Reliability and accuracy of the tape measurement method with a nearest reading of 5 mm in the assessment of leg length discrepancy

Jamaluddin S, Sulaiman AR, Kamarul Imran M, Juhara H, Ezane MA, Nordin S
Correspondence: Dr Abdul Razak Sulaiman, abdrazak@kb.usm.my

ABSTRACT
Introduction The aim of this study was to determine the reliability and accuracy of the tape measurement method (TMM) with a nearest reading of 5 mm in assessing leg length discrepancy (LLD).
Methods This was a cross-sectional study conducted on 35 patients with LLD and 13 patients without LLD. Two blinded surgeons measured the lower limbs from the anterior superior iliac spine to the medial malleolus using TMM with a nearest reading of 5 mm. Computed tomography (CT) scanograms of the lower limbs of 22 patients were conducted by two blinded radiologists. Intraclass correlation coefficient (ICC) with 95 percent confidence interval was calculated to assess the interobserver reliability of TMM. The accuracy of TMM was assessed by comparison with CT as the gold standard.
Results The interobserver reliability of LLD measurement using both TMM and CT scanogram was high, with ICCs of 0.924 and 0.971, respectively. No significant mean difference on paired sample t-test was observed for both TMM and CT scanogram. Compared to CT scanogram, TMM had good accuracy, with an ICC of 0.805. When the mean TMM readings by two observers were compared to those derived from CT scanogram, the ICC was found to be 0.847, with a mean difference of 1.95 (range -3.17 to 7.07) mm.
Conclusion There was excellent agreement in the LLD measurements between the two surgeons using TMM, between the two radiologists using CT sonogram, and between the TMM and CT measurements. This study showed that one TMM with the nearest reading of 5 mm was reliable and accurate in measuring LLD.

Keywords: leg length discrepancy, tape measurement method
Singapore Med J 2011; 52(9): 681–684