Terry Amaral

Reliability and Accuracy of MRI Scanogram in the Evaluation of Limb Length Discrepancy

The purpose of this study was to compare MRI scanogram with traditional radiographic methods for measurement of limb length. The authors hypothesized that MRI scanogram would be as reliable and accurate as radiographic scanogram in measurement of limb length without exposing patients to ionizing radiation. Twelve cadaveric femurs were measured using AP conventional radiographic scanogram, CT scanogram, MRI scanogram, and electronic caliper. Three orthopaedists performed two separate measurements using each technique. Intraobserver and interobserver variability was assessed for each of the three radiographic techniques. Accuracy was assessed by comparison of radiographic measurements to electronic caliper measurements of femur length. The reliability of all three radiographic limb length measurement techniques was excellent (ICC > 0.99). The accuracy of plain radiographic scanogram was slightly superior to CT scanogram and MRI scanogram. The mean absolute differences for radiographic, CT, and MRI scanograms compared with the gold standard, direct caliper measurement, were 0.52 mm, 0.68 mm, and 2.90 mm, respectively. All three scanogram techniques showed excellent reliability and accuracy. Radiographic scanogram remains the gold standard for leg length measurement. MRI scanogram is slightly less accurate compared with radiographic scanogram, but it does not use ionizing radiation. MRI scanogram merits clinical study and comparison with the traditional radiographic scanogram method for measurement of limb length.

Comparative analysis of perioperative differences between hybrid versus pedicle screw instrumentation in adolescent idiopathic scoliosis.

Study Design: Retrospective review of patients with adolescent idiopathic scoliosis (AIS). Objective: The objective of the study was to compare perioperative parameters and outcomes between pedicle screw and hybrid instrumentation for the treatment of AIS. Summary of Background Data: Pedicle screws have been shown to allow for better correction and fewer revisions than hybrid systems. However, no study has compared perioperative parameters and their effects on patient morbidity between these 2 types of instrumentation. Methods: Fifty-six pediatric patients with AIS were included in the study. Twenty-seven patients were treated with hybrid instrumentation and 29 patients were treated with all pedicle screw (APS) instrumentation. Intraoperative and perioperative measures were compared. Results: The mean preoperative major Cobb angle was 58.7 degrees in the hybrid group and 54.5 degrees in the APS group (P=0.222). Patients in the hybrid group required more time in the intensive care unit (2.0 vs. 1.1 d, P=0.041), more time to initial mobilization (5.1 vs. 2.1 d, P<0.001), and more days using patient-controlled analgesia (5.7 vs. 4.4 d, P=0.020). The hybrid group averaged less estimated blood loss than the APS group (619.6 vs. 947.4 mL, P=0.011). There was no difference in surgical time (P=0.183) or length of stay (P=0.072) between the groups. Thoracolumbosacral orthoses were used in 81.5% of patients in the hybrid group, but in no patients in the APS group (P<0.001). Postoperative complications occurred in 37.0% of patients in the hybrid group and 17.2% of patients in the APS group (P=0.095). Conclusions: This study demonstrates several advantages of pedicle screw constructs over hybrid constructs in the surgical treatment of AIS. The benefits of pedicle screw systems extend directly to the patient and can lower the overall cost of treatment.

Are We Underestimating the Significance of Pedicle Screw Misplacement

Study Design. A retrospective review of charts, x-rays (XRs) and computed tomography (CT) scans was performed. Objective. To evaluate the accuracy of pedicle screw placement using a novel classification system to determine potentially significant screw misplacement. Summary of Background Data. The accuracy rate of pedicle screw (PS) placement varies from 85% to 95% in the literature. This demonstrates technical ability but does not represent the impact of screw misplacement on individual patients. This study quantifies the rate of screw misplacement on a per-patient basis to highlight its effect on potential morbidity. Methods. A retrospective review of charts, XRs and low-dose CT scans of 127 patients who underwent spinal fusion with pedicle screws for spinal deformity was performed. Screws were divided into four categories: screws at risk (SAR), indeterminate misplacements (IMP), benign misplacements (BMP), accurately placed (AP). Results. A total of 2724 screws were placed in 127 patients. A total of 2396 screws were placed accurately (87.96%). A total of 247 screws (9.07%) were BMP, 52 (1.91%) were IMP, and 29 (1.06%) were considered SAR. Per-patient analysis showed 23 (18.11%) of patients had all screws AP. Thirty-five (27.56%) had IMP and 18 (14.17%) had SAR. Risk factor analysis showed smaller Cobb angles increased likelihood of all screws being AP. Sub-analysis of adolescent idiopathic scoliotic patients showed no curve or patient characteristic that correlated with IMP or SAR. Over 40% of patients had screws with either some/major concern. Conclusion. Overall reported screw misplacement is low, but it does not reflect the potential impact on patient morbidity. Per-patient analysis reveals more concerning numbers toward screw misplacement. With increasing pedicle screw usage, the number of patients with misplaced screws will likely increase proportionally. Better strategies need to be devised for evaluation of screw placement, including establishment of a national database of deformity surgery, use of intra-operative image guidance, and reevaluation of postoperative low-dose CT imaging. Level of Evidence: 3

Low-Dose Radiation 3D Intraoperative Imaging: How Low Can We Go? An O-Arm, CT Scan, Cadaveric Study

Study Design. Cadaveric study. Objective. The objective was to evaluate O-Arms ability at low-dose (LD) settings to assess intraoperative screw placement. Summary of Background Data. Accurate placement of pedicle screws is crucial because of proximity to vital structures. Malposition of screws may result in significant morbidity and potential mortality. O-arm provides real-time, intraoperative imaging of patients anatomy and provides higher accuracy in scoliosis surgeries, avoiding risk to vital structures. We hypothesize using LD or ultra-low doses (ULDs) to obtain intraoperative images allow for accurate assessment of screw placement, both minimizing radiation exposure and preventing screw misplacement. Methods. Eight cadavers were instrumented with pedicle screws bilaterally from T1 to S1. Screws were randomly placed using O-arm navigation into three positions: contained within the bone, OUT-anterior/lateral, and OUT-medial. O-arm images were obtained at three dosage settings: LD (kVp120/mAs125—lowest manufacturer recommended), very-low dose (VLD) (kVp120/mAs63), and ULD (kVp120/mAs39). Computed tomography (CT) scan was performed using institutions LD protocol (kVp100/mAs50) and gross dissection to identify screw positions. Results. LD, VLD, ULD, and CT for identifying “IN” screws relative to gross dissection had, a mean (standard deviation) sensitivity of 84.2% (±5.7), specificity of 76.1% (±9.3), and accuracy of 79.9% (±3.1) from all three observers. Across the three observers, the interobserver agreement was 0.67 (0.61–0.72) for LD, 0.74 (0.69–0.79) for VLD, 0.61 (0.56–0.66) for ULD, and 0.79 (0.74–0.84) for CT. Effective doses of radiation (mSV) for LD O-arm scan was 2.16, VLD 1.08, ULD 0.68, and our LD CT protocol was 1.05. Conclusion. Accuracy of pedicle screw placement is similar for O-arm at all doses and CT compared to gross dissection. Interobserver reliability was substantial for VLD and CT. Approximately 30% of medial screw breaches are, however, misclassified. ULD and VLDs can be used for intraoperative navigation and evaluation purposes within these limitations. Level of Evidence: N/A

A pilot cadaveric study of temperature and adjacent tissue changes after exposure of magnetic-controlled growing rods to MRI

PurposeTo test for possible thermal injury and tissue damage caused by magnetic-controlled growing rods (MCGRs) during MRI scans.MethodsThree fresh frozen cadavers were utilized. Four MRI scans were performed: baseline, after spinal hardware implantation, and twice after MCGR implantation. Cross connectors were placed at the proximal end and at the distal end of the construct, making a complete circuit hinged at those two points. Three points were identified as potential sites for significant heating: adjacent to the proximal and distal cross connectors and adjacent to the actuators. Data collected included tissue temperatures at baseline (R1), after screw insertion (R2), and twice after rod insertions (R3 and R4). Tissue samples were taken and stained for signs of heat damage.ResultsThere was a slight change in tissue temperature in the regions next to the implants between baseline and after each scan. Average temperatures (°C) increased by 0.94 (0.16–1.63) between R1 and R2, 1.6 (1.23–1.97) between R2 and R3, and 0.39 (0.03–0.83) between R3 and R4. Subsequent histological analysis revealed no signs of heat induced damage.ConclusionRecurrent MRI scans of patients with MCGRs may be necessary over the course of treatment. When implanted into human cadaveric tissue, these rods appear to not be a risk to the patient with respect to heating or tissue damage. Further in vivo study is warranted.Level of evidenceN/A.

Can Postoperative Radiographs Accurately Identify Screw Misplacements

STUDY DESIGN Retrospective case series. OBJECTIVE The objective of this study was to determine the safety of postoperative radiographs to assess screw placement. SUMMARY OF BACKGROUND DATA Previously defined criteria are frequently employed to determine pedicle screw placement on intraoperative supine radiographs. Postoperatively, radiographs are typically used as a precursor to identify screws of concern, and a computed tomographic (CT) is typically ordered to confirm screw safety. METHODS First, available postoperative PA and lateral radiographs were reviewed by 6 independently blinded observers. Screw misplacement was assessed using previously defined criteria. A musculoskeletal radiologist assessed all CT scans for screw placement. Pedicle screw position was classified either as acceptable or misplaced. Misplacements were subclassified as medial, lateral, or anterior. RESULTS One hundred four patients with scoliosis or kyphosis underwent posterior spinal fusion and had postoperative CT scan available were included. In total, 2,034 thoracic and lumbar screws were evaluated. On CT scan, 1,772 screws were found to be acceptable, 142 were laterally misplaced, 30 medially, and 90 anteriorly. Of the 30 medially placed screws, 80% to 87% screws were believed to be in positions other than medial, with a median of 73% (63% to 92%) of these screws presumed to be in normal position. Similarly, of the 142 screws placed laterally, 49% to 81% screws were identified in positions other than lateral, with a median of 77% (59% to 96%) of these screws felt to be in normal position. Of the 90 anteriorly misplaced screws, 16% to 87% screws were identified in positions other than anterior, with 72% (20% to 98%) identified as normal. The criteria produced a median 52% sensitivity, 70% specificity, and 68% accuracy across the 6 observers. CONCLUSION Radiograph is a poor diagnostic modality for observing screw position. LEVEL OF EVIDENCE Level IV.STUDY DESIGN Retrospective case series. OBJECTIVE The objective of this study was to determine the safety of postoperative radiographs to assess screw placement. Previously defined criteria are frequently employed to determine pedicle screw placement on intraoperative supine radiographs. Postoperatively, radiographs are typically used as a precursor to identify screws of concern, and a computed tomographic (CT) is typically ordered to confirm screw safety. METHODS First, available postoperative PA and lateral radiographs were reviewed by 6 independently blinded observers. Screw misplacement was assessed using previously defined criteria. A musculoskeletal radiologist assessed all CT scans for screw placement. Pedicle screw position was classified either as acceptable or misplaced. Misplacements were subclassified as medial, lateral, or anterior. RESULTS One hundred four patients with scoliosis or kyphosis underwent posterior spinal fusion and had postoperative CT scan available were included. In total, 2,034 thoracic and lumbar screws were evaluated. On CT scan, 1,772 screws were found to be acceptable, 142 were laterally misplaced, 30 medially, and 90 anteriorly. Of the 30 medially placed screws, 80% to 87% screws were believed to be in positions other than medial, with a median of 73% (63% to 92%) of these screws presumed to be in normal position. Similarly, of the 142 screws placed laterally, 49% to 81% screws were identified in positions other than lateral, with a median of 77% (59% to 96%) of these screws felt to be in normal position. Of the 90 anteriorly misplaced screws, 16% to 87% screws were identified in positions other than anterior, with 72% (20% to 98%) identified as normal. The criteria produced a median 52% sensitivity, 70% specificity, and 68% accuracy across the 6 observers. CONCLUSION Radiograph is a poor diagnostic modality for observing screw position. LEVEL OF EVIDENCE Level IV.

CT-Based Anatomical Evaluation of Pre-Vertebral Structures With Respect to Vertebral Body Using a Clock-Face Analogy.

Study Design. Retrospective Chart and CT Scan Review Objective. To define the relationship of the pre-vertebral structures for each level to assist in easier intraoperative visualization. Summary of Background Data. Vascular and visceral injuries from pedicle screws are well-known. This study will define the relationship of the pre-vertebral structures for each level to assist in avoiding potential complications. Methods. Pre- and post-operative CT scans were reviewed to define the pre-vertebral structures in relation to a clock-face. On reformatted axial slices, a clock-face was superimposed so that the left transverse process (TP) represented 8 o’clock and the right TP represented 4 o’clock. The positions of the TP on the clock-face did not change with rotation of the vertebra. Results. 108 patients had pre-operative CT scans. 78 had post-operative CT scans. Median age was 15 years, median Cobb angle was 50°, fused were 12, with 21 fixation points. 6324 axial CT slices were reformatted and analyzed. The trachea was located at 12 o’clock at T1, 1 o’clock at T2-T4, and between 12 and 1 o’clock at T5. The esophagus starts as a midline structure at 12 o’clock from T1-T2, moves to 11 o’clock from T3-T6, and further to 10 o’clock from T7-T9. The aorta starts at 10 o’clock at T5-T6, moves left at T7-T8 to 9 o’clock, and returns to 10 o’clock from T9-T11. It appears at 11’clock at T12, and at 12 o’clock from L1-L4. In about a third of cases, it is at 1 o’clock from L1 to L4, where it bifurcates. Conclusions. This CT-based anatomical study provides a simple reference frame to help surgeons visualize the vital structures at each level. This three-dimensional visualization is facilitated by fixing the position of TP on the clock-face. Knowledge of this anatomical relationship can help avoid direct injury, and is easier to recall intra-operatively. Level of Evidence: 3

Cadaveric Study of the Safety and Device Functionality of Magnetically Controlled Growing Rods After Exposure to Magnetic Resonance Imaging.

STUDY DESIGN Cadaveric study. OBJECTIVE To establish the safety and efficacy of magnetically controlled growing rods (MCGRs) after magnetic resonance imaging (MRI) exposure. MCGRs are new and promising devices for the treatment of early-onset scoliosis (EOS). A significant percentage of EOS patients have concurrent spinal abnormalities that need to be monitored with MRI. There are major concerns of the MRI compatibility of MCGRs because of the reliance of the lengthening mechanism on strongly ferromagnetic actuators. METHODS Six fresh-frozen adult cadaveric torsos were used. After thawing, MRI was performed four times each: baseline, after implantation of T2-T3 thoracic rib hooks and L5-S1 pedicle screws, and twice after MCGR implantation. Dual MCGRs were implanted in varying configurations and connected at each end with cross connectors, creating a closed circuit to maximize MRI-induced heating. Temperature measurements and tissue biopsies were obtained to evaluate thermal injury. MCGRs were tested for changes to structural integrity and functionality. MRI images obtained before and after MCGR implantation were evaluated. RESULTS Average temperatures increased incrementally by 1.1°C, 1.3°C, and 0.5°C after each subsequent scan, consistent with control site temperature increases of 1.1°C, 0.8°C, and 0.4°C. Greatest cumulative temperature change of +3.6°C was observed adjacent to the right-sided actuator, which is below the 6°C threshold cited in literature for clinically detectable thermal injury. Histologic analysis revealed no signs of heat-induced injury. All MCGR actuators continued to function properly according to the manufacturers specifications and maintained structural integrity. Significant imaging artifacts were observed, with the greatest amount when dual MCGRs were implanted in standard/offset configuration. CONCLUSIONS We demonstrate minimal MRI-induced temperature change, no observable thermal tissue injury, preservation of MCGR-lengthening functionality, and no structural damage to MCGRs after multiple MRI scans. Expectedly, the ferromagnetic actuators produced substantial MR imaging artifacts. LEVEL OF EVIDENCE Level V.STUDY DESIGN Cadaveric study. OBJECTIVE To establish the safety and efficacy of magnetically controlled growing rods (MCGRs) after magnetic resonance imaging (MRI) exposure. SUMMARY OF BACKGROUND DATA MCGRs are new and promising devices for the treatment of early-onset scoliosis (EOS). A significant percentage of EOS patients have concurrent spinal abnormalities that need to be monitored with MRI. There are major concerns of the MRI compatibility of MCGRs because of the reliance of the lengthening mechanism on strongly ferromagnetic actuators. METHODS Six fresh-frozen adult cadaveric torsos were used. After thawing, MRI was performed four times each: baseline, after implantation of T2-T3 thoracic rib hooks and L5-S1 pedicle screws, and twice after MCGR implantation. Dual MCGRs were implanted in varying configurations and connected at each end with cross connectors, creating a closed circuit to maximize MRI-induced heating. Temperature measurements and tissue biopsies were obtained to evaluate thermal injury. MCGRs were tested for changes to structural integrity and functionality. MRI images obtained before and after MCGR implantation were evaluated. RESULTS Average temperatures increased incrementally by 1.1°C, 1.3°C, and 0.5°C after each subsequent scan, consistent with control site temperature increases of 1.1°C, 0.8°C, and 0.4°C. Greatest cumulative temperature change of +3.6°C was observed adjacent to the right-sided actuator, which is below the 6°C threshold cited in literature for clinically detectable thermal injury. Histologic analysis revealed no signs of heat-induced injury. All MCGR actuators continued to function properly according to the manufacturers specifications and maintained structural integrity. Significant imaging artifacts were observed, with the greatest amount when dual MCGRs were implanted in standard/offset configuration. CONCLUSIONS We demonstrate minimal MRI-induced temperature change, no observable thermal tissue injury, preservation of MCGR-lengthening functionality, and no structural damage to MCGRs after multiple MRI scans. Expectedly, the ferromagnetic actuators produced substantial MR imaging artifacts. LEVEL OF EVIDENCE Level V.

When Do Patients Return to Physical Activities and Athletics After Scoliosis Surgery? A Validated Patient Questionnaire Based Study

Study Design. A retrospective chart review with a survey. Objectives. This study seeks to determine time of return to normal, physical and athletic activities, and delaying factors after all pedicle screw fixation. Summary of Background Data. Return to athletic activity after posterior spine fusion (PSF) in adolescent idiopathic scoliosis (AIS) is largely dependent on a surgeons philosophy. Some allow contact and collision sports by 6 and 12 months, while others avoid contact sports for 1 year and never allow collision sports. We have utilized a patient driven self-directed approach. Methods. The sports activity questionnaire (SAQ) was developed and activities were categorized into normal (school, gym, and backpack), physical (running, bending, and bicycling) and athletics (AAP criteria: noncontact, contact and collision sports). SAQ was validated through the “test-retest” method on 25 patients and retesting after 3 weeks to minimize recall bias. Questions with kappa >0.7 were included. Patient demographics, x-ray measurements, and perioperative details were recorded. Results. Ninety five patients completed the SAQ. By 3 months; 77% (72/93) returned to school, 60% (54/90) to bending, 52% (48/93) to carrying backpacks, 43% (37/87) to running, and 37% (30/81) to gym. By 6 months, 54% (27/50) returned to noncontact sports, and 63% (21/33) to contact sports. 79% and 53% returned to preoperative level of contact and noncontact sports, respectively. Higher body mass index (BMI) was a risk for delayed return (>3 mo) to school and gym (P < 0.05), while fusion below L2 and younger age for running, bending, and carrying backpacks (P < 0.05). In contrast, there was no patient/curve characteristics associated with a delay to sports. Lowest instrumented vertebra (LIV), Lenke types were not risk factors. There was no correction loss, implant failure, or complications. Conclusion. Patients return to athletics much earlier than expected; a quarter returned by 3 months, and over half by 6 months. Age and LIV are determinants for return to “physical activity.” Level of Evidence: 3

Pedicle Screw Safety: How Much Anterior Breach Is Safe? A Cadaveric and CT-Based Study

Study Design. Clinical retrospective chart review and basic science study. Objectives. To determine the safety limits of an anterior/anterorolateral misplaced pedicle screw on computed tomography (CT) scan in spinal deformity. Summary of Background Data. Although the limits of medial breaches (<4 mm) are known, the safe limits for anterior/anterolateral breaches in spine deformity are not yet defined. Methods. The present study had two parts. In part I, postoperative CT scans of 165 patients operated on for spine deformity were reviewed for screw misplacement (2800 screws). The amount of anterior/anterolateral breach was measured. Protrusions were also evaluated for proximity to vital structures. All scans were reviewed by musculoskeletal radiologist. In part II, eight cadavers were instrumented with 6 × 30 and 6 × 40 mm bilaterally from T1-S1. Screws were randomly inserted under navigation guidance either “IN” or “OUT-anterior/lateral.” CT scan was performed, followed by gross dissection to determine screw position. Results. Part I: 116(4.2%) screws were misplaced anterior/anterolaterally. Thirty-one (26.7%) were adjacent to vital structures. Fisher exact test showed 4 mm or less breach has significantly lower likelihood of impingement (P < 0.001). Screws adjacent/impinging the aorta protruded an average 5.7 ± 0.6 mm, whereas screws not involving the aorta breached an average 3.9 ± 0.2 mm, (P < 0.001). Part II: 285 screws were inserted. On CT scan, 125 were misplaced anterior/anterolaterally. On gross dissection, 89 were visibly misplaced; 23 were covered entirely by soft tissue but were palpable; and 13 were contained in bone. All 23 screws did not endanger any structures and protruded less than 4 mm on CT scan. Conclusion. Anterior/anterolateral breaches of 4 mm or less on CT poses no significant risk of impingement and therefore can be considered safe. Level of Evidence: 3