Abstract
Introduction
Comparison of the DIERS Formetric 4D Scanner and plain Radiographs in terms of accuracy in AdolIdiopathic Scoliosis (AIS) Patients. This project aims to determine the accuracy of the DIERS scanner and help decide whether it could be used instead of radiographs for some, or all, AIS patients.
Material and Methods
Two patient lists were combined; both patients who underwent an operation between 2011–2014 and patients on the Spinecor bracing program. Only preoperative radiographs were used of the operative group. Both DIERS Formetric scan and radiograph were be taken on the same day to prevent time related changes to scoliotic curve. Patients were excluded if they had had an operation to treat their scoliosis. Patients with braces were included so long as their X-ray was of them not wearing the brace. There was no restriction on BMI. Some patients had a double curve (thoracic and lumbar) and it was decided to only compare the greater curve. The radiographs were assessed to show the Cobb angle and the position of the greatest scoliotic curve. To confirm the accuracy of measurements, a senior consultant remeasured a total of 50 X-rays. The results he found averaged a 3.1 degree difference to that measured by the medical students. It was decided that this showed sufficient correlation that not all of the Cobb angles needed to be re checked. Following the radiograph assessment the DIERS Formetric scans were reviewed.
Results
A total of 85 patients (41 Spinecor, 44 preoperative) were measured providing a total of 236 X-rays. 71 X-rays were excluded: 3 due to the Cobb angle not indicating scoliosis (<10°) and 68 due to a DIERS scannot being performed on the same day. A total of 165 X-rays remained for comparison. The range of Cobb angles was between 10.3 and 82 degrees. The DIERS scanner averaged a Cobb angle of -3.49° below that measured on the X-ray. However, although this result seems very good, it is not pure correlation that needs to be taken into account. It would be expected that correlation would be found but, more importantly is the difference between the angles measured on X-ray when compared with DIERS. Interestingly the scanner seemed to overestimate curves of a small severity and underestimate larger curves.
Conclusion
Overall the Formetric scanner did average a small underestimate of the Scoliosis angle measured, and showed a good correlation when compared with X-ray. However, especially in severe curves (>65°) the level of accuracy deteriorated rapidly. It could be concluded that the Formetric scanner could replace X-rays for follow up patients within boundaries of magnitude of curve, but that it could not replace X-rays for early diagnosis or when the patient is having a pre-operative assessment.