Screw Malposition: Are There Long-term Repercussions to Malposition of Pedicle Screws?

BACKGROUND/INTRODUCTION: Pedicle screws have long been part of the continued advancements in spine surgery. Despite the many techniques that have been devised for their safe placement, malposition of screws continues to occur. Studies have evaluated the possible safe limits of screw malposition, and have given some insight on anatomic variation in spinal deformity. Review of the literature reveals several cases of deleterious long-term sequelae of malpositioned screws. DISCUSSION: With the current experience, proposed recommendations are provided to detect and avoid the potential long-term sequelae. Though the literature has helped to define possible concerning screws, there are no good studies predicting long-term risk. CONCLUSION: Improvements in technology and techniques, advancements in intraoperative confirmation and postoperative surveillance, studies that assist risk stratification, and expert consensus evaluations will help guide surgeons in their decision for addressing misplaced screws.

Are All Hardware Removals Equal?

The objective of this study is to report operative time and associated complications of six types of implants and to determine if surgeons are adequately compensated. Hardware removals were analyzed from 2014-2019. Implants were flexible nails, intramedullary rigid nails, long plates, screw(s), single guided-growth plates, and multiple guided-growth plates. Patient demographics, operative time, blood loss, complications, and relative value units (RVU)/min were collected. RVU/min was used to maximize rate. In total, 392 patients were analyzed. Long plate removals took significantly longer than screw removal, therefore RVU/min was significantly lower (p < 0.001). Long plate removals also took significantly longer, and RVU/min was significantly lower compared to guided-growth plate removal (p < 0.001). Intramedullary nails took significantly longer compared to flexible nails, nearly double the RVU/min (p = 0.02). The results from this study indicate that the RVU/ minute for these six different types of implant removals are not equal. Surgeons can use this data to set up their schedule to ensure maximum utilization. (Journal of Surgical Orthopaedic Advances 30(1):020-023, 2021).

Ultrasound elastography in children: establishing the normal range of muscle elasticity.

BACKGROUND: Ultrasound elastography allows assessment of tissue elasticity. To the best of our knowledge, the elastography appearance of muscles in normal children has not been described. OBJECTIVE: To determine the US elasticity of muscles in children at rest and following exercise. MATERIALS AND METHODS: Cine elastography of biceps brachii and rectus femoris muscles was obtained at rest and after exercise in 42 healthy children (23 males, 19 females; mean: 11.2 ± 4.4 years, range: 2-18 years). Elastography scores were assigned to each clip based on a five-point color scale. Mean elastography scores and standard deviations were calculated and resting and postexercise elastography scores were compared. RESULTS: Resting muscle elasticity was lower in the biceps brachii than in the rectus femoris (P = 0.008), and higher in the dominant than in the nondominant biceps brachii (P < 0.032). Rectus femoris elasticity was higher in males than females (P = 0.051). Postexercise muscle elasticity significantly increased in both the dominant and nondominant biceps brachii (P < 0.001) and in the rectus femoris (P < 0.001). There was no significant gender-related difference in postexercise muscle elasticity. Biceps brachii elasticity decreased and rectus femoris elasticity increased with increasing body mass index. Younger subjects had a greater change in muscle elasticity with exercise. CONCLUSION: Resting muscle elasticity in children is significantly lower in the biceps brachii than in the rectus femoris and in the nondominant biceps brachii than in the dominant biceps brachii. Elasticity significantly increases immediately postexercise in both muscle groups; resting differences between biceps brachii and rectus femoris elasticity, and dominant and nondominant biceps brachii elasticity, do not persist after exercise. The change in muscle elasticity with exercise is higher in younger children.

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.

Single Long-Incision Minimally Invasive Surgery.

STUDY DESIGN: Retrospective cohort study. OBJECTIVE: The objective of this study is to determine differences in outcomes in patients with adolescent idiopathic scoliosis undergoing spinal deformity correction surgery using a posterior spinal fusion (PSF) approach versus single and triple-incision minimally invasive surgery (MIS). SUMMARY OF BACKGROUND DATA: MIS increased in popularity as surgeons' focus moved towards soft tissue preservation, but it carries technical demands and increased surgical time compared with PSF. PATIENTS AND METHODS: Surgeries performed from 2016 to 2020 were included. Cohorts were formed based on surgical approach: PSF versus single long-incision MIS (SLIM) versus traditional MIS [3-incision MIS (3MIS)]. There were a total of 7 subanalyses. Demographic, radiographic, and perioperative data were collected for the 3 groups. Kruskal-Wallis and χ 2 tests were used for continuous and categorical variables, respectively. RESULTS: Five hundred thirty-two patients met our inclusion criteria, 294 PSF, 179 3MIS, and 59 SLIM.Estimated blood loss (mL) ( P < 0.00001) and length of stay (LOS) ( P < 0.00001) was significantly higher in PSF than in SLIM and 3MIS. Surgical time was significantly higher in 3MIS than in PSF and SLIM ( P = 0.0012).Patients who underwent PSF had significantly lower postoperative T5 to T12 kyphosis ( P < 0.00001) and percentage kyphosis change ( P < 0.00001). Morphine equivalence was significantly higher in the PSF group during total hospital stay ( P = 0.0042).Patients who underwent SLIM and 3MIS were more likely to return to noncontact ( P = 0.0096) and contact sports ( P = 0.0095) within 6 months and reported lower pain scores ( P < 0.001) at 6 months postoperation. CONCLUSION: SLIM has a similar operative time to PSF and is technically similar to PSF while maintaining the surgical and postoperative outcome advantages of 3MIS.

Ambulatory Neuromuscular Scoliosis Patients Have Superior Perioperative Results Than Nonambulatory Neuromuscular Scoliosis Patients and Can Approach Adolescent Idiopathic Scoliosis Outcomes After Posterior Spinal Fusion.

STUDY DESIGN: Retrospective cohort study. OBJECTIVE: This study aims to identify differences in perioperative outcomes between ambulatory patients with neuromuscular scoliosis (ANMS) and adolescent idiopathic scoliosis (AIS) following spinal fusion. SUMMARY OF BACKGROUND DATA: NMS patients have severe curves with more comorbidities and procedural complexity. These patients require extensive fusion levels, increased blood loss, and suffer increased periop complications. However, NMS patients have a variable severity spectrum, including ambulation status. METHODS: Chart and radiographic review of NMS and AIS patients undergoing PSF from 2005 to 2018. NNMS included NMS patients who were completely dependent (GMFCS IV-V). ANMS consisted of community ambulators without significant reliance on wheeled assistive devices (GMFCS I-III). Subanalysis matched by age, sex, levels fused and preoperative Cobb angle was conducted as well. Wilcoxon Rank-Sum, Kruskal-Wallis, χ2, and Fisher exact tests were performed. RESULTS: There were 120 patients in the NNMS group, 54 in ANMS and 158 in the AIS group. EBL was significantly lower for ANMS and AIS patients (P < 0.001). Complications within 30 days were similar between ANMS and AIS (P = 1.0), but significantly higher for NNMS (P < 0.001). Two (1.3%) AIS patients, (1.7%) nonambulatory NMS patients, and one (1.9%) ANMS patient required revision surgery (P = 1.0). However, all NMS patients had increased fusion levels, fixation points, and surgery time (P < 0.05). NNMS had significantly longer ICU (P < 0.001), hospital stay (P < 0.001), intraoperative transfusions (P < 0.001), and fewer patients extubated in the OR (P < 0.001) than ANMS and AIS patients. In the subanalysis, ANMS had similar radiographic measurements, EBL, transfusion, surgery time, extubation rate, and complication rate (P > 0.05) to AIS. CONCLUSION: Our data show radiographic outcomes, infections, revisions, and overall complications for ANMS were similar to the AIS population. This suggests that NMS patients who ambulate primarily without assistance can expect surgical outcomes comparable to AIS patients with further room for improvement in length of ICU and hospital stay.Level of Evidence: 4.

Scoliosis Surgery Normalizes Cardiac Function in Adolescent Idiopathic Scoliosis Patients.

STUDY DESIGN: Single-center retrospective chart review with minimum 2-year follow up. OBJECTIVE: To determine incidence of pulmonary hypertension in adolescent idiopathic scoliosis patients and to determine the effect of scoliosis surgery on pulmonary hypertension. SUMMARY OF BACKGROUND DATA: Spinal deformity in adolescent idiopathic scoliosis can increase right atrial and ventricular pressures secondary to restrictive lung disease. Pulmonary hypertension leading to cor pulmonale is the most feared outcome, however mild pulmonary hypertension in adolescent idiopathic scoliosis (AIS) patients has been reported. No study has previously examined changes in the improvement of right heart function following scoliosis surgery. METHODS: Cobb angle, 2D-echo signs of structural heart disease, aortic root dimensions, tricuspid regurgitant jet velocity (TRV), pulmonary function tests (PFTs), arterial blood gas (ABG), and patient demographics reviewed. Right ventricular systolic pressure (RVSP) estimated using Bernoulli equation (4[TRV]2) and right atrial pressure. RVSP ≥36 mmHg is a surrogate marker for pulmonary hypertension. All echocardiograms were read by board certified Pediatric Cardiologists. Logistic regression used to assess for differences in TRV between groups. RESULTS: Mean preoperative RVSP was significantly elevated in AIS patients (26.9 ±â€Š0.49; P < 0.001) compared with controls (17.25 + 0.88). Only 47 (21%) Group 1 patients had elevated preoperative TRV (≥2.8 m/s) versus none in Group 2 (P < 0.001). Additionally, logistic regression showed AIS patients have odds ratio of 3.29 for elevated TRV (P = 0.007)-an indirect measure of pulmonary hypertension. In all Group 3 patients, the cardiac function normalized postoperatively (mean TRV = 2.09 + 0.23; P < 0.001). No association found between Cobb angle, aortic root parameters, or pulmonary function tests. CONCLUSION: This study found 13.9% of patients with adolescent idiopathic scoliosis had elevated TRV while controls had no TRV abnormalities. Additionally, RVSP measurements demonstrated mild pulmonary hypertension in AIS patients. These abnormal values normalized postoperatively, indicating the benefits of scoliosis surgery on cardiac function in adolescent idiopathic scoliosis.Level of Evidence: 3.

Minimally Invasive Versus Standard Surgery in Idiopathic Scoliosis Patients: A Comparative Study.

STUDY DESIGN: Retrospective review of prospective case-control study. OBJECTIVE: To compare minimally invasive scoliosis surgery (MIS) and posterior spinal fusion (PSF) in a large group of patients. SUMMARY OF BACKGROUND DATA: MIS, has been shown to have benefits over standard PSF in adolescent idiopathic scoliosis (AIS). METHODS: Radiographic, clinical, and operative review of a multi-institutional prospective database from 2013 to 2018. MIS patients with minimum 2-year XR follow up were compared with open PSF technique patients. RESULTS: Four hundred eighty five patients were included; 192 MIS and 293 PSF. Preoperative Cobb (P = 0.231) and kyphosis were similar (P = 0.501). Cobb correction was comparable (P = 0.46), however percent improvement in thoracic kyphosis was significantly higher in MIS (P < 0.001). MIS had significantly lower blood loss (P < 0.001), transfusions (P < 0.001), fixation points (P < 0.001), opioid consumption (P = 0.001), and hospital stay (P < 0.001). Operative time was shorter (P = 0.001) and 30-day complications rate was similar (P = 0.81). CONCLUSION: This is the largest study comparing the surgical outcomes of MIS and PSF. MIS patients benefit from increased kyphosis, fewer transfusion, lower opioid consumption, and shorter hospital stay with similar Cobb correction. Increased postoperative kyphosis is likely from muscle sparing dissection in MIS.Level of Evidence: 3.

Seatbelts Save Lives, and Spines, in Motor Vehicle Accidents: A Review of the National Trauma Data Bank in the Pediatric Population.

STUDY DESIGN: Database study. OBJECTIVE: The purpose of this study was to use a large, nationwide database to determine prevalence of pediatric spine fractures in the United States, associated injuries, mechanisms of injury (MOI), use of safety devices, and mortality rates. SUMMARY OF BACKGROUND DATA: Spinal fractures account for 1% to 2% of pediatric injuries. However, they are associated with significant comorbidities and complications. Motor vehicle accidents (MVAs) are most responsible for increased incidence observed. METHODS: Retrospective review of National Trauma Data Bank between 2009 and 2014 (analysis in 2019) for all vertebral fractures in patients under 18 years of age. Subanalysis included those in MVAs where protective device use data were available. Patient demographics, MOI, geographical and anatomical region of injury, concomitant musculoskeletal/organ injury, protective device usage, hospital length of stay, surgical procedures, and mortality were all analyzed. RESULTS: A total of 34,563 patients with 45,430 fractured vertebrae included. Median age was 15 years. Most fractures (63.1%) occurred in patients aged 15 to 17 years, most frequent MOI was MVA (66.8%), and most common geographic location was the South (38%). Males sustained more spine fractures than females, overall (58.4% vs. 41.6%; P < 0.001) and in MVAs (54.4% vs. 45.6%; P < 0.001). Those in MVAs wearing seatbelts had lower odds of cranial (29.6% vs. 70.4%; odds ratio [OR] = 0.85, 95% confidence interval [CI]: 0.82-0.89; P < 0.001) and thoracic (30.1% vs. 69.9%; OR = 0.88, 95% CI: 0.84-0.91; P < 0.001) organ injury, multivertebral (30% vs. 70%; OR = 0.78, 95% CI: 0.73-0.83; P < 0.001) and concomitant nonvertebral fractures (30.9% vs. 69.1%; OR = 0.89, 95% CI:0.73-0.83; P < 0.001), and 21% lower odds of mortality (29.3% vs. 70.7%; OR = 0.79, 95% CI: 0.66-0.94; P = 0.009). Over 70% of drivers were not restrained during MVA, with majority of seatbelt violations incurred by males, ages 15 to 17, in the South. CONCLUSION: Over 60% of pediatric spinal fractures occur in children aged 15 to 17 years, coinciding with the beginning of legal driving. MVA is the most common cause and has significant association with morbidity/mortality. Nearly two- thirds pediatric spinal fractures sustained in MVAs occurred without seatbelts. Absence of seatbelts associated with >20% greater odds of mortality. Ensuring new drivers wear protective devices can greatly reduce morbidity/ mortality associated with MVA.Level of Evidence: 3.

Percutaneous radiofrequency epiphysiodesis in a rabbit model: a pilot study.

BACKGROUND: Techniques for epiphysiodesis have evolved from open surgical techniques requiring direct observation of the physis to percutaneous techniques performed with fluoroscopy. QUESTIONS/PURPOSES: Our purposes were to (1) describe a new minimally invasive surgical technique used to achieve epiphysiodesis using radiofrequency ablation, (2) document the effect of radiofrequency ablation on tibia length at 2, 6, and 12 weeks after ablation in a skeletally immature rabbit model, and (3) assess the effects of radiofrequency ablation on the histologic appearance of the proximal tibia physis and proximal tibia articular cartilage. MATERIALS AND METHODS: We performed epiphysiodesis of the rabbit proximal tibia on 15 skeletally immature male New Zealand White rabbits using a 22-gauge radiofrequency probe. The probe was positioned percutaneously and heated to 90 degrees C for 4 minutes on the medial and lateral (1/2) of the physis. The opposite tibia was used as a control. Five animals were sacrificed at 2, 6, or 12 weeks postoperatively. Tibia length was compared using Faxitron(R) radiographs and electronic calipers. Histology of the growth plate was assessed with light microscopy. RESULTS: We observed differences in tibia length between 4.16 mm and 11.59 mm (average 7.86 mm) at 12 weeks. The proximal tibia physis closed radiographically and histologically in all animals by 12 weeks. Histologic analysis showed no evidence of articular cartilage injury. CONCLUSIONS: This technique was reproducible and resulted in bone fusion of the rabbit proximal tibial growth plate. The use of radiofrequency ablation as described in this report may be used as an alternative to other surgical epiphysiodesis techniques. CLINICAL RELEVANCE: This technique may be useful for epiphysiodesis of small tubular bones of the hands and feet in humans.

A dual-team approach benefits standard-volume surgeons, but has minimal impact on outcomes for a high-volume surgeon in AIS patients.

STUDY DESIGN: Retrospective chart review of prospectively collected data. OBJECTIVE: This study seeks to evaluate the effect of number of surgeons, surgeon experience, and surgeon volume on AIS surgery. Recent literature suggests that utilizing two surgeons for spine deformity correction surgery can improve perioperative outcomes. However, the surgeon's experience and surgical volume are likely as important. METHODS: AIS patients undergoing PSF from 2009 to 2019 were included. Patient demographics, X-ray and perioperative outcomes were collected and collated based on primary surgeon. Analysis was performed for single versus dual surgeons, surgeon experience (≤ 10 years in practice), and surgical volume (less/greater than 50 cases/year). Median (IQR) values, Wilcoxon Rank Sums test, Kruskal-Wallis test, and Fisher's exact test were utilized. RESULTS: 519 AIS cases, performed by 4 surgeons were included. Two surgeons were highly experienced, 1 of whom was also high volume. Five cohorts were studied: a single senior high volume (S1) (n = 302), dual-junior surgeons (DJ) (n = 73), dual senior-junior (SJ) (n = 36), dual-senior (DS) (n = 21) and a single senior, standard-volume surgeon alone (S2) (n = 87). Radiographic parameters were similar between the groups (p > 0.05). Preoperative Cobb was significantly higher for DS compared to S1 (p = 0.034) Pre- and post-op kyphosis were similar (p > 0.05). Cobb correction was similar (p > 0.05). Levels fused, fixation points, anesthesia and surgical times were similar (p > 0.05). When the standard-volume surgeon operated with a second surgeon, radiographic parameters were similar (p > 0.05), but anesthesia time, surgical time, and hospital length of stay were significantly shorter (p < 0.05). Additionally, DJ had significantly shorter anesthesia and operative times (p < 0.001) and length of stay (p < 0.001) compared to S2. CONCLUSION: Standard-volume surgeons have better outcomes with a dual surgeon approach. Junior surgeons benefit operating with an experienced surgeon. A high-volume surgeon, however, does not benefit from a dual surgeon approach. LEVEL OF EVIDENCE: Level II.

A Study of Critical Events That Lead to Spinal Cord Injury and the Importance of Rapid Reversal of Surgical Steps in Improving Neurological Outcomes: A Porcine Model.

STUDY DESIGN: Porcine model. OBJECTIVE: To quantify critical vascular and mechanical events that occur before and during an evolving spinal cord injury. SUMMARY OF BACKGROUND DATA: Spinal cord injuries are one of the most devastating complications in spine surgery. Intraoperative neuromonitoring changes can occur as a secondary event of spinal cord compression and decrease in spinal cord blood flow (SCBF). Laser Doppler flowmetry has been well validated for measuring blood flow. METHODS: Seventeen pigs were studied, 14 of which completed the experiment. Multilevel, midthoracic laminectomies were performed. Laser Doppler flowmetry electrodes were placed on the dura to measure SCBF. Spinal cord injury was induced by incremental balloon inflation in the epidural space. The animals were separated into two groups. After motor-evoked potential (MEP) loss, group A underwent medical interventions and then balloon decompression approximately 20 minutes later. Group B underwent immediate balloon decompression followed by medical interventions. After interventions, wake-up test was performed and computed tomography scan measured thoracic spinal canal volume. RESULTS: Median SCBF changes were seen 15.8 (5.4-25.1) minutes before MEP loss. However, the 20% threshold interval was often reached before. At the 20% threshold, median pressure was 7 psi, balloon volume was 0.5 cm, and 50% of the spinal canal was compromised. In group A, no pigs moved and all had pathology indicating ischemia. In group B, 9 of 10 were found to be moving their hind legs with 7 indicating ischemia. CONCLUSION: Compression spinal cord injury is the end of a cascade involving increasing intracanal pressure, decreasing canal volume, and hypoperfusion. Rapid relief of compression leads to MEP return. SCBF monitoring can detect ischemia preinjury, giving surgeons an opportunity for early intervention. LEVEL OF EVIDENCE: 4.

The Screw-Aorta Dilemma: Changing Patient Position in Computed Tomography Scan Is Critical in Documenting Aortic Mobility.

STUDY DESIGN: Retrospective chart review. OBJECTIVE: To determine if obtaining a prone computed tomography (CT)-scan can better delineate a questionable screw-aorta relationship. SUMMARY OF BACKGROUND DATA: Pedicle screw misplacement rate is reported between 6% and 15%. Studies looking at misplacements on a per patient basis show up to 14% of patients have screws at risk (impinging vital structures). A screw abutting the aorta is a management challenge and often requires vascular surgery intervention. However, CT scans routinely done in supine position may overestimate screw-aorta relationship. Change in patient position may allow the aorta to roll away and, in most cases, reveal an uncompromised aorta. This will allow safe removal of pedicle screws without any vascular intervention. METHODS: One hundred eleven spinal deformity patients who underwent Posterior spinal fusion from 2004 to 2009 were evaluated. Patients with concerning screw-aorta relationship underwent additional prone CT scan. Mobility of the aorta was determined and distance was compared using prone and supine CT scans. RESULTS: Two thousand two hundred ninety five screws were reviewed, 36 screws in 18 patients were in proximity to the aorta. Fourteen screws (nine patients) appeared to be impinging the aorta. On prone CT, 13 out of the 14 instances the aorta moved away from the screw. The average distance at the screw level was 13.6 ±â€Š4.8 mm in supine position and 8.9 ±â€Š5.4 mm in prone position (P = 0.001). In one instance the relationship was unchanged on prone CT. No screw was noted to violate the lumen or distort the aorta. CONCLUSION: Supine CT scan alone is not entirely accurate in determining screw-aorta relationship. Prone-CT scan provides additional information for better delineation. This additional diagnostic step can change the treatment option by limiting the need for vascular intervention. When in doubt, the additional use of an arteriogram can allow for improved visualization. LEVEL OF EVIDENCE: 3.

Back-to-Back Surgeries in AIS Patients Can be Performed Safely Without Compromising Radiographic or Perioperative Outcomes: A 10-year Review.

STUDY DESIGN: A retrospective chart review of prospectively collected data. OBJECTIVE: The aim of this study was to determine whether back-to-back scoliosis surgeries can be performed safely without compromising outcomes and the reproducibility of the practice between institutions. SUMMARY OF BACKGROUND DATA: During the summer, spinal surgeons will often book multiple cases in one day. The complexity and demands of spinal fusion surgery call into question the safety. Change of operating room staff including anesthesiologists, nurses, and neurologists may introduce new risks. METHODS: From 2009 to 2018, index AIS surgeries were included. In Groups 1, 2, and 3, surgeries were performed by a single surgeon. In Group 4, they were performed by other institutional surgeons. Group 1: first surgery of the day, Group 2: second surgery of the day, Group 3: only surgery of the day, Group 4: only surgery of the day by different institutional surgeon. Additional analysis was done to determine reproducibility after a surgeon was moved from Institution 1 to Institution 2. RESULTS: Five hundred sixty-seven AIS patients were analyzed. Group 1 patients had similar radiographic outcomes compared with Group 2 (P > 0.05). Surgical time was similar (P = 0.51), but significantly more levels fused (P = 0.01). Compared with Group 3, Group 2 had a smaller preoperative Cobb (P = 0.02), shorter surgeries (P < 0.001), and length of stay (P = 0.04) but similar complication rate (P = 1). Compared with Group 4, Group 2 had smaller preoperative Cobb (P < 0.001), shorter surgery, and lower complication rate (P = 0.03). When determining reproducibility, institution 2 patients had significantly less blood loss, shorter surgeries, and shorter lengths of stay (P < 0.05). CONCLUSION: Although long and involved, back-to-back AIS surgeries do not compromise radiographic or perioperative outcomes. Changes in operating team do not appear to impact safety, efficiency, or outcomes. This study also found that the practice is reproducible between institutions. LEVEL OF EVIDENCE: 3.

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

MINI: The objective of this study was to evaluate the accuracy and reliability of pedicle screw placement using O-Arm at dosages below the manufactured recommended dose. O-Arm at reduced dose showed a 90% accuracy when compared with computed tomography; however, about 30% medial breaches were misclassified. STUDY DESIGN: Cadaveric study. OBJECTIVE: The objective was to evaluate O-Arm's 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 patient's 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 institution's 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.

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.

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.

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.

Loss of lower limb motor evoked potentials and spinal cord injury during the initial exposure in scoliosis surgery.

PURPOSE: To report a case of motor evoked potential changes and spinal cord injury during the initial dissection in scoliosis surgery. METHODS: Motor evoked potentials to transcranial electrical stimulation were recorded from multiple muscles. Somatosensory evoked potentials to limb nerve stimulation were recorded from the scalp. RESULTS: Clear motor evoked potentials were initially present in all monitored muscles. The patient was then pharmacologically paralyzed for the initial dissection. More than usual bleeding was encountered during that dissection, prompting transfusion. As the neuromuscular blockade subsided, motor evoked potentials persisted in the hand muscles but disappeared and remained absent in all monitored leg muscles. The spine had not been instrumented. A wake-up test demonstrated paraplegia; the surgery was aborted. There were no adverse somatosensory evoked potential changes. MRI showed an anterior spinal cord infarct. CONCLUSIONS: Copious soft tissue bleeding during the initial dissection might have lowered pressures in critical segmental arteries enough to cause spinal cord infarction through a steal phenomenon. The lack of somatosensory evoked potential changes reflected sparing of the dorsal columns. When neuromuscular blockade is used during the initial soft tissue dissection, motor evoked potentials should be assessed after this, but before spinal instrumentation, to determine whether there had been any spinal cord compromise during the initial dissection.

Scoliosis surgery in patients with adolescent idiopathic scoliosis does not alter lung volume: a 3-dimensional computed tomography-based study.

STUDY DESIGN: Retrospective study of surgically treated patients with adolescent idiopathic scoliosis. OBJECTIVE: To determine the change in lung volume after the surgical correction of scoliosis using a volumetric reconstruction of lung volume from computed tomographic (CT) scans. SUMMARY OF BACKGROUND DATA: Previously published studies have shown that pulmonary function tests improve after scoliosis correction; however, these results are not consistent. CT-based volumetric studies in patients with scoliosis have previously shown differences in lung volume and lung volume ratio when compared with a normal population. To date, no study exists that analyzes changes in these parameters after scoliosis surgery. METHODS: A total of 29 patients with adolescent idiopathic scoliosis who had pre- and postoperative CT scans on file were included in this study. Three-dimensional lung volume reconstruction was performed (TeraRecon software, TeraRecon, Inc., Foster City, CA). Appropriate masking methods were used to isolate the lung tissue. Total lung volumes, left and right lung volumes, and left/right lung volume ratio were obtained from the pre- and postoperative CT scans. Hemithoracic symmetry, pre- and postoperative Cobb angle, and kyphosis were also calculated. RESULTS: Neither total lung volume nor left/right lung volume ratio changed significantly postoperatively. Surgery did not significantly change total lung volume (P = 0.87), right lung volume (P = 0.69), left lung volume (P = 0.70), or the ratio between right and left lung volumes (P = 0.87). Hemithoracic asymmetry was significantly improved (P < 0.001). Median preoperative major Cobb angle was 53.2° and median preoperative kyphosis was 32.8°. Postoperatively, the median major Cobb angle was 15.0°, resulting in a 70% Cobb correction, and mean postoperative kyphosis was 31.1°. CONCLUSION: Corrective scoliosis surgery does not alter total lung volume or the ratio of right-to-left lung volume. Deformity correction leads to an improvement in the symmetry of the thoracic architecture and costovertebral joint mechanics, as evidenced by the improved hemithoracic asymmetry. Thus, the change in pulmonary function tests, which has been previously documented, may be a dynamic rather than a static phenomenon. LEVEL OF EVIDENCE: 4.