Limb Length Discrepancy

Definition

A limb length discrepancy is a difference in the lengths of the limbs (one arm or leg is shorter than the other arm or leg). This material will focus on leg length differences.  

Causes

A limb length discrepancy may be present at birth or acquired during childhood. Each bone has growth areas called growth plates where the bone becomes longer. One leg may grow slower than the other leg if the growth plate is disturbed or injured. Some potential causes for developing a leg length discrepancy in childhood are:

• Trauma to the growth plates
• Infection
• Paralysis
• Some bone disorders

Diagnosis

The doctor can estimate the overall limb length discrepancy by placing blocks of different sizes under the short leg until the hips are leveled. 

A special x-ray may be performed to measure the lengths of the bones and determine the difference of each bone. Based on specific calculations, the orthopaedic surgeon can predict the difference between the lengths of the legs when the child has completed growth.  

Treatment

The need to treat a limb length discrepancy depends on the amount of difference between the legs expected when the child finishes growing. The specific treatment is determined by the amount of difference and remaining growth of the child. Not everyone with a limb length discrepancy requires treatment. Treatment is often recommended when the difference nears 4 cm in order to improve walking. Sometimes more than one treatment is necessary during the course of a child’s growth to completely treat the leg length difference. Some general guidelines for treatment based on the expected differences in the lengths of the legs are:

The nonsurgical and surgical options should be discussed with your orthopaedic surgeon to determine the best treatment approach for your child. Each procedure carries certain risks and benefits.

Lengthening

A surgical procedure can be performed to gradually lengthen bones. The bone is surgically split into two segments and slowly pulled apart to lengthen the leg as the body rebuilds the bone. Traditionally an external fixator (metal bar or ring) supports the bone and gradually distracts the two ends to lengthen the bone. Alternatively, newer internal devices may be an option to support the bone for lengthening. This process may take months.