Leg length discrepancy: causes, symptoms and treatment in children and adults

Dorset HealthCare University NHS Foundation Trust describes leg length discrepancy (LLD) as the situation where the bones in each leg are different lengths or are misaligned. It stresses that a leg length difference is not uncommon, and in fact most people will have one leg that is slightly longer than the other. The American Academy of Orthopaedic Surgeons (AAOS) agrees, saying that more than half of people have a subtle difference in their leg lengths and that these mild variations usually do not cause problems.

Doctors distinguish a true (structural) difference, where the bones themselves are different lengths, from an apparent (functional) difference, where the legs are the same length but the pelvis is tilted or a joint is stiff, making one leg seem shorter. The AAOS notes that the bones most often involved in a true discrepancy are the thigh bone (femur) and the shin bone (tibia), which grow from growth plates near their ends.

The NHS trust says LLD can occur from birth, post-trauma or post-surgery or with some degenerative diseases. The AAOS, a US source, gives a fuller list for children, which is helpful for understanding why one bone can end up shorter than the other.

• Previous injury. A broken leg bone can lead to a discrepancy if it heals in a shortened position, particularly if broken in several places. A break through the growth plate can slow or stop growth, while a break that spares the growth plate can sometimes grow faster for a few years and end up longer.

• Bone infection in a growing child, especially in infancy.

• Bone diseases such as neurofibromatosis, multiple hereditary exostoses and Ollier disease.

• Neurological conditions and conditions that cause inflammation of the joints during growth, such as juvenile arthritis.

• Conditions present at birth, including underdevelopment of one of the bones between the knee and ankle, and rare conditions in which one side of the body is larger or smaller than the other.

• No known cause. The AAOS says that in some cases the cause is idiopathic, or unknown.

A slight difference may cause no symptoms at all. The AAOS says a significant difference can cause a noticeable limp and make it difficult for a child to run and play, and that a child may stand with one hip higher than the other, keep one knee bent or walk on tiptoe on the shorter leg. Because walking takes more effort, the child may tire easily. Parents are often the first to notice the way a child walks, and the AAOS says discrepancies are sometimes found at school screening for curvature of the spine.

The AAOS also says some studies suggest that people with leg length discrepancy are more likely to have low back pain and injury, while other studies do not support that finding. It is therefore reasonable to see a leg length difference as one possible contributor to symptoms rather than the automatic explanation for back, hip or knee pain.

See a GP if a child has a persistent limp, if a visible difference in leg length or in the height of the hips is getting more obvious, or if you have a leg length difference that is causing pain or affecting walking. A limp that comes on suddenly, or comes with pain, fever or a refusal to put weight on the leg, should be assessed promptly, so contact your GP or NHS 111.

The NHS trust says that the health professional responsible for care may recommend physiotherapy exercises, heel lifts, insoles or referral to another department, for example orthopaedics or orthotics, depending on the cause.

The AAOS describes a physical examination in which the doctor observes how the person sits, stands and moves, looks closely at gait, and measures the difference. In most cases the measurement is made standing barefoot with a series of measured wooden blocks placed under the short leg until the hips are level. Sometimes an X-ray is taken with the blocks in place to check whether the pelvis is truly level.

If a more precise measurement is needed, the AAOS says X-rays of the legs may be ordered, including a scanogram, which is a special X-ray using three images (hips, knees and ankles) and a ruler to measure the bones. CT is occasionally used in complex cases, although it involves a greater radiation dose. If a child is still growing, the AAOS says examination and imaging will likely be repeated every 6 to 12 months to see whether the discrepancy is increasing or staying the same.

The AAOS says treatment planning considers the size of the discrepancy, the child's age and how much growth remains, the cause if known, and any underlying neurological problem. The options below run from least to most invasive.

For many people, no treatment is needed and the difference is simply a feature of how they are built. Where a lift is advised, the NHS trust says the footwear should fit well, be comfortable and secure on the foot, fasten with laces, straps or a buckle, have a wide low heel and be in good repair, and that sandals, mules, sling backs and shoes with very flexible soles are best avoided.

If you notice a new leg length difference after an injury or an operation, mention it to the team looking after you.

On the NHS the route normally runs from a GP or physiotherapist to orthotics or orthopaedics, and heel lifts may be prescribed after measurement in millimetres. The NHS trust also notes that heel lifts can be bought over the counter. Private orthopaedic and podiatry services can offer assessment and orthotic provision, and the key question is the same on either route: how big is the difference, what is causing it, and what is the plan if it changes. Limb lengthening and growth modification operations are specialist procedures usually done in dedicated centres.