Intervertebral disc degeneration describes the vicious cycle of the deterioration of intervertebral discs and can eventually result in degenerative disc disease (DDD), which is accompanied by low‐back pain, the musculoskeletal disorder with the largest socioeconomic impact world‐wide. In more severe stages, intervertebral disc degeneration is accompanied by loss of joint space, subchondral sclerosis, and osteophytes, similar to osteoarthritis (OA) in the articular joint. Inspired by this resemblance, we investigated the analogy between human intervertebral discs and articular joints. Although embryonic origin and anatomy suggest substantial differences between the two types of joint, some features of cell physiology and extracellular matrix in the nucleus pulposus and articular cartilage share numerous parallels. Moreover, there are great similarities in the response to mechanical loading and the matrix‐degrading factors involved in the cascade of degeneration in both tissues. This suggests that the local environment of the cell is more important to its behavior than embryonic origin. Nevertheless, OA is widely regarded as a true disease, while intervertebral disc degeneration is often regarded as a radiological finding and DDD is undervalued as a cause of chronic low‐back pain by clinicians, patients and society. Emphasizing the similarities rather than the differences between the two diseases may create more awareness in the clinic, improve diagnostics in DDD, and provide cross‐fertilization of clinicians and scientists involved in both intervertebral disc degeneration and OA.

Early and non-invasive detection of osteoarthritis (OA) is required to enable early treatment and monitoring of interventions. Some of the earliest signs of OA are the change in proteoglycan and collagen composition. The aim of this study is to establish the relations between quantitative magnetic resonance imaging (MRI) and biochemical concentration and organization in knee articular cartilage. A preregistered systematic literature review was performed using the databases PubMed and Embase. Papers were included if quantitative MRI and a biochemical assay or polarized light microscopy (PLM) was performed on knee articular cartilage, and a quantified correlation was described. The extracted correlations were pooled using a random effects model. 21 papers were identified. The strongest pooled correlation was found for delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) vs proteoglycan concentration (r = 0.59). T1ρ relaxation times are inversely correlated to proteoglycan concentration (r = -0.54). A weak correlation between T2 relaxation times and proteoglycans was found (r = -0.38). No correlation between T2 relaxation time and collagen concentration was found (r = -0.02). A heterogeneous set of correlations between T2 relaxation times and PLM were identified, including strong correlations to anisotropy. DGEMRIC measures are significantly correlated to proteoglycan concentration. The needed contrast agent is however a disadvantage; the T1ρ sequence was found as a non-invasive alternative. Remarkably, no correlation was found between T2 relaxation times and collagen concentration. T2 relaxation times is related to organization, rather than concentration of collagen fibers. CRD42020168337.