Ligaments of the Uterus
Before diving straight into the deep end to understand the so-called ligaments of the uterus, it is important to firstly have a basic idea of this fascinating organ called the uterus. Just like prior to doing/learning any task or skill, one must first learn to walk before he or she can run. This article will introduce some basic concepts about the uterus and then it will delve into the structures associated with it – the ligaments.
The uterus, the compartment where every single individual in the past and present has developed and those in the foreseeable future will start to do so. It is the place where organ systems and a recognizable form start to form. In other words, it is the place where everyone becomes a human. The uterus is one of the major components of the female reproductive system, which is located within the pelvic cavity. The other major components of this system are the ovaries, uterine tubes, vagina, clitoris and the greater vestibular glands.
The uterus is a hollow organ situated in the midline within the lesser pelvis between the bladder and the rectum. The uterine tubes project laterally from the superior aspect of the uterus while the vagina joins inferiorly. Its thick and muscular walls aid the expulsion of the fetus during childbirth. Inside the uterus is a small cavity that looks like a slit if viewed laterally and an inverted triangle if examined anteriorly. A fetus is very big compared to a non-gravid uterus and one can appreciate this organ and the size of its cavity if a little perspective is introduced in the picture. A non pregnant female has a uterus the size of a tennis ball but half its thickness. In contrast, a pregnant woman right before birth has the uterus the size of a watermelon. The size expands five times while the volume 500 times. This organ is anteverted in relation to the vagina and anteflexed in relation to the cervix. These two characteristics cause the uterus to be tipped and flexed in an anterosuperior direction, resulting in it being positioned over the bladder in a nearly transverse plane. Imagine the vagina and uterus forming a slightly tilted capital P in a sagittal section of the female pelvis. This organ is divided into two parts, the body and the cervix, which are supported by several ligaments and pelvic muscles.
Ligaments of the uterus
In this discussion, a "ligament" refers to an attachment to the uterus. All of the “ligaments” connected to the uterus are collectively known as the ligaments of the uterus and are classified into peritoneal folds and true ligaments, as given below:
- Broad ligament
- Uterovesical fold
- Rectovaginal fold
- Round ligament
- Pubocervical ligaments
- Transverse cervical ligaments
- Uterosacral ligaments
Peritoneal folds are thin structures where two layers of peritoneum come very close to one another. They attach to the first part of the uterus, its body. In contrast, true ligaments have a fibrous composition and they attach to the second part of the uterus, the cervix. The exception is the round ligament which attaches to the lateral cornu of the uterus. Some of them are neither folds nor true ligaments but distinct condensations of endopelvic fascia. This fascia consists of connective tissue and lines the pelvic walls, pelvic viscera and encloses blood vessels and nerves. Before going ahead to the nitty-gritty details, try and imagine walking into a big and famous chapel or Tropicana’s Havana Room in Las Vegas and seeing an enormous chandelier hanging from the ceiling. It has all sorts of chains and cables extending outwards and supporting it from the walls and ceiling, which carry electricity or “living fluid” to it. The uterus and the ligaments are arranged in a very similar way within the pelvis – the ligaments are the chains and cables carrying the vessels and nerves or life towards the chandelier, the uterus.
The broad ligaments (Ligamentum latum uteri) of the uterus are the lateral peritoneal folds, these being reflections of the parietal peritoneum over the upper female genital tract. They essentially form a sheet-like fold in the coronal plane. There are two, one on each side of the uterus, each composed of a double layer of peritoneum. It extends from the sides of the uterus to the lateral walls and floor of the pelvis, where it becomes continuous with the parietal peritoneum, maintaining the uterus in position. These ligaments have two borders: an upper one and a lower one. The upper border is free and it contains the uterine tube, where the peritoneal layer unites following envelopment. The lower border is continuous with the peritoneum running over the bladder, rectum and side walls of the pelvis. This ligament contains two other structures, the ligament of the ovary (Ligamentum ovarii proprium) and the round ligament of the uterus within certain parts. The broad ligament is composed of three small mesenteries: mesosalpinx, mesovarium and mesometrium.
The mesosalpinx is the most superior part of the broad ligament and also its free border. It is attached superiorly to the uterine tube and posteroinferiorly to the mesovarium. The fibrous suspensory ligament of the ovary (Ligamentum suspensorium ovarii) is attached superolaterally while the ovarian ligament is attached medially. The mesosalpinx encloses and suspends the uterine tube within the pelvic cavity. In addition, it encloses anastomoses between the uterine and ovarian vessels.
The mesovarium is the posterior extension of the broad ligament, containing the ovary. It attaches to the hilum of the ovary, carrying the ovarian vessels and nerves.
The mesometrium is the most inferior and largest part of the broad ligament. It extends from the pelvic floor to the ovarian ligament and the body of the uterus. It encloses the uterine artery, the suspensory ligament of the ovary and the proximal part of the round ligament of the uterus. Ovarian nerves and vessels travel through the suspensory ligament of the ovary.
The uterovesical fold is the anterior peritoneal fold which reflects from the junction of the uterine body and cervix onto the bladder. It creates the uterovesical pouch, which occurs anteriorly between the bladder and uterus.
The rectovaginal fold is the posterior peritoneal fold which reflects from the posterior vaginal fornix onto the rectum, creating the recto-uterine pouch (pouch of Douglas) between the two organs.
While the broad and round ligaments of the uterus attach to the body of the uterus, there are three other ligaments which attach to the second component of the uterus, the cervix. These are the pubocervical, transverse cervical and uterosacral ligaments.
The round ligament of the uterus (Ligamentum teres uteri) is the remnant of the ovarian gubernaculum. This structure helped the descent of the ovaries during embryonic development from the posterior abdominal wall. There are two in total, each extending from the lateral cornu of the uterus, through the broad ligament, enters the inguinal canal through the deep inguinal ring and ends in the connective tissue of the labium majus in the perineum. The extent of smooth muscle within this ligament is greatest closer to the uterus and it keeps decreasing further away, becoming purely fibrous at the edges. The round ligament contains vessels, nerves and lymphatics draining the uterine region around the entry of the uterine tubes into the superficial inguinal lymph nodes.
The two pubocervical ligaments (Ligamentum pubocervicale) extend from the anterior aspect of the cervix and upper vagina to the posterior aspect of the pubic bones.
Transverse cervical ligaments
The two transverse cervical or cardinal ligaments (Ligamentum transversus cervicis, Mackenrodt’s) are the most important ones out of this group. They run from the lateral walls of the pelvis to the supravaginal part of the cervix and the lateral parts of the vaginal fornix. They are traversed by the ureters and pelvic blood vessels.
The two uterosacral or recto-uterine ligaments (Ligamentum rectouterinum) contain both smooth muscle and fibrous tissue. They extend from the middle of the anterior aspect of the sacrum to two points located superiorly and slightly posteriorly from the sides of the cervix and uterine body. The recto-uterine folds overlie these ligaments.
The pubocervical, transverse cervical and uterosacral ligaments radiate outwards from the cervix towards the pelvic side walls, like the spokes of a wheel.
The uterus needs support in order to remain centered inside the pelvic cavity. The support it receives comes in two flavours: dynamic and passive. The ligaments of the uterus have an important role in both. Dynamic support is provided by the pelvic diaphragm through tonic contractions while standing and sitting and active contractions during moments of increased abdominal pressure, such as coughing or sneezing. During these moments, the ligaments of the uterus transmit the force of the diaphragm towards the organ itself, maintaining its position.
The ligaments are also crucial in providing passive support. By minimizing movement of the body and the cervix, they maintain the uterus in the typical anteverted and anteflexed position directly on top of the bladder. This provides a support for the uterus when the abdominal pressure increases. Therefore, by being involved in both dynamic and passive support, the ligaments of the uterus prevent it from falling through the vagina, a condition known as uterine prolapse. Returning to the previous analogy – the cables do support the chandelier to an extent but strong chains are needed to hang it safely from the dome. It is important to realise that ligaments do not operate alone but in unison with the muscles of the pelvic floor, the perineal membrane and perineal body to support the uterus.