Densitometric comparison of 3 occipital regions for suitability of fixation (original) (raw)
Related papers
Surgical Neurology International, 2014
Background: Occipital-cervical fusion (OCF) has been used to treat instability of the occipito-cervical junction and to provide biomechanical stability after decompressive surgery. The specific areas that require detailed morphologic knowledge to prevent technical failures are the thickness of the occipital bone and diameter of the C2 pedicle, as the occipital midline bone and the C2 pedicle have structurally the strongest bone to provide the biomechanical purchase for cranio-cervical instrumentation. The aim of this study was to perform a quantitative morphometric analysis using computed tomography (CT) to determine the variability of the occipital bone thickness and C2 pedicle thickness to optimize screw placement for OCF in a South East Asian population. Methods: Thirty patients undergoing cranio-cervical junction instrumentation during the period 2008-2010 were included. The thickness of the occipital bone and the length and diameter of the C2 pedicle were measured based on CT. Results: The thickest point on the occipital bone was in the midline with a maximum thickness below the external occipital protuberance of 16.2 mm (±3.0 mm), which was thicker than in the Western population. The average C2 pedicle diameter was 5.3 mm (±2.0 mm). This was smaller than Western population pedicle diameters. The average length of the both pedicles to the midpoint of the C2 vertebral body was 23.5 mm (±3.3 mm on the left and ±2.3 mm on the right). Conclusions: The results of this first study in the South East Asian population should help guide and improve the safety in occipito-cervical region instrumentation. Thus reducing the risk of technical failures and neuro-vascular injury.
Clinical Biomechanics, 2020
Background: Occipito-cervical fusion can be necessary in case of cranio-cervical junction instability. Proximal stabilisation is usually ensured by bi-cortical occipital screws implanted through one median or two lateral occipital plate(s). Bone thickness variability as well as the proximity of vasculo-nervous elements can induce substantial morbidity. The choice of site and implant type remains difficult for surgeons and is often empirically based. Given this challenge, implants with smaller pitch to increase bone interfacing are being developed, as is a surgical technique consisting in inverted occipital hook clamps, a potential alternative to plate/screws association. We present here a biomechanical comparison of the different occipito-cervical fusion devices. Methods: We have developed a 3D mark tracking technique to measure experimental mechanical data on implants and occipital bone. Biomechanical tests were performed to study the mechanical stiffness of the occipitocervical instrumentation on human skulls. Four occipital implant systems were analysed: lateral plates+large pitch screws, lateral plates+hooks, lateral plates+small pitch screws and median plate+small pitch screws. Mechanical responses were analysed using 3D displacement field measurements from optical methods and compared with an analytical model. Findings: Paradoxical mechanical responses were observed among the four types of fixations. Lateral plates +small pitch screws appear to show the best accordance of displacement field between bone/implant/system interface providing higher stiffness and an average maximum moment around 50 N.m before fracture. Interpretation: Stability of occipito-cervical fixation depends not only on the site of screws implantation and occipital bone thickness but is also directly influenced by the type of occipital implant.
Journal of Orthopaedic Research, 2021
Our primary study aim investigated volumetric BMD (vBMD) of the trabecular table at the EOP and the upper cervical vertebrae. Our secondary aim identified age-and sex-related differences in vBMD values at these locations. Given the structural differences between occipital and load-bearing cervical bone, we hypothesized that the trabecular table at the EOP has a higher vBMD than at the upper cervical levels that is less prone to age-related changes. Occipitocervical fixation commonly includes the use of occipital plates, and bone screws of at least 8 mm length are recommended for adequate screw purchase. 1-3 The occipital bone reaches its maximum thickness at the external occipital protuberance (EOP). 4,5 Biomechanical studies showed that unicortical screw fixation at the EOP is as strong as bicortical fixation in other locations, 6 possibly highlighting the influence of the trabecular table on pull-out strength. However, studies that reliably quantify trabecular bone mineral density (BMD) in this area and the upper cervical spine are lacking.
BACKGROUND CONTEXT: Although there are many techniques for occipitocervical fixation, there have been no reports regarding occipitocervical fixation via the use of an anterior anatomical locking plate system. PURPOSE: The biomechanics of this new system were analyzed by a three-dimensional finite element to provide a theoretical basis for clinical application. STUDY DESIGN: This was a modeling study. PATIENT SAMPLE: We studied a 27-year-old healthy male volunteer in whom cervical disease was excluded via X-ray examination. OUTCOME MEASURES: The states of stress and strain of these two internal fixation devices were analyzed. METHODS: A three-dimensional finite element model of normal occiput-C2 was established based on the anatomical data from a Chinese population. An unstable model of occipital-cervical region was established by subtracting several unit structures from the normal model. An anterior occiput-to-axis locking titanium plate system was then applied and an anterior occiput-to-axis screw fixation was performed on the unstable model. Limitation of motion was performed on the surface of the fixed model, and physiological loads were imposed on the surface of the skull base. RESULTS: Under various loads from different directions, the peak values of displacement of the anterior occiput-to-axis locking titanium plate system decreased 15.5%, 12.5%, 14.4%, and 23.7%, respectively, under the loads of flexion, extension, lateral bending, and axial rotation. Compared with the anterior occiput-to-axis screw fixation, the peak values of stress of the anterior occiputto-axis locking titanium plate system also decreased 3.9%, 2.9%, 9.7%, and 7.2%, respectively, under the loads of flexion, extension, lateral bending, and axial rotation. CONCLUSION: The anterior occiput-to-axis locking titanium plate system proved superior to the anterior occiput-to-axis screw system both in the stress distribution and fixation stability based on finite element analysis. It provides a new clinical option for anterior occipitocervical fixation. Ó
The cervical end of an occipitocervical fusion: a biomechanical evaluation of 3 constructs
Journal of Neurosurgery: Spine, 2008
Object Stabilization with rigid screw/rod fixation is the treatment of choice for craniocervical disorders requiring operative stabilization. The authors compare the relative immediate stiffness for occipital plate fixation in concordance with transarticular screw fixation (TASF), C-1 lateral mass and C-2 pars screw (C1L-C2P), and C-1 lateral mass and C-2 laminar screw (C1L-C2L) constructs, with and without a cross-link. Methods Ten intact human cadaveric spines (Oc–C4) were prepared and mounted in a 7-axis spine simulator. Each specimen was precycled and then tested in the intact state for flexion/extension, lateral bending, and axial rotation. Motion was tracked using the OptoTRAK 3D tracking system. The specimens were then destabilized and instrumented with an occipital plate and TASF. The spine was tested with and without the addition of a cross-link. The C1L-C2P and C1L-C2L constructs were similarly tested. Results All constructs demonstrated a significant increase in stiffness...
Biomechanical evaluation of occipitocervicothoracic fusion: impact of partial or sequential fixation
The spine journal : official journal of the North American Spine Society
Surgical instrumentation used for posterior craniocervical instability has evolved from simple wiring techniques to sophisticated implant systems that incorporate multiple means of rigid fixation for the cervical spine. Polyaxial screws and lamina hooks in conjunction with occipital plating and transitional rods for caudal fixation theoretically allow for fixation points at each vertebra along the posterior aspect of the cervical spine. However, the potential for anatomical constraints to prevent intraoperative instrumentation at the desired vertebral level exists. The biomechanical implications of such "skipped segments" have not been well documented. The purpose of this study was to determine the biomechanical effects of partial three-point fixation versus sequential fixation at all levels of the cervical spine from the occiput to T1. Fresh frozen human cadaveric cervical spines from the occiput (CO) to T1 were prepared and mounted on a spine simulator. Motion was assess...
Occipitocervical Fixation: Long-Term Results
Spine, 2005
The study is a retrospective review of 58 patients who underwent occipitocervical fusion between 1997 and 2001. Objectives. Our objective is to study the clinical results after occipitocervical fixation with long-term follow-up and assess factors contributing to clinical success. Methods. Data from patient charts, operative notes, physician office notes, and imaging studies were incorporated in the study. Myelopathy was assessed using a Nurick scale for preoperative and postoperative evaluation. Fusion was assessed using cervical plane films with flexion and extension views. Results. Mean follow-up was 36 months, with all patients having a greater than 1-year follow-up. The most common pathology was congenital cranial settling (41%) followed by trauma (22%) and rheumatoid arthritis (17%). Myelopathy was the most common presentation (62%) followed by pain (28%). A successful fusion occurred in 48 out of 51 patients (94%). Symptoms improved in 86% of patients, whereas 35% improved 1 Nurick grade. Complications occurred in 30% of patients. The cervical wound infection rate was 5%. The rate of adjacent level degeneration was 7%. The mortality rate was 1.7%. Conclusions. Occipitocervical instrumentation allows for very high fusion rates without the need for halo vest immobilization. All patients with successful fixation have pain resolution. Myelopathy improves in most patients, whereas one-third of patients demonstrate dramatic improvement.
Journal of Neurosurgery: Spine, 1999
Object. The authors present a series of 16 patients who underwent inside—outside occipital and posterior cervical spine stabilization. Methods. In this technique, the screw was placed from the inside of the occiput to the outside. An articular (lateral) mass plate was contoured to the shape of the occipital bone and the cervical spine and affixed to the occiput with a flat-headed screw or stud placed through a burr hole in the calvaria with the flat head of the screw in the epidural space and the threads facing outward. The bone plate was then secured with a nut to the occipital screw and the cervical plate was attached to the spine with a bone screw that coursed through the plate and into the articular pillar. Our series included six children and 10 adults. In five patients, previous fusion had failed; in two patients spinal instability was secondary to Down's syndrome; two patients' instability was related to developmental anomalies; and in five patients spinal instability...
Modified inside-outside occipito-cervical plate system: Preliminary results
Asian Journal of Neurosurgery, 2019
Context: Internal rigid fixation provides immediate stability of the occipito-cervical (OC) junction for treatment of instability; however, in current practice, the optimal OC junction stabilization method is debatable. Aims: The aim of this study to test the safety and efficacy of a newly designed modified inside-outside occipito-cervical (MIOOC) plate system for the treatment of instability. Settings and Design: This was a feasibility study of MIOCC plate system. Subjects and Methods: Five male and four female patients with OC instability were treated using MIOOC plate system. Stabilization rate, safety, and efficacy were evaluated radiologically and clinically. Results: Mean age of the patients was 35 ± 11 (range: 22–58) years. Etiology of OC instability included trauma, neoplasm, congenital abnormalities, and iatrogenic. The fusion levels ranged from occiput-C3 to occiput-C6. Mean follow-up duration was 22 ± 10 (range: 6–46) months. There were neither complication nor was there ...