To quantitatively evaluate age-, sex-, and segment-related characteristics of lumbar disc degeneration (LDD) in patients with low back pain (LBP) using T1rho MRI, and assess its diagnostic value in early-stage disc degeneration.

A retrospective cross-sectional study was conducted on 89 LBP patients (balanced distribution across ages 20~29, 30~39, 40~49, 50~59 years and genders) admitted in Department of Orthopedics of First Affiliated Hospital of Army Medical University from March 2024 to February 2025. All patients underwent lumbar MRI including T1rho sequences. Two senior radiologists performed blinded Pfirrmann grading on 445 intervertebral discs and measured T1rho values of the nucleus pulposus (NP). Kappa test was used to evaluate the inter-observer agreement of Pfirrmann grading, and Spearman correlation coefficient was employed to analyze the correlation between Pfirrmann grade and NP-T1rho value. Disc degeneration characteristics were compared across different ages, sexes, and spinal segments. After adjusting for body mass index (BMI) and gender, partial correlation analysis was used to assess the correlation between NP-T1rho value of each lumbar segment and age. Receiver operating characteristic (ROC) curve was plotted to analyze the diagnostic performance of T1rho quantification for early LDD in LBP patients.

Good inter-observer agreement was observed in Pfirrmann grading across segments, with a Kappa coefficient of >0.70. The NP-T1rho values of all NP were in a strong negative correlation with Pfirrmann grades (r=-0.877, P<0.001). The NP-T1rho values were progressively decreased from Pfirrmann gradesⅠ to Ⅳ (P<0.001), with a steep decline between gradesⅡ and Ⅲ. The patients aged 20~29 and 30~39 years showed significantly higher NP-T1rho values in Pfirrmann grades Ⅰ and Ⅱ discs when compared with those aged 40~49 and 50~59 years (P<0.05). The males had significantly higher mean NP-T1rho values in grade I than the females (P=0.006). In the upper spinal segments (L1~L4), the males exhibited significantly higher mean NP-T1rho value than the females (P=0.025), and NP-T1rho value was decreased obviously with increase of age across all age groups (P<0.05). Except L5/S1 segments, NP-T1rho value and age in all spinal segments had significant negative correlations (r=-0.548~-0.349, P<0.001). The area under the curve (AUC) for distinguishing grade Ⅰ from Ⅱ discs was 0.824 (95%CI: 0.772~0.876), and for grades Ⅱ from Ⅲ was 0.978 (95%CI: 0.964~0.992).

T1rho MRI provides accurate quantitative assessment of early lumbar disc degeneration in LBP patients, with an NP-T1rho value of 79.87 ms serving as a discriminative threshold between grade Ⅱ and grade Ⅲ.