Biomechanical Assessment of Orbital Retraction in the Endoscopic Transorbital Approach : A Cadaveric Study

Abstract

Background: The endoscopic transorbital approach (ETOA) provides minimally invasive access to the skull base but requires orbital retraction across key zones to establish a surgical corridor. Retraction is essential for exposure but entails risks of orbital morbidity, such as optic neuropathy, muscle dysfunction, and venous congestion. While ophthalmologic studies describe intraorbital pressure thresholds for ischemia, their relevance to ETOA is uncertain. Quantitative data on retraction forces and pressures remain limited, and the biomechanical behavior of specific orbital zones during surgical maneuvers has not been systematically assessed. Objective: To quantify orbital retraction force and intraorbital pressure during key ETOA steps and identify location-specific biomechanical responses. Methods: Three human cadaveric specimens were studied. Retraction force (N) and intraorbital pressure (mmHg) were recorded at the optic canal (OC), superior orbital fissure (SOF), and inferior orbital fissure (IOF) under three conditions: baseline, after meningoorbital band (MOB) release, and after MOB release plus superior orbital rim (SOR) craniotomy. Stepwise comparisons, effect sizes, and correlation analyses were performed. Results: MOB release reduced force most at the OC (−0.78 N, −48.4%, p = 0.004), with smaller decreases at the SOF (−0.63 N, −32.9%) and IOF (−0.39 N, −21.8%). SOR craniotomy produced minimal additional change (≤0.03 N). For pressure, the SOF demonstrated the strongest response, with decreases of −26.1 mm Hg (−78.6%, p = 0.011) after MOB and −23.3 mm Hg (−69.3%, p = 0.015) following additional SOR craniotomy. OC (−7.1 mm Hg, −50.1%) and IOF (−7.4 mm Hg, −36.8%) showed smaller, nonsignificant changes. Force and pressure were modestly correlated overall (r = 0.39), strongest at the SOF (r = 0.67). Conclusion: Orbital retraction during ETOA shows location-specific biomechanical patterns: the OC is predominantly force-sensitive, while the SOF is pressure-sensitive. MOB release emerges as the key maneuver altering orbital mechanics, whereas SOR craniotomy contributes little additional effect. These findings provide a quantitative framework for orbital biomechanics in transorbital surgery.