Limb length discrepancy (also known as anisomelia) is where one arm or leg is shorter than the other. Most commonly the lower limbs are affected more than the upper limbs, and can affect adults and children. Limb length discrepancy affecting the legs is also called leg length discrepancy or short-leg syndrome and will be the focus of this article.

Discrepancies between the legs of up to 2cm can be tolerated without additional equipment or support such as shoe inserts or heel raises. However, discrepancies above 2cm which are not augmented by a shoe/heel raise will become symptomatic usually causing lower back pain and gait (walking) abnormalities.

Leg length discrepancy is important as unequal length legs can cause an imbalance in posture and gait, which can lead to unnecessary stresses on the lower back and hips. Over time, this stress can lead to joint degeneration and bring on early onset osteoarthritis. Almost inevitably, patients with significant leg length discrepancies will experience back pain which progresses as they get older.

Leg length discrepancy can be caused by congenital conditions (ones which you are born with) or acquired conditions (ones which develop later in life).

Acquired conditions which can lead to leg length discrepancy include:

• Severe trauma to the legs - E.g. from a car accident, fall or other high impact injury.

• Bone infections (osteomyelitis) damaging the growth plate - From organisms such as Staphylococcus travelling through the bloodstream to infect the bone.

• Non-healing or non-union fractures
• Incorrectly healed fractures (malunion fracture)
• Bone tumours - E.g. Fibrous dysplasia, Neurofibromatosis, Ollier disease.

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As part of your hospital visit, you will undergo the following in order to diagnose a leg length discrepancy:

• Physical examination
• Medical history taking
• X-rays (long leg alignment film)
• ± Computed tomography (CT) scan

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Leg lengthening is a surgical operation which corrects a leg length discrepancy by stimulating new bone to grow in the shorter leg.

Bone has a remarkable ability to naturally regenerate after a fracture or after it is surgically cut. This ability is known as osteogenesis.  Leg lengthening surgery takes advantage of this capability of the bone, and works by the surgeon cutting the bone and separating the two ends, allowing new bone to grow in between lengthening the leg. This process is known as distraction osteogenesis. Limb-lengthening can be carried out in the thigh (femur) or lower leg (tibia).

The 4 key stages of leg lengthening surgery are:

1. Osteotomy - The bone is cut and divided into two sections.
2. Distraction - The two ends of bone are seperated at a controlled rate approximately 1mm per day, known as distraction, using specialised surgical equipment (i.e. external fixators or internal nails).
3. Osteogenesis - New bone forms in the space between the two ends of separated bone.
4. Consolidation - Bone and soft tissue consolidate and heal.

Leg lengthening surgery can be performed using an external fixator or an internal lengthening nail, and the decision to use one over the other should be done in discussion with your surgeon.

External fixators (i.e. Ilizarov frame or TSF) are a metal cage built on the outside of a limb and is connected to the bone with pins, screws and wires. We can adjust the external fixator to gradually and carefully lengthen, and straighten a shortened or deformed limb. With this option, the external fixator apparatus must remain on the leg for the entire time of the procedure, however the advantage is that you can fully weight bear while it is on.

Internal lengthening nails are mechanical internal nails which are inserted into the bone marrow cavity of a bone, and can be lengthened to gradually increase the length of the bone.

Recovery time from the limb lengthening procedure varies among patients, in particular the consolidation phase can last a considerable period of time. In general, children will recover much quicker than adults.