bubble_chart Overview

The lunate bone has a unique shape, being wide on the palmar side and narrow on the dorsal side. Proximally, it articulates with the radius, and distally, it articulates with the capitate and a small portion of the hamate. On the radial side, it articulates with the scaphoid, and on the ulnar side, it articulates with the triquetrum. After dislocation, it completely shifts toward the palmar side. The blood supply to the lunate comes from the anterior and posterior ligaments.

bubble_chart Pathogenesis

Dislocation is mostly caused by indirect external force. When falling with the palm hitting the ground, the wrist is in an extremely dorsiflexed position. The external force from above and the counterforce from below compress the distal radius and the capitate bone, widening the palmar gap between the radius and the capitate bone. The palmar ligaments and joint capsule between the capitate bone and the lunate bone rupture, causing the lunate bone to dislocate toward the palmar side.

If the lunate bone remains in its original position while the other carpal bones completely dislocate, it is called perilunate dislocation.

Lunate dislocation is classified into three types based on the degree and location of the injury.

1. The radiocarpal dorsal ligament is torn or an avulsion fracture occurs at the dorsal horn of the lunate bone. After palmar dislocation, the convex surface faces backward, and the concave surface faces forward.

2. After the dorsal ligament is torn, the lunate bone rotates 270°, located at the anterior part of the distal end, with the concave surface facing backward and the convex surface facing forward.

3. With greater external force, both the dorsal and palmar radiocarpal ligaments rupture, and the lunate bone displaces to the palmar side of the distal radius, with the convex surface facing backward and the concave surface facing forward. If the dislocated lunate bone remains connected to the palmar ligament, it remains viable. If both the dorsal and palmar ligaments are ruptured, necrosis may occur.

bubble_chart Clinical Manifestations

Wrist swelling. Ask the patient to clench both fists. In cases of lunate dislocation, there is noticeable shortening of the third metacarpal head on the affected side. Wrist movement is restricted, finger flexion is difficult, wrist dorsiflexion is impaired, tenderness is present at the palmar wrist crease, and the dislocated lunate bone can be palpated. The wrist deviates ulnarly, and there is significant pain upon percussion of the fourth metacarpal head. The median nerve may also be compressed, causing numbness in the radial side of the palm.

In cases of perilunate dislocation, the lunate remains in its original position while the other carpal bones displace dorsally and shift radially, resulting in deformity.

Anteroposterior X-ray shows the dislocated lunate appearing triangular (normally it should be quadrilateral) and overlapping with the distal end of the capitate bone. The lateral view reveals the lunate displaced toward the palmar side, with its concave surface also rotated toward the palmar side.

bubble_chart Treatment Measures

For fresh lunate dislocation, manual reduction should be performed as early as possible for type 1 and 2 dislocations. Traction is applied to the affected hand distally, with the wrist joint dorsiflexed, and then the lunate bone is pressed back into place. The wrist joint is fixed in 45° palmar flexion for 1 week, followed by neutral position fixation for 2 weeks. After removing the external fixation, exercise and movement should be initiated. For type 3 dislocation, since the anterior and posterior ligaments are ruptured and blood supply is completely lost, necrosis may occur, and early excision is advisable. Perilunate dislocation is not difficult to reduce manually, and postoperative management is the same as above.

For old lunate dislocation, manual reduction is unlikely to succeed for type 1 and 2 dislocations that are 3–4 weeks post-injury. Open reduction should be performed, with postoperative management as above. If degenerative changes in the cartilage are found during surgery, excision should be performed. Movement can begin a few days after fixation. For type 3 dislocation, excision should be performed.