Introduction:
Low back pain (LBP) is associated with intervertebral disc (IVD) degeneration, however there is still poor understanding of the exact relationship between IVD degeneration and LBP [1]. The development of degenerative changes over time for individuals, as well as for specific spinal motion segments, is difficult to predict and more knowledge is needed. Discography has been demonstrated to accelerate degenerative changes in injected IVDs [2]. Even if discography today is rarely used, long-term follow up of individuals previously obtaining discography can serve as an in-vivo human model for other annular injuries and might thus provide information regarding the association between annular injury and the degenerative process.

The aim of the current study was to investigate the longitudinal MRI appearance in LBP patients, in whom discography had been performed as diagnostic guidance.

Methods:
30 LBP patients, prospectively enrolled year 2007-2010 in a comparative discography-MRI study (1.5T, sagittal T2/T1-weighted) were asked to participate in this long-term follow-up. The reason for discography at inclusion was LBP (>6 months), severe enough to consider surgery. Those accepting to participate in the follow-up performed MRI of the lumbar spine during year 2021. The MRIs were evaluated, blinded, according to Pfirrmann classification, Endplate Classification Score (EPS) and HIZ for 6 IVD´s per individual at baseline and follow-up (Th12/L1- L5/S1). At baseline discography of 2-4 discs in each individual had been performed and data on which discs that had been injected or not were used here.

Results:
17 patients (6 male/mean 58.5 years;range 49-72), accepted participation, at this 11-14 year follow-up. Reasons for not participating were; 2 deceased, 5 unreachable, 1 had obtained a non-MR compatible device and 5 declined participation. Between baseline and follow-up, 10 (27 IVDs) of the 17 included patients had undergone fusion surgery. These fused IVD segments omitted adequate longitudinal evaluation and were therefore excluded. Out of the 75 non-fused IVDs, 30 were injected (discography) at baseline. Comparing groups of injected and non-injected IVDs significant differences were found at both baseline and follow-up regarding Pfirrmann grade and HIZ, and at follow-up also for EPS, with higher degeneration grade respectively EPS for injected IVDs (Table 1). However, in terms of morphological changes over time, no significant differences between the groups of injected and non-injected IVD´s were detected (Table 1).

Discussion:
When comparing discography-injected and non-injected IVDs over more than 10 years, no significant differences in progression of degenerative changes between the groups were detected, with reservation for inherent limitations being a case study. This long-term follow-up could thus not confirm previous findings that a needle-puncture of the disc (annular injury) induce excessive degenerative progression of the IVD. This study highlights how sometimes surprisingly little progress of degenerative changes, on an individual level, may be seen over a decade in spite of needle puncture and chronic LBP (Figure 1). The findings support the concept of high complexity regarding annular injury and the progression of disc degeneration and suggest that other factors than limited annular injuries may be of larger importance in development of spinal degeneration.