Table of Contents
Introduction
After a prolonged sitting, i.e., after a seminar with boring and long lectures, you might have seen some of your colleagues complaining about pain at the very lower end of their back. This likely originates from the coccygeal complex. Depending on the circumstances, this pain may range from a mild stroke to severe enough that it can lead to being bedridden.
In a differential diagnosis, one of the diagnoses may be coccydynia, which is a typical lower back pain restricted to the lower back and anal region. This is in contrast to sciatic pain (a disease of the sacral plexus) that also originates in the lower back but radiates down through the back of the thigh up to the toe. The underlying etiology of coccydynia is related to damage to the spinal nerves at the coccygeal area forming the coccygeal plexus. In the following words, we shall discuss the coccygeal plexus, how it is formed, its course, position, relations with other body structures, and last but not least, its diseases and their management.
Coccygeal Plexus
Before going into details, first of all, we must know what a plexus is in neuroanatomy. In neuroscience, a plexus is an interconnected network of nerves. We know that the spine or vertebral column has been divided into different parts according to its location in the body. The uppermost part is known as the cervical part, then comes the thoracic, lumbar, sacral, and, in the end, coccygeal. The same is the case with the spinal cord. From every segment, some nerves arise, known as spinal nerves. These nerves are named according to the region, i.e., thoracic spinal nerves, sacral spinal nerves, lumber spinal nerves, etc. When these spinal nerves leave the spinal canal through intervertebral foramina, they divide into anterior and posterior divisions, also known as the dorsal and ventral primary rami (singular: ramus). Dorsal rami supply the skin of the back, vertebral joints, vertebral discs, and muscles of the back. They do not take part in plexus formation. A plexus is exclusively formed by the ventral rami of the spinal nerves. In the coccygeal region, the plexus formed is known as the “coccygeal plexus”. Other plexuses found in the body are “the cervical plexus”, which supplies the neck muscles and skin of the anterior and lateral neck, “brachial plexus”, which supplies the upper limb; and “the sacral plexus,” which provides innervation to the lower limb, named according to the vertebral region from where their roots emerge. These plexuses are so formed that the fibers from the ventral rami get distributed into different branches such that each branch/nerve may contain fibers from several rami or, in other words, fibers from one ramus may get distributed into different branches. All Spinal nerves except some thoracic spinal nerves form plexuses.
Origin
The origin of the coccygeal plexus is the ventral rami of S4, S5, and Cc1 spinal nerves, also known as the roots of the coccygeal plexus. Out of these, S4 contributes to the coccygeal plexus through its descending branch only. It joins the S5 and Cc1 (coccygeal nerve 1) and forms a small neural network, the coccygeal plexus.
Location, course, and relations
The coccygeal plexus is located anterior to the posterior wall of the lower aspect of the pelvis. It lies over the floor of the coccygeus muscle and anterior to the piriformis muscle. The only branch of this plexus, the anococcygeal nerve, descends down and pierces the sacrotuberous ligament to reach the anal area where it supplies.
Area of supply and Functions
The coccygeal plexus supplies a small area over the tailbone (coccyx). It provides both sensory and motor innervation. Sensory innervation is restricted to a small area between the tip of the coccyx and the anal region. The sensations carried through include fine touch, crude touch, two-point discrimination, vibration, pressure, pain, thermal sensations (cold and warmth), etc. It also transmits proprioceptive information via proprioceptive fibers innervating the sacrococcygeal joint.
Motor innervation is given to the two muscles of the pelvic diaphragm, the coccygeus, and part of the levator ani muscles. Motor functions include the contraction of these two muscles to stretch out the pelvic diaphragm, which causes closure of the natural hiatuses and prevents prolapse of internal organs.
Branches
The coccygeal plexus gives only one significant branch; the anococcygeal nerve.
Anococcygeal nerve
The anococcygeal nerve is the main branch of the coccygeal plexus. Before going into the detail of its supply area. Let us discuss something about the concept of dermatomes and myotomes. A group of muscles innervated by a single specific spinal nerve root forms a dermatome. Same as an area of the skin supplied with a single specific spinal nerve root constitutes a dermatome. The dermatomal supply is sensory in nature, while the myotomal supply is motor in nature. The anococcygeal nerve does not supply any muscular component hence it does not have myotomal or motor supply. It only gives cutaneous innervation to a small area of the skin from the tip of the coccyx to the anal region. It pierces the coccygeus muscle and sacrotuberous ligament to reach the area where it supplies.
Other Branches
Other branches of the coccygeal plexus include:
Nerve to coccygeus muscles
Its root value is S4, but a small part of S5 also contributes to its formation. This nerve causes the contraction of the coccygeus muscle. Coccygeus is a supportive muscle of the pelvic diaphragm. Along with the levator ani, it forms a nearly horizontal pelvic diaphragm and supports the pelvic viscera, and prevents any prolapse of the pelvic organs, i.e., uterus, rectum, etc. through natural hiatuses like the vagina and anus, etc. The contraction of the coccygeus pulls the pelvic structures in an anterosuperior direction which helps levator ani to occlude the hiatuses, preventing any prolapse.
Nerve to the levator ani muscle (supplies a part of this muscle)
Its root value is S4. It supplies part of this muscle. Levator ani forms a muscular sheet in the pelvis which supports pelvic organs. Its function is similar to that of coccygeus, prevention of any prolapse.
Nerve fibers to sacrococcygeal joint
It provides proprioceptive information from this joint.
Diseases and their Management
There are many diseases that affect the nervous system. Some of them are systemic, which affect the nervous system as a whole, and some are localized to particular nerves. We will limit our discussion to the coccygeal plexus and its branches.
Coccydynia
Coccydynia is the only significant disease of the coccygeal plexus. “Coccy” is for the coccyx, and “dynia” means pain, so coccydynia is simply the pain of the coccyx. It is also known as tailbone pain. It is a pain around the tip of the coccyx just above your natal cleft and area near the anus. This pain is common during bowel movement, sexual intercourse, and a change of posture after prolonged sitting to standing.
Causes of the coccydynia
There are many causes of coccydynia. A direct injury to the tailbone may damage the nerves here. A bone spur or a tumor may press the nerve. There may be dislocation or fracture of the tailbone due to a fall, road traffic accident, or blunt trauma. Apart from these, sitting for a long time on hard surfaces may cause coccydynia. Stretch injury during childbirth is a major cause in Females. Any abscess or “neuritis”, inflammation of neurons, triggered in response to infections (i.e., bacterial, viral) or autoimmune conditions can cause coccydynia. Repetitive strain injury is also a cause of coccydynia. Damage to the nerves evoked by radiation therapy, drugs, and toxins can cause coccydynia. Chronic diseases like diabetes Mellitus, hypertension, and other metabolic disorders that can result in neuropathy may responsible for precipitating tailbone pain.
In many cases, the cause is unknown, resulting in idiopathic coccydynia.
Risk Factors
Risk factors for coccydynia include gender, obesity, and age. In females, after childbirth, it is common due to stretch injury, resulting in five times more susceptibility of women towards coccydynia. An obese person is three times more likely to develop this disease. Adults and adolescents are more prone to coccydynia than children.
Diagnosis and treatment
Coccydynia is usually diagnosed in a series of examination steps. The first external examination is done to rule out any injury, wound, deformity, or abscess. Further testing is done using radiological techniques. X-Ray and CT scans are done to check for any fracture, bone spur, dislocation, or any other deformity. MRI (magnetic resonance imaging) technique is used to check for inflammation or tumors, i.e., chordoma (a tumor of the spine) etc.
Treatment of coccydynia includes both pharmacological and surgical intervention. At first, pharmacological treatment is given to the patient to avoid risks and complications of surgery. Usually, NSAIDs, Non-steroidal anti-inflammatory drugs (e.g., aspirin, ibuprofen, or naproxen, etc.), tricyclic anti-depressants, steroids, and muscle relaxants are used. A stool softener or laxative may be used to reduce pain caused by a bowel movement. If the underlying cause is an infection, it is treated using antibacterial or antiviral agents. Damages caused by chronic diseases like diabetes Mellitus and chronic inflammation can be treated by treating the parent disease. After pain suppression, rehabilitation and restoration of the functions of the damaged nerve can be effectively done by physiotherapy.
If this pharmacological treatment shows no effectiveness, surgery is the next operation. It includes partial or total coccygectomy (removal of the whole or part of the coccyx). It is effective in case of fracture, bone spur, any dislocation, etc. If the underlying cause is a tumor, tumor removal surgery is done. Unfortunately, surgical treatment has some hazards, and it provides no guarantee of complete pain resolution.
Physical therapy, regular walking and exercise, weight loss, use of a small soft pillow under the lower back while sleeping, and avoiding prolonged sitting may significantly alleviate the symptoms of coccydynia.
Summary
The coccygeal plexus is an interconnected network of ventral primary rami of spinal nerves S4 (its descending branch only), S5, and Cc1.
It provides cutaneous innervation to the skin of the tip of the coccyx bone and anal region. Cutaneous functions include the transmission of sensory information, i.e., touch, pressure, pain, temperature, and proprioception.
Motor supply includes innervation to the coccygeus, levator ani, and sacrococcygeal joint. Motor Functions include contraction of the coccygeus and levator to maintain the pelvic diaphragm in a horizontal position and supporting the pelvic viscera to prevent prolapse of internal organs such as rectal prolapse. Important branches are the anococcygeal nerve, the nerve to the levator ani, the nerve to the coccygeus, and the nerve to the sacrococcygeal joint.
Disease-related to the coccygeal plexus is coccydynia. Various etiologies for this disease include prolonged sitting, direct injury to the nerves, neuritis, radiation therapy, pressure due to tumor, bone spur, fracture, dislocation or deformities of the coccyx, and infections.
Risk factors for coccydynia are older age, obesity, and gender. Patients suffering from coccydynia complain about pain in the coccyx tip area.
Treatment includes both pharmacological using NSAIDs, steroids, nerve blocks, tricyclic antidepressants and antibiotics (in case of infections), etc., and surgical. Along with these curative measures, rehabilitation is done using physiotherapy, regular exercise, weight loss, etc.
References
Coccygeal Nerve – an overview | ScienceDirect Topics”
Thieme Atlas of Anatomy: General Anatomy and Musculoskeletal System. Thieme. 2006. ISBN 1-58890-419-9.
Image source: The Coccygeal Plexus