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Acute Lunate Dislocation following an MVC
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.
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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.
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.
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.
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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