Leg Length Discrepancy (LLD) is a common but often overlooked condition where one lower limb is shorter than the other. Even a small difference—such as 5–10 mm—can significantly affect the way a person walks, stands, and distributes load through their hips, knees, and spine. Over time, this imbalance can lead to pain, fatigue, and worn joints.
But not all LLDs are the same. Clinically, LLD falls into two major categories: Anatomical (structural) and Functional. Understanding the difference is essential for choosing the correct treatment pathway and for prescribing the right orthotic or footwear intervention.
⭐ What Is Anatomical (Structural) LLD?
Anatomical LLD occurs when there is a true, measurable difference in bone length between the left and right lower limbs. The discrepancy may be present from birth or develop later in life.
Common Causes of Anatomical LLD
- Congenital conditions (e.g., underdeveloped femur/tibia)
- Trauma or fractures, especially if growth plates were involved
- Orthopaedic surgeries such as hip replacement or joint reconstruction
- Degenerative bone diseases
- Growth disturbances during childhood or adolescence
How It Presents Clinically
Patients often show:
- A visible height difference in pelvis or hip
- Consistent gait asymmetry
- Hip hiking on the longer side
- Toe walking on the shorter side
- Chronic low back or knee discomfort
Diagnosis:
- Anatomical LLD is confirmed through physical measurement and radiographic imaging (scanogram or standing X-ray).
⭐ What Is Functional LLD?
Functional LLD occurs when the leg lengths are technically equal, but the way the body functions creates an apparent difference. In these cases, the bones are the same length, but posture or muscle imbalances make one leg behave as if it were shorter.
Common Causes of Functional LLD
- Joint contractures (hip, knee, or ankle)
- Muscle weakness or tightness (e.g., hip flexors, hamstrings, quadratus lumborum)
- Pelvic rotation or tilt
- Pronated or supinated foot types
- Foot biomechanics, such as excessive ankle pronation
How It Presents Clinically
Patients may show:
- Pelvic asymmetry without bone shortening
- Uneven stride or stance time
- Lower back tightness (especially on one side)
- Fatigue or pain during long walks
- Gait pattern changes that improve temporarily with cueing
Diagnosis:
Confirmed through gait analysis, postural assessment, and differentiation of bone length vs. functional adaptation.
⭐ Why Distinguishing Them Is Important
Treating LLD incorrectly can worsen symptoms.
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Anatomical LLD usually benefits from:
✔ Shoe build-ups
✔ Heel lifts
✔ Custom orthotic devices -
Functional LLD typically requires:
✔ Gait retraining
✔ Strengthening and stretching programs
✔ Foot posture correction
✔ Orthotic support (for pronation/supination)
A comprehensive assessment ensures patients receive the right intervention for long-term mobility and pain reduction.
⭐ Case Example Relevant to Clinical Practice
A patient with a history of foot injury and childhood polio presents with:
- 7 mm shorter left limb
- Pes cavus (high arches)
- Stomping gait
- No heel-to-toe motion on the right
- Right hip hike
Short-term goals:
- Achieve a normal-looking shoe
- Provide adequate build-up to compensate for the shortened side
Long-term goals:
- Improve gait mechanics
- Reduce hip hike
- Improve posture and reduce compensatory stress on the spine
This is a classic example where a combination of shoe build-up + biomechanical correction + gait retraining is required.
⭐ How Custom Build-Ups and Orthoses Help
- Redistribute load evenly
- Improve centre of gravity and alignment
- Restore heel-to-toe motion
- Reduce hip/pelvic compensations
- Minimise future joint degeneration
At Foot Balance Technology, each build-up is designed in-house, ensuring precision from prescription to fabrication.
⭐ Conclusion
Understanding whether an LLD is anatomical or functional is essential for delivering the right care. With accurate assessment and a tailored treatment plan—including footwear, orthotics, and gait training—patients can achieve remarkable improvements in comfort, posture, and mobility.