Leg length discrepancy (LLD) is a condition where one leg is shorter than the other, significantly affecting a person’s posture and gait. This imbalance often causes the body to compensate, potentially leading to pain in the lower back, hips, knees, or feet. While severe cases may warrant surgery, footwear modification is the most common and effective non-surgical strategy to restore balance and alleviate symptoms. The goal is to introduce a precisely measured elevation under the shorter limb, normalizing the body’s alignment and movement patterns.
Determining the Necessary Correction
Determining the required correction height is the necessary step before modifying any footwear. Professionals must first differentiate between a structural LLD, which is an actual difference in bone length, and a functional LLD, caused by issues like muscle imbalances or pelvic tilt. Functional discrepancies are often treated with physical therapy and orthotics to address underlying soft tissue issues, not necessarily a shoe lift.
For a structural LLD, the most objective measurement is obtained through medical imaging, such as a full-length standing X-ray called a scanogram. This technique superimposes a ruler onto the image of the lower extremities, providing a definitive measure of the bony difference. Other clinical methods, like the block test, involve placing blocks of known height under the shorter leg until the pelvis appears level to estimate the required height in a weight-bearing position. It is common practice to start the correction with 60 to 70% of the measured discrepancy to allow the body to gradually adjust to the change in alignment.
Internal Shoe Modifications for Minor Discrepancies
For minor leg length differences, generally considered to be 10 millimeters or less, the correction can be managed entirely within the shoe. These internal modifications include off-the-shelf heel lifts, custom orthotic inserts, or full-length insoles designed to add height. Heel lifts elevate only the heel, while full-length inserts raise the entire foot, offering better weight distribution and stability.
The advantage of an internal lift is its discretion, allowing the correction to be hidden inside the shoe. However, the space inside a shoe is limited, and adding too much height can lead to complications. A lift exceeding 10 millimeters may cause the heel to slip out or crowd the toes against the top of the toe box, leading to discomfort and an insecure fit. Internal solutions are best suited for smaller discrepancies where the lift does not compromise the shoe’s internal volume or the foot’s secure positioning.
External Shoe Modifications for Significant Discrepancies
When the leg length difference exceeds 10 millimeters, external shoe modifications become necessary to achieve the full correction without sacrificing comfort or fit. This process involves adding material directly to the outsole of the shoe, a specialized task performed by a certified orthotist or orthopedic shoe technician. The modification is integrated into the existing sole, ensuring the foot remains securely seated in the shoe’s original footbed.
The modification begins with disassembling the shoe’s outsole, followed by adding the required height using durable, lightweight materials such as cork, rubber, or specialized EVA foam. The new material is built up to the precise measurement determined by the specialist, and then carefully shaped to match the contours of the original sole. The modification must maintain the shoe’s natural rocker or gait line to ensure a smooth transition from heel strike to toe-off. This external modification offers a stable and permanent solution, preventing the instability and crowding issues associated with oversized internal lifts.
Choosing the Optimal Base Shoe for Modification
The characteristics of the base shoe are crucial for the success of a leg length correction. Shoes with a firm, non-flexible sole structure are preferred, as highly cushioned or extremely flexible running shoes can compress unevenly under the new lift, compromising stability. A flat profile is recommended, meaning the shoe should have a low or minimal heel-to-toe drop before modification.
Lace-up shoes or styles with secure straps are also recommended because they keep the foot firmly in place. This secure fit is important after modification, as the increased sole thickness can alter the foot’s position relative to the shoe’s collar and upper. Choosing a durable shoe with solid lateral support ensures the modification will last longer and provide the best foundation for balanced movement.