Thoracolumbar Spinal Deformity in Achondroplasia

Sanjay N. Misra, MD, Howard W. Morgan, MD

Disclosures

Neurosurg Focus. 2003;14(1) 

In This Article

Abstract and Introduction

Abstract

The authors review the management of thoracolumbar kyphotic deformity in cases of achondroplasia. The presence of angular thoracolumbar kyphosis in achondroplasia is well recognized. In children this is initially a nonfixed deformity that persists, however, in more than 10% of individuals and becomes a fixed thoracolumbar kyphotic deformity. Additionally, with the coexistent spinal canal stenosis, neurological damage can occur and manifest as spinal cord or cauda equina compression. The nature of this condition, the natural history, and management options are discussed. Anatomical and biomechanical factors relevant to the condition are specifically highlighted. Avoidance of pitfalls in the management of these patients is discussed for both pediatric and adult patients.

Introduction

One of the chondrodysplasias, achondroplasia has an autosomal-dominant pattern of inheritance. The majority of cases arise as spontaneous genetic mutations. Point mutation on the long arm of chromosome 4 has been identified in this population. This is a dysplasia with predominantly metaphyseal involvement. At a cellular level there is an abnormality in the chondrocytes in the growth plate, and the process of their maturation and a defect in the Type 3 FGF receptor has been demonstrated.[4,5,16,21] It is known that unlike Types 1 and 2 FGF, which are expressed early in the fetal period on the periosteum and perichondrium, Type 3 FGF is found later in fetal development and occurs on maturing chondrocytes.[5] This metabolic abnormality affects both limb growth (with the consequent rhizomelia) and intracartilaginous spine formation (with the associated spine abnormalities).[12,13,15]

As a result of this dysplasia the individual has a characteristic appearance. In infants the face is normal with a somewhat low nasal bridge accompanied by a frontal prominence of the cranial vault. As the infant grows, the abnormality in the biological growth of the skeletal system becomes more obvious. Short stature accompanied by shortened limbs is notable. Characteristically, the shortening is not uniform, the arms are shorter than the forearms and the thighs are shorter than the legs. With walking and maturation there is development of thoracolumbar kyphosis with compensatory lumbar hyperlordosis, pelvic tilt, and subsequent fixed flexion deformity of the hip joints.[15]

Thoracolumbar deformity in patients with achondroplasia is a recognized problem.[2,3,6,7,8,9,10,11,12,13,14,15,17,18,20] The deformity first occurs in infancy when the child begins sitting, and the condition follows a predictable course over time until the child is walking.[7,9,13,14,20] Management strategies for this thoracolumbar deformity must address two issues. Deformity-related neurological and structural deterioration both need to be prevented and, if already present, corrected. An understanding of the anatomy and natural history of the sagittal balance in these patients will help the surgeon avoid the pitfalls of later skeletal and neurological compromise. In this paper the authors address this management strategy in patients with achondroplasia in cases of reversible thoracolumbar kyphosis and those of a fixed kyphosis.

The overall prevalence of thoracolumbar kyphosis is estimated to be 94% in children younger than 1 year of age. The incidence decreases in older children to 11% by the age of 10 years. Subsequently the prevalence is greater than 30% in patients greater than 30 years of age.[9]

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