Mechanical Study of Various Pedicle Screw Systems including Percutaneous Pedicle Screw in Trauma Treatment.

Background and Objectives: Spine surgery using a percutaneous pedicle screw placement (PPSP) is widely implemented for spinal trauma. However, percutaneous systems have been reported to have weak screw-rod connections. In this study, conventional open and percutaneous systems were biomechanically evaluated and compared. Material and Methods: The experiments were performed in two stages: the first stage was a break test, whereas the second stage was a fatigue test. Four systems were used for the experiments. System 1 was intended for conventional open surgery (titanium rod with a 6.0 mm diameter, using a clamp connecting mechanism). System 2 was a percutaneous pedicle screw (PPS) system for trauma (titanium alloy rod with a 6.0 mm diameter, using ball ring connections). System 3 was a PPS system for trauma (cobalt-chromium alloy rod with a 6.0 mm diameter, using sagittal adjusting screw connections). System 4 was a general-purpose PPS system (titanium alloy rod with a 5.5 mm diameter, using a mechanism where the adapter in the head holds down the screw). Results: Stiffness values of 54.8 N/mm, 43.1 N/mm, 90.9 N/mm, and 39.3 N/mm were reported for systems 1, 2, 3, and 4, respectively. The average number of load cycles in the fatigue test was 134,393, 40,980, 1,550,389, and 147,724 for systems 1 to 4, respectively. At the end of the test, the displacements were 0.2 mm, 16.9 mm, 1.2 mm, and 8.6 mm, respectively. System 1, with a locking mechanism, showed the least displacement at the end of the test. Conclusion: A few PPS systems showed better results in terms on stiffness and life than the open system. The experiments showed that mechanical strength varies depending on the spinal implant. The experiments conducted are essential and significant to provide the mechanical strength required for surgical reconstruction.

[Anti-NMDA receptor encephalitis during pregnancy].

A 19-year-old female in her 2nd trimester (17 weeks) of pregnancy became irritable a few days before admission. She became unable to open her mouth and could not talk. She was admitted to the psychiatric hospital due to a rapid change in behavior and a consciousness disturbance. She was diagnosed as having schizophrenia by a psychiatrist. Her EEG showed diffuse high voltage and slow waves. Acute encephalitis was then suspected. Her past and family histories were not suggestive of viral infection. On physical examination, she had a low grade fever. She had hyperhidrosis, autophagia, and repeated oral dyskinesia. Her consciousness level fluctuated from somnolence to stupor. Although her blood CRP level was mildly elevated and she had mild pleocytosis, HSV-PCR was negative in the cerebrospinal fluid (CSF). Abdominal ultrasound examination and MRI showed no ovarian teratoma. Computed tomography (CT) and magnetic resonance imaging (MRI) showed no brain abnormalities. Before analysis for specific nervous system antibodies, the initial diagnosis was non-herpetic limbic encephalitis. She was twice treated with a 6-day course of methylprednisolone (500 mg/day) infusion. She was also given phenobarbital since she had a tonic-clonic seizure about 1 month after admission. Finally, she had a normal delivery at 37 weeks. The baby was healthy, and the patient was discharged without sequelae. We concluded that her diagnosis was anti-N-methyl-D-aspartate (NMDA) receptor (anti-NMDAR) encephalitis based on the presence of anti-NMDAR antibody in the CSF. This report is the first description of a patient with anti-NMDAR antibody encephalitis. The precise mechanism of this encephalitis is not clear, although there have been several reports of autoimmune encephalitis during pregnancy. The patient's CSF anti-NMDAR antibody titer during treatment was measured. Before treatment, the CSF anti-NMDAR antibody titer was strongly positive, but it decreased during treatment and then disappeared after delivery. We hypothesized that the presence of the embryo or placenta may have triggered an antigenic signal and/or antibody through inappropriate immunological modulation.

Clinical accuracy of 3D fluoroscopy-assisted cervical pedicle screw insertion.

OBJECT: Cervical pedicle screw (PS) misplacement leads to injury of the spinal cord, nerve root, and vertebral artery. Recently, several investigators reported on the usefulness of a spinal navigation system that improves the accuracy of PS insertion. In this study, the authors assessed the accuracy of cervical pedicle, lateral mass, and odontoid screw insertions placed using a 3D fluoroscopy navigation system, the Iso-C3D unit. METHODS: In this prospective analysis of the authors' initial 50 cases of 3D fluoroscopy-assisted cervical screw insertion, the authors inserted 176 PSs, 58 lateral mass screws, and 5 odontoid screws into the C1-7 vertebrae. They placed screws using intraoperative acquisition of data by the isocentric C-arm fluoroscope and a computer navigation system. They obtained postoperative fine-cut CT scans in all patients and assessed the accuracy of screw insertion. RESULTS: A PS (>or= 3.5 mm) could be inserted into 24 (63%) of 38 pedicles at the level of C-3, 18 (53%) of 34 pedicles at C-4, 30 (65%) of 46 at C-5, 33 (80%) of 41 at C-6, and 43 (100%) of 43 at C-7. Of 176 PSs inserted into vertebrae between C-2 and C-7, 171 screws (97.2%) were classified as Grade 1 (no pedicle perforation), and 5 screws (2.8%) were classified as Grade 2 (screw perforation of the cortex by up to 2 mm). Clinically significant screw deviation in the present study was considered Grade 3 (screw perforation of the cortex by > 2 mm), and this occurred in 0% of the placements. CONCLUSIONS: In this study, the authors were able to correctly insert cervical PSs using the 3D fluoroscopy and navigation system.

Posterior spinal fusion using a pedicle nail system with polymethylmethacrylate in a paraplegic patient after vertebral collapse caused by osteoporosis.

BACKGROUND CONTEXT: Because posterior decompression and fusion for vertebral collapse in an osteoporotic spine sometimes results in a pullout of the pedicle screw. Several authors reported that fixation of pedicle screws in severely osteoporotic bone could be improved by inserting polymethylmethacrylate (PMMA) into the hole before inserting the screw. However, pedicle screws were not designed to be used with PMMA. PURPOSE: To report a patient with vertebral collapse who were treated using a novel-concept, pedicle nail using with PMMA. STUDY DESIGN: Case report. METHODS: The patient was a 74-year-old female who experienced back pain after some heavy lifting 3 months before. She was laid up for 2 months because of the back pain and weakness of her lower legs. Radiographs and magnetic resonance imaging showed vertebral collapse and neural severe compression from the posterior wall of vertebra T12. The pedicle nail consists of an outer sheath with evenly spaced holes and an internal, removable, threaded component. The outer sheath and the internal component were connected before insertion. The pedicle nail attaches to and is bound by the PMMA through the holes of the outer sheath. We performed a T11-L1 posterior fusion and laminectomy using the pedicle nail, and we used a hydroxyapatite block to perform a transpedicular vertebroplasty of T12. RESULTS: Bone union was observed on a lateral radiograph without pedicle nail loosening. CONCLUSIONS: The authors speculate that posterior spinal fusion and vertebroplasty using the pedicle nail will be a reasonable choice for delayed paraplegia after osteoporotic vertebral fracture.