The “Phytes” of the Spine

In evaluating the spine, one observes the size, shape, and mineralization of the different vertebral bodies. These parameters become abnormal in various systemic diseases. For example, a large vertebral body is seen in Paget disease, a flattened vertebral body in eosinophilic granuloma, an H-shaped vertebral body in sickle cell disease, a sclerotic vertebral body in lymphoma, and an osteoporotic body in hyperparathyroidism. The arthropathies tend not to involve the vertebral body itself but primarily the apophyseal joints and the disc spaces. The most common arthropathy involving the apophyseal joints is osteoarthritis, which produces narrowing of the apophyseal joints, reparative bone, and osteophyte formation ( Fig. 8-1 ). The inflammatory arthropathies cause erosive changes of the apophyseal joints, with or without eventual ankylosis. The inflammatory arthropathies may affect the disc space, but the most common disc space disorder is degeneration either idiopathically or secondary to abnormal deposition of material into the disc substance. Radiographic signs of disc degeneration are vacuum phenomenon, calcification, disc space narrowing, and reparative response in adjacent vertebral bodies.

However, many of the arthropathies lead to the development of various kinds of “phytes.” The diagnosis of an arthropathy can be made through careful observation of the type of phyte that is produced. There are four different types of phytes: (1) the syndesmophyte, (2) the marginal osteophyte, (3) the nonmarginal osteophyte, and (4) the paraspinal phyte.

In order to understand the various kinds of phytes that distort the vertebral body and surround the disc, the anatomy of the disc interspace and surrounding soft tissues must be understood ( Fig. 8-2 ). The central portion of the disc is known as the nucleus pulposus. This is surrounded by a fibrous ring called the anulus fibrosus. The nucleus pulposus and the inner portion of the anulus fibrosus are surrounded superiorly and inferiorly by the cartilaginous end-plate of the vertebral body. This cartilaginous vertebral end-plate does not extend to the borders of the bony vertebral body. Where the cartilaginous end-plate ends, the outermost fibers of the anulus fibrosus, called the Sharpey fibers, penetrate and connect the bone of one vertebral body to the bone of the adjacent vertebral body. The anterior longitudinal ligament adheres closely to the anterior border of the midportion of the vertebral body. At a level approximately 3 mm from the ends of the vertebral body, the anterior longitudinal ligament pulls away from the vertebral body and no longer closely adheres. It traverses the disc area in apposition to the Sharpey fibers and becomes closely adhered to the adjacent vertebral body 3 mm beyond the end-plate. The posterior longitudinal ligament adheres to the vertebral body in its entire length and is more intimately apposed to the Sharpey fibers posteriorly.

Syndesmophyte

The syndesmophyte is a vertical ossification bridging two adjacent vertebral bodies ( Fig. 8-3 ). It is the ossification of the Sharpey fibers of the anulus fibrosus. Because these fibers extend into the bone portion of the vertebral body, the syndesmophyte becomes a contiguous part of the vertebral bodies involved. The deep layers of the longitudinal ligaments may become ossified as well in forming this bridge. The syndesmophyte is the hallmark of ankylosing spondylitis. However, it may be seen in any of the spondyloarthropathies including reactive arthritis, psoriasis, and those associated with bowel disease.

Marginal osteophyte

The marginal osteophyte is a horizontal bony extension of the vertebral end-plate ( Fig. 8-4 ). It is an integral part of the vertebral body in that it has a medullary canal contiguous with the medullary canal of the vertebral body and a cortex contiguous with the cortex of the vertebral body end-plate. Small marginal osteophytes are most commonly associated with degenerative disc disease and spondylosis deformans. Larger marginal osteophytes may turn from their horizontal course in a vertical direction and join with another marginal osteophyte from an adjacent vertebral body to form a bridge. These larger bridging marginal osteophytes are often posttraumatic but may be seen in combination with other types of phytes that are more diagnostic of the underlying disease entity.

Nonmarginal osteophyte

A nonmarginal osteophyte is a horizontal extension or osteophyte of the vertebral body observed 2 to 3 mm away from the actual vertebral end-plate ( Fig. 8-5 ). Again, a nonmarginal osteophyte appears to be an integral part of the vertebral body, with its medullary canal and cortex connecting with that of the vertebral body. Small ones are associated with degenerative disc disease and spondylosis deformans. These are called traction osteophytes and are believed to indicate an element of instability in the spine. Like the marginal osteophyte, the nonmarginal osteophyte may also turn vertically and join a similar nonmarginal or marginal osteophyte from an adjacent vertebral body ( Fig. 8-6 ). These larger nonmarginal osteophytes (sometimes called nonmarginal syndesmophytes) are seen in psoriatic arthritis and reactive arthritis.