IntroductionThe precise etiology of low back pain is difficult to establish and remains unclear. It is believed, however, that degenerative changes in the spinal motion segment play an important role. These may occur in discs and associated facet joints, which are regarded as an interdependent functional spinal unit (FSU). Biomechanical studies clearly show the importance of the facet joints as a motion-restricting, as well as a stress-and load-sharing factor for the disc [1,9,13,19]. Therefore, it is conceivable that degenerative changes within this "three joint complex" influence each other, but the sequence of changes and their outcome are still matters for debate [6,15, 28]. However, a recent histologic investigation in sheep has clearly defined the possible development of facet joint arthritis as a response to disc degeneration [22].Various classifications of lumbar disc degeneration have graded the changes macroscopically [11,23,30], by MRI [35], and by discography [2]. The histologic features of lumbar disc degeneration have been described in detail [8,26,27, 34], but no histologic grading system has been proposed.Abstract Biomechanical and histologic studies have highlighted the close functional relationship between lumbar discs and their associated facet joints, and it is conceivable that their degenerative changes are interdependent. However, separation of cause from effect remains controversial. Hitherto, no study in humans has correlated the changes histologically. The present study assessed histologic changes in lower lumbar discs and their associated facet joints in patients under the age of 40 years using classification systems developed for this investigation. A specific objective was to correlate changes in discs and facet joints. Data from 15 lower lumbar spine specimens were obtained. Three parasagittal sections per disc and one section per facet joint were graded histologically. The results were correlated with age, within the functional spinal unit (FSU), and with the adjacent level. Histologic changes were found in discs and facet joints from all FSUs. There was no correlation between the age of the subject and the degree of degeneration of the disc or facet joints at either level. The extent of disc degeneration at L4/5 correlated significantly with changes at L5/S1 (P < 0.01). There was no correlation between changes in discs and the associated facet joints at either level. The results of the study showed that microscopic changes are seen in the disc and facet joints from an early age and can be quite marked in some individuals before the age of 40 years. A correlation of degenerative changes within the FSU could not be established.
