Patient-Specific Drill Guide Template for Pedicle Screw Insertion into the Atlantoaxial Cervical Spine Using Stereolithographic Modeling: An In Vitro Study.

STUDY DESIGN: Cadaveric study. PURPOSE: This study aimed to assess the accuracy and feasibility of cervical pedicle screw (CPS) insertion into the atlantoaxial cervical spine using a patient-specific drill guide template constructed from a stereolithographic model. OVERVIEW OF LITERATURE: CPS fixation is a widely accepted procedure for posterior cervical fixation because of its biomechanical advantages, particularly in the subaxial cervical region. The extremely narrow corridors of the atlantoaxial spine make CPS insertion more difficult, requiring the development of new tools to ensure accurate placement. METHODS: Fifteen atlantoaxial cervical vertebra specimens from 15 cadavers were scanned into thin slices using computed tomography. Images of the cadaver spine were digitally processed and rendered stl files so that they could be printed to scale as threedimensional (3D) plastic models. Manually molded dental acrylic drill guide templates with pins inserted in the pedicles of the plastic cervical models were placed over the 3D printed models. The drill guide templates were used for precise placement of the drill holes in the pedicles of cadaveric specimens for pedicle screw fixation. The accuracy of screw placement was evaluated by an independent evaluator. RESULTS: A total of 60 pedicles (combined C1 and C2) from 15 cadaveric axial cervical vertebrae were evaluated. The total acceptable accuracy for pedicle screw insertion in the atlantoaxial cervical vertebrae is 95%. An accuracy rate of 100% was achieved for C1 while an acceptable accuracy rate of 90% was achieved for C2. CONCLUSIONS: The use of a patient-specific drill guide constructed using stereolithography improved the accuracy of CPS placement in a cadaveric model.

Transoral approach using a tubular retractor system in the treatment of atlantoaxial Pott's disease: a novel method of surgical decompression.

The use of tubular retractors in minimally invasive spine surgery has been described extensively in the literature. However, there are only select reports discussing their use specifically in a transoral approach for upper cervical pathologies such as an epidural abscess and a dystrophic os odontoideum.We report the first use of a transtubular transoral approach in a rare case of an adult presenting with severe neck pain with progressing neurologic signs secondary to atlantoaxial Pott's disease. Debridement and partial odontoidectomy performed using this approach allowed less trauma to surrounding soft tissues without sacrificing an excellent visualisation of the operative field. A halo vest was applied to provide temporary stability. The patient transitioned out of his halo vest after 6 months while completing medical therapy after a year without need for further intervention. The transtubular transoral approach is a suitable alternative to the conventional approach in patients with atlantoaxial Pott's disease.

Narcotrend-guided intraoperative care of a Trisomy 21 paediatric patient who underwent occipitocervical fusion.

A 9-year-old female with Trisomy 21 with complex craniovertebral instability causing severe cervicomedullary compression underwent occipitocervical fusion. This paper will discuss the anaesthetic management and highlight the use of the Narcotrend monitor not only as a depth of consciousness monitor but more importantly as a tool to detect surgery-induced cerebral hypoperfusion by monitoring the right and left cerebral hemispheres independently and simultaneously.

A Novel Patient-Specific Drill Guide Template for Pedicle Screw Insertion into the Subaxial Cervical Spine Utilizing Stereolithographic Modelling: An In Vitro Study.

STUDY DESIGN: Cadaveric study. PURPOSE: The purpose of this study was to assess the accuracy and feasibility of cervical pedicle screw (CPS) insertion into the subaxial cervical spine placed using a patient-specific drill guide template constructed from a stereolithographic model. OVERVIEW OF LITERATURE: CPS fixation is an invaluable tool for posterior cervical fixation because of its biomechanical advantages. The major drawback is its narrow corridor that allows very little clearance for neural and vascular injuries. METHODS: Fifty subaxial pedicles of the cervical vertebrae from five cadavers were scanned into thin slices using computed tomography (CT). Digital imaging and communications in medicine images of the cadaver spine were digitally processed and printed to scale as a three-dimensional (3D) model. Drill guide templates were manually moulded over the 3D-printed models incorporating pins inserted in the pedicles. The drill guide templates were used for precise placement of the drill holes in the pedicles of cadaveric specimens for pedicle screw fixation. RESULTS: The instrumented cadaveric spines were subjected to CT to assess the accuracy of our pedicle placement by an external observer. Our patient-specific drill guide template had an accuracy of 94%. CONCLUSIONS: The use of a patient-specific drill guide constructed using stereolithography improved the accuracy of CPS placement in a cadaveric model.

Successful treatment of tumour-induced osteomalacia after resection of an oral peripheral ossifying fibroma.

Tumour-induced osteomalacia is a paraneoplastic syndrome wherein bone is affected by a hormone from a tumour that causes renal phosphate wasting and hypophosphataemia. Here, we present the case of a 31-year-old man who has been suffering from generalised bone pains and a spine deformity that led to loss of height. Pertinent findings are low serum phosphorus, low vitamin D and decreased bone mineral density. These findings led to a diagnosis of osteomalacia. However, the finding of an oral mass raised some questions as to what role it plays in the patient's disease. It was suspected that the oral mass (fibroma) was producing a hormone that led to renal phosphate wasting, hypophosphataemia and then osteomalacia. This hypothesis was proven after surgical removal of the mass led to normalisation of the metabolic derangements and eventually led to a resolution of the bone pains.

Percutaneous posterior cervical fusion with the DTRAX Facet System for single-level radiculopathy: results in 60 patients.

OBJECT: The authors present 1-year results in 60 patients with cervical radiculopathy due to spondylosis and stenosis that was treated with a bilateral percutaneous facet implant. The implant consists of a screw and washer that distracts and immobilizes the cervical facet for root decompression and fusion. Clinical and radiological results are analyzed. METHODS: Between 2009 and 2011, 60 patients were treated with the DTRAX Facet System in a multicenter prospective single-arm study. All patients had symptomatic clinical radiculopathy, and conservative management had failed. The majority of patients had multilevel radiographically confirmed disease. Only patients with single-level radiculopathy confirmed by history, physical examination, and in some cases confirmatory nerve blocks were included. Patients were assessed preoperatively with Neck Disability Index, visual analog scale, quality of life questionnaire (Short Form-12 version 2), CT scans, MRI, and dynamic radiographs. Surgery was percutaneous posterior bilateral facet implants consisting of a screw and expandable washer and iliac crest bone aspirate. Patients underwent postoperative assessments at 2 weeks, 6 weeks, 3 months, 6 months, and 1 year with validated outcome questionnaires. Alterations of segmental and overall cervical lordosis, foraminal dimensions, device retention and fusion criteria were assessed for up to 1 year with CT reconstructions and radiographs. Fusion criteria were defined as bridging trabecular bone between the facets, translational motion < 2 mm, and angular motion < 5°. RESULTS: All patients were followed to 1 year postoperatively. Ages in this cohort ranged from 40 to 75 years, with a mean of 53 years. Forty-two patients were treated at C5-6, 8 at C6-7, 7 at C4-5, and 3 at C3-4. Fifty-six had bilateral implants; 4 had unilateral implants due to intraoperative facet fracture (2 patients) and inability to access the facet (2 patients). The Neck Disability Index, Short Form-12 version 2, and visual analog scale scores were significantly improved at 2 weeks and remained significantly improved up to 1 year. At the treated level, 93% had intrafacet bridging trabecular bone on CT scans, translational motion was < 2 mm in 100% and angular movement was < 5° in 83% at the 1-year follow-up. There was no significant change in overall cervical lordosis. There was a 1.6° loss of segmental lordosis at the treated level at 1 year that was significant. Foraminal width, volume, and posterior disc height was significantly increased at 6 months and returned to baseline levels at 1 year. There was no significant decrease in foraminal width and height at adjacent levels. There were no reoperations or surgery- or device-related complications, including implant failure or retained hardware. CONCLUSIONS: Results indicate that the DTRAX Facet System is safe and effective for treatment of cervical radiculopathy.

A biomechanical study on single rod spinal instrumentation system in an unstable thoracolumbar injury model: A finite element analysis

OBJECTIVES: To develop three dimensional computer models of the anterior thoracolumbar spine implants or constructs (the novel single rod-screw implant and the standard implants) and to evaluate its biomechanical properties through a graphically reconstructed testing standard. METHODS: We developed a finite element modeling technique based on actual geometry of the implant constructs and mechanical property data from standard biomechanical studies on anterior thoracolumbar spinal instrumentation systems. Seven constructs were mounted on simulated vertebral bodies. Axial load sharing was measured through a range of applied axial loads from 100 N to 1600 N. The static destructive tests were conducted. The bending strength of each construct was calculated with a full length corpectomy graft in place, simulating reconstruction of the anterior column, and with no graft in place, simulating catastrophic graft failure. RESULTS: Static testing parameter demonstrated highly significant differences between devices. The plate construct formed the highest subset in bending strength of 1000-1100 N, whereas the single rod showed the lowest value of 300-400N. However, the bending strengths of single rod and dual rod both without bone grafts were not significantly different. With the graft in place, bending strength of the constructs significantly increased beyond the maximum set of load of 1600N, underlying the importance of the graft in overall construct strength. CONCLUSION: The 3-D finite element models for anterior thoracolumbar instrumentation system were designed with mechanical properties comparable to the actual biomechanical testing results. Although single rod construct has the lowest value, its bending strength is comparable to the standard dual rod system under static axial loading. Bone graft contributed to overall construct stiffness.

Comparison of the hybrid locking plate, standard dynamic compression plate, and standard dynamic compression plate augmented with bone cement for fixation of osteoporotic humeral shaft fractures: A cadaveric biomechanical study

BACKGROUND: Studies comparing the relative strength of polymethylmethacrylate (PMMA) augmented fixation, standard plating and locked compression plate (LCP) system are few. The use of either the bone cement-augmented dynamic compression plate or the Hybrid LCP constructs may provide an additional tool for the treatment of fractures in patients with osteoporosis. METHODS: Eighteen (18) osteoporotic cadaveric humeral bones were assigned randomly to each of three groups (Dynamic Compression Plate [DCP], DCP augmented with bone cement, and the Hybrid LCP system) and tested in anterior-posterior bending and torsion/external rotation. The load to failure values were obtained and the results for each specimen compared. RESULTS: Significant differences were observed between the standard DCP and Hybrid LCP group (p-value=0.012), and in the cement-augmented and Hybrid LCP group (p-value=0.099) in torsion/external rotation loading. No significant difference was observed between the standard DCP and bone-cement augmented group (p-value=0.248). No significant difference was observed among the three groups in terms of stiffness (p-value=0.3868) in the four-point anterior-posterior bending modality. Screw pull-out of the implant was observed only in the regular DCP group in torsion/external rotation loading stress. CONCLUSION: Significant differences were seen between the three constructs in torsion/external rotation but not in anterior-posterior four-point bending. Bone failure, but not screw pull-out, was seen in the Hybrid LCP and bone cement-augmented DCP groups in torsion. This study showed that the LCP system and the bone cement-augmented constructs may provide greater screw purchase to the osteoporotic humerus.

Predictive value of lateral-bending, push-prone, and fulcrum-bending radiographs in adolescent idiopathic scoliosis

INTRODUCTION: The advent of pedicle screws which provide distraction and derotation has led to higher correction of major curves. Newer methods have been devised to evaluate preoperative coronal flexibility, including lateral-bending (LB), push-prone (PP) and fulcrum-bending (FB) radiographs. Documentation of a consistent radiographic method predictive of correction rate has not been established. OBJECTIVE: To determine the most predictive radiographic method for evaluating spine flexibility and correction by comparing the correction rate (CR), flexibility rate (FR) and correction index (CI) of the Cobb's angle using the different radiographic methods. METHODS: Preoperative radiographs of 20 patients who underwent spinal fusion for adolescent scoliosis were obtained using the LB, PP and FB method and compared with postoperative radiographs. RESULTS: Comparing the mean Cobb angles using the different methods to that of postoperative standing showed that only the FB method is not significantly different from the latter (p=0.669). There was a significant difference between the Cobb's angle measured on the LB and PP and that measured on postoperative standing (p=0.043, p=0.008). Comparing the mean flexibility of the different methods with the mean CR also showed that the mean FR of LB (p=0.007) and PP (p=0.00013) were significantly different from the CR while that of FB is not significantly different from the CR (p=0.687). CONCLUSION: The FB radiograph demonstrated no statistical difference compared to postoperative radiograph, FR, and CI.