Mingsheng Tan

Morphometric evaluation of screw fixation in atlas via posterior arch and lateral mass.

Study Design. This study is a result of manual and radiologic measurements of 50 isolated anatomic specimens of C1 and five patients of atlantoaxial instability treated by screw fixation via posterior arch and lateral mass. Objectives. To investigate the feasibility of screw placement via posterior arch and lateral mass in atlas. Summary of Background Data. Several types of posterior approaches have been adopted for stabilization and fusion of atlantoaxial complex. Before this study, Gallie in 1939 gave a report on a posterior wiring technique that depended on a structural bone graft. Since then, double-looped wiring with two bone grafts and Halifax clamp technique had been introduced. A transarticular screw fixation technique was introduced by Magerl and Seeman in 1987, and a C1 lateral mass screw fixation technique was described by Harms in 2001. However, the feasibility of screw fixation in atlas via posterior arch and lateral mass has not been addressed until now. Methods. Fifty dry samples of atlas were measured manually and radiologically with vernier calipers, protractors, and CT. The parameters of posterior arch, lateral mass, vertebral artery groove, axis length of screw path via posterior arch and lateral mass, the entry point, and screw direction were measured. Five patients of atlantoaxial instability were treated with this technique and the radiographs and CT scans were evaluated after surgery. Results. The longest trajectory distance of the screw path was about 30 mm. The outer thickness at the thinnest part of groove was 4.58 mm, and it was found to be <4 mm in four cases (8%). The entry point is 18–20 mm lateral to the midline and 2 mm superior to the inferior border of posterior arch. The direction of screw placement is perpendicular to the coronal plane and about 5° cephalad to the transverse plane. Ten screws via posterior arch and lateral mass were placed properly, without incidence of nerve or blood vessel injury in clinical practice. Conclusion. Atlas is capable for screw fixation via its posterior arch and lateral mass.

Footprint Mismatch of Cervical Disc Prostheses with Chinese Cervical Anatomic Dimensions

Background: The footprint of most prostheses is designed according to Caucasian data. Total disc replacement (TDR) has been performed widely for cervical degenerative diseases in China. It is essential to analyze the match sizes of prostheses footprints and Chinese cervical anatomic dimensions in our study. Methods: The anatomic dimensions of the C4–C7 segments of 138 patients (age range 16–77 years) in a Chinese population were measured by computed tomography scans. We compared the footprints of the most commonly used cervical disc prostheses (Bryan: Medtronic, Minneapolis, MN, USA; Prestige LP: Medtronic, Fridley, Minnesota, USA; Discover: DePuy, Raynham, MA, USA; Prodisc-C: Synthes, West Chester, PA, USA) in China with Chinese cervical anatomic dimensions and assessed the match of their size. Results: The mismatch of available dimensions of prostheses and anatomic data of cervical endplates ranged from 17.03% (C4/C5, Prestige LP, Prodisc-C) to 57.61% (C6/C7, Discover) in the anterior-posterior (AP) diameter, and 35.51% (C4/C5, Prodisc-C, Prestige LP) to 94.93% (C6/C7, Bryan) in the center mediolateral (CML) diameter. About 21.01% of endplates were larger than the largest prostheses in the AP diameter and 57.25% in the CML diameter. All available footprints of prostheses expect the Bryan with an unfixed height, can accommodate the disc height (DH), however, 36.23% of the middle DH was less than the smallest height of the prostheses. The average disc sagittal angles (DSAs) of C4–C7 junctions were 5.04°, 5.15°, and 4.13° respectively. Only the Discover brand had a built-in 7° lordotic angle, roughly matching with the DSA. Conclusions: There is a large discrepancy between footprints of prostheses and Chinese cervical anatomic data. In recent years, possible complications of TDR related with mismatch sizes are increasing, such as subsidence, displacement, and heterotopic ossification. Manufacturers of prostheses should introduce or produce additional footprints of prostheses for Chinese TDR.

In vivo analysis of cervical range of motion after revised C1-C2 pedicle screw technique for pediatric atlantoaxial instability.

Objective: The purpose of this study was to analyze the cervical range of motion (ROM) after revised C1-C2 pedicle screw fixation for pediatric patients with atlantoaxial instability. Methods: 17 pediatric patients (age range 5-14 years; mean 8.3 years) underwent the revised C1-C2 pedicle screw technique. Pre- and postoperative cervical ROM during flexion/extension, rotation and lateral bending were measured using a head-mounted motion goniometer. Plain radiographs, CT scans and MRI were performed to assess spinal cord compression, the accuracy of screw placement, and bone fusion. The American Spinal Injury Association classification was used to evaluate neurological function. Results: Revised atlantoaxial pedicle screw fixation was successfully performed in all 17 pediatric patients. There were no perioperative complications. All cases showed evidence of bone fusion 6 months after surgery by CT scan. During the follow-up period (24-92 months), of 6 patients with preoperative myelopathy, 3 improved from grade D to grade E and 3 from grade C to grade D. The final follow-up cervical ROM was significantly greater than the preoperative and 6-month postoperative ROM. There was a statistically significant difference between preoperative and 6-month postoperative ROM for flexion, extension, and left and right axial rotation movements. Conclusion: As a short-segmental fixation technique, revised C1-C2 pedicle screw fixation can provide effective biomechanical stability. Final follow-up cervical ROM is significantly increased through alleviating cervical pain and symptoms of myelopathy after surgery and possible subaxial compensation.

Long-Term Influence of C 1 -C 2 Pedicle Screw Fixation on Occipitoatlantal Angle and Subaxial Cervical Spine in the Pediatric Population

Objective: The goal of this study was to evaluate the impact of C₁-C₂ pedicle screw fixation on the occipitoatlantal angle and subaxial cervical spine for a pediatric population, and the clinical efficacy and adjacent-segment degeneration after C₁-C₂ pedicle screw fixation with a minimum of 2 years of follow-up. Methods: Twenty-two pediatric patients with atlantoaxial dislocation who were enrolled in this study underwent atlantoaxial pedicle screw fixation. The correlation between C₀-C₁, C₂-C₇, and C₁-C₂ pre- and postoperative sagittal angles was assessed using plain radiographs, and adjacent-segment degeneration (ASD) and JOA scores (Japanese Orthopaedic Association scores) were evaluated after atlantoaxial pedicle screw fixation. Results: The C₁-C₂ angle increased from 16.1 ± 13.37 to 28.1 ± 5.1° (p < 0.01). The pre- and postoperative C₁-C₂ angles were negatively correlated with the pre- and postoperative C₀-C₁ and C₂-C₇ angles, respectively. In accordance with the optimal atlantoaxial fusion angle (25-30°) obtained from the literature, postoperative JOA scores were greater in the groups with angles of more than 30° and less than 25°, although the difference in ASD was not statistically significant. Postoperative JOA scores were not relevant to the postoperative C₁-C₂ angle; however, there was a positive correlation between JOA improvement rate and the change of the C₁-C₂ angle postoperatively. Conclusion: Atlantoaxial pedicle screw fixation can be used easily to reduce atlantoaxial dislocation in the pediatric population; however, outside the range of the optimal atlantoaxial fusion angle it can change the occipitoatlantal angle and subaxial alignment, which induces ASD and influences the clinical efficacy. It is necessary to achieve an optimal atlantoaxial angle when using atlantoaxial pedicle screw fixation.

Effects of decompression joint Governor Vessel electro-acupuncture on rats with acute upper cervical spinal cord injury

Decompression is the major therapeutic strategy for acute spinal cord injury, but there is some debate about the time window for decompression following spinal cord injury. An important goal and challenge in the treatment of spinal cord injury is inhibiting or reversing secondary injury. Governor Vessel electroacupuncture can improve symptoms of spinal cord injury by inhibiting cell apoptosis and improving the microenvironment of the injured spinal cord. In this study, Governor Vessel electroacupuncture combined with decompression at different time points was used to treat acute spinal cord injury. The rat models were established by inserting a balloon catheter into the atlanto-occipital space. The upper cervical spinal cord was compressed for 12 or 48 hours prior to decompression. Electroacupuncture was conducted at the acupoints Dazhui (GV14) and Baihui (GV 20) (2 Hz, 15 minutes) once a day for 14 consecutive days. Compared with decompression alone, hind limb motor function recovery was superior after decompression for 12 and 48 hours combined with electroacupuncture. However, the recovery of motor function was not significantly different at 14 days after treatment in rats receiving decompression for 12 hours. Platelet-activating factor levels and caspase-9 protein expression were significantly reduced in rats receiving electroacupuncture compared with decompression alone. These findings indicate that compared with decompression alone, Governor Vessel electroacupuncture combined with delayed decompression (48 hours) is more effective in the treatment of upper cervical spinal cord injury. Governor Vessel electroacupuncture combined with early decompression (12 hours) can accelerate the recovery of nerve movement in rats with upper cervical spinal cord injury. Nevertheless, further studies are necessary to confirm whether it is possible to obtain additional benefit compared with early decompression alone.

Micro-architecture study of the normal odontoid with micro-computed tomography

Introduction: Odontoid fractures easily lead to instability, causing spinal cord injury. The aim of this study was to measure and analyze the micro-architecture and morphometric parameters of the normal odontoid with high-resolution three-dimensional (3D) micro-computed tomography (micro-CT). Methods: Micro-CT scans were obtained from five normal odontoid processes. The scanned data were reconstructed with micro-CT software, and the nutrient foramina and the ossification center of the base of the odontoid were revealed. The trabeculae of the odontoid were measured and divided into four parts to obtain the volume fraction of regions of interest. Results: High-resolution 3D images of the micro-structures’ parameters were obtained from the odontoid using micro-CT software. The images demonstrated sponge-like trabecular bone, with the trabeculae showing a complex, net-like micro-construction. The subchondral bone plate was of lamella-like, compact construction and extended and transformed into a net-like structure with rod-shaped trabeculae arranged radially in all directions. There was a statistically significant difference in the volume fraction compared with the region of interest in the fourth part of the trabeculae and the first part of the odontoid (P < 0.05). The nutrient foramina and the ossification center of the odontoid were also observed. Conclusions: It is feasible to use high-resolution 3D micro-CT to evaluate the micro-architecture of the normal odontoid. Other studies can benefit from use of the micro-CT images, such as finite element evaluations.

Atlantoaxial dislocation and os odontoideum in two identical twins: perspectives on etiology

PurposeThere are two theories about the origin of os odontoideum: traumatic or congenital. However, most studies favor the hypothesis of traumatic theory. To emphasize the congenital theory, we report a pair of identical twins both with atlantoaxial dislocation and os odontoideum, which is believed to be a congenital defect.MethodsWe present two 14-year-old identical twins with atlantoaxial dislocation and os odontoideum. Neither of the twins had history of trauma in head nor cervical spine. We reviewed and compared the cervical radiographs of the identical twins. Posterior atlantoaxial reduction, pedicle screw fixation and atlantoaxial fusion were performed for the two twins.ResultsRadiological examination showed the identical twins had typical atlantoaxial dislocation and os odontoideum. The twins had high similarity in the appearance of atlantoaxial dislocation and os odontoideum. The etiology of the os odontoideum in the twins is believed to be congenital. Both the twins had improvement in neurological function after surgery.ConclusionAlthough a great number of cases with os odontoideum have been reported to be traumatic, there are some cases believed to be congenital.

A Modified Personalized Image-Based Drill Guide Template for Atlantoaxial Pedicle Screw Placement: A Clinical Study

Background Atlantoaxial posterior pedicle screw fixation has been widely used for treatment of atlantoaxial instability (AAI). However, precise and safe insertion of atlantoaxial pedicle screws remains challenging. This study presents a modified drill guide template based on a previous template for atlantoaxial pedicle screw placement. Material/Methods Our study included 54 patients (34 males and 20 females) with AAI. All the patients underwent posterior atlantoaxial pedicle screw fixation: 25 patients underwent surgery with the use of a modified drill guide template (template group) and 29 patients underwent surgery via the conventional method (conventional group). In the template group, a modified drill guide template was designed for each patient. The modified drill guide template and intraoperative fluoroscopy were used for surgery in the template group, while only intraoperative fluoroscopy was used in the conventional group. Results Of the 54 patients, 52 (96.3%) completed the follow-up for more than 12 months. The template group had significantly lower intraoperative fluoroscopy frequency (p<0.001) and higher accuracy of screw insertion (p=0.045) than the conventional group. There were no significant differences in surgical duration, intraoperative blood loss, or improvement of neurological function between the 2 groups (p>0.05). Conclusions Based on the results of this study, it is feasible to use the modified drill guide template for atlantoaxial pedicle screw placement. Using the template can significantly lower the screw malposition rate and the frequency of intraoperative fluoroscopy.