BACKGROUND CONTEXT

1H magnetic resonance imaging (MRI) of the spine can rule out common causes of low back pain (LBP), such as disc protrusions or nerve root compression; however, no significant causal relation exists between morphology and the extent of symptoms. Functional MRI techniques, such as 23Na, may provide additional information, allowing indirect assessment of vertebral glycosaminoglycan concentrations, decreases in which are associated with early degenerative changes.

PURPOSE

To evaluate 23Na-MRI of asymptomatic healthy volunteers and symptomatic patients with LPB and correlate the results to the Pfirrmann classification of MRI disc morphology.

STUDY DESIGN

Retrospective cohort study at an academic medical center.

PATIENT SAMPLE

Two groups were studied: (1) 55 healthy volunteers (31 men, 24 women; mean age 28.8 years) and (2) 12 patients (6 men, 6 women; mean age: 35.3 years) with a recent history of LBP.

METHODS

Lumbar spines of the aforementioned groups were examined on a 3.0 T MRI scanner with morphological 1H and 23Na imaging. Intervertebral disc (IVD) 23Na at each level was normalized (23Nanorm). Distribution and differences between mean 23Nanorm corresponding to each Pfirrmann classification were evaluated in the two study groups (analysis of variance). Linear correlations between 23Nanorm, body mass index (BMI), and age were assessed (Pearson correlation coefficient). Gender-dependent differences were evaluated (paired t test).

OUTCOME MEASURES

Physiological measure: IVD 23Nanorm as determined by 23Na-MRI.

RESULTS

A normal distribution of 23Nanorm was confirmed for both groups (p=.072 and p=.073, respectively). The mean Pfirrmann score statistically significantly differed between them (p<.0001). 23Nanorm was statistically significantly reduced in degenerated IVDs (Pfirrmann scores 4+5) (p<.0001). No statistically significant differences were seen for the mean 23Nanorm of IVDs with the same Pfirrmann score in healthy volunteers and patients (.469<p<.967). Age (0.007<R2<0.202) and BMI (0.074<R2<0.288) showed either weak or no correlation to 23Nanorm. Mean 23Nanorm was significantly (p=.0002) greater in women relative to men.

CONCLUSIONS

The results underline the feasibility and robustness of 23Na-MRI of human IVDs and affirm, in a large cohort, decreases in 23Na IVD content seen with disc degeneration.