Leg Length Discrepancy (LLD) refers to the inequality in the measurements of the lower limbs resulting in an unlevelled musculoskeletal system. Pivotal to the efficient movement of the body, an early detection of the condition can help prevent several of the ailments occurring later in life.
But it is first important to understand the distinction between the two types of LLD namely, structural and functional.
Structural LLD is associated with anatomic differences in the length of the femur or tibia; a few possible causes include congenital abnormalities, fractures of the growth plate, bone infections, post-surgical complications following a hip or knee replacement.
Patients compensate for the shorter length of the limbs by rotating the foot externally to stabilise it thereby causing a valgus in the heel and an ultimate collapse in the arch. This can also lead to problems in the knee joints on account of an internally rotated femur.
Functional LLD, as the name suggests, is purely due to functional/postural distortions in the lower limbs, pelvis area, hip joint or sacroiliac joint. While one leg appears longer than the other, there will be no significant difference in the length of the lower extremity bones.
Some of these functional complications arise from the adduction or flexion contractures of the hip, deformities related to flexion or hyperextension in the knee or ankle, pelvic obliquity, genu valgum, calcaneovalgus, etc.
Clinical assessment techniques have traditionally involved the use of tape measure, standing blocks and now with technological advancements, computer-assisted gait analysis. Imaging methods of radiography, scanogram, ultrasound and MRI are also worthy of a mention.
Although most clinicians differ in their definition of minor and major limb length discrepancies, any length difference of more than 10mm is accepted as requiring intervention.
In the case of Structural LLD, orthotics with heel lifts can be used to treat leg length discrepancies of up to 10mm, helping restore alignment and optimal lumbopelvic biomechanics.
However, if the heel elevation exceeds half an inch, an additional heel elevation to the outside heel would require a tapering to 1/4 inch at the metatarsal region and 1/8 inch distally.
Excessive pronation on the long leg side can be treated with corrective orthotics in conjunction with heel lifts on the ipsilateral foot, to balance the sacral base and rectify the compensatory scoliosis on the shorter side.
Functional LLD does not normally necessitate the use of a heel lift and can be managed with therapeutic exercises to stabilise the pelvic region and to strengthen the muscles as well.
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