Coronoid fractures rarely occur in isolation but typically occur in the setting of fracture-dislocations of the elbow. Tip or small anterolateral fractures may occur in association with “terrible triad” injuries of the elbow, with concomitant radial head fracture and posterolateral instability. Occasionally an apparent isolated coronoid fracture is seen on imaging studies, but this may represent a subtle but potentially serious instability pattern. In the past, coronoid fractures have occasionally been dismissed as inconsequential; however, recent studies have highlighted the importance of the coronoid to stability of the elbow joint and recent interest has focused upon classification and treatment strategies.
Patients often present with an elbow fracture-dislocation. A small fleck of bone may be present on radiographs or a larger fragment may be seen. Gross or subtle instability may be a component of these injuries. It is important to recognize the presence and implications of coronoid fractures and associated injuries patterns to develop a treatment plan; some injuries are inconsequential and do not alter management of associated injuries while others may represent a serious injury pattern.
Elbow fracture-dislocations with a concomitant radial head fracture should be assumed to have a coronoid fracture until proven otherwise. These fragments may be small and be initially believed to be a fragment from the radial head.
The affected extremity is examined with attention to the major peripheral nerves and the vascular status. The skin is inspected for any lacerations or abrasions. Occasionally, the presence of ecchymoses on the medial or lateral side can be a clue to trauma in those regions. The forearm, wrist, and upper arm are examined for any other injuries to the limb.
Three view radiographs of the elbow should be obtained pre- and post- reduction. In the setting of an elbow dislocation, it is uncommon that the definitive treating surgeon is present for or performs the closed reduction. However, it is helpful if the individual who performs the closed reduction examines the elbow after closed reduction and documents how unstable the elbow is and in what positions instability occurs. Likewise, use of a fluoroscopy unit is quite helpful.
Following a closed reduction in the setting of a dislocation, plain film radiographs are obtained and evaluated. In the setting of suspected or known coronoid fracture or complex trauma, computed tomography (CT) scans with 2D and 3D reconstructions are very helpful to demonstrate the origin of fracture fragments and clarify fracture patterns. When obtaining the CT scan, it is helpful to position the patient with the elbow in as much extension as is possible without dislocation to obtain optimal images. Likewise, it is best if the patient may position the arm centrally in the machine gantry, typically overhead in the “superman” position. This avoids artifact that results from shooting the images through body or out of the “sweet spot” of the scanner.
The advent and widespread availability and use of CT scanning has altered our understanding of coronoid fractures and the classification systems available to us. Previously, coronoid fractures were classified according to the Reagan Morrey system, based upon plain film lateral radiographs, with type I fractures representing a “tip” fracture of the coronoid; type II fractures representing 50% of the coronoid height, and type III fractures representing those fractures including the base of the coronoid. This classification system remains in widespread use as it is simple, easy to apply, and remains a broad indicator of injury severity.
However, more recently, CT scans have been used to classify coronoid fractures in three dimensions.
In a series of 52 consecutive fractures, five specific injury patterns emerged, and a modification of the Regan Morrey system was proposed. In this scheme, tip type fractures represent fractures similar to Regan Morrey type I, midtransverse fractures are equivalent to Regan Morrey type II fractures, and similar to Reagan type III fractures are basal fractures. The remaining two fracture types seen by CT scanning are not well accounted for by the Regan Morrey system as they have obliquity in three dimensions. These two fracture types are distinguished by obliquity with either anterolateral or anteromedial orientation. There is a high rate of intra- and inter-observer reliability with this classification system.
In addition, O’Driscoll proposed a classification system based upon anatomy of the coronoid, which includes three types (tip, anteromedial, basal) and seven subtypes; treatment strategies may be proposed based upon type or subtype.
Nonoperative management is employed for the elbow joint that remains congruently located without need for addressing either associated instability or concomitant fracture (e.g. radial head fracture). If the elbow is stable in a certain position of flexion, it is splinted and followed closely with repeat clinical examination and radiographs over time. Gradually, the elbow is allowed to extend over time. Typically a hinged elbow brace which allows flexion but has an extension stop short of the position of instability is used, and gradually the extension is increased over a few weeks time. A supervised therapy program is helpful to reinforce compliance and to ensure motion is coming along.
If the elbow is completely stable following reduction, in some cases it may be treated similar to a simple dislocation with appropriate clinical and radiographic follow-up.
Indications for Surgery
Indications for surgery include instability that is not adequately addressed in a closed fashion, joint subluxation, or presence of concomitant injuries which mandate treatment (e.g., radial head fracture). Specific indications and techniques are outlined by fracture types.
My preference is general anesthesia. The patient is typically positioned supine with an arm board at the side. This may be swung in and out during the case to support the arm as needed or to get it out of the way. The arm may be draped over the chest with a sterile pack of towels; airplaning the bed away from the surgeon can facilitate better positioning and exposure. A sterile or nonsterile tourniquet is applied to the upper arm and inflated to 200- 250 mm Hg during the operative procedure.
The procedure starts with an examination under anesthesia and fluoroscopy. The use of a mini- C arm minimizes radiation exposure to patient, surgeon and team and is easier to maneuver than large fluoroscopy units. The elbow is examined under anesthesia to document position and amount of instability. Stressing the medial and lateral ligaments can reveal sometimes unexpected ligament incompetence.
Specific treatment is outlined by fracture types; specific exposure and treatment most commonly depends on the type and severity of associated injuries.
Tip fractures or anterolateral fractures:
These often occur in the setting of a terrible triad type injury; the mechanism of coronoid fracture is a shear injury in conjunction with posterolateral rotatory instability. There is typically a radial head fracture, injury of the lateral ulnar collateral ligament, and shear fracture of the coronoid. The medial collateral ligament may also be injured if the rotatory moment continues; injury is present in about 1/2 of cases and may or may not be clinically relevant.
If a clinically significant radial head fracture exists, the elbow is typically approached from the lateral side. Exposure of the radial head is facilitated by exploiting the often present lateral ulnar collateral ligament injury via the Kocher interval. If there is no lateral ulnar collateral injury, a split through the extensor digitorum origin at the midline of the radial head is preferred. If the radial head is removed for subsequent replacement arthroplasty, the coronoid fracture can be exposed and either excised or fixed via this incision. It is often helpful to use a targeting drill guide, such as an ACL drill guide with the tip at the tip of the coronoid fracture and the drill guide over the subcutaneous border of the ulna to facilitate reduction and fixation with screws or threaded K wires left in place. Very small coronoid fractures may be excised or left alone; larger or structurally significant fractures may be fixed.
It is unclear how much stability or structural integrity is restored when the coronoid is fixed with “suture fixation”. Following ORIF or radial head replacement, the lateral ulnar collateral ligament, if injured, is repaired through a running locking stitch and either bony tunnels or suture anchors as the lateral side of the elbow is closed. The elbow is then assessed under fluroscopic stress views and range of motion to evaluate stability. If the elbow is stable at this point, even if there is injury to the medial collateral ligament, the procedure is completed. If however, stability of the elbow joint is not restored, the medial collateral ligament is addressed.
Anteromedial coronoid fractures:
These fractures occur via a varus posteromedial rotatory force which occurs with axial loading in a “collapsed coronoid” pattern. Such fractures may include just the tip of the anteromedial facet, leaving the important sublime tubercle intact, or may include the entire anteromedial facet. As the anteromedial face of the coronoid collapses against the humerus during injury, the lateral ulnar collateral ligament is stretched and then torn. The radial head is most commonly intact.
Radiographs may appear deceptively benign with a very small coronoid fracture fragment. However, close inspection may reveal asymmetric widening and narrowing across the joint surface on PA or AP films, which is a clue to the instability. Examination under anesthesia and fluoroscopy is typically diagnostic as well. If this pattern is not recognized and treated, the subtle joint instability results in rapid destruction of the articular surface and early arthritis.
Typically, treatment of this pattern involves exposure and fixation of the coronoid fracture and fixation of the lateral ulnar collateral injury. The coronoid is exposed by making a posteromedial incision over the ulnar nerve and identifying and retracting the nerve away from the surgical field. The flexor pronator origin muscles are elevated off of the ulna anteriorly, working from distal to proximal and palpating for the sublime tubercle. This approach helps preserve the medial collateral ligament. The fracture site is exposed and reduced. Commonly a buttress type plate is used to effect repair and buttress the fracture site; alternatively, if there is a large fracture with little comminution, screws may be used for fixation, most commonly directed from the intact ulnar shaft up into the fracture fragments (posteriorly to anteriorly) as it is difficult to drill and direct screws anteriorly from the coronoid into the remaining bone. Following successful fixation of the coronoid, examination under fluoroscopy is performed to evaluate stability. If the elbow remains unstable, the lateral ulnar collateral ligament is repaired (and the surgeon should have a low threshold for repair). If the elbow remains unstable even after good repair of medial and lateral structures, placement of an external fixator may be considered.
These high energy fracture patterns include the sublime tubercle and are often transolecranon injuries. Fixation may be approached anteromedially (as above) if there is no transolecranon fracture component and may be facilitated with either screws, plates, or both. If there is a transolecranon component, this window may be exploited for fracture fixation.
Pearls and Pitfalls of Technique
It is important to ensure that stability of the elbow is restored before leaving the operating room.
In selected cases, use of an external fixator is helpful to restore congruency to the elbow. A static fixator is easy to apply and there seems to be little advantage to use a hinged fixator which can be more difficult to apply and is more costly.
Postoperative rehabilitation is important with close clinical and radiographic follow-up in complex injuries.
Recurrent instability of the elbow, failure of fixation, and ulnar nerve complications can be problematic. Subtle instability can lead to fairly rapid joint destruction.
Postoperative rehabilitation depends upon the stability obtained in the operating room and the structures injured. If stability was obtained intraoperatively, range of motion commences within a few days postoperatively. If a choice must be made between motion and stability, stability is favored with immobilization as necessary for healing.
Outcomes/Evidence in the Literature
Little information is available in the literature regarding outcomes following coronoid fractures. This is in part because these injuries rarely occur in isolation and the concomitant injuries often dictate treatment and influence outcomes.
Regan and Morrey reported upon 32 patients with coronoid fractures. Most of these patients were treated with immobilization; because of poorer outcomes, prolonged immobilization alone was condemned. Subsequently, Adams et al reported on 103 patients at the same institution. All Regan Morrey I were treated nonoperatively or excised; all type III fractures and 76% of type II fractures were treated operatively often with plates. These patients fared better than the prior cohort of patients at the same institution.
Adams, JE, Sanchez-Sotelo, J, Kallina, CF, Morrey, BF, Steinmann, SP. “Fractures of the coronoid: morphology based upon computed tomography scanning”. Journal of Shoulder and Elbow Surgery. vol. 21. 2012. pp. 782-8.
Adams, JE, Hoskin, TL, Morrey, BF, Steinmann, SP. “Management and outcome of 103 acute fractures of the coronoid process of the ulna”. J Bone Joint Surg Br. vol. 91. 2009. pp. 632-635.
O’Driscoll, SW, Jupiter, JB, Cohen, MS, Ring, D, McKee, MD. “Difficult elbow fractures: pearls and pitfalls”. Instr Course Lect. vol. 52. 2003. pp. 113-134.
Regan, W, Morrey, B. “Fractures of the coronoid process of the ulna”. J Bone Joint Surg Am. vol. 71. 1989. pp. 1348-1354.
Steinmann, SP. “Coronoid process fracture”. J Am Acad Orthop Surg. vol. 16. 2008. pp. 519-529.
Coronoid fractures can be complicated and difficult to treat. Developing an understanding of the injury patterns that occur and the structures that must be addressed to restore a stable and congruent elbow joint facilitates best outcomes.
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