force. A valgus moment placed on the elbow is resisted on the tension side by the medial collateral ligamentous complex, and on the compression side by the articulation of the capitellum with the radial head. The medial collateral ligamentous complex is composed of the anterior and posterior bundles as well as the transverse ligament. The anterior and posterior bundles are the primary contributors to valgus stability. (Morrey’s The Elbow and Its Disorders 5th Edition, Morrey, Bernard; Llusa Perez, Manuel. 2018 Elsevier, figue 2-21.)

The lateral collateral ligament (LCL) complex consists of the radial collateral ligament, the lateral ulnar collateral ligament (LUCL), the accessory collateral ligament, and the annular ligament. The LUCL serves as the primary constraint against varus stress at the elbow, with the anteromedial facet of the coronoid process providing secondary constraint ( Fig. 47.4 ).

Fig. 47.4, Elbow stability to varus force. A varus force placed on the elbow is resisted on the tension side by the lateral collateral ligamentous complex, and on the compression side by the articulation of the trochlea of the distal humerus with the anteromedial facet of the coronoid process. The anatomic image highlights the “Y-shaped” distribution of the lateral ligamentous complex for varus stability. (Morrey’s The Elbow and Its Disorders 5th Edition, Morrey, Bernard; Llusa Perez, Manuel. 2018 Elsevier, figue 2-24.)

Coronoid Fractures

Pathoanatomy

Anteroposterior (AP) translation of the ulna is resisted by the highly congruous nature of the ulnohumeral joint. The olecranon fossa and the coronoid fossa of the distal humerus accommodate the proximal ulna to allow a nearly 180-degree capture of the distal humerus by the ulna. Simple elbow dislocations, defined as an elbow dislocation without associated fracture, typically occur as the result of a fall onto an outstretched arm. Axial compression, along with a posterolateral rotatory force, causes disruption of the LCL followed by the anterior capsule and lastly the MCL. Disruption of these static structures then allows unopposed distraction, valgus, and rotation of the elbow joint, leading to dislocation.

Coronoid fractures occur in 2%–15% of elbow dislocations as a result of the humerus coming into contact with the coronoid process during an instability event. This contact produces a shear force across the coronoid process leading to fracture. The significance of this fracture on elbow stability depends on both the size of the fracture and the associated injuries to the collateral ligaments and the radial head and will be discussed in subsequent sections.

Fracture of the coronoid can also occur through a primarily varus moment on the elbow which drives the medial aspect of the trochlea into the anteromedial facet of the coronoid. This injury mechanism is best demonstrated in comparing the intraoperative resting AP and stress views shown in Fig. 47.5 . This varus moment results in disruption of the LCL (usually through avulsion off the lateral epicondyle of the humerus) as well as a shear-type fracture of the anteromedial facet of the coronoid. While these two injuries can occur in isolation, Klug et al. found 15 of 24 patients with a fracture of the anteromedial facet of the coronoid also had a concomitant avulsion of the LCL. Ring found 15 of 18 patients had an LCL injury.

Fig. 47.5, (A) Intraoperative, slightly oblique, anteroposterior view of an elbow demonstrating an anteromedial facet coronoid fracture. (B) Intraoperative varus stress applied to the elbow demonstrates significant displacement of the fracture and incongruity of the radiocapitellar and ulnohumeral joints, illustrating the significant instability imparted by anteromedial facet coronoid fractures.

Classification

Coronoid fractures are classified according to the Regan and Morrey classification ( Fig. 47.6 ). Type I injuries were described as an avulsion of the tip of the coronoid process. Type II injuries involved 50% or less of the coronoid process, while Type III injuries include fractures of >50% of the height of the coronoid process. Since the adoption of this classification, it has become evident that Type I injuries are usually the result of a shear force imparted by the distal humerus, as opposed to a capsular avulsion, as anatomic studies have demonstrated that the capsule inserts, on average, 6.4 mm distal to the tip of the coronoid.

Fig. 47.6, Reagan and Morrey classification of fractures of the coronoid process. Type I injuries are fractures of the coronoid tip. Type II fractures involve <50% of the coronoid height. Type III fractures involve >50% of the coronoid height. (Campbell’s Orthopedics Fractures and dislocations in Children, Sawyer, Jeffrey; Spence, David Elsevier 2017 fig 36-53 .)

O’Driscoll popularized a more comprehensive classification of coronoid fractures. In this classification, Type I injuries also represent injuries to the tip of the coronoid process and are subdivided based on the size of less than or greater than 2 mm, but still <50% of coronoid height. Type II fractures involve the anteromedial facet and are subdivided into three subtypes: anteromedial facet rim, anteromedial facet rim and tip of the coronoid process, and anteromedial facet rim and sublime tubercle (which is the insertion of the anterior bundle of the MCL) with or without fractures of the tip of the coronoid. Type III fractures involve the base of the coronoid and are subdivided into isolated base fractures and those associated with transolecranon fracture-dislocations of the elbow ( Fig. 47.7 ).

Fig. 47.7, (A) O’Driscoll and (B) Regan-Morrey classifications of fracture of the coronoid process.

Treatment Options

Simple elbow dislocations are typically treated with closed reduction and a brief period (7–10 days) of immobilization followed by early rehabilitation to avoid stiffness. This is typically successful at producing a stable elbow with excellent range of motion, occasionally with negligible limitations at the extremes of motion.

Early surgical intervention, when indicated by early recurrent instability, typically consists of collateral ligament repair. Other techniques including external fixation, internal fixation hinge systems, transarticular fixation, or bridge plating are less commonly employed.

Missed or neglected injuries, or failure of closed or open treatment, can result in residual instability, contractures, or a combination thereof which is referred to as the “stiff, unstable elbow” wherein the arc of motion is severely limited, but within the retained arc of motion, significant AP instability exists. In these chronic settings, treatment options depend on specific deficits and goals and include contracture release, transhumeral debridement, collateral ligament reconstruction, transarticular fixation, hinged external fixation, coronoid process reconstruction, radial head replacement, fascial arthroplasty, total elbow arthroplasty, and elbow arthrodesis. In these complex clinical scenarios, often a combination of these treatment options is utilized in an attempt to minimize pain and maximize function. It is crucial that both the clinician and the patient have realistic expectations and thoroughly discuss the functional goals of the patient to select the best treatment options.

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