The increasing popularity of mobile phones and hand held tablets incorporating micro-electromechanical system (MEMS) accelerometers has provided a new technology for accurate angle measurements. The ubiquitous nature of these devices and the ready availability of diverse software applications mean they may have a significant impact on efficiency and convenience in school screening programs and spinal clinics for assessment and diagnosis of spinal deformities. In the medical setting, software applications are available to measure Cobb angles and peripheral joint angles, display computed tomography and magnetic resonance imaging and provide alerts regarding clinical pathology results of individual patients direct to the treating doctor. These mobile technologies offer a convenient tool for the physician; however this necessitates scientific studies to ensure that measurements reported by the smartphone can be relied upon with respect to clinical management decisions for patients. In the current study, we present a novel methodology using static rib hump moulds fabricated from scoliosis patients and use this technique to assess the measurement performance of the iPhone compared to the Scoliometer. The rib humps of the plaster models ranged from 6 to 30° which represented a large range of trunkal asymmetries with the aim of being representative of those which would be encountered in clinical practice. As with the Bunnell Scoliometer, the iPhone together with the Scoliguage software application is a simple, inexpensive and portable method of measuring rib hump progression and a practical way to decrease exposure to radiation from repeated radiographs [3, 4, 12].
When the Spinal Orthopaedic Surgeons at our centre began trialling the iPhone to measure the rib hump of spinal deformity patients, it became clear that the iPhone alone, was for some patients, of inadequate length. For patients with more severe and/or angular rib hump deformities, the length of a mobile phone was unable to cover the full expanse of the ribcage rotational deformity. As a result the rib hump could be underestimated for these cases. The spinal surgeons were of the opinion that additional length was required to ensure measurement accuracy for all rib hump severities which lead to the development of the smartphone acrylic sleeve. The sleeve provides the required additional length and includes the central notch on the inferior edge of the drop-in device to mirror the shape of the traditional Scoliometer which is used to facilitate the placement of the device over the central spinous processes. Due to the larger size of the more recently available hand held tablets (iPad and similar devices), these devices are useful to measure rib hump angles in isolation but were not evaluated as part of the current study.
Although the correlation between trunkal asymmetry and vertebral column deformity is beyond the scope of this paper, it is important to recognise that when considering the correlation between trunk asymmetry measures and spinal deformity, previous work by Grivas et al., found that in children aged 7–13 years the concordance between trunk and spinal deformity was weak but became stronger for children aged 14–18 years. It should also be noted that trunkal asymmetry measurements alone are not sufficient for determining a definitive patient diagnosis and management plan .
In this study, the mean difference between pairs of iPhone and Scoliometer measurements was small, with a mean absolute difference of just over 2°, with a small bias of 1° toward higher rib hump angles with the iPhone and a 95% confidence interval of just over 3°. All of these figures are less than the minimum 5° difference which is widely accepted as signifying a clinically significant change in rib hump deformity. Therefore, we conclude that the iPhone is a clinically equivalent measuring tool to the traditional Scoliometer.
Furthermore, the inter- and intra-observer measurement variability using the iPhone were found to be similar to that of the Scoliometer in the current study. As with nearly all previous studies, the 95% confidence intervals for inter-observer variability were higher than those for intra-observer variability, for both the iPhone and the Scoliometer. Carman et al. note that the intra-observer variability is a more clinically relevant parameter than the inter-observer variability because intra-observer differences can lead to misdiagnosis of rib hump progression, thus influencing clinical treatment decisions. However we note that inter-observer variability may be equally important in large public spinal clinics where different clinicians are likely to assess patients on subsequent clinic review visits. Furthermore, the Intra-class Correlation Coefficients reported in this study (ICC = 0.92-0.95) compare favourably with ICCs reported (0.81-0.95) in previous Scoliometer studies [4–7]. This is to be expected since our use of plaster rib hump moulds eliminates the variability that is due to patient posture, patient fatigue and deformity progression which may all have contributed to the measurement variability results in previous studies. We note that using the iPhone in the clinical setting to measure trunkal asymmetry is subject to patient-positioning variability, and this variability is an unavoidable clinical factor which will occur regardless of the chosen measurement device used.