Anatomical and biomechanical features of the forearm
The forearm is a complex functional complex. The proximal and distal articulations of the radius and ulna form the elbow and wrist joints. An important anatomical feature is that the large metaepiphysis of these bones are located at opposite ends (proximal in the ulna, distal in the radius), which is why their articular contact area differs significantly.
The forearm bones are connected throughout their entire length by a dense interosseous membrane. This membrane plays a critical role in diaphyseal injuries: its tension provokes a specific converging bone displacement. This phenomenon is a unique feature of the forearm and does not occur in the diaphysis of other segments of the musculoskeletal system. Due to the strong anatomical connection, a fracture of one bone with displacement (angular or shortening) almost always predictably leads to a fracture or dislocation of the paired bone.
Influence of muscles on fragment displacement
Bone fragment displacement directly depends on the level of injury (upper, middle, or lower third of the forearm). Antagonist muscles actively participate in this process, normally ensuring the complex biomechanics of the forearm and hand (rotational pronation-supination, lateral, and flexion-extension movements).
Main muscles causing displacement:
- Biceps brachii muscle (m. biceps brachii).
- Supinator muscle (m. supinator).
- Pronator teres (m. pronator teres).
- Pronator quadratus muscle (m. pronator quadratus).
Principles of surgical and conservative treatment
The difficulties of conservatively correcting the converging displacement caused by the interosseous membrane frequently dictate the need for surgical treatment. The main goal of any intervention is the complete restoration of the correct length, spatial position of the bones, and mandatory recreation of the normal curvature of the radius.
Various fixation techniques are used. In open fractures (especially in the elbow joint area), preference is often given to pin-rod fixators with a hinged joint and bearing pads, which ensures reliable reposition and stability. In other cases, plates and screws are widely used.
Complications of forearm and elbow fractures
Inadequate reposition or the severity of the trauma itself (especially intra-articular fractures of the distal humerus and proximal forearm) can lead to a number of serious consequences:
- Alteration of the limb axis (most commonly varus deformity) due to inadequate reposition.
- Ischemic disorders (Volkmann's contracture) — develop against the background of pronounced edema and compression of neurovascular bundles.
- Restriction of motion — even with ideal osteosynthesis in adults (especially with type C fractures), joint function suffers. Early mobilization is critically important for prevention.
- Heterotopic ossification — areas of soft tissue ossification capable of completely blocking the joint. Their appearance is iatrogenic and is provoked by the prescription of physiotherapy or massage, which are strictly contraindicated for this localization.
AO/ASIF classification of proximal injuries
To systematize proximal forearm injuries (segment code 21), a universal classification is used:
- Type A — extra-articular injuries.
- Type B — intra-articular fractures involving only one bone.
- Type C — complex intra-articular fractures of both forearm bones.
Briefly: answers to topical questions
What fixation methods are used in the surgical treatment of forearm bone fractures?
In the surgical treatment of forearm bone fractures, plate osteosynthesis, intramedullary osteosynthesis, and transosseous osteosynthesis are used.
- Plate osteosynthesis — fixation of fractures with plates and screws.
- Intramedullary osteosynthesis — fixation with rods; in children, the method of choice is closed reduction with elastic stable intramedullary nailing.
- Transosseous osteosynthesis — application of compression-distraction devices.
In a fracture of the diaphysis of both bones, where one has a simple fracture and the other a comminuted one, a combined approach is used: for the simple fracture — open reduction and plate osteosynthesis; for the comminuted fracture — closed reduction and intramedullary osteosynthesis.
What is the mechanism of injury in an extension fracture of the radius (Colles' fracture)?
The mechanism of injury in an extension fracture of the radius (Colles' fracture) consists of a fall onto the hand in a position of extension (dorsiflexion). As a result, the distal bone fragment of the radius is displaced dorsally and radially. The articular surface tilts dorsally, losing its physiological palmar tilt, and the angle between the longitudinal axis of the diaphysis and the line of the articular surface in the lateral projection becomes greater than 90°.
How does Colles' fracture differ from Smith's fracture?
The main difference lies in the mechanism of injury and the direction of displacement of the distal bone fragment.
| Diagnostic signs | Colles' fracture | Smith's fracture |
|---|---|---|
| Mechanism of injury | Fall onto the hand in extension (dorsiflexion) | Fall onto the hand in palmar flexion |
| Direction of fragment displacement | Dorsal and radial direction | Palmar (volar) and medial direction |
| Palpation of the distal fragment | Fragment is palpable from the dorsal side | Fragment is palpable from the palmar side |
| Articular facet tilt angle (lateral projection) | > 90° | < 80° |
What types of displacement of bone fragments are characteristic of a distal radius fracture in a typical location?
A distal radius fracture in a typical location is characterized by angular displacements of the distal bone fragment, the direction of which depends on the type of fracture.
- Extension type (Colles' fracture) — the distal fragment is displaced dorsally and radially, forming a deformation angle open dorsally.
- Flexion type (Smith's fracture) — the distal fragment is displaced palmar (volar) and medially; the angle is open volarly.
Which nerves and tendons are most commonly damaged in a distal radius fracture in a typical location?
In a distal radius fracture in a typical location with displacement of the peripheral fragment (Colles' fracture), the posterior interosseous nerve of the forearm can be damaged. This can lead to the development of a flexion contracture of the hand (Bonnet's contracture). Information on the most frequently damaged tendons in this trauma is not contained in the provided sources.
To understand muscle pull in a fracture, remember the "forearm seesaw" rule: supinators (biceps and short supinator) pull the fragments in one direction, while pronators (round and square) outweigh them in the opposite direction depending on the level of the fracture.
Class and exam questions
Does the olecranon always undergo significant displacement during trauma?
No. Significant displacement (5 mm or more proximally) occurs only upon the destruction of the strong tendinous structure encompassing the process below the insertion site of the triceps muscle.
Can massage be prescribed for rehabilitation following an elbow joint fracture?
Absolutely not. Massage and physiotherapeutic treatment in this localization are contraindicated because they provoke the growth of heterotopic ossifications that block joint movement.
What else to study on this topic
- Pathogenetic mechanisms of Volkmann's ischemic contracture in compartment syndrome.
- Technique of pin-and-wire fixator application in open fractures.
- Causes of secondary fragment displacement in forearm shaft fractures.
- The role of the triceps brachii muscle in olecranon displacement.
- Tactics for early range of motion exercises in type C intra-articular injuries.
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