Entrapment of the median nerve in the elbow is a rare yet severe complication of elbow dislocation and reduction. Primarily a problem that occurs in children, its incidence is approximately 3% of all elbow dislocations ^[1]. In this case report, we attempt to highlight the role of ultrasonography (USG) in the localizing the nerve injury and hence its proper management.

A 10-year-old right-hand dominant male child presented to us with a history of posteromedial dislocation of the right elbow which was reduced elsewhere 2 months ago. On clinical examination, the child had pain, stiffness, 30° of fixed flexion deformity (Fig. 1), and features of high median nerve injury with weakness in the long flexors of index finger and thumb, and hypoesthesia on the tip of index finger. However, the joint was well reduced with no myositis (Fig. 2). Electromyography (EMG) and nerve conduction velocity (NCV) confirmed the axonal injury at the level of elbow (Fig. 3). USG reported the nerve being trapped in the elbow behind the medial epicondyle and further pinching in extension (Fig. 4). Review of literature has only four such reports of this rare injury with a Matev sign to predict this on X-ray. Nerve exploration corroborated this precise descriptiond a medial epicondyle osteotomy was needed to release entrapped nerve as advised in the literature.

In our case, we took anterior approach curvilinear across the cubital fossa. Nerve exploration was done tracing the median nerve distally and proximally. Entrapped nerve was released after medial epicondyle osteotomy and the nerve was placed in front of the elbow in its normal site. Nerve badly contused but intact (Fig. 5).

Four types of entrapment have been described: Types I-III by Hallet ^[2] and Type IV by Al-Qattan et al. ^[3]. Type I consists of the median nerve slipping posteriorly behind a torn medial collateral ligament and adhering to the posterior surface of the humerus. Type II is defined when a median nerve becomes entrapped by healed bone after running through a fractured epicondyle. In Type III, the nerve becomes entrapped in the humeroulnar joint ^[2]. Type IV is a combination of Types I and II ^[3]. Despite the different methods of entrapment there is one common end point: Compression leading to ischemia of the nerve. Chronic compression and ischemia in neural tissue can lead to intraneural fibrosis and eventual Wallerian degeneration ^[4]. In addition, median nerve entrapment is often diagnosed late (3 months to 2.5 years post-injury), which contributes to the extent of median nerve injury ^[5]. The late diagnosis is not uncommon because the presence of a transient neuropraxia created by contusions or stretching at the time of injury can mimic the signs of an early entrapment ^[5]. Furthermore, children often have difficulty vocalizing their symptoms, making any deficit less apparent ^[5]. Diagnosis has generally consisted of recognizing any non-resolving deficits over time and surgical exploration of the elbow. Radiological changes described by Matev ^[6] can often be found in cases presenting late due to chronic force applied to the cortex of the bone. Treatment of median nerve entrapment has ranged from simple release and neurolysis to excision and end-to-end anastomosis or nerve grafting. If entrapment does occur, early diagnosis can lead to restoration using less invasive measures. Both simple nerve release and neurolysis have demonstrated positive results when the entrapment is caught early, and the nerve is not extensively damaged ^{[7,8,9,10,11,12,13,14]}. USG is a powerful tool to aid in diagnosis pre-operatively. USG shows the course of the median nerve and can also serve as an adjunct to electromyography in evaluation of muscle denervation through assessment of muscle atrophy. Early diagnosis and treatment will favor a normal result. In a case described by Korus et al., Type III pattern of median nerve entrapment was found in a 7-year-old girl, who presented with fixed flexion deformity of 20° and anterior interosseous nerve palsy 10 months after the initial injury. On clinical evaluation, there was inability to use flexor digitorum superficialis in digits 2-5, and flexor digitorum superficialis to index finger and no function in flexor pollicis longus. Numbness of index finger and thumb and wasting of thenar muscle mass was noticed. EMG showed right median nerve neuropathy. On surgical exploration, the nerve was found to be encased in the elbow joined, the proximal and distal ends of the nerve were isolated and sural nerve grafting was done. At 3-month follow-up, nerve regeneration was present as demonstrated by Tinel’s sign ^[15]. Lars G. Danielson described a similar condition in an 11-year-old boy which was diagnosed 11 months after posterior dislocation of elbow with medial epicondyle humerus fracture. Median nerve was explored proximally and distally, bone encircling the median nerve was nibbled. Flexor muscles and ligaments were released subperiosteally from the epicondyle. Median nerve was then embedded in a fat and placed in its normal location in front of the elbow joint. Post-operatively, the boy gradually improved after 10 months ^[11]. Mannerfelt described a case of median nerve entrapment soon after the reduction of posterior dislocation of the right elbow in a 9-year-old boy. Soon after the effect of anesthesia, clinical symptoms in the hand were suggestive of median nerve injury. On surgical exploration,the tendon of biceps was found to be intact but, the tendon of brachialis was torn off. Median was traced and was found to be in the joint between humerus and ulna. With traction and joint manipulation, the median nerve was freed and was found to be in continuity. Nerve was decompressed by splitting the sublimis ridge. The boy gradually regained full function after surgery ^[14]. In our case, patient presented 2 months after the injury with pain, stiffness, deformity, and features of high median nerve injury. The type of nerve injury was evaluated with EMG NCV study and the nerve was localized with USG. USG helped in exactly localizing the nerve where it was entrapped behind the medial epicondyle in the elbow. Intraoperatively, the nerve was found to be in the same location as revealed by USG. The nerve was released by osteotomy of medial epicondyle; hence, the patient is expected to have a good outcome post-operatively.

Median nerve entrapment following the elbow dislocation is a rare entity, and the diagnosis of the nerve injury is frequently delayed. However, prompt clinical suspicion, diagnostic tools such as USG can lead to accurate diagnosis, and then provide the exact situation of trapped median nerve. After the localization of nerve, nerve release can be done which usually ensures a good functional outcome in terms of regaining of median nerve function.

Median nerve entrapment following the elbow dislocation and its reduction is a rare occurrence. The authors believe that high clinical suspicion is necessary, to make the diagnosis and at the same time the appropriate surgery to be performed to provide a good recovery. Ultrasound is an effective and economically affordable tool to confirm the clinical diagnosis.