Leg length discrepancy (LLD), a condition where one limb is measurably shorter than the other, is a common orthopedic presentation with a spectrum of causes and consequences. Its treatment is not a monolithic endeavor but a carefully calibrated process, dictated by the magnitude of the difference, the patient’s age, the underlying etiology, and the presence of symptomatic dysfunction. The management philosophy spans a continuum from simple, non-invasive compensation to complex, limb-lengthening surgery, each intervention aiming to restore functional symmetry, alleviate pain, and prevent long-term degenerative sequelae.

The foundational step in treating LLD is accurate classification and measurement. Discrepancies are categorized as either structural (anatomical), where there is a true bony deficiency, or functional (apparent), arising from asymmetries in the musculoskeletal system such as pelvic obliquity, hip or knee contractures, or scoliosis. Treatment for a functional discrepancy focuses on correcting the causative soft-tissue imbalance through physical therapy, stretching, and manual therapy, rather than addressing a non-existent bony shortfall. For true structural discrepancies, the gold standard for quantification is the scanogram, a series of calibrated X-rays that minimize magnification error. The treatment pathway is then overwhelmingly guided by one critical factor: the magnitude of the difference.

For small discrepancies, generally defined as less than 2 centimeters in a skeletally mature individual, non-operative management is typically first-line and often sufficient. The human body possesses a remarkable capacity to compensate for minor asymmetries through mechanisms like pelvic tilt, ipsilateral foot pronation, and contralateral knee flexion. However, when these compensatory mechanisms fatigue or fail, symptoms arise. These commonly include low back pain, hip pain, ipsilateral knee stress, and a propensity for overuse injuries. The cornerstone of non-operative treatment is the external shoe lift, a deceptively simple intervention with profound biomechanical implications. For differences under 1 cm, a full-sole insert inside the shoe may suffice. For discrepancies between 1 and 2 cm, an external lift attached to the outsole of the shoe is preferable, as an internal lift can crowd the foot, leading to discomfort. This elevation works by leveling the pelvis and spine, thereby normalizing gait mechanics and offloading the stressed joints of the lumbar spine and lower extremities. The lift is often introduced gradually to allow the patient’s neuromuscular system to adapt. Concurrently, a regimen of physical therapy is crucial to strengthen core and hip stabilizers, stretch contracted soft tissues, and reinforce symmetrical movement patterns, maximizing the benefit of the lift and managing any residual musculoskeletal imbalances.

When the discrepancy exceeds 2 to 2.5 cm in an adult, or is predicted to reach this threshold in a growing child, the limitations of non-operative care become apparent. A lift of such height becomes cumbersome, potentially unstable, and cosmetically unappealing. More importantly, the chronic, significant asymmetry places excessive, uneven load on the joints, accelerating the development of premature osteoarthritis in the hip and knee of the longer limb, and potentially exacerbating spinal degeneration. It is at this juncture that surgical intervention enters the therapeutic landscape, offering two fundamental philosophical approaches: shortening the longer limb or lengthening the shorter one.

Limb shortening, or epiphysiodesis, is a primary surgical strategy for children and adolescents with significant remaining growth. This minimally invasive procedure involves the targeted ablation or temporary stapling of the growth plate (physis) in the longer leg, typically around the knee. By arresting growth in a controlled manner on the long side, the shorter leg is allowed to “catch up” over time. The timing of this surgery is a precise calculation, requiring careful assessment of skeletal age and growth remaining to achieve perfect or near-perfect equality at maturity. Its advantages include a single, relatively low-risk procedure, rapid recovery, and avoidance of the complexities of lengthening. However, its application is strictly limited to the growing population.

For skeletally mature individuals with a moderate discrepancy (typically 2-5 cm), shortening of the longer limb via a femoral resection osteotomy may be considered. A segment of bone is removed from the mid-shaft of the femur, and the bone is fixed with an intramedullary nail or plate. This is a reliable, one-stage procedure with a predictable outcome and recovery timeline. The primary drawback is the reduction in overall height and the potential for disproportionate shortening if the discrepancy is in the tibia, which can affect the appearance of the knee heights. Consequently, it is less favored for taller individuals or for discrepancies originating in the lower leg.

Limb lengthening, the most complex and demanding option, is reserved for larger discrepancies, usually greater than 5 cm in adults, or for any significant shortening where preserving height is a priority. This revolutionary process, pioneered by Gavriil Ilizarov, harnesses the body’s innate capacity for bone regeneration—distraction osteogenesis. The procedure involves a controlled surgical break (corticotomy) of the bone to be lengthened, followed by the application of an external fixator (like an Ilizarov or Taylor Spatial Frame) or, increasingly, an internal motorized nail. Post-operatively, after a brief latency period, the device is meticulously adjusted by the patient—typically at a rate of 1 millimeter per day—slowly pulling the bone segments apart. In the resulting gap, new bone (regenerate) forms. The process is not merely orthopedic but a profound biological undertaking, requiring intense patient commitment over many months to years. It is accompanied by rigorous daily physical therapy to maintain joint motion and muscle strength against the powerful forces of soft-tissue contracture. Risks are considerable and include pin-site infections, stiffness of adjacent joints, muscle contractures, nerve or vascular injury, and potential complications with the regenerate bone, such as delayed healing or deformity. The psychological toll of a prolonged treatment course with a visible external frame is also significant. Despite these challenges, modern techniques have dramatically improved outcomes, making it possible to correct severe discrepancies that were once untreatable.

The treatment of leg length discrepancy is a sophisticated exercise in hierarchical decision-making. It balances the simplicity of a shoe lift against the biomechanical imperative of a level pelvis, and the predictability of an epiphysiodesis against the biological marvel of distraction osteogenesis. There is no universal solution; the optimal path is always bespoke, woven from the threads of precise measurement, astute clinical judgment, and, crucially, the patient’s own functional demands, lifestyle, and tolerance for intervention. The ultimate goal remains constant across all modalities: to re-establish the harmonious mechanical alignment that is the foundation of pain-free, efficient, and durable ambulation.