Radiohumeral Joint: Anatomy, Biomechanics, and Clinical Significance

What is Radiohumeral joint?

The radiohumeral joint is a crucial component of the elbow complex, formed by the articulation between the capitellum of the humerus and the fovea (concave depression) on the head of the radius. It facilitates both flexion/extension of the elbow and contributes to forearm pronation/supination.

Anatomy of the Radiohumeral Joint

The radiohumeral joint is one of three distinct articulations within the complex elbow joint capsule, alongside the ulnohumeral and proximal radioulnar joints. Understanding its specific anatomical features is key to appreciating its function.

• Bones Involved:
  • Humerus: The distal end of the humerus features the capitellum, a spherical prominence located laterally. This smooth, rounded structure is designed for articulation.
  • Radius: The proximal end of the radius forms the radial head, which has a shallow, cup-shaped depression on its superior surface called the fovea (or articular facet).
• Articular Surfaces: The convex capitellum of the humerus articulates directly with the concave fovea of the radial head. Both surfaces are covered with hyaline cartilage, providing a low-friction interface for smooth movement.
• Joint Capsule and Ligaments: The radiohumeral joint is enclosed within the common elbow joint capsule, which is reinforced by several key ligaments:
  • Annular Ligament: This strong fibrous band encircles the radial head, holding it firmly against the radial notch of the ulna and allowing it to pivot during pronation and supination, while also contributing to the stability of the radiohumeral articulation.
  • Lateral (Radial) Collateral Ligament Complex: This complex originates from the lateral epicondyle of the humerus and has several fascicles, some of which blend with the annular ligament. It provides significant varus stability to the elbow, preventing excessive gapping on the lateral side.
• Joint Type: Functionally, the radiohumeral joint acts primarily as a gliding joint during elbow flexion and extension, as the radial head glides over the capitellum. However, it also contributes to the pivot joint action of the proximal radioulnar joint during pronation and supination. This dual functionality makes it a unique and complex articulation.

Biomechanics and Function

The radiohumeral joint plays a vital role in both the gross movements of the elbow and the intricate rotational movements of the forearm.

• Primary Movements:
  • Elbow Flexion and Extension: During these movements, the radial head glides anteriorly and posteriorly over the capitellum. While the ulnohumeral joint is the primary contributor to the "hinge" action of the elbow, the radiohumeral joint's gliding motion is essential for full range of motion.
  • Forearm Pronation and Supination: As the radius rotates around the ulna, the radial head spins within the annular ligament. The fovea of the radial head maintains contact with the capitellum, facilitating this rotational movement.
• Role in Elbow Complex Stability: Although often overshadowed by the ulnohumeral joint's role in stability, the radiohumeral joint provides critical secondary stability, particularly against valgus (outward) stresses when the elbow is extended. The bony congruence and ligamentous support help to resist forces that would otherwise lead to dislocation or excessive movement.
• Load Transmission: During activities involving weight-bearing through the upper limb (e.g., push-ups, handstands), compressive forces are transmitted through the radiohumeral joint, distributing load across the elbow complex.

Clinical Significance and Common Conditions

Due to its anatomical position and functional demands, the radiohumeral joint is susceptible to various injuries and degenerative conditions.

• Lateral Epicondylitis (Tennis Elbow): While primarily involving the common extensor origin on the lateral epicondyle, dysfunction or stress at the radiohumeral joint can contribute to or exacerbate symptoms. Repetitive gripping and wrist extension can overload the muscles attaching near this joint.
• Radial Head Fractures: These are common elbow fractures, often resulting from a fall onto an outstretched hand (FOOSH injury). Fractures can range from simple non-displaced cracks to complex comminuted fractures affecting the joint surface, potentially leading to long-term pain and limited range of motion.
• Osteoarthritis: Degenerative changes can occur in the radiohumeral joint, particularly after trauma or with chronic overuse. This involves the breakdown of articular cartilage, leading to pain, stiffness, and crepitus (grinding sensation).
• Panner's Disease (Osteochondritis Dissecans of the Capitellum): This condition primarily affects children and adolescents, particularly those involved in repetitive overhead sports (e.g., baseball pitchers, gymnasts). It involves avascular necrosis and fragmentation of the capitellum's cartilage and underlying bone, often due to repetitive compressive forces.
• Nursemaid's Elbow (Radial Head Subluxation): This common pediatric injury occurs when the radial head is pulled partially out from under the annular ligament, typically by a sudden pull on the child's extended arm. It causes immediate pain and refusal to use the arm.
• Dislocations: While isolated radiohumeral dislocations are rare, the radiohumeral joint is often involved in more complex elbow dislocations, where the radius and ulna displace posteriorly relative to the humerus.

Assessment and Rehabilitation Considerations

Evaluating and treating conditions affecting the radiohumeral joint requires a thorough understanding of its anatomy and biomechanics.

• Physical Examination:
  • Palpation: Tenderness over the radial head or capitellum can indicate inflammation, fracture, or other pathology.
  • Range of Motion (ROM): Assessing active and passive flexion, extension, pronation, and supination can reveal limitations or pain patterns.
  • Special Tests: Specific orthopedic tests can help differentiate between various conditions affecting the elbow complex.
• Imaging:
  • X-rays: Crucial for diagnosing fractures, dislocations, and advanced arthritic changes.
  • MRI (Magnetic Resonance Imaging): Provides detailed images of soft tissues (ligaments, cartilage) and can identify subtle bone bruising, osteochondral lesions, or early degenerative changes.
• Rehabilitation Principles:
  • Pain and Inflammation Management: Initial focus on reducing symptoms through rest, ice, and anti-inflammatory medications.
  • Restoring Range of Motion: Gentle mobilization and stretching exercises to regain full elbow and forearm movement.
  • Strengthening: Progressive exercises for the muscles surrounding the elbow and forearm to improve stability and function.
  • Proprioception and Neuromuscular Control: Exercises to enhance joint awareness and coordinated muscle activation.
  • Activity Modification: Identifying and modifying activities or techniques that exacerbate symptoms, especially in athletes.

Conclusion

The radiohumeral joint, though often considered a secondary player within the elbow complex, is indispensable for the full range and function of the upper limb. Its unique design allows for both gliding and rotational movements, making it critical for everyday tasks and athletic endeavors alike. A comprehensive understanding of its anatomy, biomechanics, and common pathologies is essential for clinicians, trainers, and individuals seeking to maintain optimal elbow health and function.