Yungtai Lo

Prevalence, Distribution, and Surgical Relevance of Abnormal Pedicles in Spines with Adolescent Idiopathic Scoliosis vs. No Deformity: A CT-Based Study.

BACKGROUND A thorough understanding of pedicle morphology is necessary for pedicle screw placement. Previous studies classifying pedicle morphology, to our knowledge, have neither discussed the range of abnormal morphology nor correlated patient or curve characteristics with abnormal morphology to identify at-risk pedicles. METHODS With the use of computed tomography (CT) images, we analyzed a total of 6116 pedicles from ninety-five patients without spinal deformity (forty-two females and fifty-three males) and ninety-one patients with adolescent idiopathic scoliosis (AIS) (sixty-eight females and twenty-three males). Pedicle morphology was classified as: Type A, a cancellous channel of >4 mm; Type B, a cancellous channel of 2 to 4 mm; Type C, a cortical channel of ≥2 mm; or Type D, a cortical or cancellous channel of <2 mm. Types B, C, and D were defined as abnormal. Patient demographic data and pedicle distribution were assessed for prevalence and likelihood of abnormal pedicle morphology. Postoperative CT images from fifty-nine patients with AIS were used to assess screw placement. RESULTS There was a significantly higher rate of abnormal pedicles in patients with AIS (p = 0.001). More abnormal pedicles were located in the thoracic spine compared with the lumbar spine both in patients without deformity (13.3% versus 2.0%) and patients with AIS (31.9% versus 2.4%). Significantly more abnormal pedicles were located on the concavity (p < 0.001), within the periapical region (p = 0.02), and on the apex of the curve (p = 0.03). Three times as many pedicle screws were misplaced in abnormal pedicles compared with normal pedicles (21% versus 7%). CONCLUSIONS Our study found a significantly higher prevalence of abnormal pedicles in the patients with AIS. Of the abnormal pedicles in these patients, most were in the thoracic spine, on the concave side, and in the periapical and apical regions. CLINICAL RELEVANCE Knowledge of abnormal pedicles may enable surgeons to anticipate and plan for difficult screw placement and further decrease risk to the patient.

Pedicle screws adjacent to the great vessels or viscera: A study of 2132 pedicle screws in pediatric spine deformity

Study Design: A retrospective study. Objective: To determine the incidence of pedicle screws close to vital structures and to identify patient or curve characteristics that increase the risk of screw misplacement. Summary and Background: Most pedicle screw misplacements are asymptomatic, thus they are frequently undetected. This study identifies the rate of screw placement in proximity to vital structures using postoperative computed tomography scans. Methods: A total of 2132 screws in 101 patients, who underwent posterior spinal fusion for spinal deformity, were reviewed. Screws adjacent to great vessels and viscera were identified and evaluated. Patients with screws at risk (group B) were compared with patients without screws at risk (group A). Patient and curve characteristics were analyzed to determine whether a correlation with screw misplacement exists. Results: A total of 40 at risk screws (∼2%) were identified in 25 patients (∼25%). These 40 screws were in proximity to the aorta (31), left subclavian artery (1), esophagus (3), trachea (3), pleura (1), and diaphragm (1). Of the 31 screws close to the aorta, 10 screws in 6 patients were impinging or distorting the aortic wall. One hundred percent of misplaced screws were in the thoracic spine, 50% were misplaced laterally, 50% were 35 mm long, 57.5% were in pedicles with normal morphology, and 75% were in curves between 40 and 70 degrees. Median screw misplacement rate was 10% in group A and 13% in group B. Adjusted for age and preoperative Cobb angle, patients with a higher misplacement rate were more likely to have screws adjacent to vital organs [adjusted odds ratio: 1.06 (95% confidence interval, 1.01–1.13), P=0.033]. Conclusions: Although only a small number of screws were at risk, they occurred in a large percentage of patients (25%). A single at-risk screw causes a significant complication for the patient. Postoperative imaging beyond routine x-rays may be needed to detect at-risk screws in asymptomatic patients.

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

Minimally Invasive Surgery in Patients With Adolescent Idiopathic Scoliosis: Is it Better than the Standard Approach? A 2-Year Follow-up Study.

Study Design:This is a retrospective controlled study. Objective:To compare the safety and efficacy of minimally invasive surgery (MIS) for the surgical management of adolescent idiopathic scoliosis (AIS) to the standard open posterior approach (PSF). Summary of Background Data:MIS approaches offer the potential to reduce soft-tissue trauma, intraoperative blood loss, and surgical-site infection. Thus far, MIS has been successfully utilized for the surgical correction of multilevel spine pathology in adults. It is not yet known if these results can be replicated in the surgical management of AIS. Materials and Methods:Seven MIS patients were compared with 15 PSF patients using minimum 2-year follow-up data. Parameters studied included preoperative patient and deformity characteristics, perioperative details, extent of deformity correction, and complications. Data were compared using Mann-Whitney tests for continuous variables and Fisher exact tests for categorical variables. Results:The MIS and PSF groups were similar for all preoperative characteristics collected (P>0.05). MIS patients had fewer fixation points (P=0.015), but a longer median operative time (P=0.011). There was no significant difference in estimated blood loss (EBL) (P=0.051), EBL/fixation point (P=0.204), or amount of fluids administered (P=0.888). Postoperative recovery did not differ between the 2 groups in number of intensive care unit days (P=0.362), length of hospital stay (P=0.472), time to mobilization (P=1.00), Visual Analogue Scale pain scores (P=0.698), or patient-controlled analgesia (P=1.00). The MIS technique had similar deformity correction, screw placement accuracy, and fusion status when compared with the PSF group. MIS patients had lower blood transfusion rate (P=0.02), shorter fusion (P=0.046) and fewer pedicle screws (P=0.015). Conclusions:The short-term advantages seen in MIS for adult scoliosis were not as obvious in our series. We found similar deformity correction and adequate fusion, however shortcomings related to learning curve, and instrumentation persist. MIS surgery is an innovative treatment for AIS that is technically feasible with significantly lower transfusion rate, shorter fusion lenghts and lesser pedicle screw fixation. Despite these advanatges, its role in AIS is currently difficut to define.

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

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.

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

MRIs Are Less Accurate Tools for the Most Critically Worrisome Pedicles Compared to CT Scans

STUDY DESIGN Retrospective review of magnetic resonance imaging (MRI) and computed tomographic (CT) scan imaging modalities. OBJECTIVE To determine MRIs capability of identifying pedicle morphology. SUMMARY OF BACKGROUND DATA Understanding pedicle morphology is important for accurate placement of pedicle screws. The gold standard modality to assess pedicle morphology is CT scan. However, CT scans carry the risk of radiation exposure. We have studied MRI as a potential alternative to CT scan. METHODS Nine hundred seventy pedicles in 33 spinal deformity patients were reviewed. Pedicle morphology was classified as follows: Type A (normal pedicle): >4-mm cancellous channel; Type B: 2-4-mm channel; Type C: any size cortical channel; and Type D: <2-mm cortical or cancellous channel. Pedicles in the same patients were classified on both low-dose CT scan and MRI. Concordance and discordance rates of MRI relative to CT scan in classification of pedicles into types A, B, C, and D were calculated for the entire length of the thoracolumbar spine and subgrouped into spinal sections. All images were evaluated by a single fellowship-trained musculoskeletal radiologist. RESULTS CT scan had 809 Type A, 126 Type B, 29 Type C, and 6 Type D pedicles. Group II (MRI) had 735 Type A, 203 Type B, 30 Type C, and 2 Type D pedicles. Analysis of the entire spinal column showed a concordance rate of 86.7% in classification of the pedicles into the 4 types. In the upper thoracic region, the concordance rate was 77.1%, main thoracic 85.5%, thoracolumbar 96%, and lumbar 98.1%. MRI has a poor overall accuracy for detecting Type C pedicles, only a 44.8% concordance with CT scan. MRI overcalls Type B pedicles, often calling Type A pedicles Type B. CONCLUSIONS MRI is an inferior alternative to CT scan as it has poor accuracy to properly detect pedicle abnormalities. The more severe the pedicle abnormality, the less diagnostic value the MRI has. LEVEL OF EVIDENCE Level III, diagnostic.