TECHNIQUES FOR MEASURING LUMBAR CURVATURE AND LUMBAR SHAPE OF THE SPINE: A LITERATURE REVIEW

Todd C. MacKenzie Vermont Rehabilitation Engineering Research Center University of Vermont Burlington, VT 05401

ABSTRACT

The inward curvature of the lumbar spine is widely regarded as a natural and desirable physical adaptation for the standing posture. The consensus among researchers and clinicians is to maintain the curvature, or lordosis, as humans assume seated postures. Several techniques have been applied to measure lordosis that have yielded varying degrees of success. Radiographic methods and, to a lesser extent, segmental vertebral body tracking are the only methods identified as capable of precisely measuring intersegmental position. Alternatively, skin surface instrumentation techniques provide gross measures of spinal shape and are commonly applied clinically.

BACKGROUND

In recent decades there has been increased interest in lumbar lordosis measurement. The wide variety of historical measurement techniques may be classified as either clinical or laboratory- based approaches. Clinical methods are generally easier to administer and provide an adequate degree of precision for its intended application. The precise laboratory-based methods are characterized by increased costs due to highly specialized personnel and instrumentation. With few exceptions, both approaches are limited to the static measurement of a phenomena that is both time and posture dependant. Traditional measurement methods are marked by varying levels of reliability and the industry remains open to improved techniques of lordosis measurement.

Movement of the lumbar spine has been evaluated by researchers for over a hundred years. In 1836 Weber and Weber published an early paper that evaluated spinal mobility.1 This work was followed by several studies through this century and the body of literature is now extensive, particularly as a result of research in recent decades. In recent years, instrumentation and data collection technologies have permitted extensive analysis of the lumbar spine shape.

RESEARCH QUESTION

Clinicians and researchers have long been interested in quantifying back shape and its changes. Can a practitioner be confident that the results of common measurement methods are accurate? The quantity of journal articles that have promulgated and evaluated several methods (e.g. flexible ruler, dual inclinometer, skin distraction) is extensive. Several authors have reported high correlation between methods thus suggesting valid results. However, a close review of the literature reveals inconsistencies in reported device performance over several studies.

RESULTS

Lumbar lordosis measurement methods measures a) spinal position b) spinal motion or c) spinal shape. Physical therapists might seek a device that measures the position of the lumbar spine in flexion and extension thus permitting range of motion evaluation throughout the rehabilitation process. Alternatively, industrial applications for seating designers or ergonomics researchers may be interested in characterizing the movement of the lumbar spine during a work session. Surface techniques are reasonably accurate in the measurement of the total lumbar motion.2 However, there is poor correlation between intersegmental motion when measured radiographically and at the surface of the skin. Bryan3 points out that a direct comparison between roentgenograph measurement methods and external lumbar lordosis measurement methods cannot be done since the basis of physical measure differs. Attempts to validate results in repeat studies have been unsuccessful.3 There is no clear agreement of the validity and reproducibility of lordosis measurement methods.

DISCUSSION

Radiographic techniques have been applied to quantify lordosis and evaluate range of motion for years.4,5,6,7,8 X-ray techniques are considered the most accurate clinical method of lordosis measurement since the measure is not effected by soft tissue variation across subjects. Biplanar radiography has been used to quantify motion in three axes9,10 and can achieve highly precise measures of vertebral bodies in space. Photographic evaluation of lumbar lordosis has been attempted in several studies.11,12,13 The reliability of such techniques are dependant on the precise methodology and instrumentation applied. The inclinometer,14,15,16 Dual inclinometer,17,18,19 flexible ruler,20,21,22 and skin distraction methods23,24,25,26 are common clinical methods of quantifying lumbar lordosis. Several goniometers,27,28,29,30,31,32 and visual motion analysis systems,33,34 have also been applied in research settings but are not routinely used clinically due to relative complexity and cost. Electro-goniometers have recently been applied to obtain time-dependant change in posture when measuring the postures associated with several tasks.35,36,37,32,38 Spatial position sensors have been used to quantify relative position and movement in the spine and are regarded as highly accurate tools to characterize posture.39,40,41 Initial pilot studies from an Intervertebral Motion Device shows promise for future analysis but the process is currently limited to study trials.42,43 Widespread clinical use is not likely due to its invasive nature and high cost to implement. Considerable studies have been conducted to investigate and validate the wide variety of lumbar lordosis measurement tools. Several tools are perceived to have restrictions that limit their utility in clinical environments. Reliability, reproducibility, safety and cost are often cited as limitations to the existing measurement methods. According to Bryan, "...a nonroentgenographic method of measuring postural curves would be an excellent clinical and research tool if the method was inexpensive, expedient, reliable, and valid."3 Despite the diverse noninvasive measurement techniques, the validity of several methods have recently been challenged by investigators. The industry appears ready for a new device/technique to overcome some of these issues.

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ACKNOWLEDGEMENTS

Funding for this project was provided by the National Institute on Disability and Rehabilitation Research, US Department of Education (H133E30014-95).

Todd MacKenzie Vermont Rehabilitation Engineering Research 1 South Prospect Street Burlington, VT 05401 (802) 656-8187