Da-Geng Huang

Posterior atlantoaxial fixation: a review of all techniques

BACKGROUND CONTEXT Posterior atlantoaxial fixation is an effective treatment for atlantoaxial instability. Great advancements on posterior atlantoaxial fixation techniques have been made in the past decades. However, there is no article reviewing all the posterior atlantoaxial fixation techniques yet. PURPOSE The aim was to review the evolution and advancements of posterior atlantoaxial fixation. STUDY DESIGN This was a literature review. METHODS The application of all posterior fixation techniques in atlantoaxial stabilization, including wiring techniques, interlaminar clamp fixation, transarticular fixation, screw-plate systems, screw-rod systems, and hook-screw systems, are reviewed and discussed. Recent advancements on the novel technique of atlantoaxial fixation are described. The combination of the C1 and C2 screws in screw-rod systems are described in detail. RESULTS All fixation techniques are useful. The screw-rod system appears to be the most popular approach. However, many novel or modified fixation methods have been introduced in recent years. CONCLUSIONS Great advancements on posterior atlantoaxial fixation techniques have been made in the past decades. The wiring technique and interlaminar clamps technique have fallen out of favor because of the development of newer and superior fixation techniques. The C1-C2 transarticular screw technique may remain the gold standard for atlantoaxial fusion, whereas screw-rod systems, especially the C1 pedicle screw combined with C2 pedicle/pars screw fixation, have become the most popular fixation techniques. Hook-screw systems are alternatives for atlantoaxial fixation.

C2 Nerve Dysfunction Associated with C1 Lateral Mass Screw Fixation

The C1 lateral mass screw technique is widely used for atlantoaxial fixation. However, C2 nerve dysfunction may occur as a complication of this procedure, compromising the quality of life of affected patients. This is a review of the topic of C2 nerve dysfunction associated with C1 lateral mass screw fixation and related research developments. The C2 nerve root is located in the space bordered superiorly by the posterior arch of C1, inferiorly by the C2 lamina, anteriorly by the lateral atlantoaxial joint capsule, and posteriorly by the anterior edge of the ligamentum flavum. Some surgeons suggest cutting the C2 nerve root during C1 lateral mass screw placement, whereas others prefer to preserve it. The incidence, clinical manifestations, causes, management, and prevention of C2 nerve dysfunction associated with C1 lateral mass screw fixation are reviewed. Sacrifice of the C2 nerve root carries a high risk of postoperative numbness, whereas postoperative nerve dysfunction can occur when it has been preserved. Many surgeons have been working hard on minimizing the risk of postoperative C2 nerve dysfunction associated with C1 lateral mass screw fixation.

A new cervical artificial disc prosthesis based on physiological curvature of end plate: a finite element analysis

STUDY DESIGN The study aimed to build a new cervical artificial disc C3-C7 segment prosthesis, and perform a biomechanical comparison between the new prosthesis and the Prestige LP prosthesis using a three-dimensional non-linear finite element (FE) model. PURPOSE The study compared the biomechanical differences between the new cervical artificial disc prosthesis based on the physiological curvature of the end plate and the Prestige LP prosthesis after artificial disc replacement. BACKGROUND CONTEXT There has been no prior research on artificial disc prostheses based on the physiological curvature of the end plate; studies of biomechanical changes after cervical disc arthroplasty (CDR) are few. METHODS An FE model of the C3-C7 segments was developed and validated. A new cervical artificial disc prosthesis based on the physiological curvature of the end plate and the Prestige LP prosthesis were integrated at the C5-C6 segment into the validated FE model. All models were subjected to a follower load of 73.6 N and a 1 Nm in flexion-extension, lateral bending, and axial torsion. The segmental range of motion (ROM) and stress on the prostheses were analyzed. RESULTS The ROM in most segments after CDR with new cervical artificial disc prosthesis was more similar to that of the normal cervical spine than the Prestige LP prosthesis. However, there was no significant difference between the two prostheses. The stress on the new artificial disc was significantly less than that in the Prestige LP prosthesis. CONCLUSIONS There was no significant difference in ROM in all segments after CDR for the two prostheses. The stress on the new cervical artificial disc prosthesis based on the physiological curvature of the end plate was significantly less than that in the Prestige LP prosthesis. The new artificial disc prosthesis is feasible and effective, and can reduce the implant-bone interface stress on the end plate, which may be one of the causes of prosthesis subsidence.

The feasibility of inserting a C1 pedicle screw in patients with ponticulus posticus: a retrospective analysis of eleven patients

BackgroundPonticulus posticus is a common anatomic variation that can be mistaken for a broad posterior arch during C1 pedicle screw placement. When the atlas lateral mass screws are placed via the posterior arch, injury to the vertebral artery may result. To our knowledge, there are few clinical studies that have analyzed the feasibility of C1 pedicle screw fixation in patients with ponticulus posticus, in clinical practice.PurposeTo evaluate the feasibility of inserting a C1 pedicle screw in patients with ponticulus posticus.MethodsBetween January 2008 and January 2012, 11 consecutive patients with atlantoaxial instability, and with a ponticulus posticus at C1, underwent posterior fusion surgery in our institution. According to preoperative computed tomography (CT) reconstruction, a complete ponticulus posticus was found unilaterally in nine patients and bilaterally in two. Postoperative CT reconstructive imaging was performed to assess whether C1 pedicle screw placement was successful. Patients were followed up at regular intervals and evaluated for symptoms of ponticulus posticus syndrome.ResultsThirteen C1 pedicles (atlas vertebral artery groove), each with a complete ponticulus posticus, were successfully inserted with thirteen 3.5- or 4.0-mm diameter pedicle screws, without resection of the bony anomaly. No intraoperative complications (venous plexus, vertebral artery, or spinal cord injury) occurred. The mean follow-up period was 21 (range 14–30) months. Postoperative CT reconstructive images showed that all 13 pedicle screws were inserted in the C1 pedicles without destruction of the atlas pedicle cortical bone. In the follow-up period, none of the patients demonstrated clinical symptoms of ponticulus posticus syndrome or developed bone fusion.ConclusionThree-dimensional CT imaging should be considered prior to C1 pedicle screw fixation in patients with ponticulus posticus, to avoid mistaking the ponticulus posticus for a widened dorsal arch of the atlas. If there is no ponticulus posticus syndrome preoperatively, C1 pedicle screw fixation can be successfully performed without removing the bony anomaly.

Occipitocervical fusion: Fix to C2 or C3?

OBJECTIVE The objective of this study was to explore the differences in clinical outcome between short-segment fixation (SSF; occiput-C2) and multi-segment fixation (MSF; occiput-C2, 3). METHODS From January 2008 to January 2012, patients who underwent surgery for instability at the occipitocervical junction were included in the study. Two different groups of surgeons using two different management options completed the surgeries. One group performed SSF, whereas the other group performed MSF. A total of 53 patients met the criteria (33 SSF, 20 MSF). Mean follow-up was 33.9 months (range, 12-62 months). Fusion was demonstrated by plain radiographs and computed tomography imaging. Neurological status, pillow neck pain, operative time, blood loss during operation, and perioperative complications were compared between the SSF and MSF groups. RESULTS The fusion rate was 97% in the SSF group and 100% in MSF the group. There was no statistically significant difference in the fusion rate between the two groups (P>0.05). One patient (3%) in the SSF group and two patients (10%) in the MSF group experienced perioperative complications. Of the 25 patients who had neurological symptoms, 22 (88%) showed improvement after the operation in the SSF group and 14 (87.5%) of 16 showed improvement in MSF group. In addition, patients who suffered from pillow neck pain achieved varying degrees of improvement after the operation. CONCLUSION SSF may be the better choice for treating occipitocervical instability when no subaxial instability is present. Overall, modern instrumentation can provide the stability needed for successful clinical fusion.

Quantitative morphometric study of the subaxial cervical vertebrae end plate.

BACKGROUND CONTEXT Cervical disc arthroplasty has been gradually adopted as an alternative for the treatment of cervical degenerative disease. However, there is a large discrepancy between footprints of currently available cervical disc prostheses and anatomic dimensions of cervical end plates. PURPOSE This study aimed to accurately and comprehensively quantify the three-dimensional (3D) anatomic morphology of the cervical vertebral end plate and provide a theoretical basis for designing appropriate disc prostheses. Moreover, we introduced a novel geometric and mechanical model for 3D reconstruction techniques of the cervical end plate. STUDY DESIGN A descriptive study of the geometry of the middle and lower cervical vertebral end plates in cadaveric spines was carried out. METHODS A total of 138 cervical vertebral end plates were digitized using an optical 3D range scanning system, and then each end plate was reconstructed using the digitized image. For each end plate, the morphologic characteristics of six surface curves and the end plate concavity depth were symmetrically chosen and depicted. RESULTS The cranial end plates (relative to the disc) were concave and the caudal end plates were relatively flat at all disc levels, with mean concavity depths of 2.04 and 0.69 mm, respectively. For the caudal end plates, the end plate concavity apex was most often (81.42%) located in the posterior portion, whereas in the cranial end plates, the distribution was relatively even. For the sagittal curves, the foremost point and the rearmost point on the middle curve had a more forward position than those in the left curve and the right curve. Regarding the frontal plane curves, the length of the middle curve was longer than that of the anterior curve and posterior curve. For the cranial end plate, the maximal mean depth was the middle curve, whereas for the caudal end plate, the maximum depth was the posterior curve. CONCLUSIONS There is marked morphologic asymmetry, in that the cranial end plate is more concave than the corresponding caudal end plate. In the sagittal plane, the caudal end plates are aerofoil-shaped, whereas the cranial end plates are arc-shaped. In the transverse plane, the end plates are kidney-shaped. These morphologic characteristics of cervical vertebral end plates should be taken into consideration when designing cervical devices, such as artificial discs.

Biomechanical Analysis of a Novel Prosthesis Based on the Physiological Curvature of Endplate for Cervical Disc Replacement.

Study Design Biomechanical analysis of a novel prosthesis based on the physiological curvature of endplate was performed. Objective To compare the biomechanical differences between a novel prosthesis based on the physiological curvature of the endplate and the Prestige LP prosthesis after cervical disc replacement (CDR). Summary of Background Data Artificial disc prostheses have been widely used to preserve the physiological function of treated and adjacent motion segments in CDR, while most of those present a flat surface instead of an arcuate surface which approximately similar to anatomic structures in vivo. We first reported a well-designed artificial disc prosthesis based on the physiological curvature of the endplate. Methods Three motion segments of 24 ovine cervical spines (C2-5) were evaluated in a robotic spine system with axial compressive loads of 50N. Testing conditions were as follows: 1) intact, 2) C3–4 CDR with artificial disc prosthesis based on the physiological curvature of the endplate, and 3) C3–4 CDR with the Prestige LP prosthesis. The range of motion (ROM) and the pressures on the inferior surface of the two prostheses were recorded and analyzed. Results As compared to the intact state, the ROM of all three segments had no significant difference in the replacement group. Additionally, there was no significant difference in ROM between the two prostheses. The mean pressure on the novel prosthesis was significantly less than the Prestige LP prosthesis. Conclusion ROM in 3 groups (intact group, CDR group with novel prosthesis and CDR group with Prestige LP) showed no significant difference. The mean pressure on the inferior surface of the novel prosthesis was significantly lower than the Prestige LP prosthesis. Therefore, the novel artificial disc prosthesis is feasible and effective, and can reduce the implant-bone interface pressure on the endplate, which may be one possible reason of prosthesis subsidence.

Posterior C1-C2 screw-rod fixation and autograft fusion for the treatment of os odontoideum with C1-C2 instability

OBJECTIVE To report our experience treating os odontoideum with C1-C2 instability via C1-C2 screw-rod fixation and autograft fusion and to explore the clinical efficacy of such a treatment strategy. PATIENTS AND METHODS We retrospectively reviewed the medical records of patients who were diagnosed with os odontoideum with C1-C2 instability and treated by posterior C1-C2 screw-rod fixation and fusion. Neurological deficits were measured with the Japanese Orthopedic Association (JOA) scoring system and neck pain was assessed using the Visual Analogue Scale (VAS) score. Fusion was determined based on the presence of bridging bone in computed tomography (CT) imaging, whereas stability was determined based on the lack of movement in dynamic radiographs. RESULTS Thirty-two patients (18 males) were included in the study. The surgery was successfully accomplished in all patients. Thirty (93.8%) patients had confirmed C1-C2 bony fusion in CT images and all patients (100%) were stable in dynamic radiographs. The mean preoperative JOA score was 14.3±1.4 (range 11-16); at the final visit, it increased to 16.2±0.8 (range 14-17) (p<0.001). The mean preoperative VAS score was 3.8±0.7 (range 3-5) and decreased at the final visit to 1.0±0.6 (range 0-2) (p<0.001). CONCLUSION Our treatment strategy (C1-C2 screw-rod fixation and autograft fusion) can achieve excellent clinical results with minor complications for patients with os odontoideum with C1-C2 instability.

Posterior atlantoaxial fusion with a screw-rod system: Allograft versus iliac crest autograft

OBJECTIVE To compare the effectiveness of allograft and iliac crest autograft in atlantoaxial fusion. PATIENTS AND METHODS Between January 2012 and December 2012, 41 consecutive patients underwent posterior atlantoaxial fusion with a screw-rod fixation system in our spine center. The choice to use allograft or iliac crest autograft was made by the patient himself or herself after being informed about the advantages and disadvantages of both methods. In the allograft group, we used mixed material of morcellized demineralized freeze-dried bone allograft and local autograft for posterior atlantoaxial fusion. In the autograft group, we used the morcellized iliac crest autograft for fusion. Patients underwent regular follow up including CT scans and dynamic radiographs 6 months postoperatively and every 6 months thereafter until study completion or confirmation of fusion. RESULTS Twenty-four patients underwent posterior atlantoaxial fusion with allograft, and 17 underwent fusion with autograft. All patients were followed up for at least 24 months. At the final follow-up visit, only two (8.3%) patients in the allograft group had confirmed posterior bony fusion on CT imaging while 15 (88.2%) patients in the autograft group had confirmed posterior bony fusion. None of the 41 patients had movement on the dynamic radiographs. CONCLUSIONS Allograft is not reliable for posterior atlantoaxial fusion even with the rigid internal fixation of modern constructs. Autograft remains the first choice for atlantoaxial fusion despite the donor-site morbidity. The assessment of fusion based on a lack of movement on dynamic radiographs is not reliable. The confirmation of fusion should be based on the presence of bridging bone on CT imaging.