Which vertebrae are fused

It provides several important functions, including:. The average person is born with 33 individual bones the vertebrae that interact and connect with each other through flexible joints called facets. By the time a person becomes an adult most have only 24 vertebrae because some vertebrae at the bottom end of the spine fuse together during normal growth and development.

Sometimes a person may have an additional vertebra, which is called a transitional body and is usually found at the sixth level of the lumbar area labeled L6. The bottom of the spine is called the sacrum. It is made up of several vertebral bodies usually fused together as one. The remaining small bones or ossicles below the sacrum are also fused together and called the tailbone or coccyx.

The spine above the sacrum consists of:. The spinal column combines strong bones, unique joints, flexible ligaments and tendons, large muscles and highly sensitive nerves. Subacute and chronic low-back pain: Surgical treatment. Brunicardi FC, et al. Spine: Basic concepts. In: Schwartz's Principles of Surgery. New York, N. Spine Surgery. Rochester, Minn. McMahon SB, et al. Surgery for back and neck pain including radiculopathies. Philadelphia, Pa. Baron EM, et al. Transforaminal lumbar interbody fusion.

In: Operative Techniques: Spine Surgery. Accessed Jan. Steinmetz MP, et al. Biology of spine fusion. Bydon M expert opinion. Mayo Clinic, Rochester, Minn. Guideline: Lateral interbody fusion in the lumbar spine for low back pain IPG Accessed Jan 7, Wheeler SG, et al. Sometimes the spinal cord can react without sending information to the brain. These special pathways, called spinal reflexes, are designed to immediately protect our body from harm.

Any damage to the spinal cord can result in a loss of sensory and motor function below the level of injury. For example, an injury to the thoracic or lumbar area may cause motor and sensory loss of the legs and trunk called paraplegia. An injury to the cervical neck area may cause sensory and motor loss of the arms and legs called tetraplegia, formerly known as quadriplegia.

Thirty-one pairs of spinal nerves branch off the spinal cord. Each spinal nerve has two roots Fig. The ventral front root carries motor impulses from the brain and the dorsal back root carries sensory impulses to the brain. The ventral and dorsal roots fuse together to form a spinal nerve, which travels down the spinal canal, alongside the cord, until it reaches its exit hole - the intervertebral foramen Fig.

Once the nerve passes through the intervertebral foramen, it branches; each branch has both motor and sensory fibers. The smaller branch called the posterior primary ramus turns posteriorly to supply the skin and muscles of the back of the body. The larger branch called the anterior primary ramus turns anteriorly to supply the skin and muscles of the front of the body and forms most of the major nerves.

The spinal nerves are numbered according to the vertebrae above which it exits the spinal canal. The 8 cervical spinal nerves are C1 through C8, the 12 thoracic spinal nerves are T1 through T12, the 5 lumbar spinal nerves are L1 through L5, and the 5 sacral spinal nerves are S1 through S5. There is 1 coccygeal nerve. The spinal nerves innervate specific areas and form a striped pattern across the body called dermatomes Fig.

Doctors use this pattern to diagnose the location of a spinal problem based on the area of pain or muscle weakness. For example leg pain sciatica usually indicates a problem near the L4-S3 nerves. The spinal cord is covered with the same three membranes as the brain, called meninges.

The inner membrane is the pia mater, which is intimately attached to the cord. The next membrane is the arachnoid mater. The outer membrane is the tough dura mater Fig. Between these membranes are spaces used in diagnostic and treatment procedures. The space between the pia and arachnoid mater is the wide subarachnoid space, which surrounds the spinal cord and contains cerebrospinal fluid CSF.

This space is most often accessed when performing a lumbar puncture to sample and test CSF or during a myelogram to inject contrast dye.

The space between the dura mater and the bone is the epidural space. This space is most often accessed to deliver anesthetic numbing agents, commonly called an epidural, and to inject steroid medication see Epidural Steroid Injections. We comply with the HONcode standard for trustworthy health information. Congenital anomalies of the cervical spine. Neurosurg Clin N Am. Congenital variations of the upper cervical spine and their importance in preoperative diagnosis.

A case report and a review of the literature. Eur J Orthop Surg Traumatol. Epub Apr 6. Am J Hum Genet. Epub Jan 3. The extent of fusion within the congenital Klippel-Feil segment. Spine Phila Pa Klippel-Feil syndrome and associated abnormalities: the necessity for a multidisciplinary approach in patient management. Spine J. Congenital limb deficiences associated with Klippel-Feil syndrome: a survey of 57 subjects.

Acta Orthop Scand. Klippel-Feil syndrome: clinical features and current understanding of etiology.