Predictor index of functional limb length discrepancy

INTRODUCTION: Limb length discrepancy (LLD) of lower extremities is underdiagnosed due to compensatory mechanisms during locomotion. The natural course of compensation leads to biomechanical alteration in human musculoskeletal system leading to adverse effects. General consensus accepts LLD more than 2 cm as significant to cause biomechanical alteration. No studies were conducted correlating height and lower extremities true length (TL) to signify LLD. Examining significant LLD in relation to height and TL using dynamic gait analysis with primary focus on kinematics and secondary focus on kinetics would provide an objective evaluation method.

METHODOLOGY: Forty participants with no evidence of LLD were recruited. Height and TL were measured. Reflective markers were attached at specific points in lower extremity and subjects walked in gait lab at a self-selected normal walking pace with artificial LLDs of 0, 1, 2, 3, and 4 cm simulated using shoe raise. Accommodation period of 30 min was given. Infrared cameras were used to capture the motion. Primary kinematic (knee flexion and pelvic obliquity (PO)) and secondary kinetic (ground reaction force (GRF)) were measured at right heel strike and left heel strike. Functional adaptation was analyzed and the postulated predictor indices (PIs) were used as a screening tool using height, LLD, and TL to notify significance.

RESULTS: There was a significant knee flexion component seen in height category of less than 170 cm. There was significant difference between LLD 3 cm and 4 cm. No significant changes were seen in PO and GRF. PIs of LLD/height and LLD/TL were analyzed using receiver operating characteristic curve. LLD/height as a PI with value of 1.75 was determined with specificity of 80% and sensitivity of 76%.

CONCLUSION: A height of less than 170 cm has significant changes in relation to LLD. PI using LLD/height appears to be a promising tool to identify patients at risk.