Abstract
Work in the clinical environment led to the identification of the need for an instrument that was capable of continuously monitoring lumbar spinal curves of patients with back pain in order to establish degree of compliance with therapist advice regarding posture and activity during their normal day. Additionally, work by others in the laboratory setting has started to reveal some differences in motion parameters between those with and without back pain. Although there are changes of, in particular, maximum angular velocity associated with pathology of the spine, these changes may be considered the effects of the pathology. By looking at motion parameters taken over longer periods of time, more subtle differences, hopefully more related to possible causes of back pain, may be eventually identified. Factors such as time spent at extremes of range of motion and degree of activity or inactivity may have as great an affect on the production of back pain as vibration and heavy physical load. Unfortunately, even those factors thought most likely to contribute to the onset of back pain have only ever been proven to explain a small percentage of cases.
By logging lumbar spinal curves continuously over many hours, profiles of lumbar spinal usage can be calculated thus enabling study of the relationships between posture, activity and pain production. Conventional instrumentation can not be used in the users normal environment either because of bulk or interference from everyday appliances.
A small optical fibre goniometer (OFG) and data logger has been developed that is capable of continuously monitoring lumbar sagittal curves. It is robust and suitable for use in normal working environments. For use on the lumbar spine, the instrument’s stiffness was kept to a minimum to make it as comfortable to wear as possible. This has resulted in an instrument that is capable of reproduction of standard curves, in a jig, with a RMS error of 1°. A stiffer instrument would produce smaller errors. Comparative studies against other instruments have been carried out but are not yet published. The instrument takes the form of a small base plate, designed to be glued to the skin over the sacrum, and a flexible rod that is held in place over the lumbar spinous processes by two guide tubes also glued to the skin.
The OFG weighs 25g and the datalogger 250g. The OFG and logger can be run safely for over 30 hours at a maximum logging frequency of 50 Hz. The datalogger has a facility for entry of coded information via selector switches which allow the user to put markers on the data train which could be activity of pain behaviour related.
Initial trials have been carried out using the instrument to obtain motion profiles of 80 “normal” individuals, 10 males and 10 females from each of 4 age groupings; 20 to 29; 30 to 39; 40 to 49; 50 to 59. Logging duration was normally six hours during their working day. Data was collected at 25Hz. It was established that the instrument was able to produce basic motion parameters that were similar to other instruments. Although, no significant differences in ROM were found with age there were significant differences found between males and females in terms of end range flexion and extension. Additionally, the amplitude of oscillations of spinal curve during walking was found to significantly decrease with age. This may have been indicative of general stiffening of the lumbar spine with age or associated with a possible decrease in walking speed with age.
It is envisaged that the instrument will find use in both ergonomic analysis as well as the study of the management of back pain. Use of the instrument to investigate patient compliance with therapist advice is planned and will hopefully help to develop the management of patients with low back trouble.
Future development of the instrument is hoped to include incorporation of a sensor to monitor the angle of the base plate, as this will allow better interpretation of the data from the logger post data collection. Additionally information of base plate angle will allow some simple load calculations to be made.
Repeatability trials have been carried out using human subjects. Here, the major source of variability was found to be the subjects themselves. Reapplication error was found to be small, compared to subject variability.
Comparison with measurements taken using the flexicurve technique and also the Skill System (similar to Isotrak or Fastrak) has been undertaken. Here the two systems were found to follow each other achieving correlation coefficients of 0.99. However, more critical forms of analysis revealed relatively large differences, although these were no greater than others that have compared the inclinometer technique with the flexicurve.
The abstracts were prepared by Dr P Dolan. Correspondence should be addressed to him at the British Orthopaedic Association, Royal College of Surgeons, 35-43 Lincoln’s Inn Fields, London WC2A 3PN.
