Validation of clinical measurement of kyphosis with a simple instrument, the Arcometer

Evaluation of concordance between different clinical surface measurements and radiographic measurements of kyphosis. To validate a new instrument, the Arcometer, in the clinical assessment of kyphosis. Although a few instruments are available that are designed to study the spine in the sagittal plane, they usually are not simple to use, and radiographic concordance data, when reported, are not optimal. One hundred forty-five outpatients with different degrees of kyphosis were submitted to 1) spinal radiography and Arcometer evaluation (32 patients, 53 measurements); 2) Arcometer evaluation by two different observers (95 patients, 123 measurements); and 3) Arcometer evaluation by the same observer at two different times (16 patients, 56 measurements). The mean difference between the radiographic and Arcometer values was 2.9 degrees, whereas the interobserver difference was 1.1 degrees and intraobserver difference was 0.1 degree; the linear correlation between the first and the second measurement in the three groups was higher than 0.98. However, the standard deviation was rather wide- 8.8 degrees in sample one, 5.6 degrees in sample two, and 5.7 degrees in sample three. The Arcometer is a practical and reasonably reliable instrument. However, there is considerable disagreement with radiography and some interobserver and intraobserver variability. The arcometer may be useful in following patients with known kyphosis and in the general population screening to decrease x-ray exposure.