Emergence Point of the Infratrochlear Nerve With Reference to the Nasion and Its Clinical Implications in Craniofacial Surgery.

Abstract

Background: Infratrochlear nerve (ITN) block is widely used in craniofacial surgery to provide anesthesia and reduce perioperative discomfort. Accurate localization of the emergence point of the ITN (EP-ITN) using external landmarks may improve the precision of the block.

Purpose: This study aimed to identify the anatomical location of the EP-ITN in the medial orbital margin with reference to the nasion, and to evaluate whether the nasion may serve as a consistent external landmark for ITN block procedure.

Study design, setting, sample: This was a cross-sectional anatomic study conducted at Dong-A University College of Medicine. Inclusion criteria were cadavers with legally obtained consent for use in anatomical research. Cadavers with evidence of facial trauma, previous craniofacial surgery, skeletal deformities, or prior dissection compromising anatomical integrity were excluded.

Main outcome variables: The primary outcome variable was defined as the vertical and horizontal distances from the EP-ITN to the nasion. Secondary outcome variables included the vertical distances from the EP-ITN to the trochlea and medial canthus.

Covariates: Age and sex of the cadavers, along with facial morphological dimensions, including the vertical and horizontal dimensions of the midface and orbit.

Analyses: Descriptive statistics were calculated. Independent and dependent t-tests evaluated sex and side differences, while Pearson's correlation analyzed relationships between facial dimensions and EP-ITN distances.

Results: A total of 38 hemifaces from 19 embalmed Korean cadavers were analyzed. The mean distances from the EP-ITN to the nasion, trochlea, and medial canthus were 1.6 ± 1.3 mm, 2.4 ± 1.3 mm, and 11.7 ± 2.0 mm, respectively. Horizontal facial width and orbital width were positively correlated with the EP-ITN-to-trochlea distance (r = 0.503, P = .008; r = 0.472, P = .012) but not with the EP-ITN-to-nasion distance.

Conclusions and relevance: This cadaveric study quantified the spatial relationship between nasion and EP-ITN, finding the nasion averages 1.6 mm superior to EP-ITN with minimal variability across specimens. These findings suggest the nasion as a reliable external landmark for EP-ITN identification in ITN block planning.