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29-06-2011 | Article

Spinal landmark depth increases with BMI


Free abstract

MedWire News: The tissue depth of spinal landmarks as seen on lumbar magnetic resonance imaging (MRI) positively correlates with body mass index (BMI), study results show.

The relationship was not perfect, however, suggesting that other factors may be at play, or simply that changes in BMI may not be represented equally throughout the body.

"Assuming that there is a point where landmark depth exceeds the ability to detect it through palpation, understanding how landmark depth may change between subjects is of importance to clinicians in terms of the value they place on their palpation results," Gregory Kawchuk (University of Alberta, Edmonton, Canada, USA) and colleagues comment in the journal Manual Therapy.

Many treatment approaches for back pain often require that specific spinal structures be identified so that assessment and treatment may be directed appropriately.

While a number of imaging modalities are available for this purpose, they are not always feasible due to cost, waiting times, and availability. As a result, manual-based techniques (ie, palpation) are the most common method of identifying and locating spinal structures of interest.

To examine how BMI might affect palpation through landmark depth, Kawchuk et al recruited 105 patients who were referred for imaging for complaints of back pain or back pain associated with radiculopathy.

Four blinded examiners analysed T1-weighted MRI images with eFilm software to quantify the distance from the skin to the spinous processes of L1-L5 and the distance from the skin to the transverse process of L4 (the image series may not have included axial images at all levels of the lumbar spine).

The mean landmark depth in mm was 22.77, 23.00, 27.40, 33.40, and 36.65 for spinous processes L1-L5, respectively and 69.35 and 69.41 for the left and right L4 transverse processes, respectively.

There was a positive linear correlation between BMI and landmark depth, such that as BMI increased, so did landmark depth.

The relationship was statistically significant for all landmarks among women; however in men, statistical significance was reached only for the spinous process landmarks.

The proportion of variance in the landmark depth predicted by BMI, ranged from 39% to 62% for all landmarks except for transverse process among men, which ranged from 10% to 44%.

"Given these results, future investigations may consider exploring how the accuracy of palpation is affected by landmark depth and/or subject BMI," Kawchuk et al comment.

MedWire ( is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2011

By Andrew Czyzewski