Pseudoachondroplasia is characterized by short-limbed dwarfism in which both the epiphysis and metaphysis are involved.
Affected individuals have significantly short stature, loose ligaments, and a predisposition to premature osteoarthritis.
Pseudoachondroplasia is usually transmitted as an autosomal dominant trait.
There has been a genetic linkage of pseudoachondroplasia to the pericentromeric region of chromosome 19.
This region encodes for cartilage oligomeric matrix protein (COMP), which is a large extracellular matrix protein expressed in cartilage, ligament, and tendon tissue.
The appearance of newborns with pseudoachondroplasia is normal, and the dysplasia is not clinically apparent until 1 to 3 years of age.
Pseudoachondroplasia will have rhizomelic shortening, and the skull and facies are normal. The fingers and toes are short and thick.
They may have mild thoracolumbar kyphosis and scoliosis develops in a few patients. Lumbar lordosis usually is pronounced.
Lower limb angular deformities are common. Genu valgum or varum may occur, some might develop windswept deformity.
Pes planus is common.
Spinal radiographs reveal mild platyspondyly, with anterior tongue-like projections and irregular end-plates. The interpedicular distance in the lumbar spine is normal in pseudoachondroplasia.
Cervical spinal radiographs may reveal odontoid hypoplasia. Atlantoaxial instability may be evident in flexion-extension lateral cervical spine radiographs.
The long bones are short and broad, with flaring of the metaphyses. Ossification of epiphyses is delayed.
There are fragmented ossific nuclei of the femoral heads, with normal sciatic notches, shallow acetabulum, and wide triradiate cartilage and ischiopubic junction.
Mutation screening for abnormalities in the COMP gene is available for diagnostic purposes.
Lower extremity malalignment – Requires corrective osteotomies (Recurrence of deformity with growth is common)
Hip – Surgical treatment is difficult owing to the incongruity of the femoral head with the acetabulum.
Thoracolumbar kyphosis and lumbar lordosis – Thoracolumbar kyphosis is rarely problematic. Lumbar hyperlordosis with hip flexion deformity is treated with proximal femoral extension osteotomy.
CervicalAtlantoaxial instability – Needs Atlantoaxial posterior fusion with immobilization in a halo brace.
Scoliosis – Posterior fusion.