Lunate dislocation

Clinical History

A 28-year-old man, right handed, was admitted to the emergency room following a trauma to the left wrist due to a low-speed motorcycle crash. Clinical examination of the wrist revealed swelling, painful with any type of passive or active motion of the wrist. Neurovascular examination was without deficits. Radiographic examination of the wrist was performed.

Imaging Findings

The plain X- ray of left wrist showed a carpal malalignment, better evident on the lateral view with the lunate displaced and rotated volarly, “spilled teacup sign”.
On the A-P view the loss of the normal quadrangular shape of the lunate was evident, which took over triangular shape (piece of pie sign).
To obtain a more precise diagnosis a multiplanar CT examination was performed.
Multiplanar and volumetric reformatting images confirmed the volar dislocation of the lunate and showed small osteochondral fragments.
After administering adequate analgesia, the patient was transferred to the orthopaedic department at another hospital.

Discussion

Dislocations of the carpal bones are, uncommon but not rare, traumatic injuries of the wrist. Overall these comprise less than 10% of all wrist traumas and represent a heterogeneous group of injuries often associated with bones fractures.
They typically occur in young adults with high energy impact resulting in loading of a dorsiflexed wrist which may lead to a variety of lesions that range from dislocation of a single bone to complex carpal lesions.
The most common dislocations are those centred around the lunate that occur such as sequential and progressive stages of ligamentous damage.
The first stage is the dorsal dislocation of the capitate. The second stage is the subluxation of the lunate, due to the pressure exerted by the capitate on the lunate. The end stage is volar dislocation of lunate that thus allowing to capitate to take back a normal anatomical position.
The defining feature of this lesion is the loss of the alignment between radius and lunate that is dislocated and rotated volarly while the rest of the carpal bones is in normal anatomic position.
Clinical signs include pain, swelling, deformity of the wrist, limited range of motion.
Numbness and tingling of the first three fingers for compromise of median nerve.
Plain X-ray is the first choice imaging modality for evaluation of trauma of the wrist. The radiographic features are:triangular shape of the lunate on A.P. view (piece of pie sign) and volar displacement and rotation of lunate on lateral view (spilled tea cup sign). However, a correct diagnosis can be difficult for not appropriate radiographs.
MDCT plays an increasingly important role for these advantages: detection of lesions is independent by the wrist's position, can accurately determine the presence of occult fractures, the multiplanar and volumetric reformatting can valuate better anatomic relationships and these informations are crucial for the planning of surgical treatment.
MRI is also an effective way of evaluating joint damage but is not routinely used for the diagnosis of traumas because the limited availability in the emergency room. Closed reduction and immobilisation may be attempted but is usually not successful. If the dislocation is irreducible or the result is unstable, open reduction with internal fixation will be required. Many orthopaedic surgeons believe the treatment of choice is immediate open reduction with internal fixation for the extensive ligamentous injury and frequent unstable results that come with closed reductionInjury with median nerve symptomatology requires immediate surgical reduction, carpal tunnel release, and ligamentous reconstruction.

Differential Diagnosis List

Final Diagnosis

Lunate dislocation of the wrist

URL:	https://www.eurorad.org/case/9332
DOI:	10.1594/EURORAD/CASE.9332
ISSN:	1563-4086