Abstract
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.
Correspondence should be addressed to the editorial secretary: Dr Charles Pither, c/o British Orthopaedic Society, Royal College of Surgeons, 35-43 Lincoln’s Inn Fields, London WC2A 3PN.
