Legg-Calve-Perthes disease, also known as Legg-Perthes or Perthes disease, is an idiopathic, self-limiting condition involving avascular necrosis of the femoral head (Fig. 5) . It typically presents in the first decade of life, and for unknown reasons predominates among males aged 4 to 8 years, with a gender ratio of 5:15 . In the past 95 years, since it was first described by Legg, Calve, and Perthes, we have gained little insight into the etiology and pathophysiology of this complex condition.
Pathogenesis appears complex, and involves avascular necrosis, followed by resorption, collapse, and subsequent repair of the capital femoral epiphysis, resulting in impaired growth and development of the hip joint. The natural history of the disease is variable, and is largely dependant on the age of onset and the degree of femoral head involvement, but is also greatly influenced by intervention . The younger a child is at the onset of the disease, the greater the time he has for subsequent growth and remodeling . Moreover, in the long term, 50% of those who had childhood Perthes disease who did not receive treatment developed subsequent osteoarthritis in the fifth decade of life .
Femoral head biopsies from patients who had the disease have demonstrated lesions with varying degrees of necrosis and repair, indicating that repetitive injury to the circumflex arteries rather than a single traumatic event may be responsible for the pathological findings in Perthes disease . Several hypotheses have been formulated to explain this hypovascularity. Two thrombophilic risk factors, factor-V Leiden mutation and anticardiolipin antibodies, which enhance intravascular clotting and increase blood viscosity, are significantly associated with the disease . Also postulated is intermittent increases in intra-
Fig. 5. Frog pelvis radiograph demonstrating left hip Perthes disease.
capsular hip pressure, causing a tamponade effect and subsequent compression of the retinacular vessels as they course through the restricted intracapsular space . Unfortunately, the literature remains conflicting, and there is a lack of evidence to support either of these hypotheses at present .
Perthes disease is specific to the hip joint, and typically presents as an insidious, unilateral, painless limp . If pain is present, it is usually mild, is exacerbated by exercise, and is frequently referred to the knee. The most consistent examination findings include reduced internal rotation and abduction of the hip, and these are important prognostic indicators. In the early stages of the disease, this is attributable to muscle spasm and synovitis, whereas later on in the disease, bony impingement of the femoral head on the acetabulum results in restricted hip motion. The prevalence of bilateral cases reported in the literature ranges from 8% to 24%, and interestingly they are more common in girls . Development and outcome of the disease in each hip appears to be an independent event, with endocrinological etiologies such as hypoparathyroidism or skeletal dysplasias playing a role .
A large number of radiological classification systems have been developed that attempt to stratify patients according to the severity of their disease, predict prognosis, and provide parameters for instituting treatment . The two most commonly used classification systems include the Catterall classification, which defines four groups based on the involvement of the epiphysis (25%, 50%, 75%, or 100% involvement), and the Herring classification, which defines three groups according to the degree of collapse in the lateral epiphyseal pillar during the fragmentation stage. The Herring classification system is a more accurate predictor of long-term outcome.
The treatment of Perthes Disease remains highly controversial regarding conservative versus surgical intervention . The primary goals of intervention include maintenance of hip motion, pain relief, and containment. At present there is a lack of conclusive data in the literature regarding the indications for and the benefits of specific treatment modalities, and as a result surgical intervention largely reflects the physician's personal preference. For patients who have severe disease, surgical intervention appears preferable to nonoperative treatment, because it improves the sphericity of the femoral head and provides greater acetabular coverage . The two most common surgical methods for containment include the femoral varus osteotomy and the Salter innominate osteotomy.
Herring and colleagues, who devised the Herring lateral pillar classification system, conducted one of the largest studies on the topic to date, and concluded that patients over the age of 8 years at the time of onset that have a Herring classification of B or B/C border have a better outcome with surgical treatment (femoral osteotomy or innominate osteotomy) than they do with nonoperative treatment (brace treatment or range of motion exercises) . Children that fit into group B and were less than 8 years old at the time of onset were shown to have favorable outcomes irrespective of treatment, whereas group C children of all ages frequently had poor outcomes regardless of treatment modality .
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