Altered vertebral shape typically results from congenital conditions. Although a vertebra’s appearance may be altered in a myriad of ways, the following table includes some of the more commonly encountered alterations. Vertebral collapse and vertebral expansion are larger topics and therefore are discussed separately in this chapter.

The normal measurement of the atlantodental interval (ADI) is less than or equal to 5 mm in children and 3 mm in adults. A measurement beyond these limits suggests instability of the atlantoaxial articulation. Instability results from compromise of the transverse atlantal ligament or C2 odontoid process. Because the joint is most stressed during flexion, forward flexion radiographs provide a more specific measure of ADI enlargement than neutral lateral radiographs. If the anterior tubercle or odontoid process does not represent fixed, clearly defined points of mensuration, atlantoaxial instability can be assessed by choosing another point on the atlas and axis, such as the distance between the posterior surface of the odontoid and the anterior surface of the posterior tubercle of the atlas (this space is known as the posterior atlantodental interval or PADI).

DISEASE	COMMENTS
Congenital conditions	Occipitalization of atlas, Down syndrome (20% of cases), Morquio’s syndrome, and spondyloepiphyseal dysplasia; these are associated with atlantoaxial subluxation secondary to absence or attenuation of the transverse atlantal ligament, occurring as an isolated anomaly or in association with other defects.
Inflammatory spondyloarthropathy(FIG. 17-22)	Condition that includes rheumatoid (adult and juvenile types) arthritis, ankylosing spondylitis, psoriatic arthritis, Reiter’s syndrome, and systemic lupus erythematosus; these are associated with synovitis, ligament attenuation, and odontoid erosions, which may lead to instability of the atlantoaxial articulation; rheumatoid arthritis is the most common inflammatory arthropathy to involve the atlantodental joint.
Marfan’s syndrome [p. 441]	Genetic disorder of connective development that leads to ocular, cardiovascular, and musculoskeletal abnormalities; joint instability follows ligamentous laxity.
Odontoid anomalies [p. 309]	Aplasia, hypoplasia, or malunion of the odontoid process may lead to instability.
Regional infections	Include retropharyngeal abscesses, otitis media, mastoiditis, cervical adenitis, parotitis, and alveolar abscesses.
Trauma	Instability resulting from fracture or torn ligaments.

FIG. 17-22 A through C, Three patients, each with rheumatoid arthritis and an increased atlantodental space (arrows).

Most bony outgrowths of the spine represent osteophytes, related to degenerative arthropathy of the intervertebral disc spaces or posterior joints. An appearance of multilevel, flowing, thick, mostly anterior paravertebral outgrowths is characteristic of diffuse idiopathic skeletal hyperostosis (DISH). Large, coarse, incompletely bridging paravertebral outgrowths are associated with Reiter’s syndrome and psoriatic arthropathy. In contrast delicate, thin, completely bridging outgrowths (marginal syndesmophytes) are characteristic of ankylosing spondylitis. As the terms are generally used, osteophytes denote a degenerative etiology and syndesmophytes an inflammatory etiology. Because the condition is classified as idiopathic, the bony outgrowths of DISH are neither osteophytes nor syndesmophytes; rather, exostasis or another generic term is used to describe the changes.

DISEASE	COMMENTS
More common
Ankylosing spondylitis(FIG. 17-23) [p. 492]	Seronegative spondyloarthropathy characterized by arthritis targeted to the sacroiliac joints and spine; bilateral, symmetric, thin intervertebral connections, known as syndesmophytes, are prominent features, representing ossification of the outermost lamellae of the annulus fibrosis; posterior joint fusion is common; collectively, multiple levels produce a “bamboo spine” appearance; in addition, the anterior body margins appear straight or square.
Diffuse idiopathic skeletal hyperostosis(FIG. 17-24) [p. 583]	Idiopathic disease marked by thick, flowing anterior longitudinal ligament ossifications along the anterior and lateral body margins; diffuse idiopathic skeletal hyperostosis (DISH) is most common in the thoracolumbar region.
Reiter’s syndrome and psoriatic arthropathy(FIGS. 17-25and17-26) [p. 510] Spondylosis deformans (degenerative disc disease)(FIG. 17-27) [p. 578]	Inflammatory arthropathies associated with paravertebral ossifications incompletely bridging the intervertebral disc spaces; usual to the thoracolumbar spine; the paravertebral ossifications are typically thick, but uncommonly may appear thin; the latter appearance is identical to those of ankylosing spondylitis. as curved (“claw”) or horizontal (“traction”) vertebral osteophytes, with or without other findings of degenerative disc disease (e.g., endplate osteosclerosis and irregularity, narrowed disc space, misalignment). Osteophytes form in response to increased tension at the Sharpey’s fibers, anchoring the outer annulus into the cortical bone of the adjacent endplate. Degenerative osteophytes are moderately thick (thicker than ankylosing spondylitis, thinner than DISH) and typically incompletely bridge the intervertebral disc space.
Less common
Acromegaly [p. 907]	Excess levels of growth hormone resulting from a pituitary eosinophilic adenoma overproducing somatotropin; the disorder is marked by progressive enlargement of the hands, feet, head, jaw, and abdominal organs. Vertebrae are enlarged with posterior scalloping and new bone growth along the anterior body margins.
Fluorosis	Chronic fluoride intoxication associated with osteophytosis and vertebral hyperostosis with calcification of the paraspinal ligaments; vertebrae have increased radiodensity; fluorosis is most marked in the innominates and lumbar spine.
Hypoparathyroidism [p. 913]	Inadequate parathormone from undersecretion or surgical removal of the gland; skeletal changes include increased or decreased radiodensity, thickened calvarium, premature fusion of ossification centers, and ossification of the paraspinal ligaments.
Neuropathic spine [p. 584]	Primarily caused by diabetes mellitus, syringomyelia, and tabes dorsalis; the radiographic appearance is marked by loss of intervertebral disc height, increased bone radiodensity, misalignment, fragmentation, and prominent osteophytosis.
Ochronosis	Inherited disorder of excessive homogentisic acid production and subsequent accumulation within connective tissues; the spine is affected by multiple levels of intervertebral disc calcification and massive osteophytosis and ankylosis, especially in the elderly.
Trauma	May cause bony outgrowths from degenerative joint changes or dystrophic tissue calcifications.

FIG. 17-23 A through D, Thin, bridging syndesmophytes characteristic of ankylosing spondylitis in four patients (arrows).

FIG. 17-24 Diffuse idiopathic skeletal hyperostosis affecting, A, the cervical and, B, lumbar spines of different patients.

FIG. 17-25 Reiter’s disease with prominent syndesmophytes at multiple lumbar levels (arrows).

FIG. 17-26 Psoriatic spondyloarthropathy with characteristic thick syndesmophytes incompletely bridging the disc space (arrow).

FIG. 17-27 Degenerative osteophytes projecting from the anterior vertebral body margins (arrows).