Hipp, John A.

Study Design: Retrospective analyses of the center of rotation (COR) in asymptomatic volunteers and symptomatic patients. Objective: Document (i) level-specific COR position at radiographically normal levels in asymptomatic volunteers, (ii) preoperative COR abnormalities in symptomatic patients, and (iii) correlations between COR and other intervertebral motion metrics. Summary of Background Data: The COR has been discussed in many prior publications; however, our understanding of the normal position of the COR, the types and prevalence of COR abnormalities in patients, and the association between COR and other more common measures of intervertebral motion remains limited. Methods: Using automated, FDA-cleared software, we quantified COR and standard motion/alignment metrics from cervical flexion-extension radiographs of 341 asymptomatic volunteers and 1263 symptomatic preoperative patients. Level-specific 95% reference ellipses were derived from volunteers. Abnormality was defined as COR outside the level-matched ellipse. Associations between COR (cranial-caudal and anteroposterior) and rotation, translation, sagittal plane offset, disc height change, and standardized instability indices were evaluated. Results: In volunteers, COR was level-dependent and well summarized by 95% reference ellipses. The cranial-caudal position of COR was chiefly determined by rotation and translation, whereas the anteroposterior position related to sagittal plane offset and disc height change. COR also correlated with translational (TI-Index) and vertical (AVI/PVI) instability metrics. In symptomatic patients, most levels fell within reference ellipses; when deviations occurred, they were infrequent and multidirectional. Conclusions: COR can be automatically derived from flexion-extension radiographs. Deviations from level-specific reference ellipses provide an intuitive visualization of abnormal kinematics, complementing established motion metrics and linking cranial-caudal and anteroposterior shifts to specific patterns of translation, alignment, and instability.

Abstract Purpose: Pathologic fractures could be prevented if reliable methods of fracture risk assessment were available. A multicenter prospective study was conducted to identify significant predictors of physicians' treatment plan for skeletal metastasis based on clinical fracture risk assessments and the proposed CT-based Rigidity Analysis (CTRA). Experimental Design: Orthopedic oncologists selected a treatment plan for 124 patients with 149 metastatic lesions based on the Mirels method. Then, CTRA was performed, and the results were provided to the physicians, who were asked to reassess their treatment plan. The pre- and post-CTRA treatment plans were compared to identify cases in which the treatment plan was changed based on the CTRA report. Patients were followed for a 4-month period to establish the incidence of pathologic fractures. Results: Pain, lesion type, and lesion size were significant predictors of the pre-CTRA plan. After providing the CTRA results, physicians changed their plan for 36 patients. CTRA results, pain, and primary source of metastasis were significant predictors of the post-CTRA plan. Follow-up of patients who did not undergo fixation resulted in 7 fractures; CTRA predicted these fractures with 100% sensitivity and 90% specificity, whereas the Mirels method was 71% sensitive and 50% specific. Conclusions: Lesion type and size and pain level influenced the physicians' plans for the management of metastatic lesions. Physicians' treatment plans and fracture risk predictions were significantly influenced by the availability of CTRA results. Due to its high sensitivity and specificity, CTRA could potentially be used as a screening method for pathologic fractures. Clin Cancer Res; 21(11); 2514–9. ©2015 AACR.