Wrist Dislocation: Causes, Mechanisms, and Prevention

How is dislocation of wrist joint caused?

Wrist joint dislocations are primarily caused by high-energy trauma, most commonly a fall onto an outstretched hand (FOOSH), which subjects the intricate network of bones and ligaments to forces beyond their structural capacity, leading to the displacement of one or more carpal bones relative to the forearm bones or other carpals.

Understanding Wrist Joint Anatomy and Stability

The wrist, or carpus, is a complex anatomical region comprising eight carpal bones arranged in two rows (proximal and distal), articulating with the distal ends of the radius and ulna, and proximally with the metacarpal bones of the hand. Its stability is not solely derived from bony congruence but heavily relies on a sophisticated network of strong intrinsic and extrinsic ligaments.

• Radiocarpal Joint: The primary articulation between the forearm (radius) and the proximal row of carpal bones (scaphoid, lunate, triquetrum).
• Intercarpal Joints: Articulations between the individual carpal bones, crucial for wrist mobility and force transmission.
• Distal Radioulnar Joint (DRUJ): The articulation between the radius and ulna at the wrist, stabilized by the Triangular Fibrocartilage Complex (TFCC).

These joints, along with their surrounding ligaments, allow for a wide range of motion while maintaining stability under normal physiological loads. A dislocation occurs when these stabilizing structures are overwhelmed, causing the articular surfaces of the bones to lose their normal alignment.

Primary Mechanisms of Wrist Joint Dislocation

Wrist dislocations are typically the result of significant traumatic force, often exceeding the tensile strength of the intricate ligamentous structures. The most common mechanisms include:

• Fall On Outstretched Hand (FOOSH): This is by far the most prevalent cause. When an individual falls and instinctively extends their arm to break the fall, the impact is transmitted through the hand to the wrist.
  • Axial Loading: The compressive force travels up the arm.
  • Hyperextension: The wrist is forced into extreme extension, often with an element of ulnar deviation. This position places immense stress on the volar (palm-side) ligaments, which are critical for preventing dorsal displacement of carpal bones.
  • Rotational Forces: The body's momentum may add a rotational component, further twisting the wrist and tearing ligaments.
• Direct Impact: A direct, high-energy blow to the wrist, such as in contact sports or vehicular accidents, can force bones out of alignment.
• Extreme Hyperflexion or Ulnar/Radial Deviation: While less common than hyperextension, forced movements beyond the physiological range of motion can also lead to ligamentous failure and dislocation.
• Chronic Instability: In some cases, a history of repetitive microtrauma or pre-existing ligamentous laxity can predispose an individual to dislocation with less significant force.

Common Types of Wrist Dislocation and Their Mechanisms

The specific type of wrist dislocation depends on the exact mechanism of injury and which ligaments rupture, dictating which carpal bones displace.

• Perilunate Dislocation: This is the most common and often severe carpal dislocation. It typically occurs with a FOOSH injury involving significant hyperextension, ulnar deviation, and carpal supination. The lunate bone, due to its strong attachment to the radius via the radioscapholunate ligament, tends to remain in place relative to the radius, while the other carpal bones (scaphoid, capitate, hamate, etc.) dislocate dorsally around the lunate. This often results in a sequential pattern of ligamentous failure (e.g., scaphoid fracture with perilunate dislocation, or complete scapholunate ligament dissociation).
• Lunate Dislocation: Less common than perilunate, this usually occurs as a progression from an untreated or severely forceful perilunate dislocation. The lunate itself rotates and displaces volarly (towards the palm) into the carpal tunnel, often compressing the median nerve. This typically involves complete failure of the strong dorsal radiolunate ligament.
• Scaphoid Dislocation: Isolated scaphoid dislocation is extremely rare; the scaphoid is more prone to fracture than dislocation due to its unique shape and blood supply. However, it can be part of a complex perilunate injury.
• Radiocarpal Dislocation: Dislocation of the entire carpus from the radius is rare in isolation and usually indicates extensive ligamentous and often bony injury.
• Distal Radioulnar Joint (DRUJ) Dislocation: While technically part of the forearm, dislocation of the DRUJ (where the ulna meets the radius at the wrist) often accompanies forearm fractures (e.g., Galeazzi fracture-dislocation) or severe rotational trauma. It can be dorsal or volar depending on the mechanism.

Risk Factors for Wrist Dislocation

While severe trauma is the direct cause, certain factors can increase an individual's susceptibility:

• Participation in High-Impact Sports: Activities like gymnastics, football, snowboarding, and martial arts carry a higher risk due to the potential for falls and direct impacts.
• Occupational Hazards: Jobs involving heights, heavy machinery, or repetitive forceful movements can increase risk.
• Underlying Ligamentous Laxity: Individuals with generalized joint hypermobility (e.g., Ehlers-Danlos syndrome) may be more prone to dislocations with less force.
• Previous Wrist Injury: A history of sprains, fractures, or partial dislocations can weaken the ligamentous structures, making subsequent dislocations more likely.
• Age: Older adults are at increased risk due to reduced bone density (osteoporosis) and a higher propensity for falls, though their injuries are more often fractures than pure dislocations. Young, active individuals are also at risk due to high-energy activities.

Recognizing a Dislocation

While this article focuses on causation, it's important to note that a dislocated wrist presents with:

• Severe Pain: Often immediate and intense.
• Obvious Deformity: The wrist may appear visibly misshapen.
• Swelling and Bruising: Rapid onset due to tissue damage.
• Limited or Absent Motion: Inability to move the wrist normally.
• Numbness or Tingling: Especially with lunate dislocations compressing the median nerve.

Prevention Strategies

While not all dislocations are preventable, several strategies can reduce risk:

• Proper Falling Techniques: Learning to fall safely, avoiding landing on an outstretched hand, and rolling with the impact.
• Protective Gear: Wearing wrist guards during high-risk sports like snowboarding, skateboarding, or rollerblading.
• Strength and Conditioning: Developing strong forearm muscles and maintaining good wrist flexibility and stability through targeted exercises.
• Proprioceptive Training: Exercises that improve joint position sense can help react more quickly and appropriately to unexpected forces.
• Addressing Underlying Issues: Managing conditions that cause balance problems or bone weakness.

Conclusion

Wrist joint dislocations are severe injuries resulting from the application of forces that overwhelm the natural stability of the wrist's complex bony and ligamentous architecture. The vast majority are caused by a fall onto an outstretched hand, leading to a cascade of ligamentous failures and subsequent bone displacement. Understanding these mechanisms is crucial for prevention, prompt recognition, and effective management, emphasizing the importance of seeking immediate medical attention for any suspected wrist dislocation to ensure proper reduction and rehabilitation.