Three-dimensional reduction method with a modified C2 isthmus screw in irreducible atlantoaxial dislocation: a technical note

Background Three-dimensional reduction plays a vital role in surgical reduction of irreversible atlantoaxial dislocation (IAAD). However, the most commonly used combination of C1 pedicle screw (PS) or lateral mass screw (LMS) and C2 PS or isthmus screw often fails to achieve satisfactory reduction at one time. The difficulty is usually caused by short anteroposterior and vertical distance between heads of C1 and C2 screws, which lack enough space for reduction operation. The objective of this study is to describe a three-dimensional reduction method with a modified C2 isthmus screw and to illustrate its advantage and effectiveness for IAAD. Methods Twelve patients with IAAD underwent reduction and fixation with modified C2 isthmus screw combined with C1 PS or LMS, fusion with autologous bone graft. The insertion point was lateral to the intersection of caudal edge of C2 lamina and lateral mass, with a trajectory towards C2 isthmus, via lateral mass. The three-dimensional reduction was achieved through pulling and distracting. Radiographic evaluation included anteroposterior and direct distance between different insertion points, the occipitoaxial angle (O-C2A), clivus-canal angle (CCA) and cervicomedullary angle (CMA). Clinical outcomes evaluation included the Japanese Orthopaedic Association (JOA) score, Visual analog scale (VAS) and Neck Disability Index (NDI). Results All the patients maintained effective reduction during the follow-up. The anteroposterior and direct distance was significantly higher in modified C2 isthmus screw than C2 PS whether combined with C1 PS or LMS (P < 0.05). The degree of O-C2A, CCA and CMA, JOA score, NDI, and VAS were significantly improved after the surgery (P < 0.05). Conclusions Three-dimensional reduction method with a modified C2 isthmus screw is effective and safe in managing IAAD. It can increase the anteroposterior and vertical distance between the heads of C1 and C2 screws, which is benefit for the three-dimensional reduction operation of IAAD.

Posterior occipitocervical instrumented fusion for atlantoaxial instability in a 27-month-old child with Down syndrome: illustrative case

BACKGROUND Upper cervical spine instability is one of the most serious orthopedic problems in patients with Down syndrome. Despite the recent advancement of instrumentation techniques, occipitocervical fusion remains technically challenging in the very young pediatric population with small and fragile osseous elements. OBSERVATIONS A 27-month-old boy with Down syndrome was urgently transported to the authors’ hospital because of difficulty in standing and sitting, weakness in the upper limbs, and respiratory distress. Radiographs showed os odontoideum, irreducible atlantoaxial dislocation, and substantial spinal cord compression. Emergency posterior occipitoaxial fixation was performed using O-arm navigation. Improvement in the motor paralysis of the upper left limb was observed from the early postoperative period, but revision surgery was needed 14 days after surgery because of surgical site infection. The patient showed modest but substantial neurological improvement 1 year after the surgery. LESSONS There are several clinical implications of the present case. It warns that Down syndrome in the very young pediatric population may lead to rapid progression of spinal cord injury and life crisis. This 27-month-old patient represents the youngest case of atlantoaxial instability in a patient with Down syndrome. O-arm navigation is useful for inserting screws into very thin pedicles.

A novel 3D-printed locking cage for anterior atlantoaxial fixation and fusion: case report and in vitro biomechanical evaluation

Background Treatment of atlantoaxial dislocation is aimed at reduction and stabilization of the atlantoaxial joint. 3D printing refers to a process where additive manufacturing is achieved under precise computer control. Literature on its utilization in anterior atlantoaxial fixation and fusion is rare. This study is the first report on a 3D-printed locking cage used in the anterior procedure for atlantoaxial dislocation. Methods A middle-aged male in his 40s presented with weakness and numbness of his extremities for 3 years and could only walk slowly with assistance. Imaging studies revealed severe anterior migration of C1, irreducible atlantoaxial dislocation, and severe cervical-medullary compression. A preoperative plan consisting of trans-oral soft tissue release and fixation using tailor-designed 3D-printed cages was devised. Following fluoroscopic confirmation of reduction of the atlantoaxial joints, two customized 3D-printed cages made of titanium alloy were inserted into the bilateral facet joints, which were then locked by six screws into the lateral masses of C1 and C2. The microstructure of the inserted cages was optimized for improved biomechanical stability and enhanced osseo-integration, without the need for bone grafting. In addition, a biomechanical test was performed on seven human cadaveric specimens comparing the novel implant with the conventional C1 lateral mass-C2 pedicle screw construct in three modes of motion (flexion-extension, lateral bending, axial rotation). Results Improvement of neurologic function in the patient was evident immediately after surgery. He was able to walk independently 1 month post-operatively. At the 12-month follow-up, coronal reconstruction of CT demonstrated properly-positioned 3D-printed cages, evidence of osseo-integration at the bone-implant interface, and no subsidence or displacement of the implant. Eighteen months out of surgery, the mJOA score improved to 15, and lateral X-ray confirmed reduction of atlanto-axial dislocation. Additionally, the new construct provided strong fixation comparable to that conferred by conventional constructs as there was no significant difference observed between the two groups in all three directions of motion. Conclusions The novel implant represents a new option in the treatment of irreducible atlantoaxial dislocation. It can provide strong anterior support for solid fixation and fusion with a low profile and a microstructure that obviates the need for bone grafting.

Surgical treatment of a complex craniocervical malformation combined with posterior cranial fossa teratoma: a case report and literature review

Background Basilar invagination (BI) with atlantoaxial dislocation (AAD) is not uncommon in patients with scoliosis, Klippel-Feil syndrome (KFS), and other bone deformities. Cases with combinations of the abovementioned dislocations and deformities with posterior cranial fossa teratoma are rare in the clinic and difficult to handle. Case presentation This case presents a 34-year-old woman diagnosed with atlantoaxial dislocation and posterior cranial fossa mass. After two surgeries, the posterior cranial teratoma was completely removed with satisfactory atlantoaxial reduction. The postoperative 1-year follow-up examination showed that the bone graft fusion was successful, without remaining significant dysfunction. Conclusions The surgical risk of irreducible atlantoaxial dislocation combined with posterior cranial fossa tumor is huge. Thus, it needs to be fully preoperatively evaluated and managed carefully in accordance with sound surgical principles.

Surgical treatment for basilar invagination with irreducible atlantoaxial dislocation: transoral atlantoaxial reduction plate fixation vs occipitocervical fixation

Background Transoral atlantoaxial reduction plate (TARP) fixation or occipitocervical fixation (OF) is an effective treatment for basilar invagination (BI) with irreducible atlantoaxial dislocation (IAAD). But, all current clinical studies involved a single surgical procedure. The clinical effects of TARP and OF operation for BI with IAAD have yet to be compared. We therefore present this report to compare the treatment of TARP and OF procedure for BI with IAAD. Methods Fifty-six patients with BI with IAAD who underwent TARP or OF operation from June 2011 to June 2017 were retrospectively analyzed. Among these, 35 patients underwent TARP operation (TARP group), and 21 patients underwent OF operation (OF group). We compared the difference of clinical, radiological, and surgical outcomes between the TARP and OF groups postoperatively. Results Compared with OF group, the operative time and blood loss in TARP group were lower. There was no statistical difference in the atlantodental interval (ADI), clivus canal angle (CCA), cervicomedullary angle (CMA), distance between the top of the odontoid process and the Chamberlain line (CL) and Japanese Orthopaedic Association (JOA) score between the TARP and OF groups preoperatively, but the improvements of these parameters in the TARP group were superior to those in the OF group postoperatively. The fusion rates were higher in the TARP group than those in the OF group at the early stage postoperatively. Conclusions TARP and OF operations are effective surgical treatment for BI with IAAD, but the performance of reduction and decompression and earlier bone fusion rates of TARP procedure are superior to those of OF.

Transoral intraarticular cage distraction and C-JAWS fixation for revision of basilar invagination with irreducible atlantoaxial dislocation

Background The revision surgery of basilar invagination (BI) with irreducible atlantoaxial dislocation (IAAD) after a previous occipitocervical fusion (OCF) is challenging. Transoral revision surgery has more advantages than a combined anterior and posterior approach in addressing this pathology. The C-JAWS is a cervical compressive staple that has been used in the lower cervical spine with many advantages. Up to now, there is no report on the application of C-JAWS in the atlantoaxial joint. We therefore present this report to investigate the clinical outcomes of transoral intraarticular cage distraction and C-JAWS fixation for revision of BI with IAAD. Methods From June 2011 to June 2015, 9 patients with BI and IAAD were revised by this technique after previous posterior OCF in our department. Plain cervical radiographs, computed tomographic scans and magnetic resonance imaging were obtained pre- and postoperatively to assess the degree of atlantoaxial dislocation and compression of the cervical cord. The Japanese Orthopedic Association (JOA) score was used to evaluate the neurological function. Results The revision surgeries were successfully performed in all patients. The average follow-up duration was 18.9 ± 7.3 months (range 9–30 months). The postoperative atlas-dens interval (ADI), cervicomedullary angle (CMA), distance between the top of the odontoid process and the Chamberlain line (CL) and JOA score were significantly improved in all patients (P < 0.05). Bony fusion was achieved after 3–9 months in all cases. No patients developed recurrent atlantoaxial instability. Conclusions Transoral revision surgery by intraarticular cage distraction and C-JAWS fixation could provide a satisfactory outcome for BI with IAAD after a previous unsuccessful posterior operation.