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Posterior Interosseous Nerve (pin) Injury
 

Author: Milan Oxspring, MD
Affiliation: Mayo Clinic, Department of Physical Medicine and Rehabilitation
Co Author(s): James B. Meiling, DO
Senior Editor: Laura Mattson, DO

Clinical Vignette: A 22-year-old right-handed male presents with persistent left hand weakness and dorsal proximal forearm pain 8 months after an open reduction internal fixation (ORIF) surgery for a radius and ulna fracture from a motorcycle collision. Exam is notable for significant weakness with finger extension and thumb abduction without sensory loss.

Type of Probe Used: 4-18 MHz linear array ultrasound transducer.

View Video

The left PIN is scanned in short axis from the entrance of the radial tunnel into the radial tunnel. As the nerve is scanned distally, multifocal enlargement of a hypoechoic PIN is visualized. Given the near-normal caliber nerve in between the two areas of enlargement, this may indicate the presence of two focal neuromas-in-continuity. Deep to the PIN is the proximal radius plate from the prior ORIF.


Labeled short axis view of the left PIN within the radial tunnel. In this view, the PIN (dashed oval) becomes focally hypoechoic and enlarged (25.75 mm2). It is seen situated between hyperechoic superficial and deep heads of the supinator muscle, likely secondary to muscle denervation. As seen in the above view, the PIN sits superficial to the underlying radius plate from the prior ORIF for the proximal radius fracture.


Unlabeled short axis view of the left PIN within the radial tunnel.


Labeled long axis view of the left PIN within the radial tunnel. There is multifocal enlargement of the PIN (dashed line) which is hypoechoic with a complete loss of normal intraneural fascicular architecture. The architecture of the nerve appears as more of a “dumbbell” shape within the tunnel. These findings may be representative of two focal neuromas-in-continuity. Deep to the nerve, the proximal radius plate can be seen from the prior ORIF. The superficial and deep heads of the supinator muscle are both markedly hyperechoic which is likely suggestive of muscle denervation.


Unlabeled long axis view of the left posterior interosseous nerve (PIN) within the radial tunnel.

NOTE: For more information, please contact the AMSSM, 4000 W. 114th Street, Suite 100, Leawood, KS 66211 (913) 327-1415.
 

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