Total Knee Arthroplasty (TKA), commonly known as total knee replacement, is a highly successful procedure for relieving pain and restoring mobility. A potential outcome is a difference in leg length, referred to as Leg Length Discrepancy (LLD). This difference typically manifests as a slight lengthening of the operated leg, averaging about six millimeters. Although minor, this discrepancy can cause the patient to feel unbalanced or have an altered gait.
Identifying the Leg Length Discrepancy
The subjective experience of LLD often begins with symptoms suggesting a biomechanical imbalance. Patients frequently report new pain in the lower back or hip on the side of the shorter leg, a feeling of walking “uphill” on the longer side, or an overall unevenness in their stride. This sensation of being off-balance can lead to increased fatigue while standing or walking, as the body attempts to compensate.
While a physical examination offers initial clues, a precise diagnosis requires professional confirmation using medical imaging. The most reliable method for accurately measuring the true bone-length difference is a full-length standing X-ray, often called a scanogram. This image captures the entire length of both legs, allowing the physician to measure the distance between fixed points on the pelvis and the ankles. This objective measurement is necessary because the subjective feeling of LLD can be magnified by muscle weakness or soft tissue tightness.
Conservative Management Using Shoe Adjustments
For the majority of patients, a leg length difference is successfully managed without further surgery, using conservative options as the first line of treatment. Shoe adjustments, such as heel lifts or orthotic devices, are the most common non-invasive intervention for LLDs, especially those under one centimeter. These lifts are placed inside the shoe of the shorter leg to effectively equalize the functional length of the limbs.
Smaller discrepancies, typically less than five millimeters, can often be accommodated using an internal shoe insert or a simple heel pad. For differences between five and ten millimeters, a custom-made orthotic or a lift insert with adjustable layers allows for a gradual correction. This gradual approach is preferred, as it gives the body time to adapt and prevents sudden strain on the back and pelvis.
If the LLD exceeds one centimeter, an external shoe modification may be necessary, where a shoemaker adds material to the sole and heel to achieve the required height. This external modification is preferred for larger adjustments to maintain comfort and stability. Physical therapy also plays a significant role by addressing muscular imbalances and gait abnormalities developed to cope with the LLD. A therapist works to retrain the patient’s walking pattern, focusing on strengthening the trunk and lower extremity muscles.
When Revision Surgery Becomes Necessary
When conservative measures fail to relieve chronic symptoms, or the LLD is significantly large, a surgical solution may be considered, though this is rare after TKA. Revision surgery is generally reserved for individuals with a severe discrepancy, typically exceeding two centimeters. It may also be considered if a smaller LLD causes persistent pain and functional limitation despite extensive shoe-lift use. Uncorrected LLDs can lead to long-term issues, including chronic low back pain, gait disorders, and increased wear on the hip and ankle joints.
Surgical options to address a persistent LLD include a revision TKA, where the surgeon may adjust the polyethylene insert thickness or alter bone cuts to slightly shorten the longer leg. In rare circumstances, procedures on the opposite, non-operated leg, such as controlled bone shortening, might be discussed to achieve better limb length equality. Revision surgery is an extensive procedure that carries risks, and most surgeons require a patient to fully exhaust all non-operative therapies before proceeding.