Reduced Lumbar Lordosis in Fibromyalgia: Radiographic Evidence of Lumbar Straightening by L1-L5 Cobb Angle.

Abstract

Background: Reduced lumbar lordosis has been observed in patients with low back pain, but lumbar straightening has not been well characterized in fibromyalgia. We hypothesized that fibromyalgia would be associated with reduced lumbar curvature on standing radiographs.

Objective: To evaluate lumbar lordosis, quantified by the L1-L5 Cobb angle, in patients with fibromyalgia compared with patients with other rheumatic diseases and low back pain.

Design: Retrospective, cross-sectional observational study.

Setting: Rheumatology office practice.

Participants: A consecutive series of 245 patients aged 18 to 70 years who underwent lumbar spine radiography for moderate-to-severe low back pain between 2012 and 2014 was reviewed. Of these, 164 patients met American College of Rheumatology criteria for fibromyalgia and 81 met criteria for another rheumatic disease, including rheumatoid arthritis, osteoarthritis, or polymyalgia rheumatica.

Intervention: Not applicable.

Main outcome measures: Lumbar lordosis was measured on standing lateral lumbar spine radiographs using the Cobb angle between the superior endplate of L1 and inferior endplate of L5. The prevalence of a nearly straight lumbar spine, defined as a Cobb angle ≤10 degrees, and more complete straightening, defined as a Cobb angle ≤5 degrees, was also assessed.

Results: Mean L1-L5 Cobb angle was significantly lower in patients with fibromyalgia than in rheumatic disease controls (15.2±12.2 degrees vs. 23.3±13.4 degrees, respectively; p <0.001). A Cobb angle ≤10 degrees was present in 72 (44%) patients with fibromyalgia compared with 17 (21%) controls (p <0.001). A Cobb angle ≤5 degrees was present in 42 (26%) patients with fibromyalgia compared with 5 (6%) controls (p <0.001).

Limitations: The study was retrospective and conducted at a single site. Both groups consisted of patients referred for lumbar imaging because of low back pain, and no asymptomatic healthy control group was included. Potential confounding factors, including body mass index, age, sex, pain duration, and medication use, were not formally analyzed.

Conclusion: Patients with fibromyalgia had significantly reduced lumbar lordosis and a higher prevalence of near-complete lumbar straightening than patients with other rheumatic diseases referred for lumbar imaging due to low back pain. Because lumbar straightening was also present in the comparator group, it is not specific enough to serve as a standalone diagnostic sign. Lumbar lordotic straightening may represent an additional radiographic observation associated with fibromyalgia and warrants prospective investigation, including evaluation of its potential relationship with paraspinal muscle tension.

Primary funding source: This research was privately funded and received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Trial registration: Not applicable.