Lumbar disc herniation (LDH) is a common degenerative discogenic disease that frequently causes low back pain. LDH involves nerve root compression due to degeneration of the nucleus pulposus, and has a particularly high incidence in patients in their 20s–40s. Conservative treatment is most common, including use of drugs, physical therapy, nerve root block, and acupuncture [1,2]. However, surgery may be required if symptoms of painful radiculopathy become resistant to this treatment. Also, prolonged conservative treatment for LDH can restrict activities of daily living, cause social problems, and produce a financial burden due to loss of productivity [3]. Thus, surgical treatment may be more cost-effective once the effects on productivity are taken into account [4].

Intradiscal injection of various drugs provides a treatment option between conservative treatment and surgery [5]. This treatment is described as chemonucleolysis and results in dissolution of the nucleus pulposus of the intervertebral disc, as a less invasive treatment for LDH [6]. Excellent clinical outcomes of chemonucleolysis with chymopapain have been found in patients in Europe and the United States, but the protease activity and low substrate specificity may also produce nerve root and anaphylactic reactions [7,8]. In contrast, chondroitin sulfate ABC endolyase (condoliase), a mucopolysaccharide-degrading enzyme from Gram-negative rod Proteus vulgaris [9], specifically decomposes glycosaminoglycans in the nucleus pulposus, the moisture-retaining component of the vertebral disc, without affecting proteins. Therefore, condoliase causes less damage to surrounding tissues compared to chymopapain and may be safer due to the absence of a proteolytic effect [10].

In 2018, Matsuyama and Chiba et al. [11,12] reported favorable outcomes in phase II/III and III clinical trials of chemonucleolysis with condoliase. This method has been widely used in patients with LDH since it became clinically available in 2018, with a reported efficacy of 70–85% without any major adverse events [13,14]. After condoliase injection, a decreased herniation size is frequently observed and good clinical outcomes have been reported [[15], [16], [17], [18], [19]]. However, disc degeneration may also progress after dissolution of the nucleus pulposus [15,18] and only relatively short-term outcomes have been investigated to date using evaluation of disc degeneration on MRI [[13], [14], [15], [16], [17], [18], [19]]. Also, no reports have focused on patients in their teens and twenties. Therefore, the purpose of this study was to examine the effects of condoliase and intervertebral disc degeneration in this patient population, using Pfirrmann criteria on MRI and a particular focus on disc height.