Leg length discrepancy is an orthopedic condition that can appear in childhood or as a result of an injury or illness that causes damage to the growth plate, in which two limbs are of unequal lengths. Most people have some degree of limb length discrepancy, but larger differences can affect well-being and quality of life by keeping you from participating in the activities you like.
Common Causes of Limb Length Discrepancy
Some children are born with arms or legs of unequal lengths. At first, the difference can be small but may increase over time to be more significant later in life. An illness or injury that causes damage to the growth plate can also lead to the development of a limb length discrepancy, or short leg syndrome, later in life.
While differences in arm lengths often require no treatment, a leg length discrepancy (LLD) (anisomelia) can cause a noticeable limp, or make it difficult for a child to run or play. When the difference measures more than 1.5 to 2.0cm (5/8 in.) in length, most physicians would recommend having it evaluated. Depending on your overall height, this amount of leg length discrepancy may need to be treated.
When you or someone you know has limb length discrepancy, understanding the cause is the first step toward finding the right solution.
Congenital Limb Length Discrepancy
Some people develop limb length discrepancy in childhood, but it’s possible to be born with some degree of inequality. The limb length difference can either remain the same during growth (called static limb length discrepancy), or the difference can worsen as the child grows (called dynamic limb length discrepancy).
Congenital disorders (conditions existing at or before birth) may cause growth abnormalities that contribute to limb length discrepancy. Generally, it’s more common for congenital disorders to stall limb growth, but some rare conditions may cause accelerated growth as well.
Hemihypertrophy and hemiatrophy are congenital disorders that cause growth disparity between the two sides of the body – making one leg longer than the other. Hemihypertrophy causes one half of the body to grow faster than the other, whereas hemiatrophy refers to a condition in which one half of the body is shorter than the other. Patients with these conditions generally have a milder degree of shortening than those with other congenital disorders.
Other congenital disorders that cause limb length discrepancy include:
- Fibular hemimelia – congenital shortening or absence of the calf bone (fibula)
- Tibial hemimelia – congenital shortening or absence of the shin bone (tibia)
- Proximal femoral focal deficiency – congenital defects in the hip or thigh bone (femur), leading to a shorter leg
- Femoral hemimelia – congenital shortening or absence of the thigh bone
- Coxa vara – congenital or development deformity of the hip that leads to a shorter leg
- Posteromedial bowing of the tibia – congenital bowing of the shin bones
- Developmental dysplasia of the hip – congenital condition in which the hip joint doesn’t develop normally
Cases of congenital limb length discrepancy are often challenging. Not only may there be a greater inequality in limb length, but it also increases proportionally as children continue to grow. Before committing to a treatment plan, it’s important to find a surgeon who specializes in limb length discrepancy, and who has significant experience with lengthening of developmental and post-traumatic limb length discrepancy.
Developmental Limb Length Discrepancy
During childhood, certain illnesses or injuries can slow or damage growth plates, causing developmental limb length discrepancy.
In adolescence, growth plates close and are replaced by solid bone, but until then, they are one of the weakest areas of the growing skeleton and vulnerable to injury.
With growth plate injuries, such as a fracture, limb length discrepancy develops over time because the damaged growth plate cannot match the development of the corresponding growth plate in the opposite leg. This type of injury may not be noticed at first, but it will show over the years as the limbs grow at different rates.
Diseases of the bone, such as osteomyelitis, can also injure the growth plate. In this case, bacteria or viruses in a child’s bloodstream or tissue can infect a bone, causing osteomyelitis. Generally, this type of bone infection is found in premature infants and babies born with complications, and infection is most common in the long bones of the body.
Other conditions that may cause stalled limb growth or limb length discrepancy include Ollier’s disease, neurofibromatosis, multiple hereditary exostoses, polio, infection, radiation, cerebral palsy, spina bifida, and clubfoot, as well as other bone diseases and lower extremity deformities.
Post-traumatic Limb Length Discrepancy
A broken leg bone can lead to a limb length discrepancy if it heals in a shortened position or fails to heal properly at all. Malunion refers to a limb length discrepancy that remains after a fracture heals in the shortened position. Generally, these cases occur in adult patients, especially when the bone has sustained multiple fractures (i.e., it is broken in many pieces) or heals in an overlapped position.
In childhood, an injury that damages the growth plate can slow the growth of one bone while the corresponding bone on the other leg grows normally. These types of injuries can also lead to overgrowth of the bone during the healing process.
In the case of overgrowth, a broken bone may grow faster than the corresponding bone of the other leg for several years after healing, causing it to become longer than the bone on the opposite side. This is especially common in young children with thigh bone fractures.
When a broken bone fails to heal, it is called a nonunion. A nonunion can cause limb length discrepancy if you cannot produce the necessary bone tissue to heal the broken bone, and it happens when the bone lacks adequate stability, blood flow, or both. Stability helps the fracture heals in the proper position to avoid growth plate injury or overgrowth, and blood delivers the oxygen, healing cells, and other components necessary for healing.
High-energy injuries, such as those resulting from a car accident, can increase the likelihood of nonunion because the blood supply to the broken bone is restricted. Additionally, nonunions are more likely in areas of the body with limited blood supply, such as the upper thigh bone, shin bone, or toe bones.
Tumor-related Limb Length Discrepancy
When cells divide abnormally and uncontrollably, they can form a mass or lump of tissue, called a tumor. Bone tumors form in your bones, and as the tumors grow, abnormal tissue can displace healthy tissue.
Both bone tumors and the treatments designed to eradicate them can affect bone growth. Different types of tumors can grow into bone and soft tissues, producing pain, limping, and limb length discrepancy, including:
- Osteochondroma – As the most common type of benign bone tumors, osteochondromas develop in adolescents and teenagers. Often, they form near the actively growing ends of long bones, such as the arm or leg bones, which can damage the growth plates.
- Osteosarcoma – As the second most common type of bone tumors, osteosarcomas usually develop in the hip, shoulder, or knee. This type of tumor grows rapidly and tends to spread to growth plates of the thighbone and lower leg bone.
- Fibrous dysplasia – As a gene mutation that makes bones fibrous and vulnerable to fracture, fibrous dysplasia in the femur can cause pain, limping, bowing, and limb length discrepancy.
- Wilms’ tumor – In children, a Wilms’ tumor is a tumor of the kidney, which can cause hypertrophy of the lower limb on the same side – making one leg shorter than the other.
- Enchondroma – As cartilage cysts that grow inside the bone marrow, enchondromas are often associated with Ollier’s disease. Endochondromas of the arm and thigh can create a limb length discrepancy.
Some children are born with arms or legs of different lengths. Others may develop a limb length discrepancy later in life. When you or someone you know has a limb length discrepancy, understanding why is the first step toward finding the right solution.
Limb length discrepancy has many causes, which can be divided into four main groups:
- Congenital – With congenital cases, a limb length discrepancy is apparent at birth. Generally, the length of the discrepancy is greater, and it increases progressively over time.
- Developmental – Caused by childhood illness or a growth plate injury, developmental cases result in a discrepancy that appears over time, as the injury or illness slows the growth of one leg.
- Post-traumatic – Fractures and other traumatic injuries to the bone may heal incorrectly, causing one leg to be shorter than the other; however, in some cases, these injuries can also speed up the growth of the injured leg.
- Bone tumors – Both bone tumors and the treatments designed to eradicate them can affect bone growth. This is especially true if the illness happens in infancy.
In some cases, the cause of limb length discrepancy is “idiopathic,” or unknown. While the exact cause of the condition may not be known, a healthcare professional who specializes in limb length discrepancy can still work with you or your loved one to decide what treatment, if any, is best for your situation.