Validity of three lumbar sagittal motion measurement methods: surface inclinometers compared with radiographs

Three surface methods for measuring lumbar sagittal motion (LSM) were tested for validity using radiographs as the "gold standard" reference. The three methods used were the Pleurimeter V double inclinometer, the carpenter double inclinometer, and the computerized sensor single inclinometer. In this study, 30 volunteers were examined independently by three occupational health professionals. Each volunteer rotated twice through three stations at which LSM was measured by each of the three methods. Radiographs were made during the first rotation. Predictability of the skin marks of T12 and S1 for the corresponding bone measures was acceptable for one examiner, mixed for another, and unacceptable for a third. The intraclass correlation coefficients (ICCs) ranged from 0.81 to 0.99, with half above the acceptable level of 0.90. However, the skin marks and the bone measures showed a linear relationship for all examiners (r > or = 0.89). For flexion and extension, all ICCs between the radiograph and each surface method were far below 0.90, indicating poor validity for each surface method. We concluded that skin placement of T12 and S1 has a linear relationship to bony landmarks, and that each of the tested surface methods does not validly measure LSM.