The anococcygeal ligaments: Cadaveric study with application to our understanding of incontinence in the elderly

The term "anococcygeal ligament (ACL)" has been used to refer to two distinct structures: a superficial fibrous band originating from the myosepta of the external anal sphincter (EAS) and running upwards to the coccyx (the superficial ACL); and a deep fibrous band originating from the periosteum of the coccyx, merging with the thick presacral fascia and attaching to the superior end of the EAS (the deep ACL). In the present work, elastic fiber histology and muscle immunohistochemistry of sagittal sections obtained from 15 donated elderly male cadavers showed that superficial ACL, corresponding to a superficial fascia or skin ligament, was composed of very tortuous elastic fibers, with a fine elastic fiber mesh at their coccygeal attachment; whereas the deep ACL was composed of almost straight collagen and elastic fibers, intermingled with the coccygeal periosteum. Due to the weak insertion into the coccyx and the wavy course, the superficial ACL is unlikely to provide, even in association with contraction of the longitudinal anal muscle, a stable mechanical support to maintain the configuration of the EAS. Being similar to the suspensory ligament of breast, tissue repair of the skin ligament would not have a mechanical role. In contrast, the deep ACL, in association with the thick presacral fascia, likely plays a role in maintaining a suitable positioning of the anorectum to the coccyx. However, their relative lack of smooth muscles compared with rich elastic fibers indicates that both ACLs may become permanently overextended under conditions of long-term mechanical stress.