Purpose: Cross-sectional sonographic measurements are considered first-line confirmatory tests in diagnosing peripheral nerve entrapment syndromes. Our aim is to establish normal values of cross-sectional area of the posterior interosseous nerve (PIN) at the arcade of Frohse, the most common site of compression of this nerve.
Methods: The PIN was identified with ultrasound on 50 healthy adults and 30 cadavers. Measurements of the cross-sectional area (CSA), antero-posterior (AP) and lateral (L) distances were taken immediately proximal and distal to the arcade of Frohse.
Results: The mean AP and L distances of the PIN proximal to the arcade of Frohse were 0.111 cm (0 ± 0.021) and 0.266 cm (±0.058), respectively, while the mean AP and L distances of the PIN distal to the arcade of Frohse were 0.085 cm (±0.019) and 0.343 cm (±0.057), respectively. P squared testing showed a statistically significant difference between the AP and lateral distances of the PIN when comparing proximal and distal to the arcade (p ≤ 0.001). However, the mean CSA of the PIN measured immediately proximal to the arcade of Frohse was 0.022 cm(2) (±0.005); immediately distal to the arcade of Frohse, it was 0.023 cm(2) (±0.004). t test showed no statistical difference between the two regions (p = 0.11).
Conclusions: Our study has provided reference values for the PIN in healthy individuals at the arcade of Frohse. Although, there is a flattening of the nerve as it enters the supinator muscle, this should not be mistaken for nerve entrapment as the size of the nerve remains consistent.
Keywords: Arcade of Frohse; Peripheral nerve entrapment; Posterior interosseous nerve (PIN); Posterior interosseous nerve syndrome; Ultrasound of posterior interosseous nerve.