Medial Canthal Support Structures The Medial Retinaculum: A Review Hyera Kang, MD,*Þ Yasuhiro Takahashi, MD, PhD,* Takashi Nakano, MD, PhD,þ Ken Asamoto, MD, PhD,þ Hiroshi Ikeda, MD, PhD,§ and Hirohiko Kakizaki, MD, PhD* Abstract: The medial canthus is supported by several structures with a com- plicated 3-dimensional arrangement in a narrow space. Although the medial canthal tendon occupies a major portion of the area, the medial canthal support structures include the following entities: Horner’s muscle, the medial rectus capsulopalpebral fascia including the medial check ligament, the medial horn of the levator aponeurosis, the medial horn supporting ligament, the medial horn of the lower eyelid retractors, the preseptal part of the orbicularis oculi muscle, and 3 variations of the Lockwood’s ligament. We named the composite of these structures the ‘‘medial retinaculum,’’ which is similar to the ‘‘lateral retinaculum’’ of the lateral canthus. Profound comprehension and consideration of the medial retinaculum warrants safe and effective surgery in the medial canthal region. Key Words: medial canthus, support structure, medial retinaculum (Ann Plast Surg 2015;74: 508Y514) T he medial canthus is supported by several structures, with a com- plicated 3-dimensional arrangement in a narrow space (Figs. 1 and 2). 1 Although the medial canthal tendon (MCT) occupies a major portion of this area, the medial canthal support structures include the following entities (Fig. 3A, B): Horner’s muscle, the medial rectus capsulopalpebral fascia (mrCPF) including the medial check ligament, the medial horn of the levator aponeurosis, the medial horn supporting ligament (MHSL), the medial horn of the lower eyelid retractors (LERs), the preseptal part of the orbicularis oculi muscle (OOM), and 3 variations of the Lockwood’s ligament. We newly named the compo- site of these structures the ‘‘medial retinaculum,’’ which is similar to the ‘‘lateral retinaculum’’ of the lateral canthus. 2 Profound comprehension and consideration of the medial retinaculum warrants safe and effective surgeries in the medial canthal region. Here, we review each medial canthal support structure comprising the medial retinaculum. All the macroscopic and microscopic specimens were regis- tered in the cadaveric service of Aichi Medical University. Proper consent and approval was obtained before use and all methods for securing human tissue were humane and complied with the tenets of the Declaration of Helsinki. MEDIAL CANTHAL TENDON History of the MCT The medial canthal anatomy mainly focused on the MCT. 1,3Y5 The MCT was previously called the ‘‘medial canthal ligament.’’ 6 Because the anatomy of this region was not clear, some considered it to be a true ligament, but others saw it simply as a large adhesion to the periosteum of the frontal process of the maxilla. 6 In the 1970s, Lester T. Jones, who was the first to reconsider this classical anatomy, established a new concern about the medial canthal region. Jones and Wobig 3 reported that the medial canthal ligament was not a ligament, but rather a tendon of the OOM. The MCT has been thought to comprise 2 limbs, that is, the anterior and posterior. 4,7 The anterior limb, which is stronger than the posterior limb, 8 was thought to be situated in front of the lacrimal sac and connected the anterior lacrimal crest and the medial aspect of the tarsal plate. 4 Ritleng et al 4 also stated that the anterior part of the medial canthal ligament was actually the tendon of the pretarsal OOM, and suggested calling it the ‘‘medial palpebral tendon.’’ 4 Yamamoto et al 1 proposed that the MCT comprised an aggregate of muscle fibers from the orbital area of the OOM, as well as the tendon from the tarsal area. Although many reports have illustrated the anatomy of the MCT, the anterior limb was further disclosed to include 2 lamellae, that is, the anterior and posterior (Figs. 1 and 4). 9 The anterior lamella is the tendon of the pretarsal part of the OOM. 9 The posterior lamella is the musculotendinous junction of the preseptal and orbital parts of the OOM. 9 The anterior limb continues to the pretarsal OOM without insertion into the tarsal plate. 10 The posterior limb has been considered to be located in front of Horner’s muscle, connecting the posterior lacrimal crest and the tarsal plate. 4 However, true fixation of the nasal aspect of the tarsal plate is performed by Horner’s muscle and the mrCPF (Fig. 2), 10 and not by the posterior limb. Most researchers considered this posterior limb as a relative subsidiary structure, compared with the anterior limb, 8,11,12 although some thought the posterior limb to have the same tough fibrous consistency as the anterior limb. 13 The True Nature of the Posterior Limb of the MCT The medial canthus has been thought to be supported by the anterior and posterior limbs of the MCT (or the medial canthal liga- ment) and Horner’s muscle. The posterior limb of the medial canthal ligament, as a deep or reflected part arising from the main ligament, 4,11 was thought to be merely a thin fascial expansion 14 or simply a thin and weak structure to assist the anterior limb. 12 The posterior limb of the MCT was thought to be attached behind the lacrimal sac and to continue to the lacrimal fascia, and thus helped to support the upper part of the lacrimal sac. 11 The posterior limb of the MCT has been, however, occa- sionally regarded as Horner’s muscle. 8 Ritleng et al 4 stated that Horner’s muscle was a separate structure from the posterior limb of the MCT, and that the structure corresponding to the posterior limb was not a tendon, but Horner’s muscle. Adenis and Longueville 8 reported that the posterior component of the MCT, called Horner’s muscle, was more delicate and had more of a dynamic structure than the anterior portion, and Horner’s muscle comprised the posterior portion of the MCT. Shinohara et al 15 reported that the posterior connective tissue fibers of the MCT were interwoven with fibers of the lacrimal fascia and extended to the common lacrimal canaliculus and to the bifurcation of Horner’s muscle. REVIEW ARTICLE 508 www.annalsplasticsurgery.com Annals of Plastic Surgery & Volume 74, Number 4, April 2015 Received May 11, 2013, and accepted for publication, after revision, July 19, 2013. From the *Department of Ophthalmology, Aichi Medical University, Nagakute, Aichi, Japan; †Department of Ophthalmology, Presbyterian Medical Center, Jeonju, Korea; Departments of ‡Anatomy, and §Pathology, Aichi Medical University, Nagakute, Aichi, Japan. Conflicts of interest and sources of funding: none declared. Reprints: Hirohiko Kakizaki, MD, PhD, Department of Ophthalmology, Aichi Medi- cal University, Nagakute, Aichi 480-1195, Japan. E-mail: cosme@d1.dion.ne.jp. Copyright * 2014 Wolters Kluwer Health, Inc. All rights reserved. ISSN: 0148-7043/15/7404-0508 DOI: 10.1097/SAP.0b013e3182a6365c Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.