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Lumbar intervertebral fusion : - factors associated with the success of surgery Wing, Peter Courtenay

Abstract

After the performance of a pilot study of 28 W.W. II veterans who had all had lumbar intervertebral fusion at least two years previously, an in-depth retrospective evaluation was performed on one hundred (100) Workmen's Compensation Board patients, all with a similar follow-up period subsequent to lumbar intervertebral fusion. All patient characteristics were evaluated, including historical, social, physical, radiological and psychological parameters. A success index was derived by factor analysis of twenty (20) variables all representing various aspects of the patients current functional status. This was used as a basis to analyze the remaining data by multiple correlations. These correlations were studied and 55 highly "success"-correlated variables were selected for further factor analysis. This factor analysis identified eight (8) factors closely associated with success or failure of the fusion operation. In order of importance they were identified thus: "Normally"-functioning lumbar spine. Mobility of body. Freedom from neuroticism. High pain tolerance. Minimum number of surgical operations. Freedom from persistent nerve root deficit. Optimism, ambition. General health and fitness. These eight orthogonal (totally non-correlating) factors alone independently accounted for approximately 80% of the variance of "success" as determined by the statistical index. It is felt that certain of these factors may be etiological in connection with the low back problem and prospective work is necessary to shed further light on this. The methods used in patient evaluation were examined and it is felt that certain of these measures are inadequately objective and involve measurement of several factors at one time. For example, measures of range of movement as conventionally used in orthopaedics were found to show a very high correlation with certain of the psychological measures of abnormality. Some showed poor correlation with age which is contrary to published data on the range of motion in different planes determined radiologically. It is suggested that alternative methods be used which would provide greater specificity. Increased use of quantitative radiological methods is suggested as this provides an accurate way of comparing patients from a purely structural viewpoint. The psychological profile of the patient is shown to be of great importance as twothirds of the patients showed an elevation of one or more Minnesota Multiphasic Personality Inventory scales over a T-score of 70; in a random population this figure would be approximately 3%. It is suggested that psychological evaluation should be used at all stages of low back pain disease to assist in management of the patient. Pseudarthrosis was determined to exist in the presence of two out of three radiological features: Movement at the fusion site on bending x-rays. Presence of a defect in the bone mass. Persistence of the posterior apophyseal joints. The presence of pseudarthrosis did not correlate significantly with success or failure of the operation. It is stressed that only information obtainable in an accurate way of all patients was used in this study and this prevented the use of operative reports, from the patients time of surgery which was frequently inaccurate and was not uniform in the information they provided. It was decided not to use symptomatic information as remembered by the patient from before his operation as this would be coloured by too many subsequent events and would not be matched by comparable physical, radiological or psychometric results. Similarly, success was not correlated with the individual surgeon as some surgeons were represented by too few cases and some patients would have been seen by several surgeonsaat different stages in their illness. This evaluation of the clinical and statistical methods provides much information of use in the clinical and prospective experimental setting. It does not attempt to provide definitive answers regarding the causes of low back pain: prospective investigation is required for this, and the nature of the required studies for this is outlined.

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