Human lumbar apophyseal joint damage and intervertebral disc degeneration.

OBJECTIVES To record the extent and location of lumbar apophyseal cartilage damage, and to ascertain if the extent of damage is correlated with the grade of disc degeneration, age, or both. METHODS The extent and location of fibrillated areas of the apophyseal cartilage of the joint surfaces of 29 lumbar motion segments were examined using computer aided image processing of Indian ink stained areas, and degeneration of the associated intervertebral discs graded using the method of Nachemson. RESULTS It was found that these joints showed a greater extent and prevalence of cartilage fibrillation than the knee, hip or ankle, with significant damage in specimens younger than 30 years. Damage was predominantly located peripherally, superiorly, and posteriorly in the concave superior apophyseal surfaces, and was predominantly peripheral and posterior in the inferior surfaces, with a tendency to be located inferiorly. There was a weak correlation between apophyseal joint damage and the intervertebral disc degenerative grade, but this was inconclusive, as both increased with age. CONCLUSIONS The pattern of damage exhibited by superior joint surfaces is most probably caused by tension on collagenous joint capsule fibres which insert into the surfaces posteriorly, so producing an area of fibrocartilage unsuited to loadbearing. Tension on such fibres would be greatest during spinal flexion. The pattern of damage of the inferior surfaces lends some support to the hypothesis that their apices impact the laminae of the lumbar vertebra inferior to them, consequent upon the degeneration and narrowing of the associated intervertebral disc. The predominantly peripheral location of fibrillation of both superior and inferior surfaces may be associated with inadequate mechanical conditioning of marginal joint areas. Disc degeneration cannot be the initial cause of apophyseal fibrillation in most specimens. The study indicates a need for regular spinal exercise, starting at a young age.