Assessment of Inter- and Intraobserver Reliability and Accuracy to Evaluate Apical Vertebral Rotation Using Four Methods: An Experimental Study Using a Saw Bone Model

Abstract

Study design: After placing a thoracic three-vertebra segment saw bones model on a standardized turntable, a series of anteroposterior (AP) radiographs were obtained and then set in increments to 90° rotation. Then the specimen was instrumented with 35-mm pedicle screws bilaterally and the rotation process and image acquisition were repeated.

Objective: Assess reliability and accuracy of spine surgeons evaluating apical vertebral rotation (AVR) through surgeon's visual x-ray estimation, Nash-Moe system, Upasani trigonometric method, and Upasani grading system.

Background context: Accurate assessment of AVR is one measure surgeons can evaluate the success of intervention and potential loss of correction in scoliotic deformities.

Methods: Eighty-four representative images of uninstrumented and instrumented vertebral segments were blinded. AVR was estimated by five experienced spinal deformity surgeons using the four techniques. The surgeons' grading, estimates, and errors compared to actual rotation were calculated. Inter- and intraobserver reliability were calculated using interclass correlation (ICC).

Results: Each surgeon's error for simple visual estimation for uninstrumented segments was 8.7° to 17.4° (average error = 12.4°), and for instrumented segments it was 7.7° to 11.3° (average error = 9.5°). Error for the Upasani trigonometric method was -6.7° to 11.6° (average error = 0.9°). There was relatively poor accuracy for Nash-Moe system (38.2%-53.9%) compared with the Upasani grading system (76.74%-80.23%). Interobserver reliability using the Nash-Moe method was good (0.844), with intraobserver reliability from fair to excellent (0.684-0.949). Interobserver reliability for the Upasani grading method was good (0.829), with intraobserver reliability from fair to good (0.751-0.869). We found excellent interobserver reliability for Upasani trigonometric classification (0.935) with fair to excellent intraobserver reliability (0.775-0.991). The interobserver reliability of surgeons' visual estimates was good (0.898) and the intraobserver reliability from good to excellent (0.866-0.99) without pedicle screws, and interobserver reliability was excellent (0.948) and intraobserver reliability also excellent (0.959-0.986) with pedicle screws.

Conclusions: We confirm that both techniques described by Upasani have good reliability and accuracy, appearing more accurate than surgeon's visual estimates or Nash-Moe system.

Level of evidence: Level III.

Keywords: Apical vertebral rotation; Nash-Moe system; Observer reliability; Upasani methods; Visual x-ray estimation.