Leg Length Discrepancy (LLD)

Causes

LLD can be caused by congenital, developmental, or acquired conditions.

There are many congenital causes of LLD. This type of LLD is challenging to treat, not only due to the very young age of patients, but also because often there is a bigger discrepancy in leg length than with other causes, and this discrepancy increases as the child grows. It is important to have the help of a specialized surgical team, one that has experience with these cases.^1, 2-7 Below you can find the most common congenital causes of LLD and a short description of each:

• Hemimelia: there is a shortening or complete absence of a bone. Hemimelia is further distinguished depending on the bone that is affected: in fibular hemimelia there is a shortening or absence of the fibula (also known as the calf bone), in tibial hemimelia it is the tibia (shin bone) that is shortened or absent, and in femoral hemimelia, the femur is affected.
• Proximal femoral focal deficiency (PFFD): this is an uncommon condition in which the upper part of the femur (thigh bone) is absent or shortened. The hip socket may also be absent or not properly developed. Patients with PFFD often present with other conditions, such as fibular hemimelia.
• Congenital coxa vara: the angle between the top part of the femur and the rest of the bone is smaller than it should be. This results in poor biomechanics, with patients presenting with a limp, LLD, and being unable to move the thigh out to the side.
• Posteromedial tibial bowing: this condition usually involves the middle and lower part of the tibia, making the foot bend towards the shin to the point it almost touches it. Although the foot straightens as the child grows, some problems remain, including angular deformity (bent bone) and LLD.
• Hip dysplasia: when the ball-shaped head of the femur does not fit securely in the cup-shaped hip socket, there is a tendency for the hip to dislocate. If not treated early, hip dysplasia can cause other problems, such as hip arthritis, mobility problems, and LLD.
• Hemihypertrophy/hemiatrophy: in hemihypertrophy (also called hemihyperplasia or overgrowth syndrome), one half of the body develops faster than the other, causing one side to become bigger than the other. With hemiatrophy, one side of the body also becomes bigger than the other, but because the affected side develops more slowly than the other.
• Neurofibromatosis: this genetic condition can affect the brain, nerves, skin, and bones. It can cause bowing and thinning of the tibia, making it more likely to break. Bone healing problems and LLD are also common in patients with neurofibromatosis.

Developmental LLD is caused by conditions that are not present at birth, but that develop during childhood and/or adolescence. Bones grow only in a specific place, the physis (also known as the growth plate). Conditions or interventions that affect this growing part of the bone, such as infections, trauma or surgery, can cause LLD. The LLD may be subtle at first but will become more noticeable as the child/adolescent grows, especially because of the development of abnormal walking patterns.^2-7

Below are some of the reasons for developmental LLD:

• Fractures: if the fracture damages the growth plate in a leg bone, that bone will grow more slowly or stop growing altogether, while the non-affected leg will continue to grow as normal, causing an LLD. Sometimes, the opposite happens, and the bone that was broken grows faster than it should, making one leg longer than the other (this is more common with femur fractures).
• Bone infections: caused by viruses or bacteria, if an infection reaches the bone (osteomyelitis), it can also damage the growth plate and cause an LLD.
• Ollier’s disease: patients with this rare, non-hereditary disease have non-cancerous tumors made of cartilage forming inside their bones. The tumors grow close to the growth plates, affecting the bone’s growth and causing the bone to bow and shorten.
• Multiple hereditary exostoses: in this case, patients also have non-cancerous tumors growing inside their bones, but they are made of bone and grow outward from the growth pates. These bone tumors are called exostoses, and although they do not cause pain themselves, they can cause nerve compression and local trauma. Patients often have short stature, LLD, and joints that are bent either inwards (knees) or outwards (ankles).
• Other causes: any that affects the growth plates, such as radiation or chemotherapy, and diseases affecting the legs and/or the bones in general.

Symptoms

While the child is still growing, it is common for the difference in length of the two limbs to increase and become more noticeable over time. However, LLD is often asymptomatic, as the growing child adapts and may tiptoe on the short leg, or bend the long leg to compensate. Sometimes patients may complain of pain or fatigue in the back, hip or knee area due to the imbalance in muscle forces. There may be a bend in the spine (scoliosis) as the body tries to correct for the leg length difference. ⁵

Diagnosis

Assessment of LLD requires a reliable clinical evaluation and accurate imaging including X-rays. Sometimes more specialized scans or opinions are required to diagnose the underlying cause and decide on the best treatment. ⁸

Treatment Options

The choice of nonsurgical or surgical treatment depends on many factors, including the amount of discrepancy (the current and the expected difference once the child has fully grown) and if the patient is having problems.

A shoe raise should be worn to prevent secondary problems from the LLD, and may be the only treatment required if the LLD is not too prominent. However, it can be difficult to tolerate a big shoe raise, which would be required for larger discrepancies. If the expected difference is more than 2 cm, a surgical procedure to slow down the growth of the longer leg may be considered. This may involve a temporary surgical plate over the growing part of the bone, or permanent fusion of the growth plate.

If the final discrepancy is expected to be more than 5 cm, the option to lengthen the shorter leg may be discussed. This involves a big operation to break the shorter bone (osteotomy) and attach an external or implant an internal device to slowly grow the bone. ⁹ Children and adolescents can continue to go to school and socialize during this treatment; however, they will need multiple hospital appointments for physiotherapy.

The orthopedic surgeon will discuss these options with the family and consider the patient’s overall status. There can be some flexibility in the timing of the surgery to suit schooling and family life. ¹⁰

Complications

In time, untreated LLD may lead to painful arthritis of the leg joints and spine.

If children are treated at the right time, they may recover full and normal function. If they have surgery, the risks are greatest if they choose to have the shorter leg lengthened. Complications after surgery include an angular deformity of the leg, infections, fracture, problems with the bone failing to heal, or not healing in the intended position, joint subluxation and dislocation or failure of the bone to grow.

Since it is difficult to predict how much the child will continue to grow, there is no guarantee that having surgery will result in legs of equal length in adulthood. ¹¹