What is leg length discrepancy?
Leg length discrepancy (LLD) or lower limb discrepancy is a condition which causes the legs to differ in length. The condition can affect the thighbone (femur), or (shinbone) tibia, or both. Some people also have a length discrepancy in their arm on the same side too.
Common signs and symptoms of leg length discrepancy
A leg length discrepancy of up to 2cm can go unnoticed due to a lack of any obvious signs or symptoms. When the discrepancy is above 2cm, the condition becomes more obvious and a small limp may be present. Many people with a discrepancy of up to 2.5 cm will manage well with a lift inside their shoe and not pursue any further treatment.
Those affected by a discrepancy of over 3cm usually have quite a pronounced limp and will seek medical care. Walking with a shortened gait not only affects how a person looks when walking, it also takes extra energy from the person. It can also put more stress on the longer leg and this can result in functional scoliosis (curvature of the spine).
With extreme discrepancies, walking can become very difficult or even impossible.
Common causes of leg length discrepancy
Leg length discrepancy can be a congenital (present from birth) condition or acquired condition. Some of the congenital causes include:
- Fibular or tibial hemimelia (absence of the shinbone or thighbone)
- Congenital femoral deficiency (incomplete or abnormal development of the thighbone)
- Leg hypoplasia (underdevelopment or incomplete development of the leg)
Some of the acquired causes are:
- Severe trauma to the bone
- Bone infection
- Direct radiation
- Bone tumor
Diagnosing leg length discrepancy
Leg length discrepancy is usually noticed at first by parents due to the way the child is walking. To diagnose the condition, your doctor will conduct a thorough physical examination which involves observing how your child sits, walks and stands. Your doctor may also perform a gait analysis where they look at the way your child walks. Your child may compensate for a length discrepancy by adjusting the way they walk.
Treating leg length discrepancy
To decide on the most appropriate treatment for your child’s leg length discrepancy, it is important to work out early on what the final discrepancy will be when your child stops growing.
There are multiple ways your doctor can predict the final leg length discrepancy and the easiest method is to use a calculation based on the growth rate of the thighbone (10mm a year) or the shinbone (6mm a year) and the gender of your child. Girls are estimated to stop growing at age 14 and boys at 16. With this information, your doctor can make a good prediction about the remaining growth and the final leg length discrepancy.
As the calculation is based on averages, it is likely your doctor will also perform a special type of x-ray called a scanogram. This must be done on three separate occasions during a 12 month period. Doing so allows a more accurate estimate of the likely growth per year that your child will see. He may also do an X-ray of the left hand which helps to give an indication of your child’s bone age versus their actual age. These ages can sometimes differ but are usually reasonably close.
Another approach used to predict leg length discrepancy is a technique developed by a Dr Colin Moseley. The technique uses straight line graphs to plot growth and is now one of the most common approaches taken.
If the leg length discrepancy is predicted to be less than 2cm it is unlikely that treatment will be required. Between 2cm and 2.5cm, the discrepancy can be managed well with a lift in the shoe to compensate the difference. After 2.5cm, making adjustments to the shoe becomes a less practical option and surgery may be necessary.
There are different types of surgery that may be performed to correct a leg length discrepancy:
- Shortening the longer leg. This is usually an option after a person has stopped growing, and if the loss of height (around an inch) will not cause an issue for the person.
- Slowing or stopping the growth of the longer leg. As children get older, the growth in their legs takes place mostly in the growth plates of the lower thighbone and upper shinbone. A past practice was to staple these growth plates for a period to stop growth, but these days, a more reliable practice has been developed called Epiphyseodesis. It is the most common technique used and it is performed in the last 2-3 years of growth but only for discrepancies of less than 5cm. During this surgery, the doctor will make small cuts and drill into the growth plate to reduce it. Timing is crucial for the success of this type of surgery because it results in growth being permanently stopped.
- Leg lengthening. A less common approach is to lengthen the shorter leg by making a cut in the bone and fitting a device (called a llizarov or orthofix apparatus) that allows the leg to stretch and lengthen as it heals. This is a newer technique called callotasis and it has replaced a previous technique which required two surgeries to complete the treatment. It can be done at any age and can achieve corrections of more than 10cm. It is considered a complicated procedure with associated risks.
Where leg lengthening or shortening has been performed, rehabilitative physiotherapy will be recommended to aid recovery. Your doctor will also expect to see your child for regular follow ups after surgery, and will be able to advise when it is possible for your child to return to normal activities.
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