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Cross-sectional validity study of compressive leg checking in measuring artificially created leg length inequality
Robert Cooperstein1, Elaine Morschhauser, Anthony J Lisi
1Director of Technique and Research, Palmer College of Chiropractic West.
Objective:
To determine the accuracy of instrumented, prone compressive leg checking.
Design:
Point measures (n=29) on single participants.
Setting:
Chiropractic college research clinic.
Methods:
A pair of surgical boots was modified to permit continuous measurement of leg length inequality (LLI). The accuracy of prone leg checking for a masked examiner (n = 29) was determined, against the gold standard of artificial LLI that was created by randomly inserting zero to six 1.6 mm shims in either boot. Accuracy was defined as the examiner's ability to correctly assess the change in the number and side of shims inserted, in two consecutive observations per participant. Linear regression and Bland-Altman statistics were obtained to determine the concurrent validity of compressive leg checking compared to a reference standard.
Results:
The observed and artificial LLI shared 86% of their variation (n = 29) The mean examiner error was 2.7 mm and the accuracy of dichotomous short leg determination for two shim insertions was 86.2%. The 95% confidence interval for the Bland-Altman limits-of-agreement for observed vs. artificial change in LLI was (-7.6, +5.2).
Conclusions:
Instrumented, compressive leg checking seems highly accurate, detecting artificial changes in leg length of 2-3 mm, and thus possesses concurrent validity assessed against artificial LLI. Pre- and post leg check differences should exceed about 4-6 mm to be highly confident a real change has occurred. It is unknown whether compressive leg checking is clinically relevant.
