Lunate dislocation with median nerve entrapment

Case contributed by Dr Chifra Fenton

Presentation

Interphalangeal flexion deficit of the right thumb for two months.

Patient Data

Age: 30 years
Gender: Female

Radial translation of the right median nerve.

Deformation of the bottom of the right carpal tunnel with intratunnel volume reduction.

Irregularities of the right scaphoid surface with crushed aspect.

The arrows point at the retracted right flexor pollicis longus (FPL) on the longitudinal view and its loss of the anisotropy on the transverse view.

Crushed aspect of the scaphoid and dislocation of the lunate.

Case Discussion

The diagnosis of lunate dislocation is missed in 15-25% 1 of the cases at the initial time of evaluation, its protrusion towards the carpal tunnel may result in compression of the median nerve.
In this case, the patient also had a thenar amyotrophy and the ultrasound examination allowed us to confirm its mechanical origin, caused by the rupture of the FPL and not by the median nerve injury. Indeed, the carpal tunnel was narrowed and the median nerve was dislocated but it showed no swelling and had a regular echogenicity. Moreover, there was no fatty atrophy of the thenar eminence in favor of an innervation origin to the amyotrophy.

 

Courtesy of Dr Viviane Creteur. 

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