Radiuskopf

Radiuskopf, also known as the radial head, is the proximal end of the radius and a key component of the elbow and forearm joints. It is slightly flattened and sits at the top of the forearm bone, connected distally to the neck and shaft of the radius.

Anatomy and articulations: The radial head has a convex articular surface that contacts the capitellum of the humerus, forming the radiocapitellar joint. It also participates in the proximal radioulnar joint by articulating with the ulna at the radial notch and being encircled by the annular ligament, which stabilizes the head against dislocation. The radial head rotates during forearm pronation and supination, allowing efficient rotation of the forearm. The head's development includes ossification that appears around early childhood.

Function and biomechanics: The radial head contributes to elbow stability and to the transmission of axial loads from the hand to the rest of the upper limb. It acts as a fulcrum for forearm rotation and helps maintain the alignment of the radius and ulna during movement.

Clinical significance: Radial head injuries are common after falls on an outstretched hand. Fractures can be nondisplaced or comminuted and may require immobilization or surgical management, such as open reduction and internal fixation (ORIF) or radial head replacement, depending on fragment size and stability. Injury to the radial head can disrupt forearm stability, as seen in Essex-Lopresti injuries (radial head fracture with distal radioulnar joint disruption and interosseous membrane injury) or Monteggia fractures (proximal ulna fracture with radial head dislocation). In children, radial head subluxation, or nursemaid’s elbow, occurs when the annular ligament for a moment slips over the head after traction.

Imaging and variants: Diagnosis typically involves X-ray evaluation; CT or MRI may be used for complex fractures or associated injuries.