Topographic Anatomy of the Discomalleolar and Anterior Malleolar Ligaments in Human Adults and Fetuses

Kim, Hee Jin; Shim, Kyoung Sub; Kwak, Hyun Ho; Park, Hyun Do; Kang, Min Kyu; Chung, In Hyuk

Abstract

During temporomandibular joint (TMJ) formation, discomalleolar ligament (DML) and anterior malleolar ligament (AML) are formed within the dorsal end of the 1st branchial arch. But, DML is known as a remnant or the degenerated tissue through the TMJ development. There is few reports said that damage of AML and DML cause the damage of middle ear during surgical procedures. Especially, in case of anterior disk displacement of TMJ, aural symptom can be made via DML due to hyperextension anteriorly. A few studies have been reported about DML and AML in embryological and histological points of view, morphology and clinical aspects of DML and AML are still unclear. Four fetuses and sixteen adult hemi -sectioned heads were dissected to clarify the topographical relationship of AML and DML and to find out the anatomico -clinical relevance related with temporomandibular disorder. In fetal specimens, DML was firmly attached from the disk of the TMJ to the malleus. Also, AML in which distinguished into the superior and inferior lamellae was running anteriorly and continuous with the sphenomandibular ligament (SML) through the future petrotympanic fissure (PTF). DML attached to the malleus was observed in all adult specimens and was expanded broadly to the disk and capsule of the TMJ as shown the V -shaped ligament structures. The average distance between the anterior aspects of the malleolar head to the anterior wall of the tympanic cavity was 1.13 mm(0.75 ~1.59), and the length of the DML from the anterior aspect of the malleolar head to the attached site to the TMJ capsule at the PTF was 5.37 mm (4.53 ~6.07). The average width of the DML at the PTF was 6.06 mm (4.72 ~7.46). Most of the posterior attachments of the DML were the cases in which DML was directly attached to the malleus (68.7%). In all specimens, DML was attached to the disk and capsule of TMJ and attached to the anteromedial border of the PTF concurrently. In this study, two morphological patterns of AML were observed according to the presence of the bony ridge on the Huguiers canal in the PTF. The bony ridge of the Huguiers canal showed DML and AML separately in 56.3%, and the fused pattern of DML and AML was observed in 43.7%. AML was not distinguished with two lamellae in most specimens, superior ligament fibers were attached to the anteromedial border of the PTF and most of the inferior lamella was entering the gap in PTF and continuous with the SML. Average length from the anterior aspect of the malleolar head to the exit point of the AML on the PTF was 8.40 mm(6.62 ~11.42), and the shortest distance between the AML and chorda tympani was 2.01 mm(1.25 ~3.02). Taken all together, DML and AML were not the rudimentary, but the distinguishable structures in adults. Through the various morphological findings, DML and AML were separated ligamentous structures in which might be given rise from the divergent origin. And the anterior hyperextension of the disk of TMJ did not lead the movement of the malleus in the tympanic cavity, whereas, the movement of the malleus followed by the traction of the AML and SML was observed in a few cases. So, this results can be explained the possibility of the clinical symptom on the middle ear in case of the over -traction of the AML and SML.