Leg length discrepancy is an orthopaedic problem that usually appears in childhood, in which one's two legs are of unequal lengths. Often abbreviated as ?LLD,' leg length discrepancy may be caused by or associated with a number of other orthopaedic or medical conditions, but is generally treated in a similar fashion, regardless of cause and depending on severity. Leg length discrepancy is sometimes divided up into 'true LLD' and 'functional LLD.' Functional LLD occurs when the legs are actually equal in length, but some other condition, such as pelvic obliquity (a tilt in the position of the pelvis), creates the appearance of legs of different lengths.
The causes of LLD may be divided into those that shorten a limb versus those that lengthen a limb, or they may be classified as affecting the length versus the rate of growth in a limb. For example, a fracture that heals poorly may shorten a leg slightly, but does not affect its growth rate. Radiation, on the other hand, can affect a leg's long-term ability to expand, but does not acutely affect its length. Causes that shorten the leg are more common than those that lengthen it and include congenital growth deficiencies (seen in hemiatrophy and skeletal dysplasias ), infections that infiltrate the epiphysis (e.g. osteomyelitis ), tumors, fractures that occur through the growth plate or have overriding ends, Legg-Calve-Perthes disease, slipped capital femoral epiphysis (SCFE), and radiation. Lengthening can result from unique conditions, such as hemihypertrophy , in which one or more structures on one side of the body become larger than the other side, vascular malformations or tumors (such as hemangioma ), which cause blood flow on one side to exceed that of the other, Wilm's tumor (of the kidney), septic arthritis, healed fractures, or orthopaedic surgery. Leg length discrepancy may arise from a problem in almost any portion of the femur or tibia. For example, fractures can occur at virtually all levels of the two bones. Fractures or other problems of the fibula do not lead to LLD, as long as the more central, weight-bearing tibia is unaffected. Because many cases of LLD are due to decreased rate of growth, the femoral or tibial epiphyses are commonly affected regions.
In addition to the distinctive walk of a person with leg length discrepancy, over time, other deformities may be noted, which help compensate for the condition. Toe walking on the short side to decrease the swaying during gait. The foot will supinate (high arch) on the shorter side. The foot will pronate (flattening of the arch) on the longer side. Excessive pronation leads to hypermobility and instability, resulting in metatarsus primus varus and associated unilateral juvenile hallux valgus (bunion) deformity.
There are several orthopedic tests that are used, but they are rudimentary and have some degree of error. Even using a tape measure with specific anatomic landmarks has its errors. Most leg length differences can be seen with a well trained eye, but I always recommend what is called a scanagram, or a x-ray bone length study (see picture above). This test will give a precise measurement in millimeters of the length difference.
Non Surgical Treatment
In an adult, we find that we can add a non compressive silicone heel lift to a shoe in increments of 3-4 mm maximum per week. Were we to give a patient with a 20 mm short leg, 20 mm of lift all at once, their entire body would rebel. The various compensations that the body has made, such as curvatures and shortening of muscles on the convex side of the curve, would make such a dramatic change not just noticeable, but painful. When we get close to balancing a patient by lifting a leg with heel inserts, then we perform another gait analysis and follow up xray. At that point, we can typically write them a final prescription to have their shoe modified. A heel lift is typically fine up to 7 mm. When it gets higher than that, the entire shoe must be modified. There are two reasons for this. The back of the shoe is generally too short to accommodate more than 7-8 mm inserted inside the shoes and a heel lift greater than 7 mm will lead to Achilles tendon shortening, which then creates it?s own panoply of problems.
Limb deformity or leg length problems can be treated by applying an external frame to the leg. The frame consists of metal rings which go round the limb. The rings are held onto the body by wires and metal pins which pass through the skin and are anchored into the bone. During this operation, the bone is divided. Gradual adjustment of the frame results in creation of a new bone allowing a limb to be lengthened. The procedure involves the child having an anaesthetic. The child is normally in hospital for one week. The child and family are encouraged to clean pin sites around the limb. The adjustments of the frame (distractions) are performed by the child and/or family. The child is normally encouraged to walk on the operated limb and to actively exercise the joints above and below the frame. The child is normally reviewed on a weekly basis in clinic to monitor the correction of the deformity. The frame normally remains in place for 3 months up to one year depending on the condition which is being treated. The frame is normally removed under a general anaesthetic at the end of treatment.