The human musculoskeletal system is a multilevel and very complex mechanism that includes muscles with tendons, bones and ligaments. They determine all the possibilities of movement and movement of a person, his upright posture. Any violations at one level lead to responses to others.
A bit of anatomy
The backbone of the human musculoskeletal system is the backbone. The upper divisions of the vertebral column are less loaded and more mobile. The vertebrae here communicate with each other using discs, muscles. The lower sections carry constant enormous loads.
Nature envisaged providing additional strength in the sacral section and coccyx by fusion of the vertebrae. In this case, integral elements are formed that connect to the bones of the pelvis. Fusion of the vertebrae just increases the ability to support weight and maintain a stable position of the body.
The sacrum does not need flexibility. The vertebrae here are distinguished by the fact that their bodies are pronounced, and the processes are hardly noticeable, almost atrophied. The strength and strength of these lower joints is provided, first of all, by the sacroiliac joints and a whole set of ligaments.
Sacral topography
The human sacrum resembles a triangle, the base of which is facing the spine. Here it is connected to the last vertebra of the lower back. It is located, tapering by a wedge, in the middle between the bones of the pelvis. The lower narrow part is connected to the coccyx, which has 4-5 vertebrae, they are very small. The term "sacrum" in translation means "sacred bone."
Sacral bone structure
The sacrum consists of the following parts:
- The front, or pelvic surface - differs in a concave shape in the upper and lateral surfaces. The middle of the sacrum is streaked with 4 transverse lines - in fact, stitches from the fusion of the vertebrae. On the sides of these lines are 4 holes, which are downward decreasing in diameter. Arteries and nerves that form the plexus pass through them.
- The back surface is convex. It is narrower and rougher. In the middle are 5 scallops with a direction from top to bottom. This is the result of fusion of the processes of the vertebrae - spinous, transverse and articular.
- The lateral surfaces on the slice are triangular in shape, tapering downward.
- The base of the sacrum is the most protruding part of the bone, facing anterior and upward.
- The top is the junction with the coccygeal bone.
- The sacral canal (without the posterior wall) has a through character, is curved and expanded at the top. Here passes the nerve sacral plexus, the branches of which exit through the above holes.
Sacrum functions
Its main functions are that it distributes the arising loads on the spine and maintains the vertical position of the axis of the vertebral column. In order to understand the functioning system, you should look at the photo.
Sacroiliac Joint (CPS) and its ligaments
The sacroiliac joint (art. Sacroiliaca) is composed of the surfaces of the pelvic bone resembling the human ear, for which they are called the ear-shaped and the sacrum itself. These surfaces form the ilium wing. On these surfaces, the joint is considered flat. It has a complex relief of mating surfaces, a tight stretched capsule and ligaments.
The specified joint is paired amphiarthrosis (tight joint), semi-mobile. It carries the main load in supporting the upper body during its movement and change of position, provides cushioning, stabilizes when sitting, with such a load it partially takes over part of it. It is strong enough for high loads, that is, its main function is the supporting one. The amplitude of motion of the parts of the joint relative to each other does not exceed 4-5 degrees.
By the way, the paired joints does not mean that they are parallel to each other in the plane. If this were so, and the CPS were parallel to the midline of the body (sagittal), the sacrum would be able to rotate in the pelvic girdle and not influence it, as in modern warrior toys. But this cannot happen because the sacrum with its triangular shape is directed with the convex side back.
Ligaments of the sacrum connect the spine with the bones of the pelvis. They hold all bone elements while in a physiological position. Although they are small, they are considered the most durable in the skeleton. The two main ligaments are sacral-tuberous (KBS) and sacral-spinous (CBS). They are both one side attached to the sacrum. The second end of KBS is attached to the sciatic tubercle, which is why the ligament got its name. The CBS is much shorter and the other end is attached to the ilium. In the human body, they are considered the most durable. Thanks to them, the KPS can move.
The anatomical significance of the sacrospinous and sacral-tuberous ligaments is the formation of 2 holes (large and small) from the sciatic notch. They also limit them. In the upper large hole is the passage of the piriformis muscle. She holds the knee and foot unfolded during movement and partially participates in the abduction of the thigh. Below is a small sciatic foramen, here passes the tendon of the obturator muscle. She turns her hip outward. Through it also pass the neurovascular bundles coming from the pelvis.
While we were talking about these 2 ligaments, which are extracapsular, but inside the joint capsule itself there are also ligaments, they serve to further strengthen the joint. The ventral ligament is in front, the dorsal and iliac-lumbar ligaments are in the back. They are all sturdy and thick.
The mobility of the joints is slightly higher during pregnancy and in children. Therefore, children are free to reach and poke their toes in their mouths.
Intracapsular iliac ligaments
The iliac-lumbar or iliac-lumbar ligament has an upper and lower bundle. It connects the pelvic bone and the spine through the 4th and 5th lumbar vertebra. The upper bundle is directed from the top of the transverse process down, laterally and back. Weaves in the end into the iliac crest. The lower bundle from the 5th vertebra goes laterally and downward, it connects to the crest in front and is located medially to the upper one.
What are they doing? They participate in lateral inclinations (lateroflexion), are pulled in the opposite direction, and relax on the inclined side. Many anatomists call them a real rope stretched from the lower back to the pelvis.
The interosseous sacroiliac ligaments of the CPS are the longest and most durable. They have 2 important functions: they provide the axis of rotation and fix the bones. They also stretch from tuberosity, but already to the sacrum. They are located on the back surface of the joint and connect both articulating bones (pelvis and sacrum).
Dorsal (posterior) KPS have long and short fibers. Cover the back side of the capsule. They are most resistant to tearing.
Ventral or anterior strengthen the joint and connect the front edges of the joint. Their bundles are short. They act together with the dorsal and allow you to make rotational movements.
Extracapsular Ligaments
The sacro-tuberous ligament connects the sacrum with the pelvis. Its powerful bundle in the sacral region has a divergent fan-shaped appearance. The ligament is guided along an oblique line on the posterior surface of the sacrospinous ligament. She plays an important role.
The sacro-tuberous ligament (Latin - lig.Sacrotuberale) goes from the sciatic tubercle to the lateral edge of the sacrum and tailbone. From above, it stretches along from the posterior edge of the ilium to the 1st and 2nd coccygeal vertebrae. A continuation of it downward and anteriorly to the ischial branch is the sickle-shaped process of the sacro-tuberous ligament. The sacrum bone consists of a body and a curved branch. After 8 years, the pubic bone and the sciatic branch become one.
The sacrospinous ligament (lig. Sacrospinale) connects the sciatic bone with the lateral part of the coccyx and sacrum. The awn is a kind of bone protrusion in the lower part of the ilium, slightly above the sciatic tubercle. It goes obliquely from the sciatic spine to the lateral surface of the sacrum and tailbone. It is directed upward, medially and backward. The type of connection of the sacro-tuberous ligament is fibrous, syndesmosis, juncturaefibrosae, or connection with fibrous tissue. This is also a kind of connective. To such types of it include seams, membranes, poking and fontanelles.
Ligamenta ligaments are, in fact, connective tissue, which is based on collagen and elastic fibers. Serves to strengthen bone joints. The fibers can be very short and long. The joint capsule itself is thick, as it should with such high loads. It glistens due to tight tension, grows together with the periosteum of the sacrum and pelvic bone and is attached along the edges of the surfaces of the joint.
Functions and nutrition of extracapsular ligaments
At its core, the triangular sacrum is the key to the pelvic ring. It does not move under the weight of the human body due to its ligaments - intra- and extracapsular. This is the function of the sacro-tuberous ligaments.
Although these ligaments are located outside the capsule at a distance, they are considered as ligaments of the CPS because of the importance of the role. Blood supply and nutrition are provided by 2 arteries - the iliopsoas and the lumbar. The same veins of the same name through which there is an outflow of blood. The innervation of the joint is due to the lumbar plexus. Another important role of the sacro-tuberous ligament during childbirth will be discussed below.
The work of the ligaments when resting on one leg
Each connective structure, whether it is a ligament or aponeurosis, can always stretch only to a certain limit - physiological. It depends on their length and thickness. The function and significance of the sacro-tuberous ligaments is that they do not prohibit the movement of bones, but limit them to the level of physiological amplitude. These structures are also equipped with sensitive receptors.
Outside physiological stretching, receptors transmit information about this in the form of pain. Such incoming information leads to a reflex muscular response. He is always directed and acts, obeys the so-called law of painlessness. It controls the functioning of the body.
For example, a static or dynamic load on one leg when resting on it is the force exerted on the ligaments, which often exceeds the permissible ones, and the stretching also increases. The sacrum tends to the horizontal position, and the ilium to the back. The pyramidal muscle attached to these fibrous structures, immediately and quickly reflexively contracted. The strength of this contraction is regulated by different stretching of the KBS. In other words, the muscle is turned on to protect the sacro-spinous and sacral-tuberous ligaments. This is one of its functions.
The structure of the sacro-tuberous ligament is important in restricting certain movements. This literally means the following: part of the ligament fibers below the sacrum prevents nutation, and the part attached to the ZVGPK (posterior superior iliac crests), which are also called gluteal tubercles, resists the opposite movement.
Palpation of ligaments
According to the anatomy of the sacro-tuberous ligaments, they can be palpated in the supine position. Since they are very tight, palpations are similar to bone formations.
The small ligament is more difficult to identify, since it is under a large layer of muscles. But it plays a large role in pelvic dysfunctions, as well as in irritation of the sciatic nerve, which, of course, plays a much more important role than the functioning of the pyramidal muscle. The pyramidal muscle with the abdominal muscles is involved in the tilts of the trunk forward.
Precise palpation:
- With your thumb, determine the lower part of the sacro-tuberous ligament.
- Turn the thumb on top of it.
- At a distance of 2 fingers from the thumb there will be a projection of the sacrospinous ligament.
- They have a close relationship with the pyramidal muscle, and between them passes the sciatic nerve - the largest in humans.
- To penetrate deeper, one must wait for their relaxation.
Nutation and counternutation (tilt and counterclination) of the sacrum
The movement of the sacrum around the median transverse axis is commonly called nutation and counternutation. Nutrition from Latin nutare - nod. This movement of the sacrum is similar to nodding your head. During childbirth, the iliac bones move apart, increasing the space to expand the birth canal and promote the baby. This is the meaning of counternutation when the cape of the sacrum moves backward and the tailbone moves forward. When the baby’s head already reaches the vagina, the counternut is replaced by the nutation. The tailbone rotates backward and the sacrum forward.
This type of mobility was noticed and described in 1851 by the registry office, and in 1854 by Duncan. When nutation, the movement of the sacrum occurs in the anteroposterior direction (sagittal) inside the pelvis. The base of the sacral bone moves dorsally, and the coccyx goes in the opposite direction - back.
This is accompanied by the approach of the ilium. What does it matter? With the approach of the ilium, the projections of the sciatic scatter to the sides. The opening of the lower body occurs, and the completion of the stage of labor is simplified to advance the fetal head.