case report acute lunate dislocation

Acute Lunate Dislocation following an MVC

Case Introduction

A 22 year old male who is mildly intoxicated presents via emergency medical services following a motor vehicle crash. He is primarily concerned about his right hand. After excluding any other serious injuries, you evaluate his hand. You identify tenderness and swelling along the carpal bones along the volar and dorsal side. Radial pulse is 2+. His exam is intact in the median, ulnar and radial nerve distribution. Subsequent radiographs identify an isolated volar lunate dislocation.
Illustration of the difference between a lunate and perilunate dislocation
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Lunate Dislocation

Lunate dislocations are a rare clinical entity. They are estimated to account for less than 3% of all carpal injuries with an incidence of less than 1 per 100,000 injuries annually.[1]Kastanis G, Velivasakis G, Pantouvaki A, Spyrantis M. An Unusual Localization of Lunate in a Transcaphoid Volar Lunate Dislocation: Current Concepts. Case Rep Orthop. 2019;2019:7207856. The classic injury is fall on an outstretched hand causing hyperextension of the wrist, ulnar deviation and intercarpal supination. They can also happen in motor vehicle crashes and other high speed mechanisms. Unfortunately, lunate dislocations are frequently missed due to the subtly of radiographs and up to 25% of them may be missed initially.[2]Goodman, Avi D., et al. “Evaluation, management, and outcomes of lunate and perilunate dislocations.” Orthopedics 42.1 (2019): e1-e6. Note that lunate dislocations should not be confused with the more common perilunate dislocation in which the lunate remains articulating with the radius but the remaining carpal bones are dislocated dorsally.
The pathophysiology is the following: (a) disruption of the radioscaphocapitate ligament and scapholunate ligament, or sometimes fracture of the scaphoid, (b) disruption of the lunocapitate articulation and/or fracture through the capitate, (c) injury to the lunotriquetral ligament and/or fracture through the triquetrum and finally, (d) injury to the radiolunate ligament.[3]Aslani H, Bazavar MR, Sadighi A, Tabrizi A, Elmi A. Trans-Scaphoid Perilunate Fracture Dislocation; A Technical Note. Bull Emerg Trauma. 2016;4:110–112.
Associated injuries include radial styloid, scaphoid, capitate or triquetral fractures. Acute carpal tunnel syndrome or median nerve injury is also commonly seen with lunate dislocations.
When obtaining history, the patient will often describe some form of trauma. They often endorse pain and swelling over the palmer side of the wrist. Note that lunate dislocations often co-occur with other trauma and the patient may not endorse any wrist symptoms if other significant pathology is present. On exam, range of motion is often limited. Patients may hold their fingers in flexion due to pain with extension. They may have diminished sensation in a median nerve distribution.
PA and lateral view of a lunate dislocation. On the PA view, the lunate is displaced anteriorly (piece of pie sign). On the lateral view, the lunate is anterior to the distal radius (spilled teacup).
Standard radiographs of the wrist are the initial imaging modality of choice. Note that the dislocation is often missed. On the PA view, findings can include disruption of the normal smooth line made by tracing the proximal articular surfaces of the hamate and capitate, increased radiolunate space and lunate may overlap the capitate (piece of pie appearance). Lateral radiographs are often more enlightening. The lunate can be seen displaced and angulated volarly (spilled teacup appearance) and does not articulate with the capitate or radius. MRI is not required to make the diagnosis but may be helpful to better evaluate soft tissue injuries. CT is also not required to make the diagnosis but may better characterize osseous lesions.
Sagittal CT of a lunate dislocation. The lunate is anterior to the radius (green arrow) and dislocated form the normal radiocarpal alignment (red line).
Acute management of lunate dislocations includes emergent orthopedic or hand surgery consultation for closed reduction. The patient may require sedation or even a median nerve block to facilitate reduction. The technique involves finger traps and the elbow flexed at 90 degrees for 15 or 20 minutes. Volar reductions require wrist extension, traction and a posterior force on the lunate before bringing it back into a neutral position. Following closed reduction, the patient should be placed in a sugar tong splint.
The vast majority of cases require surgical management. Nonoperative management can be considered in consultation with the surgical team but is associated with poor functional outcomes and a high risk of re-dislocation. The most common surgical technique is open reduction, ligament repair, fixation and possible carpal tunnel release and is indicated for all acute injuries. Proximal row carpectomy and wrist arthrodesis have also been described and are potentially indicated in more chronic cases.
Lunate dislocations are associated with a poor prognosis. Delayed treatment is associated with reduced functionality, reduced range of motion, carpal instability and pain. Even patients treated surgically can develop degenerative changes as early as two months. [4]Inoue G, Shionoya K. Late treatment of unreduced perilunate dislocations. J Hand Surg Edinb Scotl. 1999;24(2):221-225. Complications include acute or chronic median neuropathy or so-called traumatic carpal tunnel syndrome. Patients can develop carpal instability which can eventually progress to scapholunate advanced collapse (SNAC). Degenerative arthritis is common. Finally, a transient ischemia of the lunate can occur. In these cases, a radiodense appearance of the lunate is seen between 1-4 months post injury but is typically self limited and can be observed.

Case Conclusion

The patient underwent a successful closed reduction of the lunate following a median nerve block. He tolerated the procedure well. He was placed in a sugar tong splint and had a follow up appointment with orthopedic hand surgery as an outpatient. Unfortunately, the patient was subsequently lost to follow up.

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