Evaluation of the iPhone with an acrylic sleeve versus the Scoliometer for rib hump measurement in scoliosis

Abstract

Background: Vertebral rotation found in structural scoliosis contributes to trunkal asymmetry which is commonly measured with a simple Scoliometer device on a patient's thorax in the forward flexed position. The new generation of mobile 'smartphones' have an integrated accelerometer, making accurate angle measurement possible, which provides a potentially useful clinical tool for assessing rib hump deformity. This study aimed to compare rib hump angle measurements performed using a Smartphone and traditional Scoliometer on a set of plaster torsos representing the range of torsional deformities seen in clinical practice.

Methods: Nine observers measured the rib hump found on eight plaster torsos moulded from scoliosis patients with both a Scoliometer and an Apple iPhone on separate occasions. Each observer repeated the measurements at least a week after the original measurements, and were blinded to previous results. Intra-observer reliability and inter-observer reliability were analysed using the method of Bland and Altman and 95% confidence intervals were calculated. The Intra-Class Correlation Coefficients (ICC) were calculated for repeated measurements of each of the eight plaster torso moulds by the nine observers.

Results: Mean absolute difference between pairs of iPhone/Scoliometer measurements was 2.1 degrees, with a small (1 degrees) bias toward higher rib hump angles with the iPhone. 95% confidence intervals for intra-observer variability were +/- 1.8 degrees (Scoliometer) and +/- 3.2 degrees (iPhone). 95% confidence intervals for inter-observer variability were +/- 4.9 degrees (iPhone) and +/- 3.8 degrees (Scoliometer). The measurement errors and confidence intervals found were similar to or better than the range of previously published thoracic rib hump measurement studies.

Conclusions: The iPhone is a clinically equivalent rib hump measurement tool to the Scoliometer in spinal deformity patients. The novel use of plaster torsos as rib hump models avoids the variables of patient fatigue and discomfort, inconsistent positioning and deformity progression using human subjects in a single or multiple measurement sessions.

Figure 1

Measurement of the rib hump of a scoliosis patient in the forward bending position using a Scoliometer where the examiner is looking for the highest reading detected in the thoracic spine.

Figure 2

Plaster moulds of eight scoliosis patient’s rib humps arranged in random order on a standard height bench in preparation for measurement by each observer with either the Scoliometer or iPhone.

Figure 3

Measurement of the rib hump on a (a) plaster model and a (b) scoliosis patient, using the iPhone and Scolioguage software in combination with the acrylic sleeve to reflect the dimensions of the traditional Scoliometer.

Figure 4

Photographs of two scoliosis patients in the forward flexed position where use of a smartphone in isolation (without the acrylic sleeve) to measure the rib hump would result in failure to cover the full extent of the trunk rotational deformity.

Figure 5

Data points for all the iPhone and Scoliometer measurements plotted versus the mean rib hump angle for each plaster torso.

Figure 6

Scatter plot showing the signed measurement difference between pairs of iPhone/Scoliometer measurements performed by the same observer on the same rib hump model, plotted versus the mean Scoliometer rib hump angle.

Figure 7

Scatter plot of intra-observer difference between successive measurements (at least one week apart) by the same observer on the same rib hump model using the same measuring tool, plotted versus mean rib hump angle for each plaster model.