RESUMEN

BACKGROUND AND IMPORTANCE: Complete posterior atlantoaxial dislocation (PAAD) with an unfractured odontoid process is a rare condition where a dislocated but intact odontoid process is positioned ventrally to the anterior arch of C1. This lesion is related to transverse and alar ligament rupture secondary to hyperextension and rotatory traumatic injury and is often associated with neurological deficit. The treatment strategy remains controversial, and in many cases, odontoidectomy is required. Traditional approaches for odontoidectomy (transnasal and transoral) are technically demanding and are related to several complications. This article describes a 360° reduction and stabilization technique through a navigated anterior full-endoscopic transcervical approach (nAFETA) as a novel technique for odontoidectomy and C1-C2 anterior transarticular fixation supplemented with posterior fusion. CLINICAL PRESENTATION: A 21-year-old man presented to the emergency room by ambulance after a motorcycle accident. On evaluation, incomplete ASIA B spinal cord injury was documented. Imaging revealed a complete PAAD. We performed a two-staged procedure, a nAFETA odontoidectomy plus C1-C2 anterior transarticular fixation followed by posterior C1-C2 wired fusion. At a 2-year follow-up, the patient had a 10-point Oswestry Disability Index score and neurological improvement to ASIA E. CONCLUSION: PAAD can be successfully treated through minimally invasive nAFETA. Noteworthy, the risks of the transoral and endonasal routes were avoided through this approach. In addition, nAFETA allows anterior transarticular fixation during the same procedure providing spinal stability. Further studies are required to expand the use of nAFETA in this field.

Asunto(s)

Asunto(s)

RESUMEN

PURPOSE: This study compared, through biomechanical evaluation under ventral flexion load, four surgical techniques for ventral stabilization of the atlantoaxial joint in dogs. METHODS: In total, 28 identical atlantoaxial joint models were created by digital printing from computed tomography images of a dog, and the specimens were divided into four groups of seven. In each group, a different technique for ventral stabilization of the atlantoaxial joint was performed: transarticular lag screws, polyaxial screws, multiple screws and bone cement (polymethylmethacrylate-PMMA), and atlantoaxial plate. After the stabilization technique, biomechanical evaluation was performed under ventral flexion load, both with a predefined constant load and with a gradually increasing load until stabilization failure. RESULTS: All specimens, regardless of stabilization technique, were able to support the predefined load without failing. However, the PMMA method provided significant more rigidity (p ≤ 0.05) and also best resisted the gradual increase in load, supporting a significantly higher maximum force (p ≤ 0.05). There was no statistical difference in flexural strength between the transarticular lag screws and plate groups. The polyaxial screws method was significantly less resistant to loading (p ≤ 0.05) than the other groups. CONCLUSIONS: The PMMA technique had biomechanical advantages in ventral atlantoaxial stabilization over the other evaluated methods.

Asunto(s)

Asunto(s)

RESUMEN

INTRODUCTION: This study aimed to highlight that atlantoaxial rotatory fixation (AARF) can be related to neurosurgery procedures in children, with an afterward demonstration of good results after halo-gravity traction and C1-C2 stabilization using the Harms technique. CASE DESCRIPTION: To the best of our knowledge, this is the first case to report a 4-year-old boy who presented with AARF after a posterior fossa craniotomy to treat a cerebellar astrocytoma. At our medical facility, AARF was diagnosed using plain radiography and computed tomography imaging. The patient was treated with continuous cranial traction for 14 days. Initially, we detected that the patient had no C1 posterior arch or C2 spinous process; therefore, the best option was to perform the Harms technique. Postoperatively, the patient was placed in a cervical collar for 4 weeks. At the 4-year postoperative follow-up, the patient was doing well and had not developed any complications. CONCLUSION: Herein, we report a case in which AARF can be developed after neurosurgical procedure. Surgical techniques used for atlantoaxial subluxation should be carefully selected. In our case, the Harms technique after cranial traction was an excellent option for correcting and stabilizing the abnormal neck position. However, further studies are required to determine the best technique to use in the pediatric population.

Asunto(s)

RESUMEN

Purpose: This study compared, through biomechanical evaluation under ventral flexion load, four surgical techniques for ventral stabilization of the atlantoaxial joint in dogs. Methods: In total, 28 identical atlantoaxial joint models were created by digital printing from computed tomography images of a dog, and the specimens were divided into four groups of seven. In each group, a different technique for ventral stabilization of the atlantoaxial joint was performed: transarticular lag screws, polyaxial screws, multiple screws and bone cement (polymethylmethacrylate­PMMA), and atlantoaxial plate. After the stabilization technique, biomechanical evaluation was performed under ventral flexion load, both with a predefined constant load and with a gradually increasing load until stabilization failure. Results: All specimens, regardless of stabilization technique, were able to support the predefined load without failing. However, the PMMA method provided significant more rigidity (p ≤ 0.05) and also best resisted the gradual increase in load, supporting a significantly higher maximum force (p ≤ 0.05). There was no statistical difference in flexural strength between the transarticular lag screws and plate groups. The polyaxial screws method was significantly less resistant to loading (p ≤ 0.05) than the other groups. Conclusions: The PMMA technique had biomechanical advantages in ventral atlantoaxial stabilization over the other evaluated methods.

Asunto(s)

RESUMEN

The instrumentation of C2 is technically challenging given the anatomic complexity of the upper cervical spine. Although the placement of C2 pedicle screws may be safer than transarticular screw placement, the inconsistent location of the transverse foramen and vertebral artery precludes placement of such screws in up to 26% of patients. In cases where vertebral artery anatomy prevents the safe placement of a pedicle screw, a pars screw is an excellent alternative. However, pars screws must stop short of the vertebral foramen, limiting the typical length of these screws to only 14-18 mm. The associated purchase and rigidity are compromised compared with the pedicle screw. A modified C2 fixation technique was developed by our group which we have named the C2 "parsicle" screw reflecting the hybrid nature of the screw incorporating aspects of pars and pedicle screw fixation.

Asunto(s)

RESUMEN

El objetivo de este estudio fue evaluar de manera integral los parámetros morfométricos de la vértebra axis (C2) en la población mexicana involucrados en la realización de procedimientos quirúrgicos con el fin de proveer datos cuantitativos indispensables en su abordaje quirúrgico. Para este estudio se utilizaron un total de 576 vértebras axis (C2) de población mexicana contemporánea. Las mediciones de las vértebras se efectuaron bilateralmente utilizando un vernier digital milimétrico con una precisión de 0.01 mm (Mitutoyo Digimatic w/Absolute Encoders- Series 500). Un total de 576 vértebras axis (C2), fueron medidas de manera bilateral, todas nuestras mediciones se reportaron en mm. El promedio del ancho del pedículo fue de 8,96 mm con una DE ± 2,11 mm. El promedio de la altura del pedículo fue de 10,82 mm con una DE de ± 1,89 mm. El promedio de la altura del proceso odontoideo fue de 16,90 mm con una DE de ± 2,99 mm. El promedio del ancho del proceso odontoideo fue de 9,99 mm con una de DE de ± 0,80 mm. El promedio del diámetro de la faceta articular fue de 8,44 mm con una DE de ± 1,04 mm. El promedio del diámetro AP del cuerpo vertebral fue de 15,11 mm con una DE de ± 1,88 mm. El promedio del diámetro trasverso del cuerpo vertebral fue de 17,93 mm con una DE de ± 2,22 mm. El promedio de la altura del cuerpo vertebral fue de 18,54 mm con una DE de 2,38 mm. El promedio de la altura de las láminas fue de 11,53 mm con una DE de ± 1,39 mm. El promedio del ancho de las láminas fue de 6,10 mm con una DE de ± 1,44 mm. Los resultados obtenidos en nuestras mediciones demuestran una variación con los resultados de otros autores en diferentes estudios de piezas osteológicas y de estudios de imagen del axis (C2), lo que sugiere, con el fin de reducir los riesgo de daño a estructuras neurovasculares, utilizar técnicas y medidas especiales para la estabilización atlantoaxial de la población mexicana.

The aim of the study was to evaluate the morphometric parameters of the axis vértebra (C2) in the Mexican population involved in the performance of surgical procedures in order to provide essential quantitative data in their surgical approach. A total of 576 axis vertebrae (C2) of contemporary Mexican population were used for this study. The measurements of the vertebrae were made bilaterally using a millimeter digital vernier with an accuracy of 0.01 millimeters (Mitutoyo Digimatic w / Absolute Encoders - Series 500). A total of 576 axis vertebrae (C2) were measured bilaterally, all our measurements were reported in millimeters. The average width of the pedicle was 8.96 mm with a SD ± 2.11 mm. The average height of the pedicle was 10.82 mm with a SD of ± 1.89 mm. The average height of the odontoid process was 16.90 mm with a SD of ± 2.99 mm. The average width of the odontoid process was 9.99 mm with a SD of ± 0.80 mm. The average diameter of the articular facet was 8.44 mm with a SD of ± 1.04 mm. The average diameter of the AP of the vertebral body was 15.11 mm with a SD of ± 1.88 mm. The average transverse diameter of the vertebral body was 17.93 mm with a SD of ± 2.22 mm. The average height of the vertebral body was 18.54 mm with a SD of 2.38 mm. The average height of the lamina was 11.53 mm with a SD of ± 1.39 mm. The average width of the lamina was 6.10 mm with a SD of ± 1.44 mm. The results obtained in our measurements show a variation with the results of other authors in different studies of osteological pieces and studies of the axis image (C2), which suggests the use of techniques and special measures for the atlantoaxial stabilization of the Mexican population in order to reduce the risk of damage to neurovascular structures.

Asunto(s)

RESUMEN

OBJECTIVES: To investigate the primary clinical value of atlantoaxial pedicle screw placement assisted by a modified 3D-printed navigation template. METHODS: We retrospectively analyzed the cases of 17 patients treated from June 2015 to September 2016 with atlantoaxial pedicle screw placement assisted by a modified 3D-printed navigation template. All procedures were performed prior to surgery, including thin-slice CT scanning, medical image sampling and computerized 3D modeling of the atlantoaxial joint, optimal pedicle screw trajectory determination, and anatomical trait acquisition for the atlantoaxial pedicle, spinous process of the axis, vertebral lamina and posterior lateral mass, and design of a reverse template. During surgery, a navigation template was tightly attached to the atlantoaxial joint to assist in pedicle screw placement. Surgeons subsequently used an electric drill to remove the template through a guide channel and then placed the atlantoaxial pedicle screw. Observed indexes included the VAS score, JOA improvement rate, surgery duration, and blood loss. RESULTS: Surgery was successful in all 17 patients, with an average operation duration of 106±25 min and an average blood loss of 220±125 ml. Three days postoperatively, the VAS score decreased from 6.42±2.21 to 3.15±1.26. Six months postoperatively, the score decreased to 2.05±1.56. The postoperative JOA score increased significantly from 7.68±2.51 to 11.65±2.72 3 d after surgery and to 13.65±2.57 after 6 months. Sixty-eight pedicle screws were inserted successfully, with 34 in the atlas and 34 in the axis. According to the Kawaguchi standard, 66 screws were in grade 0 (97.06%), and 2 were in grade 1 (2.94%). The pre- and postoperative transverse and sagittal screw angles showed no significant differences. CONCLUSIONS: Atlantoaxial pedicle screw placement assisted by a modified 3D-printed navigation template is worth recommending due to the improved accuracy in screw placement, improved patient safety and beneficial clinical effects.

Asunto(s)

RESUMEN

INTRODUCTION: Congenital disorders of the craniovertebral junction (CVJ) include a wide range of conditions, such as Chiari malformation (CM), basilar Invagination (BI), and atlantoaxial dislocation (AAD). The objective of this paper is to critically review the literature related to the management of congenital CVJ disorders focusing on: the significant developments in the past (from anterior open ventral decompression to modern CVJ realignment); the diagnosis of CVJ instability; the role of atlantoaxial fixation without posterior fossa decompression in patients with tonsillar herniation and no evidence of CVJ instability; use of C1-2 inter-articular spacers and use of C1-2 interarticular spacers with intra-operative manipulations to correct BI with AAD along with its deformity. MATERIALS AND METHODS: We performed a review of articles showing up on PubMed database without time restriction. Articles were included according to the purpose of our review and selected by two authors (AFJ and PSC). RESULTS: CVJ instability may be inferred when there is atlantoaxial abnormal motion seen on dynamic studies, facet joint subluxation or severe symptomatic CVJ kyphosis; routine fixation of patients with CM without clear CCJ instability, while based on an interesting hypothesis, still requires further studies; use of C1-2 inter-articular spacers for re-establishing CVJ alignment is probably the most effective surgery for posterior CVJ realignment and reduction of AAD and BI, potentially avoiding the need for an open or endoscopic anterior odontoidectomy (AO); current development of deformity correcting surgeries and the measurement of joint indices to plan surgery have provided new strategies for treatment. CONCLUSION: We present a critical review of important new concepts involved in the surgical treatment of CVJ congenital disease.

Asunto(s)

RESUMEN

OBJECTIVES: To investigate the primary clinical value of atlantoaxial pedicle screw placement assisted by a modified 3D-printed navigation template. METHODS: We retrospectively analyzed the cases of 17 patients treated from June 2015 to September 2016 with atlantoaxial pedicle screw placement assisted by a modified 3D-printed navigation template. All procedures were performed prior to surgery, including thin-slice CT scanning, medical image sampling and computerized 3D modeling of the atlantoaxial joint, optimal pedicle screw trajectory determination, and anatomical trait acquisition for the atlantoaxial pedicle, spinous process of the axis, vertebral lamina and posterior lateral mass, and design of a reverse template. During surgery, a navigation template was tightly attached to the atlantoaxial joint to assist in pedicle screw placement. Surgeons subsequently used an electric drill to remove the template through a guide channel and then placed the atlantoaxial pedicle screw. Observed indexes included the VAS score, JOA improvement rate, surgery duration, and blood loss. RESULTS: Surgery was successful in all 17 patients, with an average operation duration of 106±25 min and an average blood loss of 220±125 ml. Three days postoperatively, the VAS score decreased from 6.42±2.21 to 3.15±1.26. Six months postoperatively, the score decreased to 2.05±1.56. The postoperative JOA score increased significantly from 7.68±2.51 to 11.65±2.72 3 d after surgery and to 13.65±2.57 after 6 months. Sixty-eight pedicle screws were inserted successfully, with 34 in the atlas and 34 in the axis. According to the Kawaguchi standard, 66 screws were in grade 0 (97.06%), and 2 were in grade 1 (2.94%). The pre- and postoperative transverse and sagittal screw angles showed no significant differences. CONCLUSIONS: Atlantoaxial pedicle screw placement assisted by a modified 3D-printed navigation template is worth recommending due to the improved accuracy in screw placement, improved patient safety and beneficial clinical effects.

Asunto(s)

RESUMEN

BACKGROUND CONTEXT: Many etiologies can lead to atlantoaxial subluxaion. In Grisel syndrome (GS), this subluxation occurs spontaneously after inflammatory processes of the head and neck. Diagnosis is typically based on clinical history and a strong suspicion of this syndrome. Nonsurgical treatment most often resolves the symptoms; however, in some cases surgical treatment is necessary to repair the subluxation. Various surgical techniques and instrumentation systems have been used to treat atlantoaxial subluxation, although there is no consensus regarding the best treatment method for the pediatric population. PURPOSE: To describe a case of atlantoaxial subluxation in a child with GS treated surgically with an alternative construct. STUDY DESIGN/SETTING: This is a case report and literature review. MATERIALS AND METHODS: Our case study involves a 5-year-old girl with a 6-month history of unresolved Fielding type II atlantoaxial subluxation caused by GS. Despite conservative treatment, the patient's symptoms continued to progress. After two failed closed reduction attempts, open reduction and C1-C2 fusion were performed with atlas laminar hook and axis pedicle polyaxial screws. A literature review of the surgical treatment of GS was also performed. RESULTS: After surgery, the patient exhibited full clinical and functional recovery with complete resolution of symptoms. At the 36-month follow-up examination, there was continual evidence of satisfactory reduction and fusion. No complications were observed. Upon completion of the literature review, eight GS cases were found to have been treated surgically with the minimum patient age being 9 years. CONCLUSIONS: Conservative management of GS is the most common and effective treatment; however, a few surgical cases have been reported in the literature with good results. Satisfactory clinical results and fusion at 36 months post surgery were seen in a pediatric patient with atlantoaxial subluxation and instability using atlas laminar hook and axis pedicle polyaxial screws.

Asunto(s)

RESUMEN

BACKGROUND: Cranieovertebral junction lesions in the paediatric population are associated with a low survival rate, which has declined in recent years. Neurological disability is a major concern due to the high economical cost it represents. Paediatric patients are more susceptible to this lesion because of hyperextension capacity, flat articulation, and increased ligamentous laxity. Survival after these kinds of injuries has been more often reported in adults, but are limited in the paediatric population. CLINICAL CASE: A case is reported of an 8-year-old male with occipitocervical and atlantoaxial dislocation associated with clivus fracture, brain oedema, and post-traumatic subarachnoid haemorrhage (SAH). A halo vest system was placed with no traction. One month after the trauma the patient was surgically treated with C1 and C2 trans-articular screws, occipitocervical fixation with plate and screws, and C1- C2 fixation with tricortical bone graft and wires without complication. He has now returned to school and is self-sufficient. CONCLUSIONS: With better pre-hospital medical care and with improved surgical techniques the mortality rate has declined in this kind of lesion.

Asunto(s)

Asunto(s)

Asunto(s)

RESUMEN

STUDY DESIGN: Anatomic study of the C1 lateral mass using fine-cut computed tomographic scans and Mimics software. OBJECTIVE: To investigate the optimal entry point, medial angles, and effective length for safe fixation using posterior C1 lateral mass screws. SUMMARY OF BACKGROUND DATA: Placing posterior C1 lateral mass screws is technically demanding, and a misplaced screw can result in injury to the vertebral artery, spinal cord, or internal carotid artery. Although various insertion angles have been proposed for posterior C1 lateral mass screw, no clear consensus has been reached on the ideal medial angle of the C1 lateral mass. METHODS: The C1 lateral masses were evaluated using computed tomographic scans and Mimics software in 70 patients. The effective width and effective screw length of posterior C1 lateral mass screws were measured at different medial angulations relative to the midline sagittal plane. The height (H) for screw entry point on the posterior surface of C1 lateral mass and the distance (D) between screw entry point and the intersection of the midline sagittal plane and the posterior arch of the atlas were also measured. RESULTS: The mean height (H) for screw entry on the posterior surface of the lateral mass was 4.25 mm, the mean distance (D) between screw entry point and the intersection of the midsagittal plane and the posterior arch of the atlas was 27.62 mm. The optimal medial angle was 20.86° with a corresponding effective width of 10.56 mm and effective screw length of 21.87 mm. CONCLUSION: This study helps to define the specific anatomy related to C1 posterior lateral mass screw placement in an effort to facilitate instrumentation. However, variation is seen in lateral mass anatomy, and this study must be combined with customized surgical planning that includes advanced imaging for safe and effective instrumentation. LEVEL OF EVIDENCE: 1.

Asunto(s)

RESUMEN

A instabilidade da articulação atlantoaxial é uma afecção comum entre cães de raça de pequeno porte, e os sinais clínicos desenvolvem-se com menos de dois anos de idade, geralmente são progressivos e o paciente apresenta hiperestesia cervical, ataxia proprioceptiva, e em casos severos paraplegia. A instabilidade pode gerar subluxação dorsal do axis em relação ao atlas, levando a uma lesão medular em diferentes níveis. Alterações congênitas, como ausência ou hipoplasia do processo odontóide e ligamentos, ou traumáticas, como fraturas do processo odontóide e ruptura dos ligamentos estão envolvidas na fisiopatologia da afecção. O diagnóstico pode ser realizado com auxílio de radiografias lateral e ventrodorsal com a região craniocervical em posição neutra. O tratamento clínico é a escolha primária e faz-se o uso de colar cervical por três meses, confinamento e corticosteróides. Exceção a este tratamento são pacientes com apresentação clínica severa ou refratários ao tratamento conservativo, nestes casos indica-se a cirurgia para estabilização por meio de abordagens ventrais ou dorsais. Observou-se que as técnicas cirúrgicas ventrais apresentam maiores índices de sucesso e menores recorrências de recidivas, contudo, as estabilizações cirúrgicas continuam a ser um desafio pela elevada taxa de complicações e óbitos transoperatórios.

The instability of the atlantoaxial joint is a common condition among dogs small breed, and clinical signs are developed under two years of age, are usually progressive and the patient presents cervical hyperesthesia, ataxia proprioceptive, and in severe cases tetraplegia. The instability can generate subluxation dorsal of axis in relation to the atlas, leading to spinal cord injury at different levels. Congenital abnormalities, such as absence or hypoplasia of the odontoid process and ligaments, or traumatic, such as fractures of the odontoid process and rupture of ligaments are involved in the pathophysiology of the disease. The diagnosis can be performed with the aid of lateral X-rays with the DV region craniocervical in neutral position. Clinical treatment is the primary choice and makes the use of cervical collar for three months confinement and corticosteroids. Exception to this treatment are patients with severe clinical presentation or refractory to conservative treatment in these cases is indicated surgery to stabilize through the ventral or dorsal approaches. It was observed that the ventral surgical techniques have higher success rates and lower recurrence of relapse, however, surgical stabilization remains a challenge due to high rate of intraoperative complications and death.

La inestabilidad de la articulación atlantoaxial es una condición común entre los perros de raza pequeña, y los signos clínicos se desarrollan bajo dos años de edad, son por lo general progresiva y el paciente hiperestesia cervical, ataxia propioceptiva, y en casos severos tetraplejia. La inestabilidad puede generar eje dorsal subluxación en relación con el atlas, lo que lleva a una lesión de la médula espinal en los diferentes niveles. Anomalías congénitas, tales como ausencia o hipoplasia de la apófisis odontoides y ligamentos, o traumática, tales como fracturas de la apófisis odontoides y la rotura de los ligamentos están implicados en la fisiopatología de la enfermedad. El diagnóstico se puede realizar con la ayuda de los rayos X en la región lateral VD craneocervical en posición de punto muerto. El tratamiento clínico es la elección primaria y hace que el uso del collarín cervical durante tres meses de confinamiento y corticosteroides. Excepción a este tratamiento son los pacientes con presentación clínica grave o refractario al tratamiento conservador en estos casos la cirugía está indicada para estabilizar a través de los enfoques ventral o dorsal. Se observó que las técnicas quirúrgicas ventrales tienen mayores tasas de éxito y menor recurrencia de recaídas, sin embargo, la estabilización quirúrgica sigue siendo un desafío debido a la alta tasa de complicaciones intraoperatorias y muertes.

Asunto(s)

RESUMEN

OBJECT: The goal of this study was to compare the indications, benefits, and complications between the endoscopic endonasal approach (EEA) and the microscopic transoral approach to perform an odontoidectomy. Transoral approaches have been standard for odontoidectomy procedures; however, the potential benefits of the EEA might be demonstrated to be a more innocuous technique. The authors present their experience with 12 consecutive cases that required odontoidectomy and posterior instrumentation. METHODS: Twelve consecutive cases of craniovertebral junction instability with or without basilar invagination were diagnosed at the National Institute of Neurology and Neurosurgery in Mexico City, Mexico, between January 2009 and January 2013. The EEA was used for 5 cases in which the odontoid process was above the nasopalatine line, and was compared with 7 cases in which the odontoid process was beneath the nasopalatine line; these were treated using the transoral microscopic approach (TMA). Odontoidectomy was performed after occipital-cervical or cervical posterior augmentation with lateral mass and translaminar screws. One case was previously fused (Oc-C4 fusion). The senior author performed all surgeries. American Spinal Injury Association scores were documented before surgical treatment and after at least 6 months of follow-up. RESULTS: Neurological improvement after odontoidectomy was similar for both groups. From the transoral group, 2 patients had postoperative dysphonia, 1 patient presented with dysphagia, and 1 patient had intraoperative CSF leakage. The endoscopic procedure required longer surgical time, less time to extubation and oral feeding, a shorter hospital stay, and no complications in this series. CONCLUSIONS: Endoscopic endonasal odontoidectomy is a feasible, safe, and well-tolerated procedure. In this small series there was no difference in the outcome between the EEA and the TMA; however, fewer complications were documented with the endonasal technique.

Asunto(s)

RESUMEN

STUDY DESIGN: A biomechanical study comparing the fatigue strength of different types of C2 fixation in a C1-C2 construct. OBJECTIVE: To determine the pullout strength of a C2 pedicle screw and C2 pars screw after cyclical testing and differentiate differences in stiffness pre- and post-cyclical loading of 3 different C1-C2 fixations. SUMMARY OF BACKGROUND DATA: Some surgeons use a short C2 pars screw in a C1-C2 construct, because it is less technically demanding and/or when the vertebral artery is high riding. Difference in construct stiffness between use of bilateral C2 pedicle screws, bilateral C2 pars screws, or a hybrid construct is unknown. METHODS: Biomechanical testing was performed on 15 specimens. A bicortical C1 lateral mass screw was used in combination with 1 of 3 methods of C2 fixation: (1) bilateral long C2 pedicle screws (LL), (2) bilateral 14-mm C2 pars screws (SS), and (3) unilateral long C2 pedicle screw with a contralateral 14-mm C2 pars screw (LS). Each construct was subject to 16,000 cycles to simulate the immediate postoperative period. Changes in motion in flexion-extension, lateral bending, and axial rotation were calculated. This was followed by pullout testing. RESULTS: The ability to limit range of motion significantly decreased after cyclical testing in flexion-extension, lateral bending, and axial rotation for all 3 groups. After loading, the LL and LS groups had less percentage of increase in motion in flexion-extension and lateral bending than the SS group. Overall, the average pullout strength of a pedicle screw was 92% stronger than a pars screw. CONCLUSION: C2 pedicle screws have twice the pullout strength of C2 pars screws after cyclical loading. In cases in which the anatomy limits placement of bilateral C2 pedicle screws, a construct using a unilateral C2 pedicle screw with a contralateral short pars screw is a viable option and compares favorably with a bilateral C2 pedicle screw construct. LEVEL OF EVIDENCE: N/A.

Asunto(s)

RESUMEN

O objetivo deste trabalho foi realizar um estudo retrospectivo dos casos de subluxação atlantoaxial em cães, por meio de consulta dos registros neurológicos do Hospital Veterinário Universitário (HVU), entre os anos de 2003 e 2008. Foram identificados a raça, o sexo, a idade, a etiologia, os sinais neurológicos, a duração dos sinais clínicos, o tratamento empregado, a resposta ao tratamento, o tempo de recuperação, a recidiva e a relação entre a duração dos sinais clínicos e a recuperação pós-operatória. Foram feitos o diagnóstico de subluxação atlantoaxial em 14 cães, sendo as raças Poodle (35,7 por cento), Pinscher (21,4 por cento) e Yorkshire Terrier (21,4 por cento) as mais acometidas e a maioria (92,8 por cento) com idade inferior a 24 meses. A principal causa da instabilidade foi a agenesia do processo odontoide do áxis (71,4 por cento) e os sinais clínicos variaram desde hiperestesia cervical até tetraparesia não ambulatória. O tratamento predominante foi o cirúrgico, que demonstrou ser eficaz com recuperação satisfatória em 90 por cento dos casos e menor possibilidade de recidiva, quando comparado ao trata,mento clínico. O tempo de recuperação predominante foi de 30-60 dias após a cirurgia, não existindo relação deste com a duração dos sinais clínicos.(AU)

A retrospective study on atlantoaxial subluxation in dogs was done by reviewing the cases filed from 2003 to 2008 in the neurological records of the Veterinary Hospital of the Universidade Federal de Santa Maria, at Santa Maria, Rio Grande do Sul, Brazil. The following data were identified: Breed, sex, age, etiology, clinical signs, duration of clinical course, assessment of the therapy employed and its efficacy, response to treatment and relapse. Fourteen dogs were diagnosed as affected by atlantoaxial subluxation and the condition was more frequent in dogs under twenty-four month old years and of toy breeds, such as Poodle (35.7 percent), Pinscher (21.4 percent) and Yorkshire terrier (21.4 percent). The main cause found for the instability was agenesis of the odontoid process. Clinical signs ranged from cranial cervical pain to non-ambulatory tetraparesis. The predominant treatment employed was surgical which demonstrated to be efficacious in 90 percent of the cases with minor risks of relapse when compared with clinical treatment. The predominant time of recovery was 30-60 days after surgery. No correlation was found between the duration of clinical signs before surgery and the time of recovery.(AU)

Asunto(s)