A PERILUNATE DISLOCATION is defined as a disruption of the normal relationship between the lunate and the capitate. Lunate dislocations are often unrecognized at the initial evaluation as their findings on the radiograph can be subtle. A lunate dislocation is a separation of the lunate from both the capitate and the radius. One must have a high index of suspicion when a patient has a high-energy mechanism involving hyperextension of the wrist. It has been estimated that up to 25% of these perilunate dislocations are diagnosed weeks to years after the initial injury (Kennedy & Allan, 2012). This is often due to difficult radiographic interpretation and other severe confounding injuries. Prompt recognition of this injury is necessary to prevent adverse outcomes including median nerve compression, posttraumatic arthritis, reduced function, and most importantly avascular necrosis. In most circumstances, operative interventions are necessary to provide optimal outcomes (Goodman et al., 2019).

IMAGING Radiography

Plain radiographs of the wrist (posteroanterior [PA], lateral, and oblique views) should initially be obtained during the initial evaluation. Lateral radiographs should reveal a normal collinear axis of the capitate in the lunate sitting on the radius, with all three bones lying in a straight line (see Figures 1 and 2).

Figure 1.:

The lateral view of the wrist normally shows the lunate in an upright position. When you think of the lunate bone, consider the lunar aspect of the moon, sitting in an upright position, with the “U” of the lunate with the opening of the “U” superiorly, at the top. On the lateral view of the wrist, the lunate sits in the capitate, which, in turn, sits on the radius. These three bones should sit on one row.

Figure 2.:

Lateral view of the right wrist with lunate in proper position; lunate with “U” upright; normal right wrist radiograph lateral view.

The lateral view of the wrist normally shows the lunate in an upright position. When you think of the lunate bone, consider the lunar aspect of the moon, sitting in an upright position with the “U” of the lunate with the opening of the “U” superiorly, at the top. On the lateral view of the wrist, the lunate sits in the capitate, which sits on the radius. These three bones should sit on one row. A perilunate dislocation demonstrates a disruption between the lunate and the capitate (see Figures 3 and 4).

Figure 3.:

A perilunate dislocation is when the lunate remains upright, but the capitate does not sit in the lunate.

Figure 4.: Lateral radiograph of the right wrist shows a perilunate dislocation. Note volar displacement of the lunate with relative normal alignment of the capitate with the radius. From Medscape Drugs & Diseases (https://emedicine.medscape.com/). Perilunate Injury Imaging, 2020. Reproduced with permission.

When the lunate dislocates, it usually is dislocated volarly, demonstrating the “spilled teacup sign” due to the volar rotation (see Figures 5 and 6).

Figure 5.:

Lunate dislocation: Note the lunate “U” is not in the upright position, demonstrating the “spilled teacup sign.”

Figure 6.: Lateral radiograph of the wrist demonstrating a lunate dislocation of the left wrist. Image From Medscape Drugs & Diseases (https://emedicine.medscape.com/). Wrist Dislocation in Emergency Medicine, 2020. Reproduced with permission.Computed Tomography

Computed tomography can aid in the diagnosis of perilunate or lunate dislocations. Advanced imaging is usually not needed for the initial evaluation of perilunate or lunate dislocations in the emergency setting.

EMERGENCY DEPARTMENT CONSIDERATIONS

Perilunate and lunate dislocations require urgent identification of the diagnosis and emergent reduction to avoid poor outcomes with long-term disability and chronic wrist pain. Thus, one must have a high index of suspicion when the patient experiences a high-energy fall on the hand (FOOSH) injury complaining of volar wrist pain. The patient's dominant hand should be documented. Patients typically present with wrist pain aggravated by any motion of the wrist or attempting to grasp something with the injured hand. Patients often present with both dorsal and volar wrist pain and swelling. A thorough neurovascular assessment of the hand and the wrist should be done, with a focused assessment of the median nerve. Pain caused by direct injury to the median nerve tends to be sharp and burning along the nerve's distribution. To test the motor aspect of the median nerve, have the patient flex the distal interphalangeal joint of the index finger and the interphalangeal joint of the thumb, opposing the thumb and the index finger. To test the sensory aspect of the median nerve, check sensation of the dorsal aspect of the webspace between the thumb and the index finger. Patients should be evaluated for any acute parasthesias or any abnormality of 2-point discriminations in the median nerve distribution. Any abnormalities add increased urgency to obtaining orthopedic hand surgery consultation.

Radiographs must be carefully examined to be sure the lunate is in the proper position on the PA film, but especially looking for the “spilled teacup sign” on the lateral view. Once diagnosed, use a sugar tong splint to immobilize the patient's wrist while awaiting emergent orthopedic hand surgery consultation for reduction. Swelling and pain should be managed with ice application over the splint, extremity elevation, and analgesics as appropriate. Patients should be encouraged to avoid any axial loads to the injured wrist while awaiting orthopedic consultation.

CONCLUSION

Perilunate and lunate dislocations are often misdiagnosed or undiagnosed in the acute emergency setting, leading to serious complications and poor clinical prognoses. Injuries to the carpal bones can be overshadowed with more severe life-threatening injuries due to high-energy traumatic injury resulting from fall from heights and motor vehicle crashes. Radiographs may be inadequately assessed if unfamiliar with perilunate or lunate dislocations. One must be vigilant in any concerning mechanism of injuries with high-energy wrist extension injuries. After clinical evaluation and radiographic workup, the patient must be promptly splinted with urgent orthopedic surgical evaluation. Open reduction and ligament stabilization are the definitive management best performed by an orthopedic specialty hand surgeon (Garner, Rudran, Khan, Tang, & Mathew, 2021). Early treatment can help reduce long-term pain, instability, and nerve damage and improve functionality. Progressive arthrosis, permanent loss of grip strength, range of motion, and chronic pain are common complications with lunate dislocation injuries (Garner et al., 2021). Severe injuries with lunate and perilunate dislocations may fall short of restoring normal function to the hand and the wrist.

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