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Avascular Necrosis and Related Disorders

SPINE

In 1921, Scheuermann described a disorder that led to lower thoracic kyphosis and on the basis of irregularities involving the rims of the bodies, he concluded that the pathology occurred in the region of the growth areas between the vertebral bodies and the ring-like epiphyses. The predominant involvement of the epiphysis of the vertebral rim was initially interpreted as osteonecrosis, however, considerable disagreement as to the cause and pathogenesis of this disorder subsequently developed. There is also a discrepancy regarding the criteria necessary for the diagnosis of Scheuermann's disease (AKA: Idiopathic Adolescent Spondylodystrophy). Currently the criteria frequently requires the presence of abnormality is at least three contiguous vertebra, each with wedging the five degrees or more. The problem is that cases of Scheuermann's disease are exclude which do not have as prominent anterior wedging. Diagnostic criteria based on the presence of clinical findings are inadequate because many patients with this disorder are entirely asymptomatic.

Most affected persons are between the ages of 13 and 17 years and there is a slight predominance of male patients. Clinical manifestations are highly variable with some people presenting as totally asymptomatic and the radiographic change is discovered as an incidental finding. Clinical manifestations such as achy pain aggravated by physical exertion, fatigue, and tenderness to palpation are commonly encountered. A kyphotic deformity may often be associated with a mild scoliosis, predominately in a thoracic region although it can be observed in the thoracolumbar segments. Neurologic complaints are uncommon, however, there is an increased incidence of herniation of the thoracic intervertebral discs that could lead to neurological manifestations in some cases.

Radiographic abnormalities include irregularity of the vertebral endplates specifically with an undulating superior and inferior surface of affected vertebral bodies associated with Schmorl's nodes with surrounding sclerosis, a loss of intervertebral disc heights, particularly in the mid portion of the kyphotic curvature, and anterior wedging in the same region. Sometimes small osteophytes may be evident identical to the appearance of osteophytes in spondylosis deformans (degenerative disc disease). Radiographically, healing of these lesions can appear as ossification of the anterior portion of the intervertebral disc which, if occurring early, can accentuate the kyphotic deformity. Lateral spinal curvature is also present in Scheuermann's disease due to wedging of the vertebral bodies in the coronal plane or scoliosis in the region of the compensatory lordosis typically below the kyphotic portion. Scoliosis is typically more prevalent in girls.

The pathologic abnormalities in Scheuermann's disease do not reveal osteonecrosis. The importance of genetic factors is supported by reports of familial occurrence. It was suggested that cartilaginous node formation is fundamental to the disease process. When the cartilaginous endplates are congenitally weak it predisposed certain persons to intraosseous discal prolapse during periods of excessive physical stress or repetitive trauma.

A similar process in lumbar spine is so-called juvenile discogenic disease. Juvenile discogenic disease is a fairly common entity, but not much has been written about its features. Like Scheuermann's disease, there is pathology of the endplates that lead to morphologic changes in the osseous and soft tissue components of the spine. Juvenile discogenic disease is characterized by endplate irregularities, large Schmorl's nodes that lead to expansion of the vertebral bodies, primarily in the AP dimension and may be associated with lower L/S degenerative disc disease. There is a tendency for involvement of the upper lumbar region. As in Scheuermann's, there is a predilection for late adolescent boys with a history of repetitive trauma.

It is important to realize that because of the inherently weakened endplates, intervertebral disc herniations, advanced degenerative disc disease, and degenerative joint disease of the facets are common findings, making the central and/or nerve root canals vulnerable to narrowing.

The prognosis is relatively marginal for patients with juvenile discogenic disease due to the high propensity for multilevel disc herniations and advanced onset of severe degenerative disc disease, however, conservative management combined with avoidance of repetitive trauma are typically the best measures.

 
   
 

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