A Novel Laser Inclinometer-Based Method for Accurate Leg Length Discrepancy Measurement: A Comparative Study with Tape Measure and Time-of-Flight Sensor

Accurate measurement of leg length discrepancy (LLD) is critical in biomechanics, custom footwear design, and clinical orthopedics. Existing methods like tape measure, block method and CT scan have limitations in precision, repeatability, and ease of use. In our study, we have introduced two approaches for measuring the lld, one is Time-of-flight Ultrasound sensor and the another one is laser inclinometer-based method for LLD assessment, this method improves the accuracy by minimizing the human errors and this standardizes the measurement protocol and rules. This method involves measuring leg length discrepancy (LLD) using anterior superior iliac spine (ASIS) tilt. The ASIS points are marked, and their horizontal distance is recorded. A laser inclinometer measures the pelvic tilt angle, and LLD is calculated using the formula LLD = (half ASIS distance) × sin(tilt angle). Participants were assessed using all three methods, and results were analyzed based on precision, consistency, and efficiency. While the ToF sensor balanced speed and accuracy, it was affected by surface artifacts and had an accuracy limitation of ±2 mm. The tape measure, despite being cost-effective, showed the highest variability due to calf muscle curvature effects and inconsistent tension. Imaging has a high validity however, it is expensive and exposes the subject to radiation These findings suggest that the laser inclinometer is a superior alternative and offers high accuracy, repeatability, and a standardized approach for accurate LLD measurement.