Leg Length Discrepancy (LLD) is a relatively common variation in human anatomy. Many people have a minor length difference that never causes noticeable symptoms or functional problems. The severity of LLD can range from a few millimeters that go undetected to several centimeters that may affect walking and posture. Understanding the underlying type and cause of the discrepancy is the first step toward appropriate management.
Understanding Functional Versus Structural Discrepancy
LLD is categorized into two distinct types. Structural LLD represents a true anatomical difference in the length of the bony segments of the leg, specifically the femur or the tibia. This type is permanent and requires a precise measurement of the bone structure to confirm the extent of the difference.
Functional LLD means the actual bone lengths are equal, but the leg appears longer or shorter due to alignment issues elsewhere in the body. This apparent discrepancy often results from compensations in the hip, pelvis, or ankle. A common example is a pelvic tilt caused by muscle tightness or asymmetry in the hip joint, which makes one leg appear relatively shorter.
Soft tissue contractures, joint misalignments, or conditions like scoliosis can create this functional difference. Treating functional LLD involves correcting the postural or muscular imbalance, rather than modifying the leg itself. The treatment approach for functional issues is entirely different from structural ones.
Common Causes of Unequal Leg Length
Structural LLD origins are grouped into congenital, developmental, and post-traumatic/post-surgical causes.
Congenital conditions are present at birth and involve developmental issues, such as fibular hemimelia (where the fibula is partially or entirely missing) or congenital short femur. These conditions result in one leg growing significantly shorter from an early age.
Developmental causes typically occur during childhood, often affecting the growth plate. A severe infection, such as osteomyelitis, or a serious fracture that damages the growth plate can cause one leg to stop growing prematurely.
Post-traumatic or post-surgical causes are common in adults and children. A severe bone fracture that heals in a shortened or misaligned position, known as malunion, is a frequent cause. Certain orthopedic surgeries, such as a total hip or knee replacement, can also result in a small change in leg length.
How a Leg Length Discrepancy is Diagnosed
Diagnosis begins with a clinical assessment where a healthcare provider observes the patient’s posture and gait, looking for signs like a limp or a pelvic tilt. Simple physical examination techniques, such as measuring the distance from the hip bone to the ankle with a tape measure, provide an initial estimate of the difference. The provider may also use standing block tests, placing blocks under the shorter foot until the pelvis appears level.
Precise measurement requires radiographic confirmation, as imaging removes soft tissue and pelvic variables that can skew physical measurements. The gold standard imaging technique is a full-length standing AP computed radiograph (teleoroentgenogram), which captures the entire length of both legs on a single image. A CT scanogram is an alternative that provides highly accurate measurements.
The scanogram precisely measures the length of the femur and tibia by identifying specific bony landmarks. These measurements determine the true structural difference down to the millimeter, which is essential for treatment planning. Clinicians generally consider a discrepancy of less than 2 centimeters to be minor and manageable with conservative methods.
Treatment and Management Options
Treatment for LLD is tailored to the severity of the difference and whether the patient is still growing.
Conservative management is the preferred initial approach for minor structural discrepancies, typically those less than 2 centimeters. This involves using shoe inserts or heel lifts, placed inside or attached to the sole of the shoe on the shorter side, to functionally equalize the length.
For functional LLD, conservative treatment focuses on manual therapy, physical therapy, and specific exercises to address muscle imbalances and restore proper pelvic alignment. A physical therapist uses targeted stretching and strengthening to release soft tissue contractures. Addressing the underlying postural issue often resolves the symptoms without the need for a lift.
Surgical intervention is reserved for significant structural discrepancies, typically exceeding 2 to 2.5 centimeters. For growing children, a procedure called epiphysiodesis may be performed on the longer limb. This involves surgically slowing or stopping the growth of the longer leg’s growth plate, allowing the shorter leg to catch up by skeletal maturity.
For larger discrepancies or for adults, the primary surgical options are limb shortening or limb lengthening. Limb lengthening (distraction osteogenesis) involves cutting the shorter bone and using specialized devices to gradually pull the segments apart. This slow separation stimulates the body to grow new bone, increasing the overall length of the limb. Limb shortening involves removing a section of bone from the longer leg.