A Novel Construct Incorporating C2 Unilateral Pedicle and Contralateral Translaminar Screws for Occipitocervical Internal Fixation: An In Vitro Biomechanical Study.

BACKGROUND: Occipitocervical fixation using bilateral C2 pedicle screws (C0-C2BiPS) and occipitocervical fixation using bilateral C2 translaminar screws (C0-C2BiLS) provide satisfactory stability. Bilateral fixation is not feasible for cases of C2 unilateral pedicle morphology abnormality and ipsilateral laminectomy. This study proposed and evaluated novel occipitocervical fixation using C2 unilateral pedicle screw and contralateral translaminar screws (C0-C2PSLS). METHODS: In 6 human cadaveric specimens, an in vitro experiment was performed with 2.0-Nm moment control in flexion-extension, lateral bending, and axial rotation to investigate biomechanical stability. Neutral zone and range of motion (ROM) between the occiput (C0) and C2 were measured in the intact state, after destabilization, and after sequential stabilization using C0-C2BiPS, C0-C2BiLS, and C0-C2PSLS constructs. RESULTS: Flexion-extension ROM of the intact specimens at C0-C2 was 27.4° ± 2.4°. Instrumentation with C0-C2PSLS, C0-C2BiPS, and C0-C2BiLS reduced flexion-extension ROM to 3.7° ± 1.3°, 4.7° ± 1.4°, and 4.5° ± 1.4°, respectively. In lateral bending, ROM values were 7.0° ± 0.6°, 4.5° ± 1.4°, 4.2° ± 1.4°, 2.7° ± 1.0°, respectively. In axial rotation, ROM values were 65.3° ± 5.7°, 2.5° ± 0.5°, 1.4° ± 0.5°, and 0.9° ± 0.6°, respectively. Comparing destabilized and intact specimens, all 3 constructs significantly reduced ROM and neutral zone values in flexion-extension, lateral bending, and axial rotation (P < 0.05). Direct comparisons between the 3 constructs revealed no significant difference (P > 0.05). CONCLUSIONS: Novel C0-C2PSLS provides similar stabilization effect as C0-C2BiPS and C0-C2BiLS constructs and has potential for clinical use, especially for cases of C2 unilateral pedicle morphology abnormality and ipsilateral laminectomy.

Is it Suitable to Fix the Occipito-C2 Angle and the Posterior Occipitocervical Angle in a Normal Range During Occipitocervical Fusion?

STUDY DESIGN: This is a retrospective study. OBJECTIVES: The objective of this study was (1) to measure the occipito-C2 angle (OC2A) and the posterior occipitocervical angle (POCA) in a normal population, and (2) to observe the effects of OC2A and POCA selection on postoperative clinical efficacy and lower cervical curvature after occipitocervical fusion (OCF) in patients with basilar invagination (BI) and atlantoaxial fracture and dislocation (AAFD). SUMMARY OF BACKGROUND DATA: OC2A has received special attention with respect to the clinical efficacy during OCF. However, none of studies have focused on the relationship between OC2A and POCA and have assessed their impact on clinical outcomes in patients with different occipiocervical diseases. MATERIALS AND METHODS: One hundred fifty healthy subjects without any cervical disease (healthy group) were randomly selected based on sex and age. Three spine surgeons measured the OC2A and POCA in the healthy group and averaged the values. Forty-two patients with BI (BI group) and 32 patients with AAFD (AAFD group) who underwent OCF between January 2012 and January 2017 were reviewed. OC2A, POCA, and cervical spinal angle (CSA) were measured preoperatively, postoperatively immediately after surgery and ambulation, and at the final follow-up visit. The preoperative and final follow-up visual analog scale (VAS), Japanese Orthopaedic Association score (JOA), neck disability index (NDI), and the change of CSA from postoperatively immediately after surgery and ambulation to the final follow-up (dCSA) were recorded. RESULTS: The values of OC2A and POCA were 14.5±3.7 and 108.2±8.1 degrees in the healthy group, respectively, and the respective 95% confidence intervals were 7.2-21.8 and 92.3-124.0 degrees as the normal range. There was a negative correlation between OC2A and POCA (r=-0.386, P<0.001). The preoperative value of OC2A (5.6±4.3 degrees) in BI group was smaller than that in the healthy group (P<0.05); however, the preoperative value of POCA (123.0±10.4 degrees) in the BI group was larger than that in the healthy group (P<0.05). There was no significantly different of OC2A and POCA between the healthy group and the AAFD group before the operation (P>0.05). The preoperative value of CSA (25.7±9.5 degrees) in the BI group was larger than that in the AAFD group (16.5±5.1 degrees) (P<0.05). In the BI group, 26 patients had ideal OC2A and POCA (both within 95% confidence interval of the healthy group) postoperatively immediately after surgery and ambulation as a subgroup of the ideal angle group. In the remaining patients with BI (nonideal angle group), VAS, JOA, and NDI at the final follow-up were significantly better than those in the ideal angle group (P<0.05). The ideal angle group showed statistically greater dCSA than the nonideal angle group of the BI group (P<0.05). On the contrary, in the AAFD group, the NDI in the ideal angle group (20 patients) was better than that in the nonideal angle group at the final follow-up, and the ideal angle group had a smaller dCSA compared with the nonideal angle group (P<0.05). CONCLUSIONS: The biomechanical balance of occipitocervical region in patients with occipitocervical diseases with different pathogenesis is different. On the basis of the different types of occipitocervical diseases, an appropriate range of OC2A and POCA should be selected by the surgeon during OCF, which can further improve the clinical efficacy and reduce the loss of the lower cervical curvature after surgery.

Abnormalities of the craniovertebral junction in the paediatric population: a novel biomechanical approach.

The craniovertebral junction (CVJ) is the bony transition between the cranium and cervical spine. It is a biomechanically complex articulation comprising the occipital condyles (Oc) the atlas (C1) and axis (C2). Pathologies affecting the CVJ in children are myriad with clinical features resulting from biomechanical instability, deformity, or neuraxial compression. Establishing the natural history and clinical burden of a condition is challenging in infants and young children, often complicated by co-existing neuromuscular and cognitive impairment. This makes investigation and treatment planning difficult. Each disease entity has a predilection for a particular biomechanical abnormality. Investigation using dynamic imaging is most appropriate in instability, computed tomography examination in abnormalities of deformity and magnetic resonance imaging examination in neuraxial compression. Treatment comprises reduction and immobilisation of instability, re-alignment of deformity, or decompression of the neuraxis. We present a review of disease entities affecting the CVJ in children categorised according to a simple mechanistic approach to aid investigation and treatment planning.

Occiput-axis crossing translaminar screw fixation technique using offset connectors: An in vitro biomechanical study.

OBJECTIVE: Fixation with the axis vertebra (C2) using pedicle screws is commonly used to treat an unstable occipitocervical junction; however, it is accompanied by a risk of vertebral artery injury. The occiput-C2 (OC2) crossing translaminar screw fixation technique may avoid this risk, but rod implantation is difficult. Offset connectors can help facilitate this construct. This study aimed to evaluate the stability of a technique for OC2 crossing translaminar screw fixation using offset connectors (C2LAM + OF) in comparison with other methods. PATIENTS AND METHODS: Six fresh-frozen human cadaveric occipital-cervical spines were tested intact under flexion, extension, lateral bending, and axial rotation. These were then made into a type II odontoid fracture model, instrumented with an occipital plate, and tested in the following modes: C2 bilateral pedicle screws (C2P), a single C2 pedicle screw and bilateral C3 lateral mass screws (C2P + C3M), C2 crossing translaminar screws (C2LAM), and C2LAM + OF. The OC2 range of motion (ROM) for each construct was obtained and compared using a repeated-measures analysis. RESULTS: The ROM of the C2LAM + OF construct was found not to be significantly different from that of the C2P and C2P + C3M fixations in every direction (p > 0.05). However, the C2LAM + OF construct was superior to the C2LAM construct in axial rotation (p < 0.05). CONCLUSIONS: OC2 crossing translaminar screw fixation using offset connectors offers similar stability to C2 pedicle screw fixation and is an effective alternative method for treating an unstable occipitocervical junction.

Diameters and bone thickness at the margin of the foramen magnum in dry skulls from pediatric population: a cross-sectional anatomical study.

PURPOSE: The purpose of the study was to estimate the size and bone thickness at the margin of the foramen magnum in a pediatric population. METHODS: Sixty occipital bone specimens from the collection of macerated skulls at the Department of Anatomy, University of Zagreb, were examined and measured using a vernier scale/caliper. For the purpose of analysis, specimens were divided into two age groups: 1-6 years and 7-18 years of age (before and after the fusion of ossification centers in the occipital bone). We measured the following: antero-posterior and transverse diameters of the foramen magnum, bone thicknesses at the basion, opisthion, two paramedial points on the anterior and posterior margins, and at the occipito-squamous junction. RESULTS: Data presented in this study show that diameters of the foramen magnum increase with age, whereas bone thickness shows variable behavior depending on the measured area. CONCLUSIONS: Increases in diameters in specimens from the younger age group and their absence in specimens from older subjects reflect the growth pattern of the basilar part of occipital bone. Variability of bone thickness at the margin of the foramen magnum and lack of its association with age of the subjects may be attributed to various factors and may potentially affect the clinical presentation of compression syndromes at the level of foramen magnum.

Effects of suboccipital release with craniocervical flexion exercise on craniocervical alignment and extrinsic cervical muscle activity in subjects with forward head posture.

BACKGROUND: Forward head posture is a head-on-trunk malalignment, which results in musculoskeletal dysfunction and neck pain. To improve forward head posture, both the craniocervical flexion exercise and the suboccipital release technique have been used. OBJECTIVES: The purpose of this study was to compare the immediate effects of craniocervical flexion exercise and suboccipital release combined with craniocervical flexion exercise on craniovertebral angle, cervical flexion and extension range of motion, and the muscle activities of the sternocleidomastoid, anterior scalene, and splenius capitis during craniocervical flexion exercise in subjects with forward head posture. METHODS: In total, 19 subjects (7 males, 12 females) with forward head posture were recruited using G-power software. Each subject performed craniocervical flexion exercise and suboccipital release combined with craniocervical flexion exercise in random order. After one intervention was performed, the subject took a 20min wash out period to minimize any carry-over effect between interventions. Craniovertebral angle, cervical flexion and extension range of motion, and the muscle activities of the sternocleidomastoid, anterior scalene, and splenius capitis were measured. A one-way, repeated-measures ANOVA was used to assess differences between the effects of the craniocervical flexion exercise and suboccipital release combined with craniocervical flexion exercise interventions in the same group. RESULTS: Craniovertebral angle (p<0.05), cervical flexion range of motion (p<0.05), and cervical extension range of motion (p<0.001) were significantly greater after suboccipital release combined with craniocervical flexion exercise compared to craniocervical flexion exercise alone. The muscle activities of the sternocleidomastoid, anterior scalene, and splenius capitis were significantly lower during suboccipital release combined with craniocervical flexion exercise than during craniocervical flexion exercise alone across all craniocervical flexion exercise phases except the first (all p<0.05). CONCLUSION: The addition of suboccipital release to craniocervical flexion exercise provided superior benefits relative to craniocervical flexion exercise alone as an intervention for subjects with forward head posture.

The Effect of the Cervical Orthosis on Swallowing Physiology and Cervical Spine Motion During Swallowing.

Cervical orthosis is used to immobilize the neck in various disorders such as trauma and post-operation. However, it is still uncertain how cervical orthosis restricts the degree of movement of the cervical spine during swallowing and how they affect swallowing physiology. The purpose of this study was to evaluate these issues using the Philadelphia(®) Collar. We conducted videofluorography of swallowing in 39 healthy subjects (23 men, 16 women; mean age of 34.3 years) with and without cervical orthosis. To compare the two conditions regarding the cervical spine motion, we determined the angular and positional changes of the occipital bone (C0) and each cervical vertebra (C1-C7) from the oral phase to the pharyngeal phase. Similarly, to compare swallowing physiology, we assessed the start and end times and the durations of soft palate elevation, rapid hyoid anterosuperior movement, epiglottis inversion, closure of the laryngeal vestibule, and pharyngoesophageal segment (PES) opening. Finally, we compared the transit times of contrast agent in the two conditions. The respective extensions of C1, C2, and C3 were 0.31°, 0.07°, and 0.05° (mean) with cervical orthosis, and the respective flexions of C1, C2, and C3 were 0.98°, 1.42°, and 0.85° (mean) without. These results suggested that cervical orthosis restricted the flexion of C1-C3. Analysis of swallowing physiology revealed that the average durations of hyoid anterosuperior elevation, epiglottic inversion, and PES opening were prolonged by 0.09, 0.19, and 0.05 s, respectively. In conclusion, the cervical orthosis restricted the movement of the cervical spine during swallowing and changed swallowing physiology.

Impact of the O-C2 angle on the oropharyngeal space in normal patients.

STUDY DESIGN: Radiographic analysis using normal patients. OBJECTIVE: To analyze the relationship between the cervical alignment and the oropharyngeal space. SUMMARY OF BACKGROUND DATA: Few clinical studies stress the effect of the occipito-C2 (O-C2) alignment on the oropharyngeal space. A previous study showed dysphagia and/or dyspnea after occipitocervical fusion was caused by oropharyngeal stenosis resulting from O-C2 fixation in a flexed position. Other independent researchers showed that development or improvement of obstructive sleep apnea in rheumatoid arthritis patients was related to the O-C2 alignment. However, there are limited basic data demonstrating the relationship between the O-C2 alignment and the oropharyngeal space. METHODS: Plain lateral cervical radiographs in five tested positions--neutral, flexion, extension, protrusion, and retraction--of 40 asymptomatic volunteers were collected. The O-C2 angle, the C2-C6 angle, and the anterior-posterior distance of the narrowest oropharyngeal airway space (nPAS) were measured, and the changes in value from the neutral to the other four positions were calculated for each patient. RESULTS: According to the multiple regression analysis, there was an extremely strong linear correlation of the change in the O-C2 angle with the percentage change in the nPAS. Referring to the multiple regression analysis, a decrease of 10° in the O-C2 angle caused a 37% reduction in the nPAS in the neutral position. In contrast, no significant correlation was found between the change in the C2-C6 angle and the percentage change in the nPAS. CONCLUSION: Our results show the impact of the O-C2 angle on the oropharyngeal space. This knowledge will be useful for the diagnosis and treatment of the upper cervical lesion combined with the upper airway stenosis, and for the determination of the optimal fixation angle in occipitocervical fusion.

Musculoskeletal modeling of the suboccipital spine: kinematics analysis, muscle lengths, and muscle moment arms during axial rotation and flexion extension.

STUDY DESIGN: In vitro and modeling study of upper cervical spine (UCS) three-dimensional (3D) kinematics and muscle moment arm (MA) during axial rotation (AR) and flexion extension (FE). OBJECTIVE: To create musculoskeletal models with movement simulation including helical axis (HA) and muscle features. SUMMARY OF BACKGROUND DATA: Integration of various kinematics and muscle data into specific-specimen 3D anatomical models with graphical representation of HA and muscle orientation and MA is not reported for the UCS musculoskeletal system. METHODS: Kinematics, anatomical, and computed tomographic imaging data were sampled in 10 anatomical specimens. Using technical markers and anatomical landmarks digitizing, spatial position of segments was computed for five discrete positions of AR and FE using a 3D digitizer. To obtain musculoskeletal model simulation, a registration method was used to combine collected data. Processing was performed using orientation vector and HA computation and suboccipital muscle features (i.e., length and MA) relative to motion angle. RESULTS: Range of motion and coupling were in agreement with previous in vitro studies. HA (i.e., location and orientation) showed low variation at the occipitoaxial and atlantoaxial levels for FE and AR, respectively. The main orientation of the HA was vertical at C1-C2 during AR and horizontal at C0-C1 during FE. For muscles MA, absolute peak value (ranging from 20 to 40 mm) occurred at different poses depending on the analyzed muscle and motion. Poor magnitude was found for obliquus capitis inferior and rectus capitis posterior minor in FE and AR, respectively. CONCLUSION: On the basis of previous methods, we developed a protocol to create UCS musculoskeletal modeling with motion simulation including HA and suboccipital muscles representation. In this study, simultaneous segmental movement displaying with HA and muscles features was shown to be feasible.

Biomechanical implications of extending occipitocervical instrumentation to include the subaxial spine.

BACKGROUND: No clear biomechanical data exist regarding where to place the caudal end of a screw-rod occipitocervical instrumentation construct. OBJECTIVE: This study examines whether range of motion (ROM) from the occiput to C2 is altered by subaxial extension of occipitocervical instrumentation constructs. METHODS: Cadaver specimens underwent intact biomechanical testing followed by destabilization via an odontoid osteotomy. Subsequent biomechanical testing was performed of four occipitocervical constructs: occipital plate + C2 pars screws (construct 1), occipital plate + C2 pars screws + C4 lateral mass screws (construct 2), occipital plate + C1-C2 transarticular screws (construct 3), and occipital plate + C1-C2 transarticular screws + C4 lateral mass screws (construct 4). RESULTS: All constructs significantly reduced occiput-C2 ROM in all loading modes compared with the intact cervical spine, with one exception (construct 1, lateral bending). No significant ROM differences were noted when C4 lateral mass screws (construct 4) were added to construct 3. Addition of C4 lateral mass screws (construct 2) to construct 1 decreased the ROM in the flexion mode only. No significant ROM differences were seen between construct 2 and construct 3 in any loading mode. CONCLUSION: The addition of subaxial instrumentation to occipitocervical instrumentation constructs in this study decreased occiput-C2 ROM only when the construct was anchored by C2 pars screws and only in flexion. Screws that cross the C1 to C2 articulation provide stable fixation when combined with an occipital plate, and the addition of subaxial instrumentation to this construct for stabilizing the occipitocervical junction does not significantly decrease ROM.

Occipital nerve stimulator placement via a retromastoid to infraclavicular approach: a technical report.

Occipital nerve stimulation is a form of peripheral nerve stimulation used to treat refractory headache disorders. Various techniques have been described for occipital nerve stimulator implantation; these include midline cervical or retromastoid lead insertion with internal pulse generator placement in the infraclavicular, gluteal or low abdominal regions. Lead migration is one of the most common complications of occipital nerve stimulators. Implantation approaches that include remote battery sites may contribute to mechanical stress on the components, as the leads or extensions may traverse highly mobile body regions. In this technical report, we describe an occipital stimulator implantation technique that may be advantageous in terms of patient positioning, ease of surgical approach and minimization of mechanical stress on components.

The transverse occipital ligament: anatomy and potential functional significance.

BACKGROUND: Knowledge of the anatomy of ligaments that bind the craniocervical junction is important for treating patients with lesions of this region. Although the anatomy and function of these ligaments have been well described, those of the transverse occipital ligament (TOL) have remained enigmatic. OBJECTIVE: To describe the anatomy and functions of the transverse occipital ligament. METHODS: Via a posterior approach, 9 cadaveric specimens underwent dissection of the craniocervical junction with special attention to the presence and anatomy of the TOL. RESULTS: The TOL was identified in 77.8% of the specimens. The ligament was found to be rectangular with fibers running horizontally between the lateral aspects of the foramen magnum. The attachment of each ligament near the occipital condyle was consistent, and each ligament was found superior to the transverse portion of the cruciform ligament and inserted just posterior to the lateral attachment sites of the alar ligaments. The average width, length, and thickness of the TOL was 0.34, 1.94, and 0.13 cm, respectively. The TOL in some specimens also had connections to the alar and transverse ligaments. CONCLUSION: The TOL was found in the majority of our specimens. The possible functions of this ligament when attached to the alar ligaments include providing additional support to these structures in stabilizing lateral bending, flexion, and axial rotation of the head. Knowledge of this ligament may aid in further understanding craniocervical stability and help in differentiating normal from pathology via imaging modalities.

C1 lateral mass fixation: a comparison of constructs.

OBJECTIVE: We review our experience and technique for C1 lateral mass screw fixation. We compare the results of 3 different constructs incorporating C1 lateral mass screws: occipitocervical (OC) constructs, C1-C2 constructs, and C1 to mid/low cervical constructs. METHODS: We performed a retrospective chart review of 42 consecutive patients who underwent C1 lateral mass fixation by 2 of the authors (PVM and DC). The patient population consisted of 24 men and 18 women with a mean age of 64 years. Twenty-two patients had C1-C2 constructs. Twelve patients had constructs that started at C1 and extended to the mid/low cervical spine (one extended to T1). Eight patients underwent OC fusions incorporating C1 screws (2 of which were OC-thoracic constructs). All constructs were combined either with a C2 pars screw (38 patients), C2 translaminar screw (1 patient), or C3 lateral mass screw (3 patients). No C2 pedicle screws were used. Fusion was assessed using flexion-extension x-rays in all patients and computed tomographic scans in selected cases. Clinical outcomes were assessed with preoperative and postoperative visual analog scale neck pain scores and Nurick grading. The nuances of the surgical technique are reviewed, and a surgical video is included. RESULTS: Two patients (5%) were lost to follow-up. The mean follow-up for the remaining patients was 2 years. During the follow-up period, there were 4 deaths (none of which were related to the surgery). For patients with follow-up, the visual analog scale neck pain score improved a mean of 3 points after surgery (P < .001). For patients with myelopathy, the Nurick score improved by a mean of 1 grade after surgery (P < .001). The postoperative complication rate was 12%. The complication rate was 38% in OC constructs, 17% in C1 to mid/low cervical constructs, and 0% for C1-C2 construct cases. Patients with OC constructs had the statistically highest rate of complications (P < .001). Patients with C1 to mid/low cervical constructs had more complications than those with C1-C2 constructs (P < .001). Of the 42 cases, there were 3 pseudoarthroses (1 in an OC case, 1 in a C1 to midcervical construct, and 1 in a C1-C2 construct). OC constructs had the highest risk of pseudoarthrosis (13%) (P < .001). CONCLUSION: Patients treated with C1 lateral mass fixation constructs have a high fusion rate, reduced neck pain, and improved neurologic function. Constructs using C1 lateral mass screws do not need to incorporate C2 pedicle screws. Constructs incorporating C1 lateral mass screws are effective when combined with C2 pars screws, C2 translaminar screws, and C3 lateral mass screws. Constructs using C1 screws are associated with a higher complication rate and a higher pseudoarthrosis rate if extended cranially to the occiput or if extended caudally below C2.

Anatomic and biomechanical considerations of the craniovertebral junction.

An understanding of the regional anatomy and specific biomechanics of the craniovertebral junction is relevant to the specific diseases that affect the region as well as instrumentation of the occiput, atlas, and axis. This article reviews the bony, ligamentous, and vascular anatomy of the region, in relation to the posterior surgical approach to this anatomically unique segment of the cervical spine. Anatomic variations of the area are also discussed. Basic principles of instrumentation of the region are also reviewed. The kinematics of the region as they pertain to the anatomic discussion are reviewed and discussed.

Variability of human foramen magnum size.

The foramen magnum is an important landmark of the skull base and is of particular interest for anthropology, anatomy, forensic medicine, and other medical fields. Despite its importance, few osteometric studies of the foramen magnum have been published so far. A total of 110 transverse and 111 sagittal diameters from Central European male and female dry specimens dating from the Pleistocene to modern times were measured, and related to sex, age, stature, ethnicity, and a possible secular trend. Only a moderate positive correlation between the transverse and the sagittal diameter of the foramen magnum was found. Surprisingly, neither sexual dimorphism, individual age-dependency, nor a secular trend was found for either diameter. Furthermore, the relationship between the individual stature and foramen magnum diameters was weak: thus foramen magnum size cannot be used as reliable indicator for stature estimation. Further consideration of possible factors influencing the variability of human foramen magnum size shall be explored in larger and geographically more diverse samples, thus serving forensic, clinical, anatomical, and anthropological interests in this body part.

Screw fixation via diploic bone paralleling to occiput table: anatomical analysis of a new technique and report of 11 cases.

Several types of posterior approaches have been adopted for occipitocervical fusion. Prior to this study, Foerater et al. in 1927 used a fibular strut graft in the site between the occiput and the lower cervical spine to achieve fusion. Since then, various techniques including wrings, Hartshill loop, AO reconstructive plate, and AXIS occipital plate were described and used widely. As far as we know, all these techniques involve the screw placement vertical to the diploic bone; however none has ever addressed the feasibility of screw placement in occiput parallelling to the diploic bone. In our study, 30 dry specimens of human occiputs were measured manually using vernier calipers and protractors. The intradiploic screw was first supposed to be inserted inferiorly to the superior nuchal line (SNL) prominence. The entry point located at the superior edge of the SNL prominence. Afterward, the measurements of extracranial occiput in SNL area on midline and bilateral 15 mm to the midline saggital-cutting planes of the occiput were conducted. The thickness of the occipital bone at the location of SNL prominence, the entry point, the exit point and the screw orientation were measured, respectively. Afterward, 11 patients with craniocervical malformation were treated surgically using this alternative and their X-ray radiographs and CT scans were evaluated postoperatively. The data showed that the occipital at the site of SNL prominence was the thickest. The thickest point was external occipital protuberance (EOP), which was up to 14 mm. The thickness decreased gradually from the site of SNL to the superior border of surgical decompressed area. The actual length of screw channel was about 26 mm. The mean thickness for safe screw insertion ranged from 5.73 to 14.14 mm. A total of 22 intraocciput screws parallel to diploic bone were placed precisely, without injury to the cerebral and inner occipital venous sinus. The results confirm that occiput is available for holding intraocciput screw paralleling to diploic bone.

Anatomical, biomechanical, and practical considerations in posterior occipitocervical instrumentation.

BACKGROUND CONTEXT: Patients with cervical myelopathy secondary to craniocervical instability commonly present with spinal cord compression secondary to a combination of static forces and gross instability. Craniocervical arthrodesis is therefore indicated in the treatment of the majority of these conditions. In order to facilitate arthrodesis, techniques for occipitocervical instrumentation have been developed. PURPOSE: To systematically review the anatomy, biomechanics, and practical considerations involved in posterior occipitocervical instrumentation. STUDY DESIGN: Retrospective literature review. PATIENT SAMPLE: Not applicable. OUTCOME MEASURES: Not applicable. METHODS: Retrospective literature review. RESULTS: The anatomic elements of the craniocervical junction include the occipital bone, occipital condyles, atlas (C1), and axis (C2). The occiput-C1 and C1-C2 motion segments possess unique mechanical properties. Occipitocervical instrumentation constructs are comprised of points of fixation and longitudinal elements, each with characteristic strengths and weaknesses. CONCLUSIONS: Analysis of the anatomy, available points of fixation, and the movements to be controlled leads to the choice of a longitudinal element which can control movement by incorporating the strongest points of fixation. By going through this process for each patient, an informed decision may be made regarding the optimal occipitocervical instrumentation construct.

Material properties of human infant skull and suture at high rates.

Clinicians are often faced with the challenging task of distinguishing between accidental and inflicted pediatric head trauma. There is currently a disparity in the anecdotal case study literature as to what kinds of injuries can occur in children from low height falls. There is also a paucity of material property data for pediatric skull and suture at rates similar to those expected in low height falls. We tested human infant (<1 year old) cranial bone and suture from 23 calveria in three-point bending and tension, respectively, at rates ranging from 1.2-2.8 m/sec. Donor age was found to have the largest influence on the elastic modulus and ultimate stress of cranial bone, with an increase in age increasing both material properties. In adults, cranial bone and suture have similar properties and the adult calveria deforms very little prior to fracture. In contrast, pediatric cranial bone is 35 times stiffer than pediatric cranial suture. In addition, pediatric cranial suture deforms 30 times more before failure than pediatric cranial bone and 243 times more than adult cranial bone. The large strains in the pediatric bone and suture result in a skullcase that can undergo dramatic shape changes before fracture, potentially causing substantial deformation in the brain. The sizeable difference between pediatric bone and suture material properties also underscores the crucial role that sutures play in the unique response of the pediatric head to impact in low height falls. These data provide necessary information to enhance our understanding of mechanisms of head injury in young children.

Stresses at the cranial base induced by rapid maxillary expansion.

OBJECTIVE: An analysis of the distribution of stresses at the juvenile and adult cranial base after implementation of a rapid palatal suture expansion was the goal of this study. Of particular interest were stresses occurring near the cranial foramina containing vulnerable structures. MATERIALS AND METHODS: The stresses were simulated and analyzed using a finite elements model of the human cranial base. The model consisted of several skull bones (sphenoid, frontal bone, occipital bone, and the two temporal bones) with a total of 41,556 finite elements. To illustrate the differences between reactions in the juvenile and the adult, the differing bone elasticity was depicted as variations in the modulus of elasticity. RESULTS: At the juvenile cranial base only moderate stresses occurred during rapid palatal suture expansion, apparently precluding the likelihood of any serious complications in the area of the foramina. The situation in the adult, however, was different. Because of the reduced elasticity of the bony structures, considerable stress already occurred on light bending of the pterygoid process, especially in the area of the round foramen, the oval foramen, and the superior orbital fissure, all of which might lead to microfractures with injury of nervous and vascular structures. CONCLUSIONS: The lower the bone elasticity on carrying out a rapid palatal suture expansion, the more important safety measures are for protecting the cranial base. For this reason the pterygomaxillary connection should be severed on both sides in adults when carrying out a surgically assisted palatal suture expansion.

Biomechanics of occipitocervical fixation.

STUDY DESIGN: A human cadaveric biomechanical study comparing occipital fixation techniques. OBJECTIVES: To compare ranges of motion between midline and lateral occipital fixation and between rigid and nonrigid occipital fixation of an unstable craniocervical spine. SUMMARY OF BACKGROUND DATA: New fixation techniques using rods and screws increase surgical choice on where fixation is placed onto the occiput. Lateral fixation theoretically gives improved resistance to deformation because of its increased effective moment arm and bilateral purchase. Midline fixation allows significantly longer screw purchase. This study compares these two fixation location. METHODS: Cadaveric occipital cervical spine specimens were tested biomechanically intact and under six different fixation techniques. Range of motion between the skull and C2 at 1.5 N-m and 2 N-m bending moments was measured in flexion-extension, lateral bending, and axial rotation. Mechanical testing of different rod diameters and a reconstruction plate was performed and compared with biomechanical testing. Results were compared between the intact condition and all fixations, between the medial and lateral fixations, and between the rigid and nonrigid fixations by analysis of variance. RESULTS: The range of motion of all constructs was significantly reduced compared with intact. Significant differences between groups were only seen in lateral bending in fixation placed laterally. Mechanical testing demonstrated that construct stiffness was predicted by area moment of inertia of the rod and plate to a greater degree than variation in placement of occipital screws or locking of the implant. CONCLUSION: The choice of location of occipital fixation should be based more on the ease of use and instability pattern. The decreased stiffness of the newer small rod systems should be considered.