Definition: Limb length discrepancy, or anisomelia or limb length inequality, is defined as a condition in which paired limbs are noticeably unequal. When the discrepancy is in the lower extremities, it is known as leg length discrepancy (LLD). LLD is a relatively common problem found in as many as 40 to 70 per cent of the population. Discrepancy in the length of upper limbs is not very disabling or noticeable unless the difference is very gross. Since LLD is clinically more relevant, our discussion shall be confined to it.
- Several classification systems or categories of limb length inequality have been proposed. The most common classification scheme for limb length inequality identifies two types – anatomical and functional.
- Anatomical limb length inequality, which has also been referenced as true or structural limb length inequality, occurs when a physical shortening of a unilateral lower limb exists.
- Functional, or apparent, limb length inequality can be described as a unilateral asymmetry of the lower extremity without any concomitant shortening of the osseous components of the lower limb, like a flexion deformity at hip/knee.
Causes: Congenital (from birth) & acquired
Congenital causes include dislocation of hip from birth (DDH), congenital deficiency in length of the long bones of lower limbs etc. Acquired causes can further be divided into traumatic (associated with accidents) and non-traumatic.
Traumatic causes include previous injury to a bone in the leg. A broken leg bone may lead to a limb length discrepancy, if it heals in a shortened position or bone fragments are lost from a wound over the fracture site. Atraumatic causes include bone infection, arthritis of the joints etc. By far the most common cause of LLD in adults is arthritis of the hip and knee joints which may lead to either true or apparent LLD. In such cases, the inequality can be rectified by doing joint replacement by primary implant or by customised implants.
Impact of LLD on health & lifestyle
Apart from the obvious biomechanical changes that will occur due to LLD, there is also a situation that can arise that has the potential for a huge impact on the quality of life of the ageing population. Research has showed that both oxygen consumption and the rating of perceived exertion were greater with a two cm artificial limb-length discrepancy than they were with no artificial limb-length discrepancy, implying that an LLD of two cm or greater needs treatment. LLD also is associated with low back pain. The limp associated with LLD is a social stigma in addition to being a biomechanical handicap.
Diagnosis: Limb length discrepancy can be measured by a physician during a physical examination and through X-rays. The patient may have drooping of the shoulder and bending of the spine secondary to LLD.
- Nonsurgical treatment: For minor limb length discrepancy in patients with no deformity, treatment may not be necessary. Because the risks may outweigh the benefits, surgical treatment to equalize leg lengths is usually not recommended if the difference is less than one inch. For these small differences, the orthopaedician may recommend a shoe lift. A lift fitted to the shoe can often improve walking and running, as well as relieve any back pain that may be caused by the limb length discrepancy.
- Surgical treatment: In growing children, legs can be made equal or nearly equal in length with relatively simple surgical procedures. The involved limb may be lengthened or the normal limb may be shortened to achieve equal length of both extremities. This procedure will not cause an immediate correction in length. Instead, the limb length discrepancy will gradually decrease as the opposite extremity continues to ‘catch up.’ However, an LLD in an adult is a different problem altogether. A marked LLD due to arthritis may be treated with joint replacement. The joint replacement implants may be custom made to suit each person’s exact status of LLD.
Take home message: LLD is a very common and easily treatable condition. Do not neglect LLD as it may lead to chronic health and social issues. Contact a good orthopaedician in your city for treatment of the same.