Grading apical vertebral rotation without a computed tomography scan: a clinically relevant system based on the radiographic appearance of bilateral pedicle screws.
METHODS
Bench-top and retrospective analysis to assess vertebral rotation based on the appearance of bilateral pedicle screws in patients with adolescent idiopathic scoliosis (AIS).


OBJECTIVE
To develop a clinically relevant radiographic grading system for evaluating postoperative thoracic apical vertebral rotation that would correlate with computed tomography (CT) measures of rotation.


BACKGROUND
The 3-column vertebral body control provided by bilateral pedicle screws has enabled scoliosis surgeons to develop advanced techniques of direct vertebral derotation. Our ability to accurately quantify spinal deformity in the axial plane, however, continues to be limited.


METHODS
Trigonometry was used to define the relationship between the position of bilateral pedicle screws and vertebral rotation. This relationship was validated using digital photographs of a bench-top model. The mathematical relationships were then used to calculate vertebral rotation from standing postoperative, posteroanterior radiographs in AIS patients and correlated with postoperative CT measures of rotation.


RESULTS
Fourteen digital photographs of the bench-top model were independently analyzed twice by 3 coauthors. The mathematically calculated degree of rotation was found to correlate significantly with the actual degree of rotation (r = 0.99; P < 0.001) and the intra- and interobserver reliability for these measurements were both excellent (kappa = 0.98 and kappa = 0.97, respectively). In the retrospective analysis of 17 AIS patients, the average absolute difference between the radiographic measurement of rotation and the CT measure was only 1.9 degrees +/- 2.0 degrees (r = 0.92; P < 0.001). Based on these correlations a simple radiographic grading system for postoperative apical vertebral rotation was developed.


CONCLUSIONS
An accurate assessment of vertebral rotation can be performed radiographically, using screw lengths and screw tip-to-rod distances of bilateral segmental pedicle screws and a trigonometric calculation. These data support the use of a simple radiographic grading system to approximate apical vertebral rotation in AIS patients treated with bilateral apical pedicle screws.
Upasani
Vidyadhar V
VV
Rady Children's Hospital and Health Center, San Diego, CA, USA.
Chambers
Reid C
RC
Dalal
Ali H
AH
Shah
Suken A
SA
Lehman
Ronald A
RA
Newton
Peter O
PO
D000293:Adolescent; D000886:Anthropometry / Q000295:instrumentation / Q000379:methods; D001863:Bone Screws / Q000592:standards*; D002648:Child; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation / Q000379:methods; D008297:Male; D019635:Neurosurgical Procedures / Q000295:instrumentation / Q000379:methods; D015588:Observer Variation; D017063:Outcome Assessment, Health Care / Q000379:methods; D011237:Predictive Value of Tests; D019651:Plastic Surgery Procedures / Q000295:instrumentation / Q000379:methods; D012189:Retrospective Studies; D012399:Rotation; D012600:Scoliosis / Q000000981:diagnostic imaging* / Q000473:pathology / Q000601:surgery; D012680:Sensitivity and Specificity; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods; D013131:Spine / Q000000981:diagnostic imaging* / Q000473:pathology / Q000601:surgery; D014057:Tomography, X-Ray Computed / Q000379:methods