Reproducibility and validity of digital inclinometry for measuring cervical range of motion in normal subjects

Measurements of cervical range of motion (CROM) have been extensively reported in the past decade employing simple (goniometers) as well as sophisticated (electro-, magneto- and ultrasonography-based) systems. The recent introduction of the simple, user-friendly and relatively cheap digital inclinometer (DI) has opened a potentially new venue for measurement of this segment's motion. The purpose of the present study was to assess intra-tester reproducibility of DI-based findings as well as its validity in comparison to the ultrasonography-based Zebris CMS 70P (Zebris Medizintechnik Gmbh, Isny, Germany) for measuring CROM in normal subjects.

Active CROM of healthy women (n = 15) and men (n = 15) aged 24.2(2.4) years was measured on two sessions, Test 1 and Test 2, spread over 7.2(+/-0.7) days apart. On Test 1, the six primary movements of the neck (flexion, F; extension, E; right and left lateral flexion, RLF and LLF; and right and left rotations, RR and LR) were measured using the DI and the Zebris. On Test 2, the same measurements were performed using the DI only. All measurements were conducted by the same tester, with the subject in the seated position. The only exception was DI measurement of cervical rotation that was performed in the supine position due to the DI gravity-dependence, rendering DI measurements in the transverse plane irrelevant.

No significant differences were revealed between the two instruments with respect to the sagittal and frontal planes, whereas the DI-based CROM in rotation was significantly greater then its Zebris-based counterpart. The inter-device interclass correlation coefficients (ICCs) for the frontal were 0.72 (RLF) and 0.62 (LLF), and 0.77 (F) and 0.83 (E). Poor correlations were indicated for the rotations. The intra-tester reproducibility derived from the test-retest DI measurement indicated good to excellent reproducibility in all planes with ICCs ranging from 0.82 (LLF) to 0.94 (E). The Standard Error of Measurement ranged from 1.6 degrees (RR) to 2.6 degrees (F).

DI-based CROM measurements are reproducible and valid for recording sagittal and frontal plane motions in healthy subjects. The higher range in rotations, relative to the Zebris-based findings, is most probably attributable to the test position. Being relatively cheap, portable and convenient for tester and subject alike, the DI seems to be an effective instrument for assessing CROM.