Traumatic Anteromedial Radial Head Dislocation in an Adult: A Case of Brachialis Tendon Entrapment

Isolated traumatic anteromedial radial head dislocation is an uncommon injury in adults. The brachialis tendon interposition rarely interferes with the radial head reduction procedure. In the present paper, we report the case of an 18-year-old male who sustained an injury to his right elbow during a wrestling match and developed isolated anteromedial radial head dislocation. Open reduction had to be performed due to entrapment of the radial head at the brachialis tendon.


Introduction
Traumatic radial head dislocation is usually observed with Monteggia type fractures, and children are more likely to suffer with isolated radial head dislocation than adults [1][2][3]. Isolated radial head dislocation without fracture and bowing in the ulnar bone is a rare occurrence in adults, with posterior dislocation being a more common manifestation [1][2][3][4][5][6][7].
Isolated traumatic anteromedial radial head dislocation in adults is rarely reported in the literature [4][5]. Only two cases of an irreducible anteromedial radial head dislocation due to soft tissue interposition have been reported in adult patients [4][5]. Moreover, inability to perform the radial head reduction due to brachialis tendon interposition is a very rare situation, with only one such case previously published in the literature [1,[4][5][6][7].
In this study, we report a rare case of isolated anteromedial radial head dislocation in an adult. Open reduction was performed due to entrapment of the radial head at the brachialis tendon.

Case Presentation
An 18-year-old male patient presented to our emergency polyclinic with pain, swelling, deformity, and limited joint mobility in the right elbow. He had sustained an injury to his right elbow during a wrestling match. He had fallen backwards on an outstretched hand with his wrist in dorsiflexion and hyperpronation. The patient had a restricted active range of motion, especially the supination-pronation movements of the forearm. However, flexion-extension movements of the elbow joint were intact. Ecchymosis was present on the anteromedial aspect of the right elbow. Neurovascular status of the limb was normal. X-ray images indicated isolated anteromedial radial head dislocation ( Figure 1).

FIGURE 1: Radiographic images of the patient immediately after injury.
Anteroposterior (a) and lateral (b) radiographic images of the patient indicating isolated anteromedial radial head dislocation of the right elbow.
A computed tomography (CT) scan of the elbow was performed ( Figure 2).

FIGURE 2: Computed tomography (CT) images of the elbow
show isolated traumatic anteromedial radial head dislocation.
Closed reduction was attempted in the emergency room using various maneuvers; however, successful reduction could not be achieved.
Thus, an open reduction was considered. Boyd's approach was used to expose the radial head. A plane was made between the extensor carpi ulnaris and anconeus, and the radiocapitellar joint was exposed. We found that the brachialis tendon was wrapped around the radial neck and noted that the tendon pulled the dislocated radial head anteromedially. The brachialis tendon restricted radial head reduction. We also detected that the annular ligament was ruptured. The brachialis tendon was released from the radial head and the joint was reduced ( Figure 3). However, the reduction was unstable. Therefore, the annular ligament was repaired and a radioulnar Kirschner wire (K-wire) was used to maintain reduction of the proximal radioulnar joint ( Figure 4).

FIGURE 4: Postoperative radiographic images of the patient.
Radiographic image of the patient shows a K-wire was used to maintain the stability of the reduction of the proximal radioulnar joint.
Postoperatively, a hinged long arm cast brace was applied and the patient was allowed to perform flexion-extension movements. Ectopic ossification was observed anterior to the joint at the time of first follow-up. Then, a single dose of 7-Gy radiotherapy was administered to the patient. No progression was detected in ectopic ossification at the subsequent follow-up. The wire and cast brace were removed after four weeks and elbow mobilization was initiated ( Figure 5).

FIGURE 5: Radiographic images at follow-up.
Radial head in reduced position (a, b). Minimal ectopic ossification developed at the anterior of the joint capsule (arrow).
During the course of subsequent follow-ups, it was observed that the patient had gradually resumed his normal activities. The functional outcome of the patient improved without pain or disability ( Figure 6).

FIGURE 6: Postoperative upper-extremity images.
The appearance of the patient's right elbow range of motion at the end of follow-up.
Radial head dislocations are caused by a variety of mechanisms [1,[3][4][5][6][7][9][10]. Injury resulting from a fall in a hyperextended and supination position may cause anterolateral radial head dislocation [3-4, 6, 9]. This situation may be followed by hyperpronation which displaces the head medially, and subsequent flexion of the elbow entraps the tendon around the radial neck [3-4, 6, 9]. This blocks the head in a medial position and prevents closed joint reduction [3-4, 6, 9]. Takami et al. reported a case of a patient with an isolated anterior radial head dislocation after a direct blow to the posterior aspect of a semi-flexed elbow [7]. Salama et al. reported an anterior radial head dislocation after a biceps contraction caused by an electric shock [10]. Sasaki et al. suggest that hyperpronation plays an important role in causing such an injury [3]. In our case, the mechanism of dislocation was considered to be related to extension of the elbow and dorsiflexion-hyperpronation of the wrist.
The annular ligament is the primary stabilizer of the proximal radioulnar joint [1,7]. Other structures such as the quadrate ligament and interosseous membrane also provide stability to this joint [9]. The annular ligament provides multidirectional stability to the proximal radioulnar joint in patients with gross instability of the radial head [9]. Thus, the authors recommend performing annular ligament repair [6]. Radial head dislocation is usually accompanied by damage to the annular ligament. In the presented case, the annular ligament was found to be disrupted and was, therefore, repaired.
Ectopic ossification can often appear after joint dislocation [1]. Accordingly, in our case, an ectopic ossification appeared at the time of follow-up. A single dose of 7-Gy radiotherapy was administered to the patient. No progression in ectopic ossification was detected at subsequent follow-up.

Conclusions
We presented a rare case of isolated radial head dislocation in an adult patient. The brachialis tendon was wrapped around the radial head, pulling the dislocated radial head anteromedially. We suggest that transposed brachialis tendon or other soft tissues should be taken into consideration in the management of a radial head dislocation if radiographs indicate that the radial head is dislocated anteromedially. Consequently, surgical reduction may be required in such cases.

Additional Information Disclosures
Human subjects: Consent was obtained by all participants in this study.

Conflicts of interest:
In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.