What is Limb Length Discrepancy?
A visible notable difference in the length of the lower or upper limbs is called Limb length discrepancy (LLD).
Within the physiological limits, a very minor difference in limb lengths does not affect lifestyle but difference more than the physiological limit can affect gait, posture and cause associated musculoskeletal anomalies.
Types of Limb length discrepancy & Causes:
- Anatomical/Structural: can be caused due to birth anomalies, developmental delayed milestones, trauma, fractures in growing age, orthopaedic degenerative diseases or surgical joint replacements.
- Functional/postural: Mostly there is unilateral asymmetry of the lower extremity, without any shortening of the bony component. This is a very common result due to faulty biomechanics, abnormal hip/knee/ankle or foot motion, contractures, shortened soft tissues, FOOT BIOMECHANICS, sacroiliac joint dysfunction or even postural scoliosis or chronic poor core muscle control.
More than 20 mm of limb length discrepancy can cause muscular compensatory measures in the body, leading to muscular strains and joint pains if not addressed.
EMPHASIS OF LLD IN POSTURE & GAIT (Walking pattern ):
LLD causes improper foot biomechanics, thereby affecting the kinetic chain of lower limb joints right from the ankle upto the hip joint and the sacroiliac joint.
- In Standing: LLD can cause excessive foot supination/pronation, knee joint position differences and maximally it affects the hip and pelvic bone alignment, causing either excessive rotation in either flexion or extension.
- Uncompensated LLD can be a causative factor for stress on the anterior and posterior iliac spine on the side of the short leg resulting in sacral unleveling or scoliosis.
- While walking: Notable gait asymmetry is seen throughout the kinetic chain, increased vertical shift in the centre of mass , thus leading to exaggerated energy consumption by the body, the muscles work more hard to achieve the same movements as compared to a normal individual walking with no limb length discrepancy.
The hip, knee and spine have the greatest impact of this LLD, leading to compensatory mechanisms like calcaneum eversion or knee hyperextension or hip rotation in walking, steppage gait, unequal arm swing while walking (one of the LLD indicators).
Other anomalies include decreased stance and stride length in shorter leg, decreased walking or running velocity. This impacts active population like marathon runners or sprinters threefold if the LLD is left uncompensated.
Other musculoskeletal disorders due to LLD:
- Low back pain
- Lumbar scoliosis
- Osteoarthritic changes in the lumbosacral joint
- Hip joint pain
- Stress fractures
- Knee pain
- Faulty ankle biomechanics, leading to plantar fasciitis and calcaneal spurs
- Sacroiliac joint dysfunction
Lower extremity scanogram to determine the exact difference in both the lower limb bone lengths. Or by a physical therapy assessment, wherein a tape is used between two defined bony points (between the ASIS and the medial malleolus) in lying position.
This depends on whether the patient exhibits symptoms or not. Mild (0-30mm), moderate (30-60mm), severe (>60mm).
Mild cases can be treated by adding external heel raises under an orthotic insole or addition of extra sole under the regularly used footwear, in order to compensate for the LLD by a podiatrist/orthotist evaluation, after a lower limb scanogram is done. Physical therapy management will be needed for strengthening and stretching of the affected muscles.
Dr. Janhvi Vayada (Sports Physiotherapist, Mind Your Fitness!)