Tendinous Arch of Levator Ani

The tendinous arch of levator ani, also known as the *arcus tendineus levator ani*, is a linear thickening of the obturator internus fascia that serves as a key origin point for the middle and posterior portions of the levator ani muscle. It acts as a functional and anatomical boundary between the pelvic wall and the pelvic floor, anchoring the iliococcygeus and parts of the pubococcygeus. Though a non-muscular structure, it plays a critical role in organizing the musculofascial layout of the pelvic diaphragm and is essential for maintaining pelvic organ support and pelvic floor integrity.

Structure

The tendinous arch is a condensation of the pelvic fascia overlying the obturator internus muscle. It extends as a fibrous band from the posterior aspect of the body of the pubis to the ischial spine. It is composed primarily of collagen fibers, with some elastic content, and forms a dense white ridge visible in cadaveric dissection. Though often described as a “line,” it has measurable width and depth and provides a distinct fascial plane that guides the insertion of muscle fibers from the levator ani group.

Dimensions

• Length: Approximately 6–8 cm in adults
• Thickness: 2–4 mm
• Orientation: Obliquely downward and posterior from pubis to ischial spine

Attachments

Related Muscular Attachments

The tendinous arch serves as the origin point for:

• Iliococcygeus
• Portions of the pubococcygeus (especially lateral fibers)

It does not give attachment to the puborectalis, which arises directly from the pubic bone.

Location

The tendinous arch is located within the lateral pelvic wall, spanning from the pubic bone anteriorly to the ischial spine posteriorly. It lies medial to the obturator internus and deep to the parietal pelvic fascia. The levator ani fibers sweep downward and medially from this arch to contribute to the pelvic diaphragm. It forms the superior boundary of the levator hiatus and separates the obturator internus from the pelvic floor musculature.

Surrounding Structures

Function

• Muscle Anchor: Provides a firm origin line for the iliococcygeus and part of the pubococcygeus
• Structural Divider: Separates the muscular pelvic wall (obturator internus) from the muscular pelvic floor (levator ani)
• Maintains Pelvic Floor Shape: Ensures organized orientation of levator ani fibers, contributing to the concave upward dome shape of the pelvic diaphragm
• Surgical Landmark: Serves as a crucial reference point in pelvic reconstructive surgery, including prolapse repairs

Development

The tendinous arch develops during fetal life as part of the condensation of the obturator internus fascia, paralleling the development of the surrounding levator ani musculature. As the levator ani differentiates from sacral myotomes, the fascial interface with the pelvic wall thickens and forms the tendinous arch. It is identifiable by the second trimester and becomes structurally functional by the third trimester.

Histology

The arch is composed primarily of dense regular connective tissue rich in type I collagen. It is interspersed with elastic fibers and small fibroblast populations. There is little to no vascularity or innervation within the arch itself, though adjacent muscle and fascia carry neurovascular elements. Elastic recoil in this region is minimal; its function is purely mechanical as a muscular anchor.

Imaging and Surgical Importance

• MRI: Can be visualized as a linear hypointense band on axial T2-weighted imaging, especially in prolapse assessment
• Ultrasound: Difficult to visualize directly but its location can be inferred by muscle fiber orientation
• Palpation: Not easily palpable, but its insertion at the ischial spine is an important tactile landmark during pelvic surgery

In Surgery

• Sacrospinous fixation: Surgeons must distinguish this structure from the sacrospinous ligament to avoid misplacement of sutures
• Paravaginal repair: The tendinous arch is used to reattach avulsed vaginal wall fascia to restore lateral support
• Mesh anchoring: In prolapse procedures, mesh arms are sometimes anchored to the arch for optimal support

Clinical Significance

• Pelvic Organ Prolapse: Avulsion or detachment of the levator ani from the tendinous arch is a major risk factor for prolapse of the uterus, vagina, or rectum
• Levator Avulsion Injury: Common in vaginal childbirth, especially instrumental deliveries; detectable on ultrasound or MRI
• Lateral Defect Prolapse: Occurs when endopelvic fascia detaches from the arch, allowing lateral vaginal wall descent (paravaginal defect)
• Pelvic Floor Dysfunction: Compromised attachment of pelvic muscles due to degeneration or trauma may contribute to chronic pelvic pain, incontinence, or prolapse
• Postpartum Pelvic Imaging: Imaging after childbirth often focuses on the integrity of the pubovisceral muscle origin at the tendinous arch