Hypoplasia


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Hypoplasia,
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incomplete formation or underdevelopment of a tissue or organ. In the musculoskeletal system, an entire bone or muscle or portions of these structures may fail to form in a normal fashion. Hypoplasia is particularly liable to involve the fibula, radius, ulna, and glenoid neck of the scapula.

Congenital absence or severe hypoplasia of the fibula can be combined with bowing of the ipsilateral tibia (Fig.1), equinovalgus deformity of the foot, absence of one or more of the lateral rays of the foot, tarsal aplasia or fusion, or shortening of the ipsilateral femur. Radial anomalies may be combined with hypoplasia or absence of the thumb or radial carpal bones, especially in association with VATER syndrome, cardiac abnormalities and thrombocytopenia with absent radius (TAR syndrome). The ulna may also be hypoplastic.

In proximal femoral focal deficiency partial absence and shortening of the proximal portion of the femur occurs. On radiographs a short femur that is displaced superiorly, posteriorly and laterally to the iliac crest is seen, with delayed ossification of the femoral capital epiphysis. Later changes include subtrochanteric varus deformity or pseudarthrosis, a dysplastic shaft and secondary abnormalities of the pelvis and acetabulum.

Hypoplasia of the glenoid neck of the scapula, also termed dentate glenoid anomaly, frequently leads to shoulder pain and limitation of motion. In some cases severe glenohumeral joint instability may also be seen. Dysplasia of the scapular neck, irregularity of the glenoid surface, a notched articular surface, hypoplasia and varus deformity of the humeral head and neck, and bowing of the acromion and the clavicle are additional findings. Osteoarthritis may develop prematurely at this site.


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The Encyclopaedia of Medical Imaging Volume III 1
Hypoplasia, Fig. 1
AP radiograph demonstrates hypoplasia of the fibula. At the ankle, note the mild valgus angulation and rounding of the talar dome owing to altered ankle biomechanics.