Is the inclinometer a valid measure of thoracic kyphosis? A cross-sectional study.

Background: Radiographs are used to monitor thoracic kyphosis in individuals with certain pathologies (e.g. osteoporosis), exposing patients to potentially harmful radiation. Thus, other measures for monitoring the progression of thoracic kyphosis are desirable. The gravity-dependent inclinometer has been shown to be reliable but its validity as a measure of thoracic kyphosis has not been investigated.

Objectives: To determine the validity of the gravity-dependent (analogue) inclinometer for measuring thoracic kyphosis.

Design: Cross-sectional study.

Method: Participants (n=78) were recruited as part of a larger study of shoulder impingement syndrome. Healthy participants (n=39) were age and gender matched to the shoulder impingement syndrome group (n=39). Measurements of thoracic kyphosis using a gravity-dependent inclinometer were compared with modified Cobb angle results obtained from a sagittal view of lateral radiographs. A Bland-Altman plot assessed agreement. The Pearson correlation coefficient and linear regression was used to determine the association between modified Cobb angles and inclinometer measurements.

Results: The Bland-Altman plot demonstrated good agreement. The Pearson correlation coefficient, r=0.62 (p<0.001), and linear regression model established a strong association between the thoracic kyphosis angle from the inclinometer readings and the modified Cobb angle measured from the radiographs (β=0.47, 95% CI 0.29, 0.65, p<0.001, R=0.52, n=78). Age as a confounder was included in the model (β=0.35, 95% CI 0.19, 0.51, p<0.001).

Conclusions: The gravity-dependent (analogue) inclinometer produces angles that are comparable to the modified Cobb angle obtained from radiographs, establishing its criterion validity as a safe clinical tool for measuring thoracic kyphosis.