Does a dedicated "Scoliosis Team" and surgical standardization improve outcomes in adolescent idiopathic scoliosis surgery and is it reproducible?

PURPOSE: The objective of this study was to determine if standardization improves adolescent idiopathic scoliosis (AIS) surgery outcomes and whether it is transferrable between institutions. METHODS: A retrospective review was conducted of AIS patients operated between 2009 and 2021 at two institutions (IA and IB). Each institution consisted of a non-standardized (NST) and standardized group (ST). In 2015, surgeons changed institutions (IA- > IB). Reproducibility was determined between institutions. Median and interquartile ranges (IQR), Kruskal-Wallis, and χ2 tests were used. RESULTS: 500 consecutive AIS patients were included. Age (p = 0.06), body mass index (p = 0.74), preoperative Cobb angle (p = 0.53), and levels fused (p = 0.94) were similar between institutions. IA-ST and IB-ST had lower blood loss (p < 0.001) and shorter surgical time (p < 0.001). IB-ST had significantly shorter hospital stay (p < 0.001) and transfusion rate (p = 0.007) than IB-NST. Standardized protocols in IB-ST reduced costs by 18.7%, significantly lowering hospital costs from $74,794.05 in IB-NST to $60,778.60 for IB-ST (p < 0.001). Annual analysis of surgical time revealed while implementation of standardized protocols decreased operative time within IA, when surgeons transitioned to IB, and upon standardization, IB operative time values decreased once again, and continued to decrease annually. Additions to standardized protocol in IB temporarily affected the operative time, before stabilizing. CONCLUSION: Surgeon-led standardized AIS approach and streamlined surgical steps improve outcomes and efficiency, is transferrable between institutions, and adjusts to additional protocol changes.

Effect of Pedicle Screw Size on Surgical Outcomes Following Surgery for 412 Adolescent Idiopathic Scoliosis Patients.

STUDY DESIGN: Retrospective Review. OBJECTIVE: The objective of this study was to determine differences in surgical and post-operative outcomes in AIS patients undergoing spinal deformity correction surgery using standard or large pedicle screw size. SUMMARY OF BACKGROUND: Use of pedicle screw fixation in spinal deformity correction surgery is considered safe and effective. Still, the small size of the pedicle and the complex 3D anatomy of the thoracic spine makes screw placement challenging, with improper pedicle screw fixation leading to catastrophic complications including injuries to nerve roots, spinal cord, and major vessels. Thus, insertion of larger diameter screw sizes has raised concerns amongst surgeons, especially in the pediatric population. MATERIALS AND METHODS: AIS patients undergoing PSF between 2013 and 2019 were included. Demographic, radiographic, and operative outcomes collected. Patients in the large screw size group (GpI) received 6.5 mm diameter screw sizes at all levels while standard screw size group (GpII) received 5.0 to 5.5 mm diameter screw sizes at all levels. Kruskall-Wallis and Fisher's exact test performed for continuous and categorical variables respectively.Subanalyses included (1) screw accuracy in patients with available CT scans, (2) stratified analysis of large- and standard-screw patients with ≥60% flexibility rate, (3) stratified analysis of large- and standard-screw patients with <60% flexibility rate, and (4) matched analysis of large- and standard-screw patients by surgeon and year of surgery. RESULTS: GpI patients experienced significantly higher overall curve correction ( P <0.001), with 87.6% experiencing at least one grade reduction of apical vertebral rotation from preoperative to postoperative visit( P =0.008).Patients with larger screws displayed higher postoperative kyphosis. No patient experienced medial breaching. CONCLUSION: Large screw sizes have similar safety profiles to standard screws without negatively impacting surgical and perioperative outcomes in AIS patients undergoing PSF. Additionally, coronal, sagittal, and rotational correction is superior for larger-diameter screws in AIS patients.

The Volume-Cost Relationship: How Does Surgical Volume Affect Cost and Value in AIS Surgery.

STUDY DESIGN: Retrospective review. OBJECTIVE: The objective of this study was to evaluate and compare distribution of hospital and operating room charges and outcomes during posterior spinal fusion for adolescent idiopathic scoliosis (AIS) patients by high-volume (HV) and standard-volume (SV) surgeons at one institution and examine potential cost savings. SUMMARY OF BACKGROUND DATA: Increased surgical volume has been associated with improved perioperative outcomes after spinal deformity correction. However, there is a lack of information on how this may affect hospital costs. METHODS: Retrospective study of AIS patients undergoing posterior spinal fusion between 2013 and 2019. Demographic, x-ray, chart review and hospital costs were collected and compared between HV surgeons (≥50 AIS cases/y) and SV surgeons (<50/y). Comparative analyses were computed using Wilcoxon rank-sum, Kruskal-Wallis, and the Fisher exact tests. Average values with corresponding minimum-maximum rages were reported. RESULTS: A total of 407 patients (HV: 232, SV: 175) operated by 4 surgeons (1 HV, 3 SV). Radiographic parameters were similar between the groups. HV surgeons had significantly lower estimated blood loss (385.3 vs. 655.6 mL, P <0.001), fewer intraoperative transfusions (10.8% vs. 25.1%, P <0.001), shorter surgery time (221.6 vs. 324.9 min, P <0.001), and lower radiation from intraoperative fluoroscopy (4.4 vs. 6.4 mGy, P <0.001). HV patients had a significantly lower length of stay (4.3 vs. 5.3, P <0.001) and complication rate (0.4% vs. 4%, P =0.04).HV surgeons had significantly lower total costs ($61,716.24 vs. $72,745.93, P <0.001). This included lower transfusion costs ( P <0.001), operative time costs ( P <0.001), screw costs ( P <0.001), hospital stay costs ( P <0.001), and costs associated with 30-day emergency department returns ( P <0.001). CONCLUSION: HV surgeons had significantly lower operative times, lower estimated blood loss and transfusion rates and lower perioperative complications requiring readmission or return to emergency department resulting in lower health care costs. LEVEL OF EVIDENCE: Level III.

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.

Effects of Fellowship Training on Pediatric Anterior Cruciate Ligament Reconstruction Techniques and Outcomes.

The purpose of this study is to examine differences in pediatric anterior cruciate ligament reconstruction (ACLR) between surgeons with either pediatric or sports medicine fellowship training. Patients were divided into two groups, those performed by either a pediatric or sports medicine fellowship-trained surgeon. One hundred and forty-one patients were identified: 91 (64.5%) by pediatric trained surgeons and 50 (35.4%) by sports medicine trained surgeons. Patients that had ACLR by a pediatric trained surgeon were younger (p = 0.02), had larger body mass index (BMI) (p = 0.027), and more likely to have government assisted insurance (p = 0.006). Pediatric trained surgeons had longer procedure time (p < 0.001), used smaller graft sizes (p = 0.016), used soft tissue grafts (p < 0.001) and used button fixation at both the femur and tibia (p < 0.001). There were no differences regarding meniscus surgery, surgical technique (transphyseal versus physeal sparing), arthrofibrosis, graft failure, and intraoperative complications (p > 0.05). This study shows favorable and comparable results after ACLRs with either pediatric or sports medicine fellowship training. (Journal of Surgical Orthopaedic Advances 30(3):161-165, 2021).

Predicting Autologous Hamstring Graft Diameter in the Pediatric Population Using Preoperative Magnetic Resonance Imaging and Demographic Data.

BACKGROUND: Anterior cruciate ligament (ACL) reconstruction before 18 years of age has been linked with an increased risk for failure when the graft diameter is <8 mm. PURPOSE/HYPOTHESIS: The purpose of this study was to determine whether autologous hamstring graft size can be reliably predicted with the use of preoperative magnetic resonance imaging (MRI) measurements. We hypothesized that the average of multiple axial cross-sectional area MRI measurements for the semitendinosus tendon and gracilis tendon would alone accurately predict graft diameter. Additionally, factoring in specific demographic data to the MRI cross-sectional areas would provide a synergistic effect to the accuracy of graft diameter predictions. STUDY DESIGN: Cohort study (diagnosis); Level of evidence, 2. METHODS: We retrospectively reviewed 51 pediatric patients undergoing ACL reconstructions (age <18 years) performed using either a quadruple-strand semitendinosus tendon or combined double-bundle semitendinosus tendon-gracilis tendon autograft. Preoperative axial MRI scans at multiple points along the craniocaudal axis-specifically, at the level of the joint line, 3 cm cephalad to the medial tibial plateau, and 5 cm cephalad to the medial tibial plateau-were used to determine the combined cross-sectional area of the semitendinosus and gracilis tendons. The MRI measurements were analyzed using Pearson correlation as well as regression analysis to evaluate strength of correlation between measurements. Binomial linear regression was used to analyze the same predictive variables assessed by multiple regression. RESULTS: The predicted graft diameter was within 0.5 mm of the intraoperative graft size in 37 of 51 (72.5%) patients and within 1 mm of the intraoperative graft size in 49 of 51 (96.1%). With the addition of demographics, the accuracy of predictions increased to 78.4% within 0.5 mm and 98% within 1 mm of the actual graft size. Additionally, 38 of 42 patients whose true graft diameter was ≥8 mm were correctly classified, giving a sensitivity of 90.4%. For those whose true graft diameter was <8 mm, 8 of 9 patients were correctly classified; therefore, the specificity was 88.9%. CONCLUSION: The results of our study suggest that taking the average of multiple preoperative MRI measurements can be used to accurately predict autologous hamstring graft size when approaching pediatric patients undergoing ACL reconstruction.

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.

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.

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.

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.

Uniplanar Versus Taylor Spatial Frame External Fixation For Pediatric Diaphyseal Tibia Fractures: A Comparison of Cost and Complications.

BACKGROUND: The purpose of this study was to compare the outcomes and cost variations between uniplanar (UNI) and Taylor Spatial Frame (TSF) external fixation for unstable pediatric tibial diaphyseal fractures. METHODS: We performed an IRB approved, retrospective review of 44 diaphyseal tibial fractures in 42 children treated with external fixation (16 TSF and 28 UNI) between 2003 and 2011, at a single level 1 pediatric trauma center. Data on demographic, clinical, radiographic, treatment cost, and complication differences were analyzed between the 2 groups. The Student t tests, Fisher's exact tests, χ trend tests, logistic regression, and a cost analysis comparison was used to assess the differences. RESULTS: The mean age in both groups was 13 years (range: 6 to 18 y TSF, 9 to 17 y UNI). The mean follow-up was 8 months (TSF) and 13 months (UNI). According to the AO classification, there were 28 type A, 13 type B, and 3 type C fractures with no significant difference between the 2 groups (P=0.69). Total time in the fixator was not different between the 2 groups (UNI 14 wk, TSF 12 wk, P=0.10), but time to union was less in the TSF group (UNI 16 wk, TSF 13 wk, P<0.01). There were no differences in the final radiographic alignment between the groups. The UNI group experienced more complications (7 pin-site infections and 9 reoperations) compared with 4 pin-site infections and 2 reoperations in the TSF group. A cost analysis revealed significant differences in equipment cost (UNI frame=$5074 vs. TSF frame=$10,675; P<0.0001); however, after corrected cost analysis with calculated return to the operating room for complications, there was no difference in cost of treatment (UNI treatment=$20,113 vs. TSF treatment=$19,138). CONCLUSIONS: Despite an initial equipment cost difference between UNI and TSF frames, corrected cost analysis reveals equivalent costs for care delivery. Therefore, TSF can be considered as a cost-conscious device for the treatment of unstable pediatric tibial diaphyseal fractures. LEVEL OF EVIDENCE: Level III-retrospective comparative cohort study.

Osteonecrosis After Femoral Neck Fractures in Children and Adolescents: Analysis of Risk Factors.

BACKGROUND: The most serious complication of femoral neck fractures in children and adolescents is osteonecrosis. Although a number of factors have been implicated in the development of osteonecrosis, no specific cause-and-effect relationship has been determined. The primary purpose of this study was to determine the prevalence of osteonecrosis in children and adolescents after femoral neck fractures and to identify risk factors for its development. METHODS: This retrospective review identified 70 patients between the ages of 1.3 and 18.1 years who were treated for a femoral neck fracture between 2000 and 2011 at a single level I pediatric trauma center and followed until clinical and radiographic union. Demographic information, injury event details, type of surgical treatment, associated injuries, time from injury to treatment, and postoperative alignment were recorded from chart and radiographic review. The primary outcome was the presence of osteonecrosis, which was determined by review of available imaging. Multivariable logistic regression analysis tested age, time to treatment, type of fixation, mechanism of injury, postoperative alignment, and capsular decompression as possible risk factors for the development of osteonecrosis. RESULTS: Osteonecrosis occurred in 20 (29%) of the 70 patients. The median time to diagnosis of osteonecrosis was 7.8 months. Multivariable predictors of osteonecrosis included fracture displacement (P=0.01) and fracture location (P=0.02). Patient age, type of fixation, mechanism of injury, capsular decompression, postoperative alignment, and performance of reduction were not predictive of osteonecrosis after femoral neck fracture. Finally, time to treatment also was found to be a positive predictor of osteonecrosis (P=0.004), with osteonecrosis more likely in patients treated in less than 24 hours, but this finding is likely due to confounding because injury severity was closely linked to time to treatment. CONCLUSIONS: Regardless of the treatment, the prevalence of osteonecrosis after femoral neck fractures remains high. Recognizing factors that are predictive of the development of osteonecrosis can help surgeons counsel patients and families appropriately about the risk of this complication.

Fracture of the radial styloid and concomitant first dorsal compartment musculotendinous injuries.

In the absence of preexisting inflammatory conditions, pure traumatic rupture of the extensor pollicis brevis (EPB) and abductor pollicis longus (APL) tendons are rare injuries. We present a report of 2 cases of extensor tendon ruptures at the musculotendinous junction occurring after concomitant fractures of the radial styloid in patients who were involved in high-energy trauma. The presence of a radial styloid fracture should raise suspicion for a greater spectrum of injury that can contribute to multidirectional instability. The spectrum might even include proximal damage to the EPB and APL tendons. Although the associated tendon injuries might or might not contribute to functional loss, their presence should be noted when evaluating a patient with this injury pattern.

Bioenergetic abnormalities in discrete cerebral motor pathways presage spinal cord pathology in the G93A SOD1 mouse model of ALS.

Multiple cell death pathways are implicated in the etiology of amyotrophic lateral sclerosis (ALS), but the cause of the characteristic motor neuron degeneration remains unknown. To determine whether CNS metabolic defects are critical for ALS pathogenesis, we examined the temporal evolution of energetic defects in the G93A SOD1 mouse model of familial ALS. [14C]-2-deoxyglucose in vivo autoradiography in G93A mice showed that glucose utilization is impaired in components of the corticospinal and bulbospinal motor tracts prior to either pathologic or bioenergetic changes in the spinal cord. This was accompanied by significant depletions in cortical ATP content in presymptomatic mice, which was partially ameliorated by creatine administration. Findings suggest that bioenergetic defects are involved in the initial stages of mSOD1-induced toxicity in G93A mice and imply that the selective dysfunction and degeneration of spinal cord motor neurons in this model may be secondary to dysfunction within cerebral motor pathways.