summary Metaphyseal Chondrodysplasia is a heterogeneous group of congenital disorders caused by variety of mutations leading to metaphyseal changes of the tubular bones with normal epiphyses. Patients present with short-limb dwarfism characterized by genu varum, coxa vara, and spinal abnormalities. Diagnosis is made based on family history associated with typical radiographic and clinical features. No commercially available diagnostic test exists due to the variety of genetic mutations. Treatment involves a multidisciplinary approach to improve and maintain function. Surgical spinal fusion is indicated in patients with atlantoaxial instability. Epidemiology Incidence skeletal dysplasias occur at a rate of 2 to 3 newborns per 10,000 births Etiology Pathophysiology metaphyseal dysplasia involving the proliferative and hypertrophic zone of the physis (epiphysis is normal) Genetics three main subtypes Jansen (rare, most severe form) autosomal dominant genetic defect in parathryoid hormone-related peptide (PTHrP) Schmid (more common, less severe form) autosomal dominant genetic defect in type X collagen McKusick autosomal recessive most commonly occurs in Amish and Finnish populations cartilage-hair dysplasia (hypoplasia of cartilage and small diameter of hair) Associated conditions birth defects can be mimicked by teratogenic rickets Schmid type often confused for rickets Classification Table of Metaphyseal Chondrodysplasias Type Genetics Characteristics Comments Jansen's Autosomal dominant Defect in parathyroid hormone related peptide (PTHRP) receptor Mental retardation Short limbed dwarfism Wide eyes Monkey like stance Ostebulbous metaphyseal expansion of long bones seen on xray Schmid's Autosomal dominant Defect in Type X collagen Short limbed dwarfism Excessive lumbar lordosis Severe thigh and leg bowing, genu varum Wrist swelling, elbow contractures Trendelenburg gait Diagnosed when patient older due to coxa vara and genu varum Often confused with Ricketts McKusicks Autosomal recessive Cartilage hair dysplasia (hair had small diameter) Atlantoaxial instability Ankle deformity due to fibular overgrowth Immunologic deficiency and increased risk for malignancy Seen in Amish population and in Finland Presentation Jansen type mental retardation markedly-short limbed dwarfism with: wide eyes monkey-like stance hypercalcemia Schmid type often not diagnosed until older age due to marked coxa vara and genu varum short-limbed dwarf involving: Trendelenburg gait predominate proximal femur involvement increased lumbar lordosis normal laboratory results McKusick type common associated with atlantoaxial instability secondary to odontoid hypoplasia ankle deformity due to fibular overgrowth associated with: abnormal immunocompetence increased risk for malignancies intenstinal malabsorption megacolon Imaging Radiographs Jansen type AP pelvis, hip, knee, and upper extremity radiographs reveals bulbous expansion of metaphysis Schmid type AP pelvis and hip radiographs rule out coxa vara standing lower extremity films rule out genu varum McKusick type cervical AP, lateral, flexion and extension views rule out atlantoaxial instability ankle AP, oblique and lateral views surveillance of potential distal fibular overgrowth Metaphyseal dysplasia involving the proliferative and hypertrophic zone of the physis (epiphysis is normal) Treatment Operative posterior atlantoaxial fusion indications atlantoaxial instability measuring 8 mm or more myelopathy techniques posterior instrumentation valgus intertrochanteric osteotomy indications coxa vara angle <100 degrees progressive coxa vara symptomatic hip arthritis techniques valgus + extension osteotomy may help to decrease an associated hip flexion deformity reconstructive measures may be indicated in patients with subluxation, hinge abduction, or osteoarthritis. open reduction and fixation of proximal femur and acetabulum to treat hip dislocations. tibial osteotomies or hemiepiphysiodeses indications symptoms are severe nonoperative modalities have failed limb lengthening through a metaphyseal corticotomy indications controversial due to high rate of complications