Abstract
Background Data: Radiography has been the mainstay of patient monitoring in scoliosis, but there is an increasing demand for its reduction to specific situations where treatment is to be decided or modified. There is concern that substitution of traditional methods with clinical impression and surface topography might not be feasible or safe.
Study Design: An outcome study of a year’s intake of new patients with adolescent idiopathic scoliosis using a protocol derived from experience with surface topography.
Method: Tolerance limits for observer and subject variation and observed changes over time were established and correlated with recorded Cobb angle changes. A “derived Cobb angle” was calculated from topographic spinal angles and radiographs of 75 patients with non-congenital scoliosis and tested against 141 similar patients. Cobb angle = 15.3 + 1.22* topographic spinal angle. A protocol was adopted with topography at every clinic visit, radiography reserved for cases with severe deformity, additional symptoms or where surgical intervention was considered. This protocol was tested on new adolescent idiopathic scoliosis (AIS) presentations to the general clinic in a single year (2001) with regard to status at presentation and outcome (n=49).
Results: Measurement error, on the average of four repositioned scans on 105 consecutive patients rounded up to 10 units on all parameters. In 75 patients with non-congenital scoliosis, change ≥10° in Cobb angle was always accompanied by a similar change on at least one topographic parameter. The mean difference was −3.9°, SD 14.7, and was greater in very small, larger or double curves and in obese patients. There was significant correlation (p< 0.01) between changes in the Cobb angle over time and that derived from the spinal angle. 49 girls presenting with a presumptive diagnosis of AIS were diagnosed thus: Normal, n=8, 4 after radiograph, all now discharged; Asymmetry, n=24, no radiographs, 11 discharged immediately, 10 after 0.5 – 1.5 years, 3 lost; AIS, n=17, Cobb angle 10–93°, 5 surgery, 6 discharged, 4 currently followed, 2 non-attendees.
Discussion: The incomplete correlation is acceptable, since within-subject variation of the Cobb angle is unknown but the observer variation was shown by Carman et al (JBJS 72(A):328–333) to be over 8°. The discrepancy between actual and derived Cobb angles at the extremes is understandable as small curves are inflated by the obligatory constant, while increased subcutaneous tissue smoothes the surface, and both double and large curves show more rotation of vertebral bodies than of spinous processes. This can be tolerated because in small curves, prediction is made on maturity indicators rather than Cobb angle, while at higher values, cosmesis is the issue, small changes in Cobb angle are less relevant, and pubertal status determines progression potential more effectively than radiographic measures.
Conclusion: Topography and reduced use of radiography allows safe monitoring of adolescent idiopathic scoliosis. It provides a validated cosmetic score which documents deformity progression, is an adjunct to clinical decision making and is mathematically related to the Cobb angle. Basic clinical modalities and careful consideration of every patient on an individual basis are still essential.
The abstracts were prepared by Emer Agnew. Correspondence should be addressed to Irish Orthopaedic Association, Secretariat, c/o Cappagh National Orthopaedic Hospital, Finglas, Dublin 11, Ireland.
