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142. Clinical Magnification Error in Lateral Spinal Digital Radiographs
68S
Proceedings of the NASS 22nd Annual Meeting / The Spine Journal 7 (2007) 1S–163S
PURPOSE: The purpose of this study was to determine the accuracy and reliability of CT or MR assessment of lumbar facet degeneration by comparing it to histological grading. STUDY DESIGN/SETTING: A prospective study of consecutive patients undergoing posterior lumbar fusion surgery. PATIENT SAMPLE: The patients were recruited from lumbar fusion candidates. Nineteen excised facets (inferior articular processes) from 9 patients were evaluated by radiographic and histological study. The average age of the patients was 58.2 (46–74) years. The diagnoses were of spinal stenosis in 5 patients and spondylolisthesis in 4. OUTCOME MEASURES: Using the four-point scale, the facet joints were graded by axial CT, T2-weighted MR images, MR cartilage imaging, and histological examination. Weighted kappa statistics and percentage agreement between the radiological and histological grading were calculated. Interobserver and intraobserver agreements were also evaluated. METHODS: All patients prospectively underwent CT scanning, routine axial T2-weighted MR scanning, and axial MR cartilage imaging using a DESS (double echo steady state) sequence. An experienced musculoskeletal radiologist graded the severity of facet joint degeneration on axial T2weighted, axial DESS sequence images, and axial CT scans separately, using the four point scale. The inferior articular processes including the cartilage and subchondral bone of the corresponding facets were resected during the surgery, and they were prepared for histological evaluation. A musculoskeletal pathologist graded the facet joint fragment also using the four-point scale. RESULTS: The histological grading of the facet joint degeneration was almost always grade 3 or 4 in our series, except for one facet which was graded as 2, even though many facets were graded as 2 or 1 on the CT and MR evaluation. The figures relating to underestimated grading on radiologic evaluations were 10(53%) by CT, 5(26%) by MR, and 7(37%) by DESS. It shows a tendency of underestimating the degree of the facet degeneration in current radiologic studies. The weighted kappa coefficients showed only mild to moderate correlation between histological and radiological grading by three different techniques. (0.30 for CT, 0.45 for T-2 axial MR, and 0.33 for DESS, respectively) Correlations between the three different imaging techniques were moderate to mild degree but they are statistically significant. The weighted kappa coefficients were 0.41 for CT and MR (p50.006), 0.39 for MR and DESS (p50.015), and 0.47 for CT and DESS (p50.004). CONCLUSIONS: The results of current study shows that the degree of facet degeneration can be underestimated by current radiologic modalities and a surgeon should be aware of this tendency during the preoperative evaluation of the patients considered for disc arthroplasty. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs.
referring clinicians with respect to the need for assessment by a spine specialist. PURPOSE: To determine the range of in-vivo magnification error in lateral spinal digital radiographs, and determine the effect of BMI on this error. STUDY DESIGN/SETTING: Observational case series. PATIENT SAMPLE: Patients who had undergone elective spine surgery by the senior investigator, and who had lateral spinal digital radiographs and CT/MRIs. OUTCOME MEASURES: Magnification of antero-posterior vertebral body dimensions (VBD) in lateral digital radiographs compared with CT/MRI. METHODS: An analysis of 250 patients with digital radiographs and CT/MRIs was performed. Digital imaging software was used to measure the VBD at C2, C5, L1, and L4. Magnification values were determined in comparison to CT/MRI. CT measurements were also compared to MRI. BMI for each patient was obtained by chart review. A paired t-test was performed to determine if the difference between CT and MRI values was significant. Tukey Multiple ANOVAs were performed on all magnification values at each level, comparing each BMI group to the other at that level. Linear regression analysis was performed at each level to determine the relationship, if any, between BMI and magnification values. RESULTS: Difference between the mean VBD as measured on CT and MRI was !0.1mm (n5130, p!0.2514, paired t-test). Mean magnification at the cervical spine was 21% (1.2160.01; range51.06–1.57 (n5177)) and 31% at the lumbar spine (1.3160.01; range51.09–1.63 (n5284)). Linear regression showed a significant positive correlation between BMI and magnification at both cervical and lumbar spine (Cervical: n596; p50.0019; Lumbar: n5144; p!0.0001). There was a significant difference in magnification between non-obese and obese patients at both the cervical and lumbar levels. Cervical: 1.1960.01 magnification for non-obese (n5136), versus 1.2660.01 for obese (n539) (p!0.0001). Lumbar: 1.2860.01 (n5207), versus 1.3860.01 (n571) (p!0.0001), respectively. CONCLUSIONS: Linear in-vivo measurements obtained on digital radiographs are subject to magnification errors at both cervical and lumbar spine. This error correlates to the patient’s BMI. Consequently, clinicaldecision making, regardless of the anatomical area, that is based on linear measurements obtained from radiographs that do not account for this error are invalid. In the scenario that this measurement is crucial (e.g. dynamic radiographs), this error can be corrected by comparison to morphometric data from CT/MRI. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. doi: 10.1016/j.spinee.2007.07.168
doi: 10.1016/j.spinee.2007.07.167
142. Clinical Magnification Error in Lateral Spinal Digital Radiographs Bheesma Ravi, BSC1, Raja Rampersaud, MD1; 1University of Toronto, Toronto, Ontario, Canada
143. Does Availability of Pre-operative Computed Tomography Improve the Accuracy of Pedicle Screw Placement? Lauren Friend, MD1, John Czerwein, Jr., MD1, Beverly Thornhill, MD1, Terry Amaral, MD1, Alok Sharan, MD1, Vishal Sarwahi, MD1; 1Montefiore Medical Center, Bronx, NY, USA
BACKGROUND CONTEXT: Currently, most radiology departments are shifting away from conventional radiograph images, and utilizing digital plain radiographs. From a diagnostic perspective, digital images have been shown to be comparable to conventional hard copy films, and are subject to the same magnification error. Clinicians may not always be aware of the magnitude or variability of magnification error on plain radiographs and consequently may accept linear measurements obtained from a digital spine radiograph as absolute or apply a commonly quoted mean magnification error of 15–20%. Linear measurements may play an integral role in the decision to recommend surgical intervention, particularly when used to assess stability. Furthermore, they may also influence the decisions of
BACKGROUND CONTEXT: Fine cut CT scans are often obtained as part of a standard preoperative work-up for patients who are to undergo spine surgery for deformity that may affect pedicle morphology and therefore complicate appropriate transpedicular screw placement. The benefit of such examination for accuracy of screw positioning is yet unproven in the literature. Pre-op CT scan is used as the standard protocol by most scoliosis su´rgeons utilizing thoracic pedicle screws for scoliosis correction. The advantage of CT scan is to assess the size of the pedicle, its orientation and morphology. The disadvantage of the use of CT scan is exposure to radiation, particularly when 2mm cuts are required.
Proceedings of the NASS 22nd Annual Meeting / The Spine Journal 7 (2007) 1S–163S
PURPOSE: The purpose of this study was to determine the accuracy and reliability of CT or MR assessment of lumbar facet degeneration by comparing it to histological grading. STUDY DESIGN/SETTING: A prospective study of consecutive patients undergoing posterior lumbar fusion surgery. PATIENT SAMPLE: The patients were recruited from lumbar fusion candidates. Nineteen excised facets (inferior articular processes) from 9 patients were evaluated by radiographic and histological study. The average age of the patients was 58.2 (46–74) years. The diagnoses were of spinal stenosis in 5 patients and spondylolisthesis in 4. OUTCOME MEASURES: Using the four-point scale, the facet joints were graded by axial CT, T2-weighted MR images, MR cartilage imaging, and histological examination. Weighted kappa statistics and percentage agreement between the radiological and histological grading were calculated. Interobserver and intraobserver agreements were also evaluated. METHODS: All patients prospectively underwent CT scanning, routine axial T2-weighted MR scanning, and axial MR cartilage imaging using a DESS (double echo steady state) sequence. An experienced musculoskeletal radiologist graded the severity of facet joint degeneration on axial T2weighted, axial DESS sequence images, and axial CT scans separately, using the four point scale. The inferior articular processes including the cartilage and subchondral bone of the corresponding facets were resected during the surgery, and they were prepared for histological evaluation. A musculoskeletal pathologist graded the facet joint fragment also using the four-point scale. RESULTS: The histological grading of the facet joint degeneration was almost always grade 3 or 4 in our series, except for one facet which was graded as 2, even though many facets were graded as 2 or 1 on the CT and MR evaluation. The figures relating to underestimated grading on radiologic evaluations were 10(53%) by CT, 5(26%) by MR, and 7(37%) by DESS. It shows a tendency of underestimating the degree of the facet degeneration in current radiologic studies. The weighted kappa coefficients showed only mild to moderate correlation between histological and radiological grading by three different techniques. (0.30 for CT, 0.45 for T-2 axial MR, and 0.33 for DESS, respectively) Correlations between the three different imaging techniques were moderate to mild degree but they are statistically significant. The weighted kappa coefficients were 0.41 for CT and MR (p50.006), 0.39 for MR and DESS (p50.015), and 0.47 for CT and DESS (p50.004). CONCLUSIONS: The results of current study shows that the degree of facet degeneration can be underestimated by current radiologic modalities and a surgeon should be aware of this tendency during the preoperative evaluation of the patients considered for disc arthroplasty. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs.
referring clinicians with respect to the need for assessment by a spine specialist. PURPOSE: To determine the range of in-vivo magnification error in lateral spinal digital radiographs, and determine the effect of BMI on this error. STUDY DESIGN/SETTING: Observational case series. PATIENT SAMPLE: Patients who had undergone elective spine surgery by the senior investigator, and who had lateral spinal digital radiographs and CT/MRIs. OUTCOME MEASURES: Magnification of antero-posterior vertebral body dimensions (VBD) in lateral digital radiographs compared with CT/MRI. METHODS: An analysis of 250 patients with digital radiographs and CT/MRIs was performed. Digital imaging software was used to measure the VBD at C2, C5, L1, and L4. Magnification values were determined in comparison to CT/MRI. CT measurements were also compared to MRI. BMI for each patient was obtained by chart review. A paired t-test was performed to determine if the difference between CT and MRI values was significant. Tukey Multiple ANOVAs were performed on all magnification values at each level, comparing each BMI group to the other at that level. Linear regression analysis was performed at each level to determine the relationship, if any, between BMI and magnification values. RESULTS: Difference between the mean VBD as measured on CT and MRI was !0.1mm (n5130, p!0.2514, paired t-test). Mean magnification at the cervical spine was 21% (1.2160.01; range51.06–1.57 (n5177)) and 31% at the lumbar spine (1.3160.01; range51.09–1.63 (n5284)). Linear regression showed a significant positive correlation between BMI and magnification at both cervical and lumbar spine (Cervical: n596; p50.0019; Lumbar: n5144; p!0.0001). There was a significant difference in magnification between non-obese and obese patients at both the cervical and lumbar levels. Cervical: 1.1960.01 magnification for non-obese (n5136), versus 1.2660.01 for obese (n539) (p!0.0001). Lumbar: 1.2860.01 (n5207), versus 1.3860.01 (n571) (p!0.0001), respectively. CONCLUSIONS: Linear in-vivo measurements obtained on digital radiographs are subject to magnification errors at both cervical and lumbar spine. This error correlates to the patient’s BMI. Consequently, clinicaldecision making, regardless of the anatomical area, that is based on linear measurements obtained from radiographs that do not account for this error are invalid. In the scenario that this measurement is crucial (e.g. dynamic radiographs), this error can be corrected by comparison to morphometric data from CT/MRI. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. doi: 10.1016/j.spinee.2007.07.168
doi: 10.1016/j.spinee.2007.07.167
142. Clinical Magnification Error in Lateral Spinal Digital Radiographs Bheesma Ravi, BSC1, Raja Rampersaud, MD1; 1University of Toronto, Toronto, Ontario, Canada
143. Does Availability of Pre-operative Computed Tomography Improve the Accuracy of Pedicle Screw Placement? Lauren Friend, MD1, John Czerwein, Jr., MD1, Beverly Thornhill, MD1, Terry Amaral, MD1, Alok Sharan, MD1, Vishal Sarwahi, MD1; 1Montefiore Medical Center, Bronx, NY, USA
BACKGROUND CONTEXT: Currently, most radiology departments are shifting away from conventional radiograph images, and utilizing digital plain radiographs. From a diagnostic perspective, digital images have been shown to be comparable to conventional hard copy films, and are subject to the same magnification error. Clinicians may not always be aware of the magnitude or variability of magnification error on plain radiographs and consequently may accept linear measurements obtained from a digital spine radiograph as absolute or apply a commonly quoted mean magnification error of 15–20%. Linear measurements may play an integral role in the decision to recommend surgical intervention, particularly when used to assess stability. Furthermore, they may also influence the decisions of
BACKGROUND CONTEXT: Fine cut CT scans are often obtained as part of a standard preoperative work-up for patients who are to undergo spine surgery for deformity that may affect pedicle morphology and therefore complicate appropriate transpedicular screw placement. The benefit of such examination for accuracy of screw positioning is yet unproven in the literature. Pre-op CT scan is used as the standard protocol by most scoliosis su´rgeons utilizing thoracic pedicle screws for scoliosis correction. The advantage of CT scan is to assess the size of the pedicle, its orientation and morphology. The disadvantage of the use of CT scan is exposure to radiation, particularly when 2mm cuts are required.