Posterior interosseous nerve (PIN) syndrome

1. PIN syndrome is distinct from radial tunnel syndrome as it involves motor deficits.

True

Although radial tunnel syndrome and PIN syndrome share an anatomical substrate — compression of the deep branch of the radial nerve in the radial tunnel — they are distinguished clinically: PIN syndrome presents with motor weakness of the finger and thumb extensors, while radial tunnel syndrome presents with proximal lateral forearm pain without motor or sensory deficit.

• Węgiel A, Karauda P, Zielinska N, Tubbs RS, Olewnik Ł. Radial nerve compression: anatomical perspective and clinical consequences. Neurosurg Rev. 2023;46(1):53. PMID 36781706
• Moradi A, Ebrahimzadeh MH, Jupiter JB. Radial tunnel syndrome, diagnostic and treatment dilemma. Arch Bone Jt Surg. 2015;3(3):156-162. PMID 26213698

2. The PIN is compressed most commonly by space-occupying lesions such as lipomas.

False

Anatomical compression at the arcade of Frohse predominates as the cause of PIN syndrome. Space-occupying lesions — most commonly lipoma, ganglion or rheumatoid synovial proliferation — account for a minority of cases and warrant cross-sectional imaging when suspected on clinical or electrodiagnostic grounds.

• Węgiel A, Karauda P, Zielinska N, Tubbs RS, Olewnik Ł. Radial nerve compression: anatomical perspective and clinical consequences. Neurosurg Rev. 2023;46(1):53. PMID 36781706
• Moradi A, Ebrahimzadeh MH, Jupiter JB. Radial tunnel syndrome, diagnostic and treatment dilemma. Arch Bone Jt Surg. 2015;3(3):156-162. PMID 26213698

3. MRI is the gold standard investigation for PIN syndrome.

False

Electrodiagnostic studies — electromyography combined with nerve-conduction studies — are the standard confirmatory investigation in PIN syndrome and demonstrate denervation in the muscles supplied by the PIN. MRI is reserved for identifying space-occupying causes when these are clinically suspected.

• Verhaar J, Spaans F. Radial tunnel syndrome. An investigation of compression neuropathy as a possible cause. J Bone Joint Surg Am. 1991;73(4):539-544. PMID 1849515
• Węgiel A, Karauda P, Zielinska N, Tubbs RS, Olewnik Ł. Radial nerve compression: anatomical perspective and clinical consequences. Neurosurg Rev. 2023;46(1):53. PMID 36781706

4. The presence of wrist drop confirms a diagnosis of PIN syndrome.

False

Extensor carpi radialis longus is innervated by branches arising from the deep radial nerve proximal to its entry into the supinator and is therefore typically spared in PIN compression at the arcade of Frohse. The clinical sign is wrist extension with radial deviation rather than complete wrist drop; complete wrist drop indicates a more proximal radial-nerve lesion.

• Sawyer FK, Stefanik JJ, Lufler RS. The branching and innervation pattern of the radial nerve in the forearm: clarifying the literature and understanding variations and their clinical implications. Diagnostics (Basel). 2020;10(6):366. PMID 32498404
• Węgiel A, Karauda P, Zielinska N, Tubbs RS, Olewnik Ł. Radial nerve compression: anatomical perspective and clinical consequences. Neurosurg Rev. 2023;46(1):53. PMID 36781706

5. Surgical decompression is indicated in all cases of PIN syndrome.

False

An initial trial of activity modification, splinting and observation is reasonable when motor weakness is mild and no space-occupying lesion is identified. Surgical decompression is indicated for established or progressive motor weakness, when a compressing mass is demonstrated, or when conservative measures fail over an agreed observation window. Universal early surgery is not supported.

• Węgiel A, Karauda P, Zielinska N, Tubbs RS, Olewnik Ł. Radial nerve compression: anatomical perspective and clinical consequences. Neurosurg Rev. 2023;46(1):53. PMID 36781706
• Moradi A, Ebrahimzadeh MH, Jupiter JB. Radial tunnel syndrome, diagnostic and treatment dilemma. Arch Bone Jt Surg. 2015;3(3):156-162. PMID 26213698