Validity and reliability of the metric measurements in the assessment of lumbar spine motion in patients with ankylosing spondylitis.

Study Design: A prospective, controlled clinical study performed in a tertiary care center.

Objective: To determine reliability and validity of low-tech measurements in assessment of range of motion (ROM) of lumbar flexion in ankylosing spondylitis (AS).

Summary Of Background Data: ROM measurements of lumbar flexion in patients with AS and healthy subjects are evaluated using original Schober test (OST), modified Schober index (MSI), and modified-modified Schober test (MMST) and compared with radiography.

Methods: Fifty patients with AS and 17 healthy subjects were included. A tape measure was used for measuring OST, MSI, and MMST, and goniometer was used for measuring angle of lumbar ROM on lateral radiographical views in erect position and maximal forward bending position.

Results: Angle between L1 and S1 vertebrae displayed a change upon flexion by 18.2° ± 18.7° in AS group and 30.4° ± 11.1° in controls (P = 0.002). Angle between L3 and S1 vertebrae was detected to change upon flexion by 25.3° ± 25.4° in AS group and 46.7° ± 14.2° in controls (P = 0.0001). A weak correlation was observed between MSI, OST, and L1-S1 radiographical mobility measurements as (P = 0.018 and P = 0.063) and MSI, OST, and L3-S1 radiographical mobility measurements as (P = 0.009 and P = 0.024), respectively for AS. There were correlations between MSI, OST, and radiographical mobility measurements in patients with AS (r = 0.333, P = 0.018, and r = 0.363, P = 0.009, respectively). There was a correlation between OST and radiographical mobility measurements in controls (r = -0.504, P = 0.039). Intrarater reliability was determined to be excellent for OST, MSI, and MMST.

Conclusion: Despite excellent intrarater reliabilities for OST, MSI, and MMST, only a weak correlation could be established between OST, MSI, and MMST and radiographical analysis. MMST was found not to reflect lumbar spine angular motions. Although MSI reflected spinal mobility better than OST, both seemed to reflect lumbar spine angular motion poorly.