Generality
The acetabulum, or acetabulum, is the particular lateral hollow of the iliac bone, used to house the head of the femur and form, with the latter, the hip.
Like all bony elements, the acetabulum can be subject to fractures.
Furthermore, it can play a leading role in some hip pathologies, such as coxarthrosis (hip arthrosis) or congenital hip dysplasia.
What is the acetabulum?
The acetabulum is the characteristic hollow of the iliac bone of the pelvis, which serves to house the so-called femoral head (thigh bone) and to constitute the important hip joint (or more simply hip).
The acetabulum is, therefore, a concave area of the iliac bone, in which the upper portion of the femur takes place - the one that previously was defined as the head - thus generating the hip.
Synonyms
In human anatomy, the acetabulum is also known as the cup .
Anatomy
Premise: to understand the anatomy of the acetabulum, it is necessary to start from an anatomical description of the iliac bone.
The iliac bone is the even, symmetrical and flat bone, which develops laterally to the sacrum (uneven bone) and converges on the front, taking contact with the contralateral iliac bone and constituting the so-called pubic symphysis .
The iliac bone consists of three parts, known as ilio, ischio and pubis ; initially separated, these three parts merge with each other at the 14th / 15th year of life of a human being.
The terms " hip bone " and " bone coxal " are synonymous with iliac bone .
The acetabulum is located on the outer face of the hip bone, in the lower half.
All three parts of the hip bone contribute to its formation, so both ilium, ischio and pubis; here, specifically, how:
- The ilium participates with the so-called body of the ilium, constitutes the upper portion of the acetabulum and represents slightly less than 2/5 ;
- The ischium participates with the superior branch of the ischium, forms the posterior portion and part of that inferior of the acetabulum and represents little more than the 2/5 ;
- Finally, the pubis participates with the so-called upper branch of the pubis; forms the anterior portion and part of the lower portion of the acetabulum and represents approximately 1/5 of it .
In general, when describing the essential anatomical elements of the acetabulum, the experts talk about: acetabular lip, the lunate side of the acetabulum, acetabular notch and acetabular fossa.
Note: the acetabulum is an equal skeletal element, as it is equal to the bone structure to which it belongs.
Acetabular lip
The acetabular lip is a fibrocartilaginous structure, similar to a ring and fixed all around the circular perimeter of the acetabulum, like a seal.
Its tasks are substantially two: to facilitate the correct housing of the femoral head and to guarantee stability to the hip joint.
The lunar face of the acetabulum
Semicircular in shape, the semi- lunar face of the acetabulum constitutes the upper part of the inner surface of the acetabulum.
Smooth and covered with a layer of articular cartilage, the lunate face represents an anatomically relevant element because it is the only portion of the acetabulum that truly interacts with the femoral head, forming the hip.
Curiosities about the iliac bone
The two iliac bones, together with the sacrum and coccyx, are two of the four so-called pelvic bones .
The bones of the pelvis cover two important functions: supporting the weight of the upper part of the body and connecting the latter to the lower limbs.
Acetabular notch
- It guarantees the passage of the so-called transverse acetabular ligament, a fundamental structure to maintain the femoral head in the appropriate place.
- It inserts part of one of the two terminal ends of the important ligament which attaches the head of the femur to the acetabulum (the seat of the other end); this ligament is called ligament of the femoral head or round ligament of the femur .
- It constitutes the so-called acetabular foramen, a space that allows the passage of the blood vessels deputed to spray (blood) the head of the femur.
Acetabular fossa
The acetabular fossa is the central and deepest portion of the acetabulum.
With a quadrilateral shape and a rough surface, the acetabular fossa is a continuity of the acetabular notch, so that with the latter it contributes to the insertion of one of the terminal ends of the round ligament of the femoral head.
Another important feature of the acetabular fossa is the presence, in the center, of adipose tissue.
| Table. As the various parts of the iliac bone contribute to the formation of the acetabulum. | |||
| Part of the iliac bone | Which region do you participate in? | What portion of the acetabulum constitutes? | What is your contribution in numerical terms |
| Ilio | Body of the ilium | Upper portion | Just under 2/5 |
| ischium | Upper branch of the ischium | Rear portion and part of the lower portion | Just over 2/5 |
| pubis | Upper branch of the pubis | Front portion and part of the lower portion | About 1/5 |
Vascularization of the acetabulum
The acetabulum receives oxygenated blood from:
- The acetabular branch . Passing through the acetabular notch, it is a small arterial derivation of the obturator artery, which in turn originates from the internal iliac artery .
The main task of the acetabular branch is to supply the adipose tissue located in the center of the acetabular fossa with blood.
- The pubic branches . They are also derivations of the obturator artery.
They take care of oxygenating the surface of the anterior portion of the acetabulum.
- The deep branches of the upper gluteal artery . They supply the upper portion of the acetabulum with blood.
- The deep branches of the inferior gluteal artery . They supply the posterior inferior portion of the acetabulum with blood.
Functions
As stated on more than one occasion, the acetabulum contributes significantly to the formation of the hip joint.
The hip is an arthrosis, that is an articulation endowed with extreme mobility and resulting from the housing of a convex bone portion in a concave bone portion.
Surrounded by synovial fluid to prevent friction between the various bone and ligament components, the hip is indispensable to the human being's ability to move; thanks to her, in fact, a healthy individual can take up the standing position, walk, run, jump etc.
diseases
From the clinical point of view, the acetabulum is important for at least two reasons:
- Because it can be subject to fractures ( acetabular fractures );
- Because it is the protagonist of some important hip pathologies .
Acetabular fractures
Definitely less common than femoral head fractures, acetabular fractures are almost always the result of traumatic events that involve the violent impact of the femoral head against the acetabulum; a typical cause of such events is frontal motor vehicle accidents, where the collision between the knees and the dashboard is quite usual (the violent impact between knee and dashboard pushes the femur abnormally and vehemently against the acetabulum, which may not withstand the impact, thus breaking).
More rarely, acetabulum fractures are a possible consequence of the weakened bone produced by osteoporosis, a bone disease typical of old age.
The severity of an acetabular fracture depends on various factors, including:
- The number of bone fragments that were created after the fracture. A large number of fragments is indicative of a serious fracture;
- The fact that the fracture is broken down or not. If it is broken down, it is more serious;
- The presence or absence of a fracture of the femoral head. In fractures due to the violent collision between the femoral head and the acetabulum, it may happen that not only the acetabulum, but also the femoral head, suffer an injury; clearly, where there is a fracture of the femoral head, the situation is more serious;
- The presence or absence of an injury to the surrounding soft tissues (muscles, ligaments, tendons, etc.). Also typical of violent-impact acetabular fractures, the involvement of surrounding soft tissues is a major cause for concern.
Acetabulum fractures always cause hip pain that gets worse with movement.
If the event responsible for the fracture has also produced some nerve injury, the victim of the injury may experience symptoms such as tingling and / or weakness in the affected lower limb.
The treatment of an acetabular fracture varies according to the severity of the lesion: for less serious injuries, a conservative treatment may be sufficient (rest, braces for walking and not supporting the affected limb, painkillers, etc.); for more severe injuries, however, surgery is required.
Hip disorders involving the acetabulum
Among the hip pathologies that see the acetabulum as the protagonist, there are coxarthrosis - that is hip arthrosis - and congenital dysplasia of the hip .
In coxarthrosis, the acetabulum contributes to the pathology, because it is the object of that degenerative process, affecting the articular cartilage, which characterizes the phenomena of arthrosis.
In congenital dysplasia of the hip, on the other hand, the acetabulum contributes to the disease because it is less deep than normal and this prevents the correct insertion, inside it, of the head of the femur (NB: in such circumstances, the current condition is all the more serious as the anatomical abnormalities affecting the acetabulum are more relevant).
