Wrist Dislocations: Understanding Types, Symptoms, Diagnosis, and Treatment

What are the different types of wrist dislocations?

Wrist dislocations involve the abnormal separation of bones at the wrist joint, primarily affecting the carpal bones and their articulations with the forearm bones (radius and ulna), often resulting from significant trauma.

Understanding Wrist Anatomy and Dislocation Mechanics

The wrist is a complex joint, comprising eight carpal bones arranged in two rows (proximal and distal) that articulate with the distal radius and ulna, and proximally with the five metacarpal bones. This intricate arrangement, stabilized by numerous ligaments, allows for a wide range of motion but also makes it susceptible to injury, particularly dislocations. A dislocation occurs when the articulating surfaces of bones are completely displaced from their normal alignment, disrupting the joint's integrity and function.

General Principles of Wrist Dislocation

Wrist dislocations are typically high-energy injuries, often resulting from a fall onto an outstretched hand (FOOSH) with the wrist hyperextended. The precise type of dislocation depends on the exact force vector, wrist position at impact, and the specific ligaments that fail.

• Mechanism of Injury: Most commonly, an axial load through a hyperextended wrist. This force often propagates through the carpal bones, leading to predictable patterns of ligamentous failure and bone displacement.
• Symptoms: Acute pain, swelling, deformity, and significant loss of wrist motion are hallmark symptoms. Nerve impingement (especially median nerve) can also occur, leading to numbness or tingling in the hand.
• Diagnosis: Clinical examination revealing deformity and instability, coupled with detailed imaging studies (X-rays, CT scans, MRI) are crucial for accurate diagnosis and to identify associated fractures or ligamentous injuries.

Primary Types of Wrist Dislocations

While numerous variations exist, wrist dislocations primarily involve the carpal bones relative to each other or to the radius, or the distal radioulnar joint.

Perilunate Dislocation

This is the most common and often the initial stage of severe carpal instability. In a perilunate dislocation, the entire carpus (the other carpal bones) dislocates around the lunate bone, which typically maintains its articulation with the radius.

• Mechanism: Typically a severe hyperextension injury. The force causes a sequential disruption of ligaments, often starting with the scapholunate ligament, leading to the capitate (the central carpal bone) displacing dorsally relative to the lunate.
• Anatomy Involved: The lunate remains aligned with the radius, but the capitate and the rest of the carpus dislocate dorsally (or sometimes volarly) relative to the lunate. This can be associated with a scaphoid fracture (trans-scaphoid perilunate dislocation), which is a common variant.
• Clinical Presentation: Significant wrist deformity, severe pain, and often median nerve compression symptoms due to the displaced carpal bones compressing the nerve within the carpal tunnel.

Lunate Dislocation

Often considered the final stage of a progressive perilunate injury, a true lunate dislocation occurs when the lunate itself displaces from its articulation with the radius.

• Mechanism: This usually follows an untreated or inadequately reduced perilunate dislocation. The lunate, which was initially stable relative to the radius, rotates and displaces volarly (towards the palm) into the carpal tunnel.
• Anatomy Involved: The lunate is completely displaced from the radiocarpal joint and often rotates significantly. The capitate and other carpals may then realign with the radius, but the lunate is "out of place."
• Clinical Presentation: Marked median nerve compression is almost universal due to the lunate's direct impingement on the nerve within the narrow carpal tunnel. This can lead to acute carpal tunnel syndrome symptoms (numbness, tingling, weakness in median nerve distribution). The wrist may appear less deformed than a perilunate dislocation, but the functional deficit is often more severe.

Scapholunate Dislocation/Dissociation

While often a ligamentous injury rather than a frank bone dislocation, scapholunate dissociation is a critical form of carpal instability that can lead to progressive carpal collapse and is sometimes referred to as a "predislocation" state or a partial dislocation.

• Mechanism: A fall onto an outstretched hand with radial deviation. This tears the scapholunate interosseous ligament, the primary stabilizer between the scaphoid and lunate bones.
• Anatomy Involved: The scaphoid and lunate bones lose their stable connection, leading to abnormal motion between them. Over time, this can result in a dorsal intercalated segment instability (DISI) deformity, where the lunate extends dorsally.
• Clinical Presentation: Chronic wrist pain, clicking, weakness, and reduced range of motion. Acute cases may present with swelling and tenderness over the scapholunate interval.

Distal Radioulnar Joint (DRUJ) Dislocation

This involves the articulation between the distal ends of the radius and ulna, typically occurring with forearm fractures (e.g., Galeazzi fracture-dislocation) or high-energy rotational injuries.

• Mechanism: Direct trauma to the wrist or forearm, or a fall with a rotational component.
• Anatomy Involved: The ulna head displaces from its articulation with the ulnar notch of the radius, often tearing the triangular fibrocartilage complex (TFCC).
• Types:
  • Dorsal DRUJ Dislocation: More common, where the ulna head displaces dorsally relative to the radius.
  • Volar DRUJ Dislocation: Less common, where the ulna head displaces volarly.
• Clinical Presentation: Pain, swelling, and obvious deformity at the wrist, particularly on the ulnar side. Restricted forearm rotation (pronation and supination) is a key finding.

Carpometacarpal (CMC) Joint Dislocations

These involve the joints between the distal carpal bones and the bases of the metacarpals. While any CMC joint can dislocate, the most common is the first CMC joint (thumb CMC).

• Mechanism: Often a direct blow to the thumb or a fall onto the hand with the thumb abducted and flexed.
• Anatomy Involved: The base of the first metacarpal dislocates from the trapezium carpal bone. Other CMC dislocations are rarer and usually associated with significant crush injuries or high-energy direct trauma.
• Clinical Presentation: Severe pain, swelling, and deformity at the base of the thumb or involved metacarpal. Loss of thumb opposition or grip strength.

Radiocarpal Dislocation

This is a less common and very severe injury where the entire carpus dislocates from the distal end of the radius.

• Mechanism: Extremely high-energy trauma, such as a motor vehicle accident or a fall from a significant height.
• Anatomy Involved: The entire proximal carpal row (scaphoid, lunate, triquetrum) displaces from the radial articular surface.
• Clinical Presentation: Gross deformity of the wrist, severe pain, and often associated with extensive soft tissue damage and neurovascular compromise.

Importance of Prompt Diagnosis and Treatment

Given the intricate anatomy and potential for long-term complications such as chronic pain, stiffness, arthritis, and nerve damage, prompt and accurate diagnosis of wrist dislocations is paramount. Misdiagnosis or delayed treatment can lead to chronic instability, avascular necrosis (especially of the lunate or scaphoid), and permanent functional impairment. Treatment typically involves urgent reduction (repositioning the bones), often under anesthesia, followed by immobilization and frequently surgical repair of damaged ligaments or fixation of associated fractures.

Rehabilitation and Long-Term Considerations

Following reduction and initial healing, a structured rehabilitation program is essential. This typically involves:

• Immobilization: To allow ligamentous healing.
• Gradual Mobilization: To restore range of motion.
• Strengthening Exercises: To rebuild muscle strength around the wrist and forearm.
• Proprioceptive Training: To improve joint stability and control.

Long-term outcomes depend heavily on the severity of the initial injury, the presence of associated fractures or nerve damage, and the adherence to a comprehensive rehabilitation plan. Some individuals may experience residual stiffness, pain, or a predisposition to post-traumatic arthritis.

Conclusion

Wrist dislocations are complex and potentially devastating injuries that require immediate medical attention. Understanding the different types—from the common perilunate and lunate dislocations to the less frequent DRUJ and CMC dislocations—is crucial for healthcare professionals. For fitness enthusiasts and trainers, recognizing the signs of such severe injury and ensuring prompt referral to a specialist is vital for optimal recovery and preservation of long-term wrist function.