Endoscopic Anatomy of Posterior Malleal Ligament: Variation and Surgical Implications

The enhanced visualization provided by endoscopes has allowed for the identification of several anatomical structures that were previously unnoticed or overlooked when using a microscope. This study focused on the endoscopic anatomy of the posterior malleal ligament (PML), examining its presence, attachment sites, relationship with the chorda tympani, and its physiological function and surgical relevance.

A retrospective study and theoretical analysis.

Tertiary referral center.

Thirty-seven out of 64 cases of tympanoplasty performed as initial operations at Ota General Hospital between July 2023 and June 2024 were analyzed.

A detailed examination of surgical findings was conducted using a 2.7-mm endoscope with a 4K camera and recorded surgical videos to evaluate the following items: presence of a ligament or fold, attachment sites of the PML, and the anatomical relationship between the PML and the chorda tympani. Specimens of the PML were evaluated histopathologically. The effect of the stiffness of the PML on the vibration of the malleus and stapes was assessed using the finite-element method (FEM).

Variants were documented photographically and organized into tables. The change in vibration velocity at different PML stiffness levels was calculated using the FEM model.

The PML, originating from the pretympanic spine, runs anteriorly, lateral to, and on the chorda tympani, reaching the manubrium in all cases. The thick ligament was present in 32 of 37 cases (86.5%), whereas in 5 of 37 cases (13.5%), the apparent thick ligament was absent, but a fold was present. The ligament terminated at the upper part of the manubrium (type 1: 13.5%) or branched out and terminated at both the upper part of the manubrium and the tympanic membrane (TM) (type 2: 73.0%). In cases where a thin loose connective tissue was present, it had a wider attachment to the manubrium (type 3: 13.5%). Histopathological analysis revealed the presence of dense or thinly stretched fibrous connective tissue. The FEM model demonstrated that the stiffness of the PML has a minimal effect, less than 2 dB, on the vibration of the ossicle.

Our study suggests that the PML has a suspensory role in anchoring the malleus to the pretympanic spine and does not play a significant role in sound transmission. The PML and the pretympanic spine are reliable landmarks for identifying the chorda tympani. Our findings provide fundamental evidence that cutting the PML and removing the pretympanic spine to improve surgical access can be done safely without significantly impacting auditory function.