The menisci are not shock absorbers: A biomechanical and comparative perspective.

The lateral and medial menisci are fibrocartilaginous structures in the knee that play a crucial role in normal knee biomechanics. However, one commonly cited role of the menisci is that they function as "shock absorbers." Here we provide a critique of this notion, drawing upon a review of comparative anatomical and biomechanical data from humans and other tetrapods. We first review those commonly, and often exclusively, cited studies in support of a shock absorption function and show that evidence for a shock absorptive function is dubious. We then review the evolutionary and comparative evidence to show that (1) the human menisci are unremarkable in morphology compared with most other tetrapods, and (2) "shock" during locomotion is uncommon, with humans standing out as one of the only tetrapods that regularly experiences high levels of shock during locomotion. A shock-absorption function does not explain the origin of menisci, nor are human menisci specialized in any way that would explain a unique shock-absorbing function during human gait. Finally, we show that (3) the material properties of menisci are distinctly poorly suited for energy dissipation and that (4) estimations of meniscal energy absorption based on published data are negligible, both in their absolute amount and in comparison to other well-accepted structures which mitigate shock during locomotion. The menisci are evolutionarily ancient structures crucial for joint congruity, load distribution, and stress reduction, among a number of other functions. However, the menisci are not meaningful shock absorbers, neither in tetrapods broadly, nor in humans.

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.

Is step width decoupled from pelvic motion in human evolution?

Humans are the only primate that walk bipedally with adducted hips, valgus knees, and swing-side pelvic drop. These characteristic frontal-plane aspects of bipedalism likely play a role in balance and energy minimization during walking. Understanding when and why these aspects of bipedalism evolved also requires an understanding of how each of these features are interrelated during walking. Here we investigated the relationship between step width, hip adduction, and pelvic list during bipedalism by altering step widths and pelvic motions in humans in ways that both mimic chimpanzee gait as well as an exaggerated human gait. Our results show that altering either step width or pelvic list to mimic those of chimpanzees affects hip adduction, but neither of these gait parameters dramatically affects the other in ways that lead to a chimpanzee-like gait. These results suggest that the evolution of valgus knees and narrow steps in humans may be decoupled from the evolution of the human-like pattern of pelvic list. While the origin of narrow steps in hominins may be linked to minimizing energetic cost of locomotion, the origin of the human-like pattern of pelvic list remains unresolved.

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.

Academic Metrics Do Not Explain the Underrepresentation of Women in Orthopaedic Training Programs.

BACKGROUND: Among medical specialties, orthopaedic surgery persistently has one of the lowest representations of women in residency programs. This study examined whether differences exist in the academic metrics of the orthopaedic residency applicants and enrolled candidates by sex, which may be contributing to the persistent underrepresentation of women. Differences in enrollment rate in orthopaedic residency programs also were analyzed. We hypothesized that academic metrics were similar for female and male applicants and thus do not explain the underrepresentation of women in training programs. METHODS: Academic data of first-time applicants (n = 9,133) and candidates who enrolled in an orthopaedic residency (n = 6,381) in the U.S. from 2005 to 2014 were reviewed. The United States Medical Licensing Examination (USMLE) Step-1 and Step-2 Clinical Knowledge (CK) scores, Alpha Omega Alpha (AΩA) Honor Medical Society status, number of publications, and volunteer experiences were compared by sex and were analyzed over time. RESULTS: From 2005 to 2014, representation of female applicants increased from 12.6% to 16.0%, corresponding with an increase in the percentage of enrolled female residents (from 12.9% to 16.1%); 70.3% of male and 67.1% of female applicants to orthopaedic residency enrolled as residents (p = 0.082). Mean academic metrics increased significantly over time for applicants and enrolled candidates, irrespective of sex. Comparing by sex, the mean USMLE Step-1 scores of male applicants and enrolled candidates were approximately 2% higher than those of female applicants (p < 0.0001). Volunteer experiences of female applicants and enrolled candidates were 12% higher compared with male applicants (p < 0.0001). There was no significant difference in USMLE Step-2 CK scores, number of publications, or AΩA status by sex. CONCLUSIONS: The enrollment rate of male and female applicants in orthopaedic residencies was similar and did not change during the 10-year study period. The academic metrics of applicants and enrolled candidates have increased significantly. The academic metrics were found to be comparable by sex; the differences in USMLE Step-1 scores and volunteer experiences were small relative to the magnitude of accomplishments that these values represent. The growth rate of the proportion of women in orthopaedic residencies lags other surgical subspecialties but appears to be independent of academic metrics.

Fentanyl versus remifentanil-based TIVA for pediatric scoliosis repair: does it matter?

INTRODUCTION: Opioid-induced hyperalgesia (OIH) and acute opioid tolerance have been demonstrated extensively in patients undergoing adolescent idiopathic scoliosis (AIS) repair. Remifentanil infusion has been strongly linked to both tolerance and OIH in these patients; however, the impact of using an intraoperative fentanyl infusion has not been well studied. This study aims to determine if patients undergoing operative management of AIS have decreased opioid consumption and pain scores when an intraoperative fentanyl infusion is used as compared with a remifentanil infusion. METHODS: This is a retrospective chart review of patients with AIS who underwent posterior spinal fusion. During the period January 2012-June 2013, patients received remifentanil infusion as part of total intravenous anesthesia. From July 2013 to June 2015, remifentanil was replaced by fentanyl as standard protocol. The remifentanil cohort included 37 patients and the fentanyl cohort included 25 patients. The primary outcome was the total opioid consumption (morphine equivalents) in the first 24 hours postsurgery. Secondary outcomes included mean postoperative pain score in the first 24 hours postsurgery, postoperative opioid consumption 24-48 hours after surgery, time to extubation, time to assisted ambulation, length of stay, and incidence of postoperative nausea and vomiting. RESULTS: Compared with the remifentanil group, the fentanyl group had significantly higher postoperative opioid usage during the first 48 hours and significantly higher postoperative mean pain score during the first 24 hours. There was no difference between the two groups in mean pain score for 24-48 hours, extubation time, time to assisted ambulation, length of stay, or postoperative nausea and vomiting. DISCUSSION: Despite concerns for hyperalgesia and acute tolerance, remifentanil is widely used for intraoperative opioid infusions for surgical correction of AIS. This retrospective study examined a practice change from intraoperative remifentanil to intraoperative fentanyl as a potential approach to avoid OIH. Surprisingly, patients receiving fentanyl intraoperatively showed increased postoperative opioid use and pain scores in the first 24 hours postsurgery compared with the prior cohort receiving remifentanil. Substitution of fentanyl for remifentanil during surgical correction of AIS does not appear to solve the problem of OIH or acute tolerance. Prospective studies are needed to confirm this unexpected result.

Current Trends in Sex, Race, and Ethnic Diversity in Orthopaedic Surgery Residency.

BACKGROUND: The representation of minorities among medical students has increased over the past two decades, but diversity among orthopaedic residents lags behind. This phenomenon has occurred despite a recent focus by the American Academy of Orthopaedic Surgeons on the recruitment of minorities and women. OBJECTIVE: To analyze the impact of recent efforts on diversity in orthopaedic residents in comparison with other surgical specialties from 2006 to 2015. METHODS: Data from the American Association of Medical Colleges on residents in surgical specialty programs in the years 2006 to 2015 were analyzed. Linear regression models were used to estimate trends in diversity among orthopaedic residents and residents in other surgical specialties. A mixed model analysis of variance was used to compare rates of diversification among different specialties over time. RESULTS: Female representation in orthopaedic programs increased from 10.9% to 14.4% between 2006 and 2015. However, the rate of increase was significantly lower compared with other specialties (all P < 0.05) studied, except for urology (P = 0.64). Minority representation in orthopaedics averaged 25.6% over the 10-year period. Residents of Hispanic origin in orthopaedic programs increased (P = 0.0003) but decreased for Native Hawaiian/Pacific Islander (P < 0.0001). During the same period, white representation increased (P = 0.004). No significant changes were found in African Americans or Asian American representation. Diversity decreased among orthopaedic residents over the period studied (P = 0.004). CONCLUSIONS: Recruitment efforts have not reversed the sex, racial, and ethnic disparities in orthopaedic residents. Orthopaedics has the lowest representation of women and minorities among residencies studied. The rate of increase in women lags behind all surgical subspecialties, except for urology.

Underrepresented Minority Applicants Are Competitive for Orthopaedic Surgery Residency Programs, but Enter Residency at Lower Rates.

INTRODUCTION: Orthopaedic surgery residency programs have the lowest representation of ethnic/racial minorities compared with other specialties. This study compared orthopaedic residency enrollment rates and academic metrics of applicants and matriculated residents by race/ethnicity. METHODS: Data on applicants from US medical schools for orthopaedic residency and residents were analyzed from 2005 to 2014 and compared between race/ethnic groups (White, Asian, Black, Hispanic, and Other). RESULTS: Minority applicants comprised 29% of applicants and 25% of enrolled candidates. Sixty-one percent of minority applicants were accepted into an orthopaedic residency versus 73% of White applicants (P < 0.0001). White and Asian applicants and residents had higher USMLE Step 1. White applicants and matriculated candidates had higher Step 2 Clinical Knowledge scores and higher odds of Alpha Omega Alpha membership compared with Black, Hispanic, and Other groups. Publication counts were similar in all applicant groups, although Hispanic residents had significantly more publications. Black applicants had more volunteer experiences. CONCLUSIONS: In orthopaedic surgery residency, minority applicants enrolled at a lower rate than White and Asian applicants. The emphasis on USMLE test scores and Alpha Omega Alpha membership may contribute to the lower enrollment rate of minority applicants. Other factors such as conscious or unconscious bias, which may contribute, were not evaluated in this study.

Evaluation of Sex, Ethnic, and Racial Diversity Across US ACGME-Accredited Orthopedic Subspecialty Fellowship Programs.

In recent years, there has been an increasing trend toward subspecialization in orthopedic surgery via fellowships. This study sought to characterize sex, ethnic, and racial representation within each fellowship program and to examine their changes over time to identify trends and/or gaps. Demographic data were obtained from the National Graduate Medical Education Census. Diversity was assessed using proportions of minority and female trainees. The trends in racial, ethnic, and sex diversity from 2006 to 2015 for orthopedics as a whole and within each subspecialty were analyzed. Of 3722 orthopedic fellows, 2551 identified as white (68.5%), 648 as Asian (17.4%), 175 as Hispanic (4.7%), 161 as black (4.3%), 8 as Native Hawaiian/Pacific Islander (0.21%), and 3 as American Indian/Alaskan Native (0.08%). Further, 479 identified as female (12.9%). Racial and ethnic minority representation among orthopedic fellows did not increase over time. Female representation did increase proportionally with female residents. Asian fellows preferred reconstructive adult and spine, whereas white fellows preferred sports medicine, hand surgery, and trauma. Female fellows preferred pediatrics, hand surgery, and musculoskeletal oncology. Although sex diversity among orthopedic fellows has increased in the past 10 years, racial and ethnic minority representation lacked similar growth. Asian and female fellows preferred specific subspecialties over others. These data are presented as an initial step in determining factors that attract minority groups to different orthopedic subspecialties. Further research should define specific factors and identify ways to increase minority distribution among fellowship programs. [Orthopedics. 2018; 41(5):282-288.].

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. 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 manufacturer's 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 surgeon's 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.

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.

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

MINI: The objective of this study was to determine the safety limits of anterior/anterolateral pedicle screw breaches. Through clinical and cadaveric study, it appears that less than 4 mm of breach has a significantly lower likelihood of impingement on vital structures (P < 0.001). 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 ±â€Š0.6 mm, whereas screws not involving the aorta breached an average 3.9 ±â€Š0.2 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.

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

PURPOSE: To test for possible thermal injury and tissue damage caused by magnetic-controlled growing rods (MCGRs) during MRI scans. METHODS: Three 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. RESULTS: There 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. CONCLUSION: Recurrent 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 EVIDENCE: N/A.

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 MRI's 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.

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.

Triggered EMG Potentials in Determining Neuroanatomical Safe Zone for Transpsoas Lumbar Approach: Are They Reliable?

STUDY DESIGN: In vivo analysis in swine model. OBJECTIVE: The purpose of this study was to determine the accuracy of triggered EMG (t-EMG) and its reliability in lateral lumbar interbody fusions surgery. We also aim to document changes in psoas muscle produced during the approach. SUMMARY OF BACKGROUND DATA: Lateral lumbar interbody fusions is preferred over direct anterior approach because of lower complications, blood loss, and shorter recovery time. Threshold-EMGs are utilized for real-time feedback about nerve location; however, neurological deficits are widely reported, and are unique to this approach. Multiple factors have been hypothesized including neuropraxia from retractors and compression from psoas hematoma/edema. The variable reports of neurological complication even with t-EMGs indicate the need to study them further. METHODS: Eight swines underwent left-sided retroperitoneal approach. The nerve on the surface of the psoas was identified and threshold-EMGs were obtained utilizing a ball-tip, and needle probe. First EMG and threshold responses required to elicit 20-µV responses were recorded for 2 mm incremental distances up to 10 mm. In the second part, a K-wire was inserted into the mid-lumbar disc space, and a tubular retractor docked and dilated adequately. Postmortem CT scans were carried out to evaluate changes in psoas muscle. RESULTS: A t-EMG stimulus threshold of <5 mA indicates a higher probability that the probe is close to or on the nerve, but this was not proportional to the distance suggesting limitations for nerve mapping. Negative predictive value of t-EMGs is 76.5% with the ball-tipped probe and 80% with the needle probe for t-EMG ≥10 mA and indicates that even with higher thresholds, the nerve may be much closer than anticipated. Postoperative hematoma was not seen on CT scans. CONCLUSION: Threshold measurements are unreliable in estimating distance from the nerve in an individual subject and higher values do not always correspond to a 'safe zone." LEVEL OF EVIDENCE: 5.

Minimally Invasive Scoliosis Surgery: A Novel Technique in Patients with Neuromuscular Scoliosis.

Minimally invasive surgery (MIS) has been described in the treatment of adolescent idiopathic scoliosis (AIS) and adult scoliosis. The advantages of this approach include less blood loss, shorter hospital stay, earlier mobilization, less tissue disruption, and relatively less pain. However, despite these significant benefits, MIS approach has not been reported in neuromuscular scoliosis patients. This is possibly due to concerns with longer surgery time, which is further increased due to more levels fused and instrumented, challenges of pelvic fixation, size and number of incisions, and prolonged anesthesia. We modified the MIS approach utilized in our AIS patients to be implemented in our neuromuscular patients. Our technique allows easy passage of contoured rods, placement of pedicle screws without image guidance, partial/complete facet resection, and all standard reduction maneuvers. Operative time needed to complete this surgery is comparable to the standard procedure and the majority of our patients have been extubated at the end of procedure, spending 1 day in the PICU and 5-6 days in the hospital. We feel that MIS is not only a feasible but also a superior option in patients with neuromuscular scoliosis. Long-term results are unavailable; however, short-term results have shown multiple benefits of this approach and fewer limitations.