Having one leg feel longer than the other after a total knee replacement (TKR) is a common concern. This difference, known as Leg Length Discrepancy (LLD), occurs when the operated leg feels or is measurably longer than the non-operated leg. Surgeons meticulously plan to restore natural alignment, but achieving perfect equality is challenging due to the complexities of the joint and surrounding tissues. This article explores the underlying reasons for this phenomenon, the immediate steps to take, and the long-term management strategies.
Why Leg Length Discrepancy Occurs
The perception of a longer leg after TKR is often functional rather than a true anatomical change in bone length. The primary reason for this feeling is the surgeon’s goal of restoring proper soft tissue tension around the knee. To ensure the new joint is stable, the collateral ligaments and joint capsule must be taut, which creates the sensation of the leg being stretched or lengthened.
This soft tissue tightening is necessary for the long-term stability and function of the knee implant. The feeling of lengthening often fades as the soft tissues gradually stretch out and the body adjusts to the new alignment over the first few months of recovery. A true anatomical LLD, where the bone length is measurably different, is less common in TKR compared to hip replacement surgery.
A measurable LLD can still occur due to surgical factors, such as minor variations in the thickness of implanted components or the amount of bone removed. The goal of TKR is to correct pre-existing deformities, such as bowed (varus) or knock-kneed (valgus) alignment, which may have caused the leg to be functionally shorter before surgery. Correcting this alignment to a neutral position can make the operated leg appear longer compared to the unoperated leg, especially if the other knee remains misaligned.
Immediate Non-Surgical Management
The first step upon noticing an LLD is to consult the surgical team for an accurate assessment and measurement. A standing X-ray, often a full-length scanogram, is the gold standard for determining the true anatomical difference between the legs. Knowing the precise measurement is necessary before attempting any correction.
For small or perceived discrepancies, a period of observation is recommended, as many cases resolve naturally within the first six to twelve months post-surgery. This resolution occurs as post-operative swelling decreases and the tightened soft tissues relax and adapt to the new joint mechanics. The body often compensates for minor differences without intervention.
Physical therapy (PT) plays a significant role in managing functional LLD and resulting muscle imbalances. Targeted PT focuses on regaining full knee extension, as even a small lack of extension can make the leg functionally shorter and contribute to an uneven gait. Strengthening exercises, particularly for the gluteal muscles and core, help correct compensatory walking patterns and stabilize the pelvis.
For a confirmed, measurable LLD, the most common non-surgical intervention is the use of external shoe lifts or orthotics. These devices are placed inside the shoe of the shorter leg to equalize the difference in height. The lift height is prescribed by a physician or physical therapist based on the X-ray measurement and is introduced gradually.
Starting with a lift that is slightly less than the measured discrepancy is a conservative approach that allows the body to adapt to the correction. For instance, a measured difference of 10 millimeters might initially be treated with a 6- or 8-millimeter lift. Using a shoe lift helps normalize the gait, reduce strain on the spine and hip, and improve overall walking comfort.
Long-Term Effects and Advanced Interventions
If a significant LLD remains uncorrected, it can lead to long-term biomechanical consequences affecting the entire musculoskeletal system. The discrepancy forces the body to compensate, resulting in an uneven distribution of weight and strain. This compensatory mechanism can manifest as secondary pain in the hip, lower back, or ankle of the non-operated side.
The body attempts to manage the difference through gait deviations, such as “vaulting,” where the person rises on the toes of the shorter leg during the swing phase of the longer leg to clear the ground. This walking pattern places excessive stress on the joints and soft tissues that were not the original focus of the surgery. Over time, this altered gait can contribute to accelerated wear or arthritis in other joints due to chronic uneven loading.
Revision surgery to correct LLD is a rare consideration, reserved for cases where the discrepancy is severe and cannot be managed conservatively. Surgeons typically consider revision only for a large, measured discrepancy, often exceeding 15 to 20 millimeters, that causes persistent symptoms despite dedicated physical therapy and orthotic use. The goal of a revision procedure is to adjust the implant size or position to re-establish true limb length equality.