Coccyx

Generality

The coccyx is the unequal bone structure, generally composed of 4 vertebrae, which constitutes the last part of the vertebral column.
Triangular in shape and located inferior to the sacrum, the coccyx is the last testimony of the tail present in our ancestors, in very remote times.
From the anatomical point of view, it has at least 6 regions of some importance: the base of the coccyx, the apex of the coccyx, the anterior surface, the posterior surface and the two lateral surfaces.

Coccyx (in red): Rear view. Image from wikipedia.org

The coccyx participates in only one joint: the "sacro-coccygeal joint, which - com" is easily understood - joins the sacrum to the base of the coccyx.
Its functions include: protecting the terminal portion of the bone marrow, supporting the weight of the body in a sitting position and, finally, inserting muscles (eg gluteus maximus and ani levator), ligaments, tendons, etc.

What is the coccyx?

The coccyx is the terminal part of the spinal column. To be precise, it is the set of vertebrae, forming a triangle-shaped structure, which resides below the sacrum.

BRIEF ANATOMICAL REVIEW OF THE SPINE

The backbone of the human body, the vertebral column or rachis is a bony structure of about 70 centimeters (in the adult human being), which includes 33-34 vertebrae stacked on top of each other.
The vertebrae of the spinal column have a fairly similar general structure. In fact, they all have:

• A body (anteriorly);
• A horseshoe-like arch (rear);
• A vertebral hole, resulting from the union of the arch to the body.

The vertebral holes of each vertebra coincide and this determines the formation of a long canal - the so-called spinal canal or vertebral canal - which serves to house the spinal cord.
The spinal cord is, together with the brain, one of the two elements that make up the central nervous system (CNS).

Anatomy

The coccyx is an uneven and symmetrical bone structure, basically derived from the overlap of the coccygeal vertebrae.
In most human beings, there are 4 coccygeal vertebrae; more rarely, they are 3, 5 or 6.
Their size decreases from top to bottom: this means that the first coccygeal vertebra is the largest, while the last is the smallest.
The first coccygeal vertebra has two notable transverse processes; all coccygeal vertebrae lack peduncles, laminae and spinous processes.
As a rule, the vertebral elements of the coccyx undergo a fusion process, which begins in adulthood and ends within a few years.
In describing the coccyx, anatomists identify in the latter at least 6 regions of some importance: the base of the coccyx, the apex of the coccyx, the anterior surface, the posterior surface and the two lateral surfaces.

• Base of the coccyx: it is the flat portion, located in the upper part of the coccyx and representing the junction point with the "sacrum. Here, in fact, there is a flat space, a sort of" facet ", which serves to articulate the first vertebra coccygeal with the last sacral vertebrae.
  The base of the coccyx also includes two particular prominences, called the horns of the coccyx. The coccyx horns are the articular processes of the first coccygeal vertebra; oriented upwards, they make contact with the horns of the sacrum, located on the dorsal surface of the latter and oriented downwards;
• Apex of the coccyx: it is the lower portion of the coccyx, the one that coincides with the last coccygeal vertebra and the end of the vertebral column. It has a rounded shape.
  On the apex of the coccyx, the tendon of the external anal sphincter muscle is hooked;
• Anterior surface (or ventral 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 to the tendon of the levator anus muscle.
• Posterior surface (or dorsal surface): moderately convex, it is the surface of the coccyx that looks backwards, therefore in the opposite direction to the anterior surface. It has three characteristic transverse grooves - just like the anterior surface - and the sketches of the articular processes of the coccygeal vertebrae.
• Lateral surfaces: rather thin, they are the sides of the coccyx. At each vertebral element, they have bony eminences, which are the so-called transverse processes of the coccygeal vertebrae. The transverse processes are reduced, in dimensional terms, from top to bottom: as stated, in the first coccygeal vertebra they are very evident; in the subsequent vertebral elements, they are reduced.

ARTICULATIONS

The coccyx takes part in a "joint: the so-called sacro-coccygeal joint (or sacro-coccygeal symphysis).
The sacro-coccygeal joint represents the point of contact between the last sacral vertebra and the first vertebrae of the coccyx.
On the joint "facet", which resides at the base of the coccyx and forms the so-called sacro-coccygeal joint, there is a layer of fibrous cartilage.
The sacro-coccygeal joint is an articular element that is not very mobile and works passively: it allows, in fact, minimal movements of extension and flexion of the coccyx, with respect to the sacrum, during particular moments such as defecation or labor.

LIGAMENTS

The ligaments that establish relations with the coccyx are:

• The anterior sacro-coccygeal ligament: it is in fact the continuation of the anterior longitudinal ligament of the vertebral column. It serves to connect the anterior faces of the vertebral bodies of the coccygeal vertebrae;
• The deep posterior sacro-coccygeal ligament: it is the ligament that connects the posterior side of the fifth sacral vertebra with the dorsal surface of the coccyx;
• The superficial posterior sacro-coccygeal ligament: it is the ligament that connects the median sacral crest (on the sacrum) to the posterior surface of the coccyx;
• THE lateral sacro-coccygeal ligaments: they are the ligaments that run from the lateral surfaces of the sacrum to the transverse processes of the first coccygeal vertebra;
• THE interarticular ligaments: are the ligaments that connect the horns of the sacrum with the horns of the coccyx.

MUSCLES

The coccyx inserts one of the original ends of the gluteus maximus muscle and one of the terminal ends of the levator ani muscle.

Origin and insertion

Functions

Gluteus maximus muscle

It has numerous heads of origin, including:

• Iliac crest;
• Posterior face of the iliac bone;
• Lateral surfaces of the sacrum;
• Lateral surfaces of the coccyx;
• Sacrotuberous ligament;
• Lumbar band.

It ends on the gluteal tuberosity of the femur.

It allows:

• External rotation and hip extension;
• Supports knee extension;
• Contributes to walking;
• It contributes to the maintenance of an upright position.

Levator anus muscle

It has 3 chiefs of origin:

• Two on the inner face of the pubis;
• One on the hipbone.

It ends on the anterior surface of the coccyx.

It has support functions towards the viscera of the pelvic cavity.

Development

In the embryo, the coccyx derives from a structure called the caudal eminence. Its formation occurs approximately between the fourth or eighth week of gestation. As embryonic development continues, the caudal eminence regresses, but the coccyx remains.
Immediately after the constitution of the coccyx, the vertebrae of the latter are separated and remain so for all the first years of life.
As stated, the fusion of the coccygeal vertebrae is a process that takes place during adult life; it can have numerous variations: for example, it can affect all vertebrae, except the first or the first two.

Function

The functions of the coccyx are at least three:

• Offer protection to the terminal tract of the spinal cord;
• Supporting the weight of the body, when the human being is seated and projecting backwards (N.B: when projecting forward, the support function belongs to the ischial tuberosity of the iliac bones);
• Inserting very important muscles, ligaments and tendon structures.

Associated pathologies

The pathologies that can affect the coccyx include: bone fractures, coccygodynia and sacro-coccygeal teratoma.

FRACTURES OF THE COCCIGE

Coccyx fractures are injuries of a traumatic nature, which usually occur after accidental falls, car accidents or impacts during the practice of sports in which physical contact is required (eg rugby, American football, etc.).
In most cases, the treatment is conservative.

COCCIGODINIA

Coccygodynia is a painful inflammatory syndrome that affects the coccyx and / or the area surrounding it.
Causes of coccygodynia include: trauma, falls, childbirth, overload in the sacro-coccygeal region due to certain types of sports or work activities, incorrect postures and "wear and tear - due to" age - of the cartilage discs , which hold the tailbone in place.
Among the risk factors of coccygodynia, it is worth mentioning: 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).

SACRED-COCCIGEO TERATOMA

The sacro-coccygeal teratoma is a tumor that develops at the base of the coccyx and which, most likely, derives from an embryonic structure called the primitive lineage.
Generally, sacrococcygeal teratomas are benign in nature; in fact, according to some statistical studies, only 12% of patients have a malignant tumor.
Sacrococcygeal teratoma affects one in every 35,000 newborns and is the most common cancer found in newborns.
Usually, treatment consists of surgical resection of the coccyx and, sometimes, part of the sacrum.