Case Report: Ultrasound-guided nerve mobilization and rehabilitation for non-traumatic posterior interosseous nerve palsy associated with a ganglion cyst.

Nontraumatic posterior interosseous nerve (PIN) palsy is an uncommon entrapment neuropathy, and there is limited evidence regarding ultrasound-guided nerve mobilization as part of rehabilitation. Here, we report a case of PIN palsy associated with a ganglion cyst in the radial tunnel, focusing on the clinical course and ultrasound-based evaluation of nerve morphology and motion. The patient presented with dorsal forearm pain, marked weakness of the fingers, and thumb extension. Ultrasonography revealed a hypoechoic ganglion compressing and flattening the PIN near the arcade of Frohse. The initial management consisted of weekly ultrasound-guided aspiration of the ganglion combined with conventional physical therapy, including low-frequency electrical stimulation, stretching, and active-assist exercises for finger extension. Although pain decreased promptly after decompression, motor recovery remained limited, and follow-up ultrasonography showed persistent nerve flattening and reduced longitudinal gliding. Therefore, an ultrasound-guided nerve mobilization program was added to restore nerve gliding around the compression site while continuously monitoring the nerve and its surrounding structures. Over subsequent sessions, finger extension strength and hand function improved in parallel with a reduction in the nerve cross-sectional area, normalization of the flattening ratio, and qualitative recovery of nerve sliding on ultrasonography. This case suggests that ultrasound-guided nerve mobilization may be a useful adjunct to decompression and exercise therapy in PIN palsy related to ganglion compression and highlights the value of serial ultrasound assessment, including quantitative evaluation such as particle image velocimetry (PIV), for guiding and validating rehabilitation in peripheral nerve disorders.