LEARN ABOUT DISLOCATION OF THE LUNATE BONE

Dislocation of the lunate bone may be overlooked and can prove serious.

MECHANISM OF INJURY

This is produced from a fall on an outstretched hand with the wrist-joint in a dorsiflexed position. The small piece of bone is squeezed between the radius and proximal row of the carpal bones. The dorsal ligament is ruptured while the anterior ligament remains intact. The bone being detached posteriorly is pushed forward in the carpal tunnel.

 

DIAGNOSIS

Clinical examination

There may be swelling and tenderness over the anterior aspect of the wrist-joint. In the carpal tunnel the displaced bone displaces bone produces pressure on the flexor tendons and the median nerve. An attempt to flex the fingers produces pain. In late cases median nerve lesion can develop as a result of compression by the displaced lunate bone.

Radiographic interpretation: It is mainly the lateral view which shows the displacement of bone, characterized by the concavity of the lunate directed anteriorly. Sometimes associated fracture of the scaphoid bone may be present and this must be looked for.

 

TREATMENT

Closed reduction can be done only up to two weeks after injury. This method usually fails at the end of this period. Failure of the conservative method requires open reduction. Open reduction needs orthopedic implants and orthopedic medical equipment which are provided by orthopedic manufacturers. Excision of the bone is done in late cases where avascular necrosis of the lunate bone has already taken place.

Technique of closed reduction

Traction: Traction and counter-traction are maintained on the wrist-joint in a slightly dorsiflexed position.

Reduction: Pressure is applied over the lunate bone with the aid of both thumbs directing posteriorly. The joint is gently flexed.

Immobilization: The wrist-joint is immobilized by a plaster cast extending from the metacarpal heads to below the elbow-joint.

 

Complications

  • Median nerve palsy: This condition develops as a result of pressure on the nerve and can be prevented by early reduction.
  • Avascular necrosis: This is a delayed manifestation and requires excision of the bone.
  • Osteo-arthritis of the wrist-joint: This may develop when the dislocation remains undiagnosed and is improperly managed.

 

PERILUNAR DISLOCATION

In perilunar dislocation the carpal bones are displaced posteriorly whereas the lunate bone maintains its normal relationship with the radius. The carpal bones are therefore placed in a dorsal position in relation to the lunate.

 

MECHANISM OF INJURY

This is the result of a hyperextension injury to the wrist-joint after a fall on an outstretched hand.

RADIOGRAPHIC INTERPRETATION

X-ray reveals the disruption of the normal relationship of the carpal bones. The lateral view is important to recognize this condition. There may be associated fracture of the scaphoid or fracture of the radial styloid process.

 

TECHNIQUE OF REDUCTION

Traction: Traction and counter-traction are applied under general anaesthesia.

Reduction: Reduction is done by applying pressure on the dorsal aspect of the carpal bones while exerting pressure with the other hand on the forearm bones in an opposite direction.

Immobilization:  Immobilization is maintained by applying a short arm plaster with the wrist in a slightly flexed position. After 4-6 weeks the plaster is removed. In cases where the fracture is associated with dislocation, the principles of treatment should be directed accordingly.



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