The association of lumbar intervertebral disc calcification on plain radiographs with the UTE Disc Sign on MRI.

Purpose: The pathogenesis and the clinical impact of disc calcification are not well known. Utilizing ultra-short time-to-echo (UTE) magnetic resonance imaging, the UTE Disc Sign (UDS) (i.e., hypo/hyper-intense disc band) was developed and found to be more significantly related to pain and disability than the conventional T2-weighted (T2W) MRI. It has been hypothesized that the UDS may represent mineralized deposits in the disc. The following study addressed the relationship between disc calcification on plain radiographs to that of the UDS on MRI.

Methods: A cross-sectional study was performed on 106 Southern Chinese subjects (50% male; mean age 52.3 years). Standing lateral plain radiographs as well as T2W and UTE MRI of L1-S1 (n = 530 discs) were performed of all subjects. Lateral radiographs were used to localize disc calcification of the lumbar spine, T2W MRI was utilized to assess disc degeneration based on a defined grading scheme, and the UTE MRI was implemented to detect the UDS (hyper- or hypo-intense band across a disc). Disc degeneration and UDS scores were summed to represent cumulative scores. Subject demographics and disability profiles (Oswestry Disability Index: ODI) were obtained.

Results: Disc calcification on plain radiographs was observed in 33.9% of subjects (55.5% males; mean age 54.3 years), whereas UDS was noted in 40.5% of subjects (51.1% males; mean age 55.0 years). Of these subjects, 66.6% calcification and 74.4% UDS occurred at the three lowest lumbar levels, while multilevel calcification and UDS involved 19.4 and 39.5%, respectively. 72.2% of subjects with plain radiographic disc calcification had corresponding UDS on UTE MRI (p < 0.001). Multilevel disc calcification on plain radiographs was associated with multilevel UDS (71.4%, p < 0.001). Both the number of calcified disc levels on plain radiographs and the number of UDS levels were also significantly and positively correlated with each other (r = 0.58, p < 0.001). Subjects with disc calcification and positive UDS as well as individuals with increased disc degeneration scores on T2 W MRI were significantly older (p < 0.05). The cumulative UDS score on UTE MRI significantly correlated with worse ODI scores (r = 0.31; p = 0.001), whereas cumulative disc calcification scores on plain radiographs did not (r = 0.15; p = 0.19).

Conclusions: This is the first study to compare the UDS on UTE MRI with disc calcification on plain radiographs. Disc calcification was correlated with the UDS on UTE, suggesting that the UDS may represent disc calcification. However, UTE MRI appears to be a more sensitive imaging modality in identifying subtle and unique disc changes that may not be revealed on plain radiographs or conventional MRI. This disconnect may rationalize the significant correlation of UTE with disability in comparison with the conventional imaging, further stressing its potential clinical importance.