Reliability and validity of rigid lift and pelvic leveling device method in assessing functional leg length inequality

Clinicians commonly include an assessment of leg length inequality (LLI) as a component of a musculoskeletal examination. Little research is available, however, documenting reliability and validity of clinical methods for assessing LLI. The purpose of this study was to determine the reliability and validity of assessing functional LLI using a pelvic leveling device. Subjects were 19 women and 13 men between the ages of 18 and 55 who reported having a diagnosed or suspected LLI. Clinical determination of LLI was made by placing rigid lifts under the suspected shorter lower extremity until the leveling device indicated that the iliac crests were level. This measurement was made twice by one investigator and once by a second investigator. Standing radiographic measurements of LLI using rigid lifts were used to establish validity of the clinical method. Intraclass correlation coefficients [ICC(2,1)] and absolute difference values were computed to assess reliability and validity. The mean absolute difference between the two clinical measurements of LLI by the same investigator was 0.29 cm (+/- 0.52), with an ICC = 0.84. The mean absolute difference between clinical measurements of LLI by the two investigators was 0.49 cm (+/- 0.46), with an ICC = 0.77. The ICC and mean absolute difference reflecting agreement between radiographic measurements and clinical measurements of LLI was 0.64 and 0.58 cm (+/- 0.58), respectively, for one investigator and 0.76 and 0.55 cm (+/- 0.37), respectively, for the second investigator. The intratester reliability, intertester reliability, and validity assessments included instances in which paired observations disagreed regarding which lower extremity was the shorter lower extremity. Factors that may be associated with the unacceptable reliability and validity of the clinical assessment method include asymmetric positioning of the ilia, body composition of the patient, and design of the clinical instrument. The authors discuss clinical implications related to assessment of LLI.