Generality
The pelvic bones, also known as pelvic bones, are four: the sacrum, the two iliac bones and the coccyx.
The pelvic girdle represents the connection between the so-called axial skeleton and the skeleton of the lower limbs.
The sacrum and coccyx are, respectively, the penultimate and the last part of the vertebral column, therefore they reside posteriorly. The iliac bones, on the other hand, are the bony elements that develop laterally to the sacrum and give life to the hips and the pubic symphysis.
The pelvic bones have two basic functions: they support the weight of the upper part of the body and connect the latter to the lower limbs.
Short anatomical revision of the pelvis
The anatomists call the lower part of the trunk of the human body the pelvis or pelvis .
Located between the abdomen and thighs, the pelvis includes: the so-called pelvic bones (or pelvic bones), the so-called pelvic cavity, the so-called pelvic floor and the so-called perineum.
Definition of pelvic bones
The pelvic bones, also known as pelvic bones, are the sacrum, the two iliac bones and the coccyx.
The particular arrangement of the pelvic bones gives rise to a circular skeletal structure, which anatomy experts define with the term pelvic girdle .
The pelvic girdle represents the connection between the so-called axial skeleton - which includes the head, the vertebral column, the thoracic cage etc. - and the skeleton of the lower limbs .
Anatomy
The sacrum and coccyx represent the posterior part of the pelvic girdle and complete the spine, where the spinal cord resides.
The sacrum resides superiorly to the coccyx and inferiorly to the last lumbar vertebra; at the sides of it the iliac bones develop. The latter constitute the lateral and anterior parts of the pelvic girdle: the lateral parts are the bony portions which form the so-called hips and which compose the hips, while the anterior part coincides with the pubic symphysis, ie the point of connection between the two iliac bones.
SACRED BONE
The sacrum is an uneven, asymmetrical and triangular-shaped bone. Concave towards the inside, it includes the 5 sacral vertebrae, which, in the adult human being, are fused together in an extremely compact and solid structure. The fusion of the 5 sacral vertebrae is a process that takes place between 18 and 30 years of life.
In describing the sacrum, the anatomists recognize at least 6 extremely relevant regions on the latter: the so-called sacrum base, the so-called apex of the sacrum, the two lateral surfaces, the pelvic surface and the dorsal surface.
- Base of the sacred : it is the broad and flat bone region, projected upwards, which borders and articulates with the fifth lumbar vertebra. The fifth lumbar vertebra is the last vertebra of the lumbar spine.
- Apex of the sacred : it is the bone region projected downwards and has a flat and oval-shaped area ("oval facet"), which articulates with the coccyx;
- Pelvic surface : moderately inclined downwards, it is the region of the sacrum that looks anteriorly (therefore towards the inside of the human body). It is slightly curved, with the concavity, to which it gives rise, which is turned inwards.
- Dorsal surface : angled slightly upwards, it is the region of the sacrum that looks posteriorly. In fact, it represents the posterior (or opposite) face of the pelvic surface. This means that it is also curved, but it is convex rather than concave.
- Lateral surfaces : they are the regions of the sacrum that articulate with the right iliac bone and the left iliac bone, giving life to the two so-called sacrum iliac joints .
COCCYX
The coccyx is an unequal bone, symmetrical and shaped like a triangle, which resides below the sacrum and represents the last section of the spine.
It derives, in fact, from the superposition of the coccygeal vertebrae. In most humans, the coccygeal vertebrae are 4; more rarely, they are 3, 5 or 6. Their size is reduced from top to bottom: this means that the first coccygeal vertebra is the largest, while the last is the smallest. In general, the coccygeal vertebrae undergo a process of fusion, which occurs in adulthood.
In describing the coccyx, the anatomists identify in the latter at least 6 regions of a certain relevance: the base of the coccyx, the apex of the coccyx, the front surface, the posterior surface and the two lateral surfaces.
- Base of coccyx : it is the flat portion, located in the upper part of the coccyx and representing the point of connection with the sacrum. Here, in fact, there is an articular "facet", which serves to articulate the first coccygeal vertebra with the last sacral vertebra (sacro-coccygeal joint).
The base of the coccyx also includes two particular prominences, called coccyx horns. The horns of the coccyx make contact with the horns of the sacrum, located on the dorsal surface of the latter;
- Apex of coccyx : it is the inferior portion of the coccyx, the one that coincides with the last coccygeal vertebra and the end of the vertebral column. On the tip of the coccyx, the tendon of the external anal sphincter muscle is hooked;
- Front surface : slightly concave, it is the surface of the coccyx that looks towards the inside of the body. It has three characteristic transverse grooves and attaches to the sacro-coccygeal ligament and tendon of the levator ani.
- Posterior surface : moderately convex, it is the surface of the coccyx that looks posteriorly, therefore in opposite sense to the front surface. It has three characteristic transverse grooves - just like the front surface - and the sketches of the articular processes of the coccygeal vertebrae.
- Side surfaces : the sides of the coccyx are rather thin. In correspondence of each vertebral element, they have bony eminences, which are the so-called transverse processes of the coccygeal vertebrae. Transversal processes are being reduced, in terms of size, from top to bottom.
ILIACHE BONES
The iliac bone, or hip bone or coxal bone, is the even, symmetrical and flat bone, which develops laterally to the sacrum and converges on the front, taking contact with the contralateral iliac bone and forming the so-called pubic symphysis .
The iliac bone consists of three regions, which merge with each other at the age of 14th and 15th. The three regions in question are the bones known as: ilio, ischio and pubis.
- Ilium : represents the upper portion of the iliac bone; of the latter, it is also the largest and largest portion.
From the anatomical point of view, it presents two relevant sections, known as the body of the ilium and wing of the ilium.
The body includes part of the acetabulum; the acetabulum is the hollow within which the head of the femur takes place, in what is called the hip joint.
The wing of the iliac bone is the section that is above the body, which connects to the sacrum and gives life to a bone structure, certainly known to most people, called with the name of iliac crest. On the wing, two surfaces are recognizable: the inner surface (or iliac fossa) and the external surface (or gluteal surface).
The iliac fossa is concave and represents the point of origin of the iliac muscle; the gluteal surface, on the other hand, is convex and represents the attachment point of the buttocks
- Ischio : represents the lower and posterior part of the iliac bone. Therefore, it lies inferiorly on the ilium and behind it and on the pubis. Of the three bony elements that form the iliac bone, the ischium is the strongest and most resistant.
The ischium consists of three portions: the body, the lower branch and the upper branch.
The body is the bone portion that interposes between the lower branch and the upper branch of the ischium.
The inferior branch is important because it combines with the inferior branch of the pubis, giving life to the so-called ischio-pubic branch. The ischio-pubic branch forms a hole, which is called the obturation hole. Through the obturator hole, the obturator nerve, the obturator artery and the obturator vein pass.
Finally, the upper branch is relevant because it includes about one third of the acetabulum and a bony prominence called the ischial spine.
The ischium is the portion of the hip bone, which, when one sits and stretches forward, supports the weight of the human body. To be precise, the anatomical region of the ischium on which the weight of the human body bears when in a sitting position is the so-called ischial tuberosity.
The ischio acts gives insertion to two important ligaments: the sacrospinous ligament and the sacrotuberous ligament.
- Pubis : represents the anterior part of the iliac bone. In fact, he resides both before the ilium and before the ischium.
It includes three relevant portions, which are: the body, the upper branch and the lower branch.
The body locates between the inferior branch and the superior branch and is important, because, articulating with the pubis of the contralateral iliac bone, it forms the so-called pubic symphysis.
The upper branch extends laterally to the body and is important, because it constitutes another part of the acetabulum (about a fifth); its medial region is flat, while its lateral region is prismoid.
Finally, the lower branch projects in the direction of the ischium and joins with the latter, forming the so-called ischio-pubic branch; it is thin and flat.
JOINTS
In describing the pelvic bones, some joints have been named.
In this section, it was decided to summarize the joint elements that the sacrum, iliac bones and coccyx form during the interaction between them or with other bone structures.
The joints of the sacrum:
- The two sacral iliac joints: they are the articular elements that connect the sacrum to the two iliac bones.
- The lumbo-sacral articulation: it is the articular element that connects the last lumbar vertebra with the first sacral vertebra.
- The sacro-coccygeal joint: it is the articular element that connects the last sacral vertebra with the first coccygeal vertebra.
The joints of each iliac bone:
- The sacral iliac joint.
- The pubic symphysis: it is the articulation that unites, on the front, each iliac bone.
- The hip joint: is the joint element that connects the iliac bone to the femur.
The coccyx joints:
- The sacro-coccygeal joint.
Functions
The pelvic bones have two basic functions: they support the weight of the upper part of the body and connect the latter to the lower limbs.
The function of support, in relation to the upper part of the body, is important especially when the human being stands up, sits, walks, runs etc.
Turning then to the second task of the pelvic bones, the link that the latter establish with the lower limbs is extremely important for the walking mechanism.
Associated pathologies
Among the various pathologies that can affect the bones of the pelvis, include: bone fractures, sacroiliitis, coccygodynia, hip pathologies.
BONE FRACTURES
Fractures to the bones of the pelvis are traumatic injuries, which usually occur after accidental falls, car accidents or impacts during the practice of sports where physical contact is required (eg rugby, American football, etc.).
The sections of the pelvic bones most likely to fracture are:
- The wings of the hip bones;
- One of the two lateral edges of the sacrum;
- The upper or lower branches of the pubis.
Fractures to the pelvic bones are divided into two categories: stable fractures and unstable fractures. All fractures characterized by a single breaking point are stable; all fractures marked by a two or more break points are unstable.
sacroiliitis
Sacroiliitis is the unilateral or bilateral inflammation of the sacral iliac joint. Various factors / circumstances can determine their appearance, including: the presence of arthritis, the state of pregnancy, infections affecting the sacral iliac joint, Crohn's disease, ulcerative colitis, urinary tract infections, trauma to the sacral iliac joint, etc.
The characteristic symptom of sacroileitis is pain with seat in the buttocks and in the lower part of the back; sometimes, this painful sensation is so strong and widespread that it also involves the legs, the groin region and even the feet.
Behaviors and circumstances that aggravate the pain resulting from the sacroileitis:
- Stand up for many hours consecutively;
- Taking the stairs;
- Running, jumping etc;
- Assume incorrect postures, which go particularly to affect one of the two legs;
- Walking at length;
- Roll in bed;
- Sitting for a long time.
coccydynia
Coccygodynia is a painful inflammatory syndrome that affects the coccyx and / or the area surrounding it.
The causes of coccyginia include: traumas, falls, childbirth, overload in the sacro-coccygeal region due to certain types of sports or work, incorrect postures and wear - due to age - of the disks of cartilage that keep the coccyx in place.
Among the risk factors of coccyginia, they deserve a mention: belonging to the female sex and obesity.
In addition to pain in the coccyx area, coccygodynia can cause: muscle pain in the back, legs, buttocks and hips and discomfort during sexual intercourse (rare).
ANCIENT PATHOLOGIES
The two most important hip pathologies, which arise from a disorder of one of the pelvic bones, are coxarthrosis and congenital dysplasia of the hip .
