Surgical Anatomy. The surgical anatomy of luxations of the upper end of the ulna alone is similar to that already given in 'Dislocations of the Elbow' on page 154. Dislocations of this type are quite rare, whereas luxations of the elbow (both bones) are by no means uncommon.
The upper end of the ulna may be displaced either backward or forward, describing the arc of a circle, of which the undisplaced radial head is the center. Both types are exceedingly rare, but of the two the posterior is the more common. In either form the interosseous membrane and oblique ligament are probably not torn, and the head of the radius remains in position on the capitellum. The injury is probably produced by trauma which twists the forearm at the same time adducting or abducting it.
<Callout type="important" title="Key Anatomy">Understanding the relationship between the ulna, radius, and elbow joint is crucial for proper diagnosis and treatment.</Callout>
Symptoms. The posterior variety presents a characteristic clinical picture. The forearm is more or less extended and there is a pronounced 'gunstock deformity.' The olecranon is prominent and raised, though the displacement is usually not as pronounced as seen in posterior luxations of both bones. The tip of the coronoid may rest on the trochlea, or behind it, or the upper end of the bone may be still further displaced so that it rests behind the external condyle. The further the backward displacement of the upper end of the ulna, the more external will be the position occupied by the olecranon and the more pronounced will be the cubitus varus. The epitrochlea is prominent and more anteriorly situated than normal, with relation to the forearm. There is a compensatory outward rotation of the humerus to accommodate the altered position of the forearm. The internal lateral ligament may be ruptured or an equivalent avulsion of the epitrochlea may exist.
In forward luxations the ligamentary laceration, especially on the inner side of the elbow, is greater and the causative trauma is more severe. The forearm may lie anywhere between semiflexion and complete extension. There is abnormal lateral mobility in the direction of abduction. The top of the olecranon lies either on, or in front of, the trochlea and the position of the forearm is one of pronounced abduction. In other words, the carrying angle is greatly exaggerated.
A third form of luxation, so rare as to scarcely deserve description, is one of inward luxation. In this type the upper end of the ulna is displaced inward so that the sigmoid embraces the epitrochlea, while the radius remains in contact with the capitellum. The interosseous membrane, oblique and orbicular ligaments are of necessity ruptured and the upper part of the forearm is greatly broadened.
In all three forms of luxation of the ulna the head of the radius probably suffers a slight subluxation, but since it remains in contact with the capitellum it may for practical purposes be considered in normal position.
Treatment. In backward luxations reduction is easily accomplished by extension and counter-extension in much the same way as has been described in 'Treatment' of 'Dislocations of the Elbow.' The adduction, which is due to the radius remaining in place, must be taken into account and requires a forced abduction of the elbow as extension and counter-extension are being made.
In forward luxations the ulna is returned to its normal position by inward rotation of the upper end of the forearm, accompanied by adduction of the forearm as the olecranon clears the trochlea.
Key Takeaways
- Dislocations of the ulna alone are rare and can be either backward, forward, or inward.
- Symptoms include a 'gunstock deformity' for posterior dislocation and exaggerated carrying angle for anterior dislocation.
- Treatment involves extension and counter-extension for posterior dislocation and inward rotation for anterior dislocation.
Practical Tips
- Recognize the characteristic 'gunstock deformity' to diagnose posterior ulnar dislocation quickly.
- Use forced abduction of the elbow during treatment to account for adduction caused by the radius remaining in place.
- Inward luxation is extremely rare but involves significant broadening of the upper forearm.
Warnings & Risks
- Misdiagnosis can lead to improper treatment and potential worsening of injury.
- Forced abduction or rotation without proper technique may exacerbate damage.
- Ignoring ligament ruptures during treatment can result in long-term instability.
Modern Application
While the anatomical descriptions and basic principles remain relevant, modern emergency responders should use advanced imaging techniques like MRI for accurate diagnosis. Treatment methods have evolved with better understanding of soft tissue injuries, but the fundamental approach to manual reduction remains valuable.
Frequently Asked Questions
Q: What are the key symptoms of a posterior dislocation of the ulna?
The key symptom is a pronounced 'gunstock deformity' where the olecranon process is prominent and raised, though not as much as in full elbow dislocations. The epitrochlea is also more anteriorly situated.
Q: How does one treat an inward luxation of the ulna?
Inward luxation involves significant broadening of the upper forearm due to ruptured ligaments and interosseous membrane, making it extremely rare. Treatment would involve careful manual reduction under medical supervision.
Q: What is the treatment for forward dislocation of the ulna?
Forward luxation can be treated by returning the ulna to its normal position through inward rotation of the upper end of the forearm, accompanied by adduction as the olecranon clears the trochlea.