THE JOINT SYSTEM OF THE SPINE

By Dr. KM Liau

The spine is made up of both synovial joints and non-synovial joints. The synovial joints are found in the facet joints, the unco-vertebral joints of cervical spine, the costovertebral joints and the sacroiliac joints. The non-synovial joints are made up of the intervertebral disc joints.

Although the intervertebral disc joint is a non-synovial joint, there are several structures which are analogous to the structures found in a true synovial joint. The cartilaginous endplate, the annulus fibrosus, and the nucleus pulposus are analogous to the articular cartilage, the joint capsule and the synovial fluid of the synovial joint.

DEGENERATIVE DISORDER - OSTEOARTHRITIS

This is the most common type of arthritis seen in humans.

By definition, osteoarthritis occurs in a synovial joint.

In the spine, therefore, osteoarthritis occurs in the facet joints, the uncovertebral joints of cervical spine, the costovertebral joints, and the sacroiliac joints.

Osteoarthritis may be primary or secondary.

FACET JOINT OSTEOARTHRITIS

Marked osteophytes and joint space narrowing is noted in the facet joints in the lumbar spine of this patient.

The osteophytosis is causing significant encroachment on the lateral recesses bilaterally causing impingement of the nerve root.

DEGENERATIVE NUCLEAR DISEASE

Another very common disorder is degeneration of the nucleus pulposus.

With age, the nucleus tends to become more and more dehydrated, and gradually begins to degenerate.

As this happens, the intervertebral disc height begins to decrease.

When this happens, the altered pattern of stress will lead to formation of marginal osteophytes adjacent to the affected endplates.

As the disc space decreases in height, increased stress is also placed on the facet joints, leading to the frequent association of osteoarthritis of the facets at the same level.

DEGENERATIVE ANNULAR DISEASE

Another extremely common degenerative disorder involves degeneration of the annulus fibrosus.

This leads to marginal osteophyte formation at the endplates, especially in the thoracolumbar spine (the junction between the rigid thoracic spine and the mobile lumbar spine) in most persons over 50 years of age.

The height of the disc space is largely preserved.

In practice, one often sees evidence of degeneration of both the annulus and the nucleus.

It doesn't make a lot of difference as to which component of the disc has degenerated.

Therefore, we use the term "degenerative disc disease" to refer to these entities.

DEGENERATIVE ANNULAR DISEASE 2

Marked marginal osteophytosis is noted at each disc space in this patient with predominantly annular degeneration.

The traction osteophytes tend to be initially oriented horizontally at their attachment to the vertebral bodies.

They then curve slightly and form a complete bony bridge across the disc space (picture).

NOTE the preserved disc space.

DEGENERATIVE DISC DISEASE

Disc space narrowing is noted at multiple levels in this patient with degenerative disc disease.

SYNDESMOPHYTES

Syndesmophytes are generally seen only in the seronegative spondyloarthropathies (eg.Ankylosing Spondylitis)

These are due to inflammation and ossification of the outer fibers of the annulus fibrosus, known as the Sharpey's fibers(In Ankylosing Spondylitis)-See picture.

Note the abscence of osteophytes.

DISC SPACE NARROWING

Disc space narrowing

This almost always means degenerative nuclear disease or infection.

The two entities can often be distinguished by looking at the adjacent endplates.

In degenerative disc disease, the endplates are often dense, sclerotic, and associated with osteophytosis.

In infection, the subchondral line of the endplate often becomes ill-defined and discontinuous.

BONY PROLIFERATION

This is a striking feature of the seronegative spondyloarthropathies, particularly psoriatic arthritis.

The bony proliferation occurs about erosions, and probably relates to an exaggerated healing response of the injured bone.

This proliferation may take the form of irregular excrescences, subperiosteal deposition of bone, and intra-articular osseous fusion.

EROSIONS

In general, the presence of erosion signifies inflammatory disease, whether the erosions are due to synovial hypertrophy, crystalline deposits, or infection.

SUBLUXATION

Stability of the spine is maintained by the spinal ligaments, articular capsules, and discs.

Any arthropathy which causes degeneration or destruction of these structures may lead to instability of the spine and subluxation in several locations.

DIFFUSE IDIOPATHIC SKELETAL HYPEROSTOSIS (DISH)

Flowing ossification along the anterior longitudinal ligament.

Idiopathic disorder.

A diagnosis by exclusion.

Criteria:

1. SI and facet joints must be normal

2. Disc spaces must be of normal height

3. Ossification must be seen along four contiguous vertebral bodies.

DISH - CERVICAL

Prominent, flowing ossification is noted along the anterior margin of the cervical spine in this patient with DISH -- it is easy to see why such patients often complain of dysphagia

DISH - THORACIC