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Clinical case: Ulnar nerve subluxation

Everyone is familiar with a sharp pain that radiates down the forearm after punching the elbow onto something sharp. That happens anytime when one of upper extremity nerves, the ulnar nerve is hurt. Luckily, that kind of pain lasts less than a minute because the ulnar nerve usually is not physically damaged. 

In some cases, if the mechanical stress is just too high, it will cause the ulnar nerve to dislocate or subluxate, with every movement resulting with that annoying electroshock-like pain. That kind of injury can happen to anyone and it will be presented in this clinical case.

Key Facts
Ultrasound vs. MRI in assesing musculoskeletal injuries Ultrasound
- does not depict anatomy most clearly
- operator-dependent technique
- rapid and inexpensive
- visualizes almost every injury
- more expensive and time consuming
The "sail sign" Elevated anterior fat pad (looks like a sail) seen in the fractures involving elbow joint
Ulnar nerve paradox Rule for peripheral nerve injuries: the more proximal injury -> the greater the disability -> the more abnormal appearance of the limb
Ulnar nerve paradox: the more proximal injury -> the greater the disability -> less abnormal limb appearance ("claw hand")

After reviewing this case you should be able to describe the following:

  • The utilization of ultrasound to assess musculoskeletal injuries. What other imaging modality could have better visualized the torn ligament than ultrasound?
  • How clinician could have recognized an intra-articular elbow fracture on the lateral elbow radiographs had there been one (the “sail” sign)? 
  • What is meant by the ulnar nerve paradox

This article is based on a case report published in the Journal "Case Reports in Surgery" in 2015, by Caroline C. Jadlowiec, Beata E. Lobel, Namita Akolkar, Michael D. Bourque, Thomas J. Devers, and David W. McFadden.

  1. Case description
    1. Imaging
    2. Management
  2. Anatomical and medical considerations
  3. Explanation to objectives
    1. Objectives
    2. Ultrasound in assessing musculoskeletal injuries
    3. The "sail sign"
    4. Ulnar nerve paradox
  4. Sources
+ Show all

Case description

A 31-year-old obese patient visited the emergency clinic after a fall onto his left hand with the elbow flexed. Patient’s chief complaint was of severe pain in the left elbow, radiating to the forearm. He also had pain and swelling of the left ankle. Immediately after the fall, he experienced an electric shock-like sensation that radiated along the medial aspect of the forearm. The physical exam revealed edema around the posteromedial aspect of the left elbow, and tenderness in the posterior aspect of the medial epicondyle (Figure 1).

Figure 1. Osteology of the left elbow joint (anterior view).

He showed severe, radiating pain along the ulnar nerve distribution whenever the elbow was flexed beyond 80 degrees. Valgus stress test for integrity of ulnar collateral ligament was negative (no pain or excessive laxity). A neurological exam failed to find any sensory or motor deficit along the ulnar nerve distribution (Figure 2).

Figure 2. Skin areas showing the cutaneous innervation of the hand by ulnar, median and radial nerves.

A medial epicondyle fracture was suspected. Orthogonal radiograph views of the elbow did not reveal any fracture or abnormality of the medial epicondyle. Traumatic subluxation of the ulnar nerve was thus suspected as it passed posterior to the medial epicondyle (Figure 3).

Figure 3. Intraoperative view showing the ulnar nerve passing posterior to the medial epicondyle of the humerus (arcuate ligament of Osborne has been removed; this image is not from the current case; the ulnar nerve is shown in its normal position). The image is courtesy of: Citisli V, KocaogluM, Göçmen S, Korucu M. Unusual presentation of multiple nerve entrapment: a case report. Pan African Medical Journal. 2014; 19:283 doi:10.11604/pamj.2014.19.283.5665


Dynamic ultrasound of the elbow showed subluxation of the ulnar nerve: the distance between the floor of the cubital tunnel and the left nerve increased, compared to the contralateral elbow, when the left elbow was flexed more than 90 degrees (Figure 4).

Figure 4. Still images from a dynamic ultrasound exam showing the subluxation of the ulnar nerve with movement. The nerve is shown in its normal position during extension (A) but in an abnormal position during flexion (B). The skin surface is at the upper border of the images. The transducer was placed approximately sagittal along the posterior aspect of the elbow.


The upper limb was placed in a broad arm sling for three weeks in 45 degrees of flexion, a position in which the patient did not have pain. He also had a lateral collateral ligament sprain of the ipsilateral ankle which was treated by a below the knee cast.

At three week follow-up, the patient’s pain had subsided, but showed a fixed flexion deformity of 15 degrees at the elbow. He was advised to initiate an active range of motion exercises, and the use of the sling was discontinued. At final follow up, one year after the injury, the patient was asymptomatic with full range of pain-free motion at the elbow and no neurological deficits in the upper limb.

Anatomical and medical considerations

The ulnar nerve (C8, T1) branches from the medial cord of the brachial plexus (Figure 5).

Figure 5. Cadaver photograph showing the major lower components of the brachial plexus. The “M” formed by the median, ulnar and musculocutaneous nerves is highlighted in for identification purposes.

It innervates the flexor carpi ulnaris, ulnar component of the flexor digitorum profundus, and almost all of the intrinsic muscles of the hand. The ulnar nerve also provides cutaneous innervation to the ulnar side of the anterior and posterior aspects of the hand (Figure 2). After the ulnar nerve branches from the medial cord of the brachial plexus it passes distally along the arm but then travels posteriorly and superficially alongside the medial epicondyle of the elbow in the cubital tunnel (Figure 3&6).

Figure 6. Top. Cadaver image showing ulnar nerve passing posterior to the medial epicondyle of the elbow. In the lower image the ulnar nerve can be seen to originate in the brachial plexus.

Here, it is predisposed to trauma and entrapment neuropathy. Subluxation or dislocation of the nerve at this site can occur normally in some individuals, or can result from trauma. The posterior roof of the cubital tunnel is formed proximally by the fascia aponeurosis between the two heads of origin of the flexor carpi ulnaris and distally by its muscle belly. This aponeurosis is continuous with the ligament of Osborne (Figures 6&7).

Figure 7. Cadaver photograph showing the Ligament of Osborne between the two heads of origin of the flexor carpi ulnaris, and the ulnar nerve within the cubital tunnel. M, medial epicondyle. O, olecranon. Courtesy of: Granger A, Sardi J P, Iwanaga J, et al. (March 06, 2017) Osborne’s Ligament: A Review of its History, Anatomy, and Surgical Importance. Cureus 9(3): e1080. DOI 10.7759/cureus.1080

The patient, in this case, fell onto his non-dominant hand with the elbow in flexion. Such flexion stretches Osborne's ligament. A rapid upward thrust on the flexed elbow will further stress this ligament and cause it to tear, rendering the ulnar nerve susceptible to subluxation or dislocation. When the elbow is flexed beyond 90 degrees, the strain on the ulnar nerve increases and it tends to translate anteriorly over the medial epicondyle, as shown in Figure 4, when Osborne's ligament is not intact.

This explains the reproduction of symptoms of ulnar neuropathy with increasing elbow flexion. It is likely that the splinting of the elbow for three weeks in this patient lead to healing of Osborne's ligament, which thereby, eliminated nerve subluxation. There is no consensus or evidence for the best treatment for chronic or recurrent ulnar nerve subluxation, and data for traumatic nerve subluxation is scarce. Patients with persistent symptoms or painful snapping or those refractory to a conservative line of management likely would need surgical treatment.

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