A new concept for measuring leg length discrepancy

Abstract

Leg length discrepancy (LLD) has been a controversial issue among researchers and clinicians for many years. Its presence obviously is not in doubt, however, there is little consensus as to its many aspects, including the extent of LLD considered to be clinically significant, the prevalence, reliability and validity of the measuring methods, the effect of LLD on function and its role in various neuromusculoskeletal conditions.1 LLD can be caused by structural deformities originating from true bony leg length differences.2, 3, 4 Nevertheless, it can also be due to functional deformity derived from abnormal hip, knee, ankle and foot movements in each of the three planes of motion.2, 3, 5 LLD has been found to be a significant factor influencing several pathological and physiological conditions which affect function and quality of life.6, 7 For example, it has been suggested that LLD has a significant effect on pelvic and lower limb biomechanics, may cause pelvic obliquity in the frontal plane thus leading to functional scoliosis, posture deformation, gait asymmetry and low back pain, as well as gonarthrosis or coxarthrosis and other lower limbs symptoms.4, 8, 9, 10, 11, 12, 13, 14 Moreover, LLD has also been correlated with gait deviations.15 The inconsistency in the literature regarding the effect and role LLD plays in several pathological conditions is due to poor reliability and validity of the measurement methods. In addition, it is impossible to confine the effect of LLD to pathological conditions where several other abnormal findings are also present. 1.1. Definition of LLD 1.1.1. There are basically two definitions of LLD True leg length discrepancy (TLLD) is defined as the anatomical difference between the lengths of the two limbs between the proximal edge of the femoral head to the distal edge of the tibia which can be congenital or acquired. Congenital conditions include mild developmental abnormalities found at birth or childhood, whereas acquired conditions include trauma, fractures, orthopedic degenerative diseases and surgical disorders such as joint replacement. A systemic review evaluating the prevalence of LLD by radiographic measurements revealed that 90% of the normal population had some type of variance in bony leg length, with 20% exhibiting a difference of >9 mm.16 Functional leg length discrepancy (FLLD) is defined as a condition of asymmetrical leg length, not necessarily a result or compensation of a true bony length difference. FLLD may be caused by an alteration of lower limb mechanics, such as joint contracture, static or dynamic mechanical axis malalignment, muscle weakness or shortening. It is impossible to detect these faulty mechanics using a non-functional evaluation, such as radiography. FLLD can develop due to an abnormal motion of the hip, knee, ankle or foot in any of the three planes of motion.