Biomechanical Analysis Comparing Three C1-C2 Transarticular Screw Salvaging Fixation Techniques
ABSTRACT This is an in vitro biomechanical study.
To compare the biomechanical stability of the 3 C1-C2 transarticular screw salvaging fixation techniques.
Stabilization of the atlantoaxial complex is a challenging procedure because of its complicated anatomy. Many posterior stabilization techniques of the atlantoaxial complex have been developed with C1-C2 transarticular screw fixation been the current gold standard. The drawback of using the transarticular screws is that it has a potential risk of vertebral artery injury due to a high riding transverse foramen of C2 vertebra, and screw malposition. In such cases, it is not recommended to proceed with inserting the contralateral transarticular screw and the surgeon should find an alternative to fix the contralateral side. Many studies are available comparing different atlantoaxial stabilization techniques, but none of them compared the techniques to fix the contralateral side while using the transarticular screw on one side. The current options are C1 lateral mass screw and short C2 pedicle screw or C1 lateral mass screw and C2 intralaminar screw, or C1-C2 sublaminar wire.
Nine fresh human cervical spines with intact ligaments (C0-C4) were subjected to pure moments in the 6 loading directions. The resulting spatial orientations of the vertebrae were recorded using an Optotrak 3-dimensional Motion Measurement System. Measurements were made sequentially for the intact spine after creating type II odontoid fracture and after stabilization with unilateral transarticular screw placement across C1-C2 (TS) supplemented with 1 of the 3 transarticular salvaging techniques on the contralateral side; C1 lateral mass screw and C2 pedicle screw (TS+C1LMS+C2PS), C1 lateral mass and C2 intralaminar screw (TS+C1LMS+C2ILS), or sublaminar wire (TS + wire).
The data indicated that all the 3 stabilization techniques significantly decreased motion when compared to intact in all the loading cases (left/right lateral bending, left/right axial rotation, flexion) except extension. All the 3 instrumented specimens were equally stable in extension/flexion and lateral bending modes. TS+C1LMS+C2PS was equivalent to TS+C1LMS+C2ILS (P > 0.05) and superior to TS + wire in axial rotation (P < 0.05). Also, TS+C1LMS+C2ILS was superior to TS + wire in axial rotation (P < 0.05).
Fixation of atlantoaxial complex using unilateral transarticular screw supplemented with contralateral C1 lateral mass and C2 intralaminar screws is biomechanically equivalent to C1 lateral mass and C2 pedicle screws and both are biomechanically superior to C1-C2 sublaminar wire in axial rotation.
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ABSTRACT: OBJECT The unique and complex biomechanics of the atlantoaxial junction make the treatment of C1-2 instability a challenge. Several screw-based constructs have been developed for atlantoaxial fixation. The biomechanical properties of these constructs have been assessed in numerous cadaver studies. The purpose of this study was to systematically review the literature on the biomechanical stability achieved using various C1-2 screw constructs and to perform a meta-analysis of the available data. METHODS A systematic search of PubMed through July 1, 2013, was conducted using the following key words and Boolean operators: "atlanto [all fields]" AND "axial [all fields]" OR "C1-C2" AND "biomechanic." Cadaveric studies on atlantoaxial fixation using screw constructs were included. Data were collected on instability models, fixation techniques, and range of motion (ROM). Forest plots were constructed to summarize the data and compare the biomechanical stability achieved. RESULTS Fifteen articles met the inclusion criteria. An average (± SD) of 7.4 ± 1.8 cadaveric specimens were used in each study (range 5-12). The most common injury models were odontoidectomy (53.3%) and cervical ligament transection (26.7%). The most common spinal motion segments potted for motion analysis were occiput-C4 (46.7%) and occiput-C3 (33.3%). Four screw constructs (C1 lateral mass-C2 pedicle screw [C1LM-C2PS], C1-2 transarticular screw [C1-C2TA], C1 lateral mass-C2 translaminar screw [C1LM-C2TL], and C1 lateral mass-C2 pars screw [C1LM-C2 pars]) were assessed for biomechanical stability in axial rotation, flexion/extension, and lateral bending, for a total of 12 analyses. The C1LM-C2TL construct did not achieve significant lateral bending stabilization (p = 0.70). All the other analyses showed significant stabilization (p < 0.001 for each analysis). Significant heterogeneity was found among the reported stabilities achieved in the analyses (p < 0.001; I(2) > 80% for all significant analyses). The C1LM-C2 pars construct achieved significantly less axial rotation stability (average ROM 36.27° [95% CI 34.22°-38.33°]) than the 3 other constructs (p < 0.001; C1LM-C2PS average ROM 49.26° [95% CI 47.66°-50.87°], C1-C2TA average ROM 47.63° [95% CI 45.22°-50.04°], and C1LM-C2TL average ROM 53.26° [95% CI 49.91°-56.61°]) and significantly more flexion/extension stability (average ROM 13.45° [95% CI 10.53°-16.37°]) than the 3 other constructs (p < 0.001; C1LM-C2PS average ROM 9.02° [95% CI 8.25°-9.80°], C1-C2TA average ROM 7.39° [95% CI 5.60°-9.17°], and C1LM-C2TL average ROM 7.81° [95% CI 6.93°-8.69°]). The C1-C2TA (average ROM 5.49° [95% CI 3.89°-7.09°]) and C1LM-C2 pars (average ROM 4.21° [95% CI 2.19°-6.24°]) constructs achieved significantly more lateral bending stability than the other constructs (p < 0.001; C1LM-C2PS average ROM 1.51° [95% CI 1.23°-1.78°]; C1LM-C2TL average ROM -0.07° [95% CI -0.44° to 0.29°]). CONCLUSIONS Meta-analysis of the existing literature showed that all constructs provided significant stabilization in all axes of rotation, except for the C1LM-C2TL construct in lateral bending. There were significant differences in stabilization achieved in each axis of motion by the various screw constructs. These results underline the various strengths and weaknesses in biomechanical stabilization of different screw constructs. There was significant heterogeneity in the data reported across the studies. Standardized spinal motion segment configuration and injury models may provide more consistent and reliable results.Journal of Neurosurgery Spine 12/2014; 22(2):1-11. DOI:10.3171/2014.10.SPINE13805 · 2.36 Impact Factor
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ABSTRACT: Background: Posterior, atlantoaxial (AA) fusions of the cervical spine may include either standard (26 mm) or short (16 mm) C2 pedicle screws. This manuscript focused on an in vitro biomechanical comparison of standard versus short C2 pedicle screws to perform posterior C1-C2 AA fusions. Methods: Twelve human cadaveric spines underwent C1 lateral mass screw and standard C2 pedicle screw (n = 6) versus short C2 pedicle screw (n = 6) fixation. Six additional controls were not instrumented. The peak torque, peak rotational interval, and peak stiffness of the constructs were analyzed to failure levels. Results: The peak torque to construct failure was not statistically significantly different among the control spine (12.2 Nm), short pedicle fixation (15.5 Nm), or the standard pedicle fixation (11.6 Nm), P = 0.79. While the angle at the peak rotation statistically significantly differed between the control specimens (47.7° of relative motion) and the overall instrumented specimens (P < 0.001), the 20.7° of relative rotation in the short C2 pedicle screw specimens was not statistically significantly higher than the 13.7° of relative rotation in the standard C2 pedicle screw specimens (P = 0.39). Similarly, although the average stiffness was statistically significantly lower in control group (0.026 Nm/degree) versus the overall instrumented specimens (P = 0.001), the standard C2 pedicle screws (2.54 Nm/degree) did not differ from the short C2 pedicle screws Conclusions: Both standard and short C2 pedicle screws allow for equally rigid fixation of C1 lateral mass-C2 AA fusions. Usage of a short C2 pedicle screw may be an acceptable method of stabilization in carefully selected patient populations.Surgical Neurology International 08/2014; 5(Suppl 7):S343-6. DOI:10.4103/2152-7806.139664 · 1.18 Impact Factor
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ABSTRACT: Several methods for C1-C2 stabilization have been described in the literature. These include C1-C2 transarticular screws and C1 lateral mass screws. In patients with aberrant anatomy such as a high-riding VA or the presence of an arcuate foramen at C1 there exists a higher risk of VA injury. This may lead to excessive bleeding, stroke, and possibly death. There have been several studies determining the incidence of arcuate foramen and high-riding VA occurring individually in the general population, but none have determined their occurrence simultaneously. To determine the prevalence of ponticulus posticus and high-riding vertebral artery (VA) occurring simultaneously in the general population. Radiological study. One hundred consecutive CT scans of the cervical spine were reviewed. Scans that contained an arcuate foramen were identified, and it was indicated whether the foramen was right-sided, left sided, or bilateral. In the same group the thickness of the isthmus and the internal height of the lateral mass of C2 were measured. The VA was considered high-riding if the isthmus thickness was less than 5mm or isthmus internal height was less than 2mm. Fourteen out of one hundered (14%) patients had a fully-formed arcuate foramen. Of these, six were left-sided, three were right-sided, and five were bilateral. In addition there were 24 (24%) patients with partially formed ponticulus posticus. Thirty-two (32%) of patients were identified to have a high-riding VA. Of these 13 were left-sided, 9 were right-sided, and 10 were bilateral. Five (5%) had an ipsilateral arcuate foramen and high-riding VA. The arcuate foramen and high-riding VA are common anomalies that are often not recognized. Although ipsilateral high-riding VA and arcuate foramen rarely occur in the general population, proper identification of these anomalies on preoperative CT scan facilitates planning the safest technique for C1-2 instrumentation.The spine journal: official journal of the North American Spine Society 02/2014; 14(7). DOI:10.1016/j.spinee.2014.01.054 · 2.80 Impact Factor