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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.
| Ultrasound vs. MRI in assesing musculoskeletal injuries |
Ultrasound - does not depict anatomy most clearly - operator-dependent technique - rapid and inexpensive MRI - 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.
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).
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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).
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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).
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Imaging
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).
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Management
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).
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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).
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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).
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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.
Explanation to objectives
Objectives
- 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?
Ultrasound in assessing musculoskeletal injuries
Ultrasound uses high-frequency sound waves and the echoes from these sound waves to create an image of body tissues and structures. The images created by ultrasound units typically do not depict anatomy as clearly as most other imaging modalities and are further complicated by ultrasound being a very operator-dependent technique in which slight changes in pressure or orientation of the transducer result in significant changes in the image.
Nevertheless, ultrasound is very rapid and inexpensive, and can be used to diagnose musculoskeletal issues when an experienced ultrasonographer performs the evaluation. An elbow MRI would likely have allowed visualization of the tear in Osborne’s ligament as an accumulation of fluid in the space occupied by the ligament. MRI, however, is much more expensive and time-consuming than ultrasound.
The "sail sign"
It is often difficult to visualize an elbow fracture on standard radiographic views of the elbow. However, the effusion of blood resulting from an elbow fracture causes displacement of the anterior and posterior fat pads that are found in the joint. The sail sign derives its name from the fact that the elevated anterior fat pad has the shape of a spinnaker (sail).
The anterior fat pad located in the coronoid fossa may be seen in a normal lateral elbow radiograph as a line parallel to the distal humerus. The posterior fat pad, which is located in the much deeper olecranon fossa, is not visible on lateral images. Anterior and posterior fat pads are intra-articular but extrasynovial structures. If there is a fracture involving the elbow joint, effusion or blood in the synovial space can cause displacement of fat pads, which results in their altered visualization in lateral images of the elbow (Figure 8).
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Ulnar nerve paradox
In all cases except that of the ulnar nerve paradox, in peripheral nerve injuries, the more proximal the location of the injury, the greater the disability and the more abnormal the appearance of the limb. However, in the ulnar nerve paradox, a proximal elbow injury remains more disabling than if the injury occurs more distally at the wrist, but the patient’s hand actually looks more normal with the more proximal elbow injury than with the distal wrist injury.
An ulnar nerve injury is associated with a “claw hand” posture because of the loss of function of almost all of the intrinsic hand muscles. In an elbow ulnar injury the loss of function of half of the flexor digitorum profundus muscle results in less of a clawing posture in digits 4 and 5 than if the injury occurred at the wrist. This is the paradox. There remains less function with an ulnar injury at the elbow than at wrist, but the hand appears less clawed.
Clinical case: Ulnar nerve subluxation: want to learn more about it?
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