Comparison of supine and prone methods of leg length inequality assessment
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Assessments of leg length are common, both with the patient lying down or standing. Either could be reliable, but in this test they did not agree with each other. Two chiropractors with more than 30 years experience each assessed the same few dozen patients, and agreement between their results when they felt confident in them was “perfectly nil.“ Despite the widespread and confident use of each method, this test clearly suggests that at least one of them is unreliable, but it’s also entirely possible that both of them are.
original abstract
OBJECTIVE: The primary objective of the current study was to determine the reliability between methods of supine and prone leg length inequality (LLI) assessment. The secondary objective was to determine if the degree of examiner confidence affected the degree of intermethod agreement.
METHODS: Two experienced doctors of chiropractic assessed 43 participants for LLI, one using a prone and the other a supine method. They stated whether they were confident or not confident in their findings.
RESULTS: Kappa values for intermethod agreement were 0.16 for the full data set; 0.00 for the n = 20 subgroup with both examiners confident; 0.24 for the n = 18 subgroup with 1 examiner confident; and 0.55 for the n = 5 subgroup with neither examiner confident. Supine and prone measures exhibited slight agreement for the full data set, but no agreement when both examiners were confident. The moderate agreement with both examiners not confident may be an artifact of small sample size.
CONCLUSIONS: This study found that supine and prone assessments for leg length inequality were not in agreement. Positioning the patient in the prone position may increase, decrease, reverse, or offset the observed LLI that is seen in the supine position.
related content
- “Does unequal leg length cause back pain? A case-control study,” an article in Lancet, 1984.
- “Relationship between mechanical factors and incidence of low back pain,” an article in Journal of Orthopaedic & Sports Physical Therapy, 2002.
- “Leg-length discrepancy is associated with low back pain among those who must stand while working,” an article in BMC Musculoskeletal Disorders, 2015.
- “Interrater reliability: the kappa statistic,” an article in Biochem Med (Zagreb), 2012.
- “The measurement of observer agreement for categorical data,” an article in Biometrics, 1977.
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