Coronal shear fracture of distal humerus associated with olecranon fracture: A case report and pathomechanism

Abstract

Distal humeral coronal shear fractures are rare and account for around 1% of all fractures at the elbow level and 6% of the distal humeral fractures. Many studies have reported on the associated injuries involving the lateral collateral ligament injuries and radial head fractures in up to 40% and 30% of humeral fractures, but this combination of coronal shear fracture of the trochlea and capitellum associated with olecranon fracture is unusual. Here, we report two cases of distal humerus coronal shear fracture with olecranon fracture treated surgically and establish and discuss the pathomechanisms, diagnosis, and therapeutic issues relating to this fracture.

Introduction

Distal humeral coronal shear fractures are rare and account for around 1% of all fractures at the elbow level and 6% of the distal humeral fractures. ^{1 –4} The pathomechanism of injuries usually includes axial loading of the capitello-trochlear area by the force transmitted through the radial head from a low-energy fall or from spontaneous reduction of a posterolateral subluxation or dislocation. ^{2 –5} Many studies ^2,3,5 have reported on the associated injuries, which involve the lateral collateral ligament injuries and radial head fractures in up to 40% and 30% of humeral fractures, respectively, but this combination of coronal shear fracture of the trochlea and capitellum associated with olecranon fracture is unusual.

Here, we report two cases of distal humerus coronal shear fracture with olecranon fracture treated surgically. The aim of this study was to establish and discuss the pathomechanisms, diagnosis, and therapeutic issues relating to this type of fracture.

IRB approval

This study was approved by the Institutional Review Board of the Asan Medical Center (IRB number: S2017-0477-001, approved date: March 26, 2017).

Case report 1

A 55-year-old woman presented to the emergency department after injuring her left elbow following a fall landing directly onto the elbow. She had severe swelling and a bruise on the elbow; pain was noted, but there was no neurologic deficit or external wound. Initial radiographic examination revealed fracture of the olecranon (Mayo classification II), ⁶ with involvement of the distal humeral articular surface of the capitellum and trochlea, presenting a double arc sign (Figure 1). Computed tomography (CT) scan was performed to define the fracture configuration and make the preoperative plan. Upon CT scan, a coronal outline extending from the capitellum to the trochlea in a single fragment with olecranon fracture was observed (Figure 1).

Figure 1.

Preoperative plain radiographs (a–c) and three-dimensional CT images (d–f) of case 1: (a) anteroposterior view; (b) lateral view, white arrow shows double arc sign; (c) oblique view; (d) anterior view; (e) lateral view; and (f) posterior view.

Surgery was performed 4 days following the initial injury. The patient was placed in the right lateral decubitus position, and a posterior skin incision allowed for visibility of the olecranon and displaced capitellum fracture through the olecranon fracture site. The olecranon fracture site was used to approach the capitellum and trochlea (using the fracture site window technique) (Figure 2). During the surgery, we found the olecranon fracture was at 1 cm proximal to the bare area and the capitellum and trochlea fracture was at the anterior half with obvious displacement. Temporary fixation with K-wires followed by fixation using headless screw (Synthes, Oberdorf, Switzerland) was performed from posterior to anterior and medial to lateral (Figure 2). Tension band wire fixation using K-wires was applied for the olecranon fracture (Figure 2).

Figure 2.

(a–c) Intraoperative findings: (a) the fracture configuration, (b) temporary fixation, and (c) final reduction after fixation. (d–f) Postoperative radiographic images: (d) anteroposterior view, (e) lateral view, and (f) oblique view. RH: radial head; Ole: olecranon; Tro: trochlea; Cap: capitellum; Uln: ulna.

At the final follow-up (2 years), the patient had minimal pain and minor stiffness with active range of motion from 15° to 135° flexion. Plain radiographs presented no bony nonunion and arthritic changes.

Case report 2

A 58-year-old woman fell directly onto her right elbow 4 days prior to admission to the emergency department. Initially, pain, swelling, and a bruise around the elbow with multiple bullae were noted, but there was no external wound.

Radiographic evaluation revealed a comminuted fracture of the distal humerus and olecranon with the double arc sign (Figure 3). A CT evaluation was performed to define the fracture pattern and for preoperative plan (Figure 3).

Figure 3.

Preoperative plain radiographs of case 2 (a–c) and three-dimensional CT images (d–f): (a) anteroposterior view; (b) lateral view, white arrow shows double arc sign; (c) oblique view; (d) anterior view; (e) lateral view; and (f) posterior view.

Surgery was performed 12 days after all the bullae reduced. Similar to the first case, the posterior olecranon fracture site window approach was used to expose the fracture site. Headless screws (Synthes) were applied to fix the fractures in the coronal plane; the anatomical plate (Synthes) was used to fix the fracture on lateral side of the distal humerus (Figure 4).

Figure 4.

Postoperative radiographic images. (a) Anteroposterior view; (b) lateral view; and (c) oblique view, white arrow shows mild ectopic ossification.

At 2-year final follow-up, the patient had minimal elbow pain and minor stiffness with active range of motion from 7° to 133° flexion. X-Rays showed no arthritic changes, but mild ectopic ossification was found on the anterior face of distal humerus on a plain radiograph lateral view (Figure 4(c)). However, the patient had not experienced any associated symptoms related to the ectopic ossification.

Discussion

Coronal shear fractures of the distal humerus are rare and account for about 1% of all elbow fractures and 6% of distal humerus fractures ^{1 –3} and usually result from an axial load force on the capitello-trochlear area. However, this type of fracture also involving the olecranon is rarer, and the pathomechanism and surgical method have not been clear yet.

Watts et al. maintain that the mechanism of coronal shear fracture is a low-energy fall and direct compression of the distal humerus by the radial head in a hyper-extended or semi-flexed elbow or from spontaneous reduction of a posterolateral subluxation or dislocation, which is currently widely accepted. ⁷ However, the mechanism of injury was different in our cases. First, the elbow was considerably flexed when the patients fell. The position change of the elbow resulted in a change of the acting point of force and thus the biomechanical effects. Second, the humeroradial joint and humeroulnar joint have different structures. The humeroradial joint is classified as a simple hinge joint, which allows for movements of flexion, extension, and circumduction. However, the humeroulnar joint is a limited ball-and-socket join, which allows movement in all directions. We suggest that if an axial loading force is directly applied to the radial head, it results in the rupture of the ligament around by the radial head and subsequent subluxation or dislocation to absorb the energy. If the same force acts on the olecranon, there is no physical space to absorb energy, and contact on the distal humerus articular surface occurs directly due to its unique structure. Thus, the mechanism could be explained as axial loading force acting directly on an elbow in considerable flexion leading to an olecranon fracture first, and due to the olecranon’s inability to absorb all of the external force, propagation to the articular surface of distal humerus causing a coronal shear fracture. The suggested mechanism of injury is illustrated in Figure 5.

Figure 5.

A suggested mechanism of injury for coronal shear fractures associated with olecranon fracture. (a) Intact elbow; (b) the olecranon fractures firstly under external force; and (c) coronal shear fracture of the distal humerus due to force transmitted from the olecranon.

At present, several surgical approaches and fixation techniques are available to reconstruct the articular surface of the distal humerus. However, open reduction with internal fixation is the mainstream choice for managing coronal shear fractures showing good to excellent outcomes, which is superior to other methods such as fracture excision, arthroscopic reduction and fixation, or total elbow arthroplasty. ^{1 –5,8} Although the lateral extensile approach and fixation are commonly used, ^{2 –4,9} in our opinion, the posterior approach may be better in those cases. When the posterior approach is used to expose the coronal shear fragment, a surgical osteotomy to expose the fracture site is mandatory. However, in these cases, we can optimally use the original olecranon fracture site to approach and expose the coronal shear fragment without causing additional surgical damage. This is the so-called fracture site open window technique. In our cases, anatomical reduction and fixation were achieved much easier with this surgical approach. To preserve blood supply and avoid disruption of the posterior soft tissue, many surgeons preferred an anterior-to-posterior direction approach to employ the interfragmentary screw and fix the fracture. ^{2 –4,9} In these cases, however, considering the already disrupted posterior soft tissue, we fixed the screws in the posterior-to-anterior fashion.

The “double arc sign,” a half-moon shaped, dissociated fragment from the capitellum, appearing on the lateral view of the radiograph is useful for diagnosis. ⁶ This sign may not be present in all cases ^4,10 ; thus, it cannot be the sole diagnostic criterion. Adjuvant three-dimensional CT can assist in determining fracture configuration and in preoperative planning.

Conclusion

We propose a mechanism for an unusual coronal shear fracture of the distal humerus with olecranon fracture, which is caused by an axial loading force applied to a flexed elbow propagating into the distal humerus from the olecranon. A posterior approach with fracture site open window technique and fixation with posterior-to-anterior interfragmentary screws are recommended as a surgical intervention.