Background: Intervertebral motion is often assumed to be altered with back pain, however, the patterns are inaccessible to measurement in live subjects. A method for digitally tracking and analysing fluoroscopic images of the vertebrae of subjects who are undergoing standardised passive motion has recently been brought into clinical use for the assessment of surgical fusions. We have studied the differences between the behaviour of spinal linkages in subjects who are asymptomatic, and those who have had fusion operations. This paper describes the reliability, ranges and qualitative features of intervertebral motion patterns in 27 asymptomatic subjects and 3 fusion patients.

Methods and results: Thirty asymptomatic male volunteer subjects aged 19–40, underwent 2 –20 second sessions of fluoroscopic screening during 80 degrees of lumbar spine bending within 20 minutes of each other. Intervertebral sidebending motion from L2–5 was measured in 27 subjects whose images were judged suitable for tracking. Approximately 120 digitised images throughout each motion sequence were analysed 5 times by 2 blinded observers for intervertebral range and each result averaged. The intra-subject biological error (RMS), for range of intervertebral motion was 2.75° for Observer1 and 2.91° for Observer 2. The interobserver error for tracking the same screenings was 1.86° (RMS). At almost all levels, these motion patterns were remarkably regular.

Four male patients aged 33, 44, 45 and 52 years, who had undergone different spinal stabilisation procedures consisting of flexible stabilisation (DNESYS), posterior instrumented fusion, and anterior interbody fusion with facet fixation were investigated. Images were acquired and analysed in the same way except that a larger number of images (500 per screening) was utilised in each case. Four operated levels and 2 adjacent levels were analysed. All motion patterns were easily distinguishable from those of the normal subjects. The PLIF and DYNESYS stabilisations demonstrated no motion at the instrumented levels. The anterior inter-body fusion-transfacet fixation patient was shown to have developed a pseudarthrosis.

Conclusions: Detailed lumbar intervertebral bending patterns in asymptomatic subjects were distinguishable from the fused and adjacent-to fused segments in operated patients. Results suggest that there is sufficient reliability in the method to evaluate lumbar intersegmental ranges and motion patterns for fusion assessment.

Background: The prospect of a second operative procedure following an apparently unsuccessful spinal fusion is an unwelcome one. Since 1987, we have worked to develop an objective method of measuring the motion between vertebrae from fluoroscopic images. Successive versions have been evaluated for their reliability and validity. However, only the current one combines sufficiently reduced operator interaction with acceptable error limitation to be operationally useful as a tool for reporting findings about graft integrity for spinal surgeons. The current work brings this to an advanced prototype stage.

Methods and results: The measurement of lumbar intervertebral coronal and saggital plane motion in vivo using this technique is in 3 stages: Fluoroscopic screening of patients lying on a passive motion table Co-ordinated real-time digital acquisition of the intensifier images.

Registration of the images of each vertebra by templates which are automatically tracked and whose output is converted to inter-vertebral kinematic parameters and averaged for display and reporting.

Results are currently displayed as inter-vertebral angles throughout the motion that indicate whether or not solid fusion has been achieved. The Instrument Measurement Error is quantifiable and will vary with image quality, but can be improved by averaging. The technology is applicable to any imaging system of sufficient speed and resolution and may, for example, be used with MR in the future.

Conclusions: An advanced prototype version of this device is now approaching readiness for service as a routine procedure for use by specially trained radiographers. Its limitations will be determined mainly by the quality of the intensifier images. This can be expected, in the future, to benefit from yet further advances in the technology.

This study compared the effect of manipulation with a period of normal activity on the range of intervertebral sidebending.

Thirty asymptomatic male volunteers were randomised to treatment or control groups. All were subjected to low-dose X-ray screening through 80° of passive lumbar spine side-bending. Motion sequences were digitised at a 5Hz sampling rate. The treatment group (n=16) had rotary manipulation to each lumbar linkage, followed by normal activity. The control group (n=14) had normal activity only. Both groups were then re-screened. Each vertebral pair was tracked and intervertebral rotation throughout the motion measured. Three subjects were analysed 10 times for reliability and all intervertebral motion was tracked twice.

Twenty-one manipulated linkages and 10 controls met the reliability criteria. For non-manipulated segments the mean range at first screening was 14.2° (SD 1.39) and manipulated segments 12.8° (SD 3.81). The range of the non-manipulated segments increased by +0.9o and the manipulated segments by +0.4°.

The change in manipulated segments was negligible and similar to controls, although the instrument can be sufficiently reliable to measure a 2° difference. The technique is sufficiently robust to determine if spinal manipulation changes these ranges in selected patients.