A New Method for Measuring Structural Limb-Length Discrepancy: A Quasi-Experimental Study

Background/Objectives: Limb-length discrepancy (LLD) is a relatively common condition, with structural LLD characterized by true shortening of a bony structure. Although various clinical and radiological methods are available, none rely exclusively on position of malleoli relative to one another. This study aims to introduce a novel method for measuring structural LLD using malleoli in conjunction with a ruler. A quasi-experimental study. Methods: Eighteen participants with structural LLD were recruited from an orthopaedic clinic. Each participant underwent four tests: Paired Medial Malleolus Level Test (PMMLT) (new method), measuring tape method (Anterior Superior Iliac Spine (ASIS) to Medial Malleoli (MM), standing-block test, and full-length standing (long bone) radiography. Validity was assessed against radiography. Results: The mean ± SD LLD measured by radiography was 2.99 ± 1.69 cm. Corresponding values were obtained with the PMMLT (2.98 ± 1.69 cm), measuring tape method (2.95 ± 1.66 cm), and the standing-block test (2.92 ± 1.73 cm). No significant differences were found among the methods (χ²(3) = 3.43, p = 0.330). Correlations with radiography were very strong (PMMLT r = 0.996; measuring tape method r = 0.990; standing-block test r = 0.991; all p < 0.001). PMMLT showed negligible bias (-0.01 cm), the narrowest 95% limits of agreement (-0.32 to 0.30 cm), and the lowest RMSE (0.15 cm). Conclusions: The PMMLT demonstrates accuracy and practicality while being simple, cost-effective, and free of radiation exposure, making it a valuable alternative for clinical assessment of LLD in settings where imaging is unavailable or contraindicated.