Anatomical and biomechanical features
The elbow joint has a complex structure: it consists of three joints enclosed in a single joint capsule. The distal part of the humerus, as well as the proximal parts of the ulna and radius, take part in their formation.
Biomechanics of movements:
- Flexion and extension occur due to the movement of the forearm bones relative to the humerus.
- Rotation is provided by the rotation of the radial head in relation to the ulna and humerus.
The ulnar and radial collateral ligaments are responsible for the lateral stabilization of this complex. The radial head itself is securely fixed by the annular ligament.
Displacement limiters and bony landmarks
Normally, the joint is protected from excessive anteroposterior displacements by powerful bony structures:
- Anterior limiter — the coronoid process of the ulna. It is clinically important to remember that when a posterior dislocation occurs, this process can fracture.
- Posterior limiter — the olecranon. Accordingly, in the rare anterior dislocation, there is a high risk of its fracture.
For correct clinical diagnosis, physicians rely on three prominent points: the tip of the olecranon and the two epicondyles of the humerus.
- If the forearm is fully extended, these three points align in a straight line — Hueter's line.
- If the arm is flexed at the elbow to 90°, these same landmarks form an equilateral Hueter's triangle. Disruption of these lines indicates displacement.
Classification and injury mechanism
Isolated dislocations of the radius in adult patients are extremely rare. As a rule, displacement of both forearm bones occurs simultaneously.
According to the direction of displacement, two main types are distinguished:
- Posterior dislocations: The absolute leader, accounting for about 90% of all clinical cases. The mechanism is classic — a person falls on an outstretched arm, which leads to severe hyperextension in the elbow joint.
- Anterior dislocations: Much less common. They occur with a direct blow to the flexed elbow, causing the olecranon to shift sharply anteriorly. Despite their rarity, this injury is more dangerous due to frequent concomitant damage to neurovascular bundles.
Clinical diagnostics
Immediately after the injury, a characteristic clinical picture appears:
- Acute, severe pain in the joint area.
- Complete inability to perform active movements.
- Visual enlargement of the elbow volume.
- Sharp tenderness upon palpation and a forced position of the injured limb.
Specific signs of posterior dislocation: The victim's forearm is usually in a flexed position at an angle of 45 to 90 degrees. When examining the limb from the front, the injured forearm looks visually shortened compared to the healthy arm.
Briefly: answers to topical questions
Specifically, which vessels and nerves are at risk of injury in an anterior forearm dislocation?
In an anterior forearm dislocation, peripheral nerves and blood vessels are at risk of injury. In particular, the most frequently injured are:
- Ulnar nerve (n. ulnaris) — a peripheral nerve of the upper extremity, damage to which causes specific motor and sensory disturbances.
- Brachial artery — a main blood vessel.
Thorough assessment of neurological status and peripheral circulation is strictly mandatory both before and after reduction of the dislocation.
Which fractures most commonly accompany a posterior forearm dislocation?
Posterior forearm dislocation is frequently accompanied by a fracture of the coronoid process of the ulna. The coronoid process serves as the anterior limiter of anteroposterior displacement; falling on an outstretched arm with hyperextension in the elbow joint can result in a posterior dislocation with a coronoid process fracture.
In which radiographic projections should images be taken to confirm a forearm dislocation?
To confirm a forearm dislocation, images must be taken in anteroposterior and lateral projections. Radiography in these two standard views is strictly mandatory both before and after manipulation to achieve reduction. This allows for accurate diagnosis of the dislocation, identification of potential concomitant bone injuries, and verification of successful reduction of the articular surfaces.
Hueter's line and triangle: straight arm — straight line, bent arm — equilateral triangle.
Class and exam questions
What is the main danger of an anterior dislocation?
With this displacement, severe injuries to surrounding blood vessels and nerves occur much more frequently.
How to clinically determine a posterior forearm dislocation?
The arm is flexed at an angle of 90–45°, and upon anterior inspection, the forearm appears shortened compared to the healthy arm.
What else to study on this topic
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- Specific symptoms of Weinstein, Babich, and Khitrov
- Bankart and Hill-Sachs lesions
- Classical (Boychev-II) and arthroscopic methods of surgical treatment
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