Anatomy of the lateral orbital wall: A topographic investigation for identification of the lateral canthal attachment.

BACKGROUND

There is a growing effort to develop implantable bionics for restoring eye closure in paralytic lagophthalmos. Knowledge of the natural eyelid attachments is important for active implants that mobilise these attachments or replace them with a sling. Whitnall's tubercle (WT) is traditionally used to identify lateral canthal attachments; however, it is not always present. This study seeks an alternative means of identifying the insertion of the lateral canthus to aid the application of bionic implants.

METHODS

Complete CT head scans of patients in the Sydney Head and Neck Cancer Institute database were retrieved for analysis. The CT scans were segmented using bone and soft-tissue thresholding and then reconstructed. The location of WT and the lateral canthal insertion were recorded and their relation to key anatomical landmarks assessed.

RESULTS

Ninety orbits from 45 complete head scans were analysed. WT could be identified bilaterally in 18/45 (40%) samples. The average distance from WT to zygomaticofrontal suture and to lateral orbital margin was 10.8 ± 0.4 mm and 4.4 ± 0.2 mm, respectively. The average height of the lateral canthal insertion from the Jugale point was 13.9 ± 1.8 mm. On regression analysis, the height of lateral canthal insertion was strongly predicted by the height of lateral orbital wall as the determined by the maximum distance of the ZFS from the Jugale point (p = <0.001).

CONCLUSION

In the absence of WT, the height of the lateral orbital wall can be reliability used to localise the insertion site of the lateral canthus.