Morphological Differences Between The Pedicles In Nondystrophic Scoliosis Secondary To Neurofibromatosis Type 1 And Those In Adolescent Idiopathic Scoliosis

BackgroundScoliosis is the most common paediatric musculoskeletal disorder and is defined as a structural three-dimensional deformity of the spine with a lateral curvature of>10°(Cobb angle),accompanied by the rotation of the vertebral,the change of Lordosis or kyphosis in the sagittal plane,the rotation and deformity of the ribs and pelvis tilt,and anomaly of paraspinal ligament,muscle.The most common types of scoliosis are adolescent idiopathic scoliosis(AIS)and congenital scoliosis(CS),while other cases occur as a consequence of disorders such as neurofibromatosis or Marfan syndrome that have distinguishing features in addition to scoliosis.Scoliosis Secondary to Neurofibromatosis Type 1(NF1-S)is clinically characterized clinically by pigmatic lesions(milk-coffee patches on the trunk or limbs,freckles in the groin or armpit,and Lisch nodules in the iris)and cutaneous neurofibromatosis.Generally,according to natural history and vertebral morphology,NF1-S is divided into two types:Nondystrophic and Dystrophic,with an incidence of 40%and 60%,respectively.Nondystrophic Scoliosis Secondary to Neurofibromatosis Type 1(ND-NF1-S),which has similar imaging features and surgical treatment to AIS,and usually presents with a uniform right chest curvature and different flexibility,thus it is also known as Idiopathic-like.However,previous studies that reported similar radiographic characteristics between nondystrophic NF1-S and AIS were based on digital radiography,and no studies have been conducted comparing the pedicle morphology of these two scoliosis types with computed tomography(CT)in a uniform criterion.ObjectiveTo compare the pedicle morphology of nondystrophic scoliosis secondary to neurofibromatosis type 1(ND-NF1-S)and adolescent idiopathic scoliosis(AIS)using computed tomography(CT)in a consistent classification system.MethodsPatients with ND-NF1-S and AIS in our hospital were retrospectively analyzed and divided into ND-NF1 group and AIS group according to etiological diagnosis,from January 2011 to June 2019,with CT scan of thoracic and lumbar spine.According to the cross-sectional width of the vertebral pedicle,the vertebral pedicles were divided into A-E types,of which type B,C,D,and E were defined as abnormal vertebral pedicles.A subset of 15 ND-NF1-S patients and 51 AIS patients,a postoperative CT was performed to evaluate the accuracy of pedicle screw placement.According to the perforation of the medial or lateral pedicle walls by the pedicle screw,the placement of screw was classified by a grade ranging from 0 to 3,and grades 2 and 3 were regarded as misplacement.The basic data,imaging parameters and related complications of the two groups were statistically analyzed by independent sample t-test,Pearson chi-square test or Fisher’s exact test.ResultsWe eventually included 95 patients with scoliosis,and a total of 3230 pedicles were measured and classified using the axial CT images.In the ND-NF1 group,there were 20 patients,including 13 females and 7 males,with an average age of 13.2±2.9 years,an average height of 152.6±11.3 cm,an average weight of 46.3±9.7 kg,and an average of Body Mass Index 19.9±2.0 kg/m2.In the AIS group,there were 75 patients,including 56 females and 19 males,with an average age of 14.0±3.1 years and a BMI of 20.2± 1.9 years.There was no difference between the ND-NF1 and AIS groups in terms of baseline parameters except for the flexibility of the major curve(P=0.04).Based on the objective CT classification system,the incidence rate of abnormal pedicles in the ND-NF1 group was significantly higher than that of the AIS group(65.9%vs.61.4%,P=0.03).In the end,15 ND-NF1-S patients and 51 AIS patients received one-stage posterior pedicle screw implantation,with a total of 1100 screws implanted,and the accuracy of screw placement was evaluated by postoperative CT scan.The misplacement rate in the ND-NF1 group was significantly higher than that in the AIS group(12.2%vs.7.4%;P=0.01),in terms of the corresponding 1100 pedicles,and the incidence rate of abnormal pedicles in the ND-NF1 group was higher than that in the AIS group(71.7%vs.64.9%;P=0.02).ConclusionThe incidence rate of abnormal pedicles in patients with nondystrophic NF1-S is significantly higher than that of patients with AIS,and it may the reason for the higher misplacement rate of pedicle screws in patients with nondystrophic NF1-S.