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BMC Musculoskeletal Disorders

, 11:275

First Online: 30 November 2010Received: 20 July 2010Accepted: 30 November 2010


BackgroundNo prior studies have examined systematic bias in the musculoskeletal physical examination. The objective of this study was to assess the effects of bias due to prior knowledge of lumbar spine magnetic resonance imaging findings MRI on perceived diagnostic accuracy of the physical examination for lumbar radiculopathy.

MethodsThis was a cross-sectional comparison of the performance characteristics of the physical examination with blinding to MRI results the -independent group- with performance in the situation where the physical examination was not blinded to MRI results the -non-independent group-. The reference standard was the final diagnostic impression of nerve root impingement by the examining physician. Subjects were recruited from a hospital-based outpatient specialty spine clinic. All adults age 18 and older presenting with lower extremity radiating pain of duration ≤ 12 weeks were evaluated for participation. 154 consecutively recruited subjects with lumbar disk herniation confirmed by lumbar spine MRI were included in this study. Sensitivities and specificities with 95% confidence intervals were calculated in the independent and non-independent groups for the four components of the radiculopathy examination: 1 provocative testing, 2 motor strength testing, 3 pinprick sensory testing, and 4 deep tendon reflex testing.

ResultsThe perceived sensitivity of sensory testing was higher with prior knowledge of MRI results 20% vs. 36%; p = 0.05. Sensitivities and specificities for exam components otherwise showed no statistically significant differences between groups.

ConclusionsPrior knowledge of lumbar MRI results may introduce bias into the pinprick sensory testing component of the physical examination for lumbar radiculopathy. No statistically significant effect of bias was seen for other components of the physical examination. The effect of bias due to prior knowledge of lumbar MRI results should be considered when an isolated sensory deficit on examination is used in medical decision-making. Further studies of bias should include surgical clinic populations and other common diagnoses including shoulder, knee and hip pathology.

Electronic supplementary materialThe online version of this article doi:10.1186-1471-2474-11-275 contains supplementary material, which is available to authorized users.

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Autor: Pradeep Suri - David J Hunter - Jeffrey N Katz - Ling Li - James Rainville


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