scholarly journals Atlantoaxial fixation using C1 posterior arch screws: feasibility study, morphometric data, and biomechanical analysis

2019 ◽  
Vol 30 (3) ◽  
pp. 314-322 ◽  
Author(s):  
Gilbert Cadena ◽  
Huy T. Duong ◽  
Jonathan J. Liu ◽  
Kee D. Kim
Keyword(s):  
Biomechanical Testing ◽  
Axial Rotation ◽  
Biomechanical Analysis ◽  
Posterior Arch ◽  
Lateral Mass ◽  
Morphometric Data ◽  
Lateral Bending ◽  
Freehand Technique ◽  
Flexion Extension ◽  
Low Incidence

OBJECTIVEC1–2 is a highly mobile complex that presents unique surgical challenges to achieving biomechanical rigidity and fusion. Posterior wiring methods have been largely replaced with segmental constructs using the C1 lateral mass, C1 pedicle, C2 pars, and C2 pedicle. Modifications to reduce surgical morbidity led to the development of C2 laminar screws. The C1 posterior arch has been utilized mostly as a salvage technique, but recent data indicate that this method provides significant rigidity in flexion-extension and axial rotation. The authors performed biomechanical testing of a C1 posterior arch screw (PAS)/C2 pars screw construct, collected morphometric data from a population of 150 CT scans, and performed a feasibility study of a freehand C1 PAS technique in 45 cadaveric specimens.METHODSCervical spine CT scans from 150 patients were analyzed to determine the average C1 posterior tubercle thickness and size of C1 posterior arches. Eight cadavers were used to compare biomechanical stability of intact specimens, C1 lateral mass/C2 pars screw, and C1 PAS/C2 pars screw constructs. Paired comparisons were made using repeated-measures ANOVA and Holm-Sidak tests. Forty-five cadaveric specimens were used to demonstrate the feasibility and safety of the C1 PAS freehand technique.RESULTSMorphometric data showed the average craniocaudal thickness of the C1 posterior tubercle was 12.3 ± 1.94 mm. Eight percent (12/150) of cases showed thin posterior tubercles or midline defects. Average posterior arch thickness was 6.1 ± 1.1 mm and right and left average posterior arch length was 28.7 mm ± 2.53 mm and 28.9 ± 2.29 mm, respectively. Biomechanical testing demonstrated C1 lateral mass/C2 pars and C1 PAS/C2 pars constructs significantly reduced motion in flexion-extension and axial rotation compared with intact specimens (p < 0.05). The C1 lateral mass/C2 pars screw construct provided significant rigidity in lateral bending (p < 0.05). There was no statistically significant difference between the two constructs in flexion-extension, lateral bending, or axial rotation. Of the C1 posterior arches, 91.3% were successfully cannulated using a freehand technique with a low incidence of cortical breach (4.4%).CONCLUSIONSThis biomechanical analysis indicates equivalent stability of the C1 PAS/C2 pars screw construct compared with a traditional C1 lateral mass/C2 pars screw construct. Both provide significant rigidity in flexion-extension and axial rotation. Feasibility testing in 45 cadaveric specimens indicates a high degree of accuracy with low incidence of cortical breach. These findings are supported by a separate radiographic morphometric analysis.

scholarly journals Biomechanical comparison of a C1 posterior arch clamp with C1 lateral mass screws in constructs for C1-C2 fusion

2021 ◽  
pp. 095441192110324
Author(s):  
Timothy L Lasswell ◽  
John B Medley ◽  
Jack P Callaghan ◽  
Duane S Cronin ◽  
Colin D McKinnon ◽  
...  
Keyword(s):  
Axial Rotation ◽  
Atlantoaxial Instability ◽  
Posterior Arch ◽  
Lateral Mass ◽  
Lateral Bending ◽  
Intact State ◽  
Significant Difference ◽  
Flexion Extension ◽  
Translaminar Screw ◽  
Fresh Frozen

The aim of this experimental study was to assess the biomechanical performance of a novel C1 posterior arch (C1PA) clamp compared with C1 lateral mass (C1LM) screws in constructs used to treat atlantoaxial instability. These constructs had either C2 pedicle (C2P) screws or C2 translaminar (C2TL) screws. Eight fresh-frozen human cadaveric ligamentous spine specimens (C0-C3) were tested under six conditions: the intact state, the destabilized state after a simulated odontoid fracture, and when instrumented with four constructs (C1LM-C2P, C1LM-C2TL, C1PA-C2P, C1PA-C2TL). Each specimen was tested in a spinal loading simulator that separately applied axial rotation, flexion-extension and lateral bending. In each test condition, displacement controlled angular motion was applied in both directions at a speed of 2 deg/s until a resulting moment of 1.5 Nm was achieved. The measured ranges of motion (ROM) of the C1-C2 segments were compared for each test condition using nonparametric Friedman tests. The destabilized state had significantly more C1-C2 motion ( p < 0.05) than the intact state in all cases, and all constructs greatly reduced this motion. C2 pedicle screw constructs that used the C1PA clamp had significantly less C1-C2 motion ( p < 0.05) than those with C1LM screws in flexion-extension as well as axial rotation and no statistically significant difference was detected in lateral bending. C2 translaminar screw constructs that used the C1PA clamp had significantly less C1-C2 motion ( p < 0.05) than those with C1LM screws in flexion-extension and no statistically significant difference was detected in axial rotation or in lateral bending. Data from the current study suggested that constructs using the novel C1PA clamp would provide as good, or improved, biomechanical stability to the C1-C2 segment compared with constructs using C1LM screws.

The cervical end of an occipitocervical fusion: a biomechanical evaluation of 3 constructs

2008 ◽  
Vol 9 (3) ◽  
pp. 296-300 ◽  
Author(s):  
Michael A. Finn ◽  
Daniel R. Fassett ◽  
Todd D. Mccall ◽  
Randy Clark ◽  
Andrew T. Dailey ◽  
...  
Keyword(s):  
Tracking System ◽  
Plate Fixation ◽  
Axial Rotation ◽  
Lateral Mass ◽  
Lateral Bending ◽  
Cross Link ◽  
3D Tracking ◽  
Flexion Extension ◽  
Biomechanical Evaluation ◽  
Rotation Motion

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 after instrumentation. The C1L-C2P construct was equivalent to the TASF in all moments. The C1L-C2L was significantly weaker than the C1L-C2P construct in all moments and significantly weaker than the TASF in lateral bending. The addition of a cross-link made no difference in the stiffness of any construct. Conclusions All constructs provide significant immediate stability in the destabilized occipitocervical junction. Although the C1L-C2P construct performed best overall, the TASF was similar, and either one can be recommended. Decreased stiffness of the C1L-C2L construct might affect the success of clinical fusion. This construct should be reserved for cases in which anatomy precludes the use of the other two.

scholarly journals Biomechanical Analysis of an Anterior Cervical Discectomy and Fusion Pseudarthrosis Model Revised With Machined Interfacet Allograft Spacers

2019 ◽  
Vol 10 (8) ◽  
pp. 973-981
Author(s):  
Raymond J. Hah ◽  
Ram Alluri ◽  
Paul A. Anderson
Keyword(s):  
Range Of Motion ◽  
Study Design ◽  
Axial Rotation ◽  
Biomechanical Analysis ◽  
Anterior Cervical Discectomy ◽  
Lateral Bending ◽  
Cervical Discectomy ◽  
Single Level ◽  
Flexion Extension ◽  
Potential Applications

Study Design: Biomechanics study. Objectives: To evaluate the biomechanical advantage of interfacet allograft spacers in an unstable single-level and 2-level anterior cervical discectomy and fusion (ACDF) pseudoarthrosis model. Methods: Nine single-level and 8 two-level ACDF constructs were tested. Range of motion in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) at 1.5 N m were collected in 4 testing configurations: (1) intact spine, (2) ACDF with interbody graft and plate/screw, (3) ACDF with interbody graft and plate/loosened screws (loose condition), and (4) ACDF with interbody graft and plate/loosened screws supplemented with interfacet allograft spacers (rescue condition). Results: All fixation configurations resulted in statistically significant decreases in range of motion in all bending planes compared with the intact spine ( P < .05). One Level. Performing ACDF with interbody graft and plate on the intact spine reduced FE, LB, and AR 60.0%, 64.9%, and 72.9%, respectively. Loosening the ACDF screws decreased these reductions to 40.9%, 44.6%, and 52.1%. The addition of interfacet allograft spacers to the loose condition increased these reductions to 74.0%, 84.1%, and 82.1%. Two Level. Performing ACDF with interbody graft and plate on the intact spine reduced FE, LB, and AR 72.0%, 71.1%, and 71.2%, respectively. Loosening the ACDF screws decreased these reductions to 55.4%, 55.3%, and 51.3%. The addition of interfacet allograft spacers to the loose condition significantly increased these reductions to 82.6%, 91.2%, and 89.3% ( P < .05). Conclusions: Supplementation of a loose ACDF construct (pseudarthrosis model) with interfacet allograft spacers significantly increases stability and has potential applications in treating cervical pseudarthrosis.

scholarly journals Axial Spondylectomy and Circumferential Reconstruction via a Posterior Approach

Neurosurgery ◽  
2012 ◽  
Vol 72 (2) ◽  
pp. E300-E309 ◽  
Author(s):  
Rahul Jandial ◽  
Brandon Kelly ◽  
Brandon Bucklen ◽  
Saif Khalil ◽  
Aditya Muzumdar ◽  
...  
Keyword(s):  
Spinal Metastases ◽  
Cervical Vertebra ◽  
Biomechanical Analysis ◽  
The Novel ◽  
Lateral Mass ◽  
Lateral Bending ◽  
Patient Case ◽  
Flexion Extension ◽  
Anterior Column Reconstruction ◽  
Flexion And Extension

Abstract BACKGROUND: Spinal metastases of the second cervical vertebra are a subset of tumors that are particularly difficult to address surgically. Previously described techniques require highly morbid circumferential dissection posterior to the pharynx for resection and reconstruction. OBJECTIVE: To perform a biomechanical analysis of instrumented reconstruction configurations used after axial spondylectomy and to demonstrate safe use of a novel construct in a patient case report. METHODS: Several different published and novel reconstruction configurations were inserted into 7 occipitocervical spines that underwent axial spondylectomy. A biomechanical analysis of the stiffness of the constructs in flexion and extension, lateral bending, and rotation was performed. A patient then underwent a posterior-only approach for axial spondylectomy and circumferential reconstruction. RESULTS: Biomechanical analysis of different constructs demonstrated that anterior column reconstruction with bilateral cages spanning the C1 lateral mass to the C3 facet in combination with occipitocervical instrumentation was superior in flexion-extension and equivalent in lateral bending and rotation to currently used constructs. The patient in whom this construct was placed via a posterior-only approach for axial spondylectomy and instrumentation remained at neurological baseline and demonstrated no recurrence of local disease or failure of instrumentation to date. CONCLUSION: When C1 lateral mass to C3 facet bilateral cage plus occipitocervical instrumentation is compared with existing anterior and posterior constructs, this novel reconstruction is biomechanically equivalent if not superior in performance. In a patient, the posterior-only approach for C2 spondylectomy with the novel reconstruction was safe and durable and avoided the morbidity of the anterior approach.

Biomechanical analysis of Goel technique for C1–2 fusion

2011 ◽  
Vol 14 (5) ◽  
pp. 639-646 ◽  
Author(s):  
Jon Park ◽  
Justin K. Scheer ◽  
T. Jesse Lim ◽  
Vedat Deviren ◽  
Christopher P. Ames
Keyword(s):  
Motion Tracking ◽  
Tracking System ◽  
Testing Machine ◽  
Pedicle Screws ◽  
Axial Rotation ◽  
Biomechanical Analysis ◽  
Lateral Bending ◽  
Flexion Extension ◽  
Rod System ◽  
Harms Technique

Object The Goel technique, in which C1–2 intraarticular spacers are used, may be performed to restore stability to a disrupted atlantoaxial complex in conjunction with the Harms technique of placing polyaxial screws and bilateral rods. However, it has yet to be determined biomechanically whether the addition of the C1–2 joint spacers increases the multiaxial rigidity of the fixation construct. The goal of this study was to quantify changes in multiaxial rigidity of the combined Goel-Harms technique with the addition of C1–2 intraarticular spacers. Methods Seven cadaveric cervical spines (occiput–C2) were submitted to nondestructive flexion-extension, lateral bending, and axial rotation tests in a material testing machine spine tester. The authors applied 1.5 Nm at a rate of 0.1 Nm/second and held it constant for 10 seconds. The specimens were loaded 3 times, and data were collected on the third cycle. Testing of the specimens was performed for the following groups: 1) intact (I); 2) with the addition of C-1 lateral mass/C-2 pedicle screws and rod system (I+SR); 3) with C1–2 joint capsule incision, decortication (2 mm on top and bottom of each joint [that is, the C-1 and C-2 surface) and addition of bilateral C1–2 intraarticular spacers at C1–2 junction to the screws and rods (I+SR+C); 4) after removal of the posterior rods and only the bilateral spacers in place (I+C); 5) after removal of spacers and further destabilization with simulated odontoidectomy for a completely destabilized case (D); 6) with addition of posterior rods to the destabilized case (D+SR); and 7) with addition of bilateral C1–2 intraarticular spacers at C1–2 junction to the destabilized case (D+SR+C). The motion of C-1 was measured by a 3D motion tracking system and the motion of C-2 was measured by the rotational sensor of the testing system. The range of motion (ROM) and neutral zone (NZ) across C-1 and C-2 were evaluated. Results For the intact spine test groups, the addition of screws/rods (I+SR) and screws/rods/cages (I+SR+C) significantly reduced ROM and NZ compared with the intact spine (I) for flexion-extension and axial rotation (p < 0.05) but not lateral bending (p > 0.05). The 2 groups were not significantly different from each other in any bending mode for ROM and NZ, but in the destabilized condition the addition of screws/rods (D+SR) and screws/rods/cages (D+SR+C) significantly reduced ROM and NZ compared with the destabilized spine (D) in all bending modes (p < 0.05). Furthermore, the addition of the C1–2 intraarticular spacers (D+SR+C) significantly reduced ROM (flexion-extension and axial rotation) and NZ (lateral bending) compared with the screws and rods alone (D+SR). Conclusions Study result indicated that both the Goel and Harms techniques alone and with the addition of the C1–2 intraarticular spacers to the Goel-Harms technique are advantageous for stabilizing the atlantoaxial segment. The Goel technique combined with placement of a screw/rod construct appears to result in additional construct rigidity beyond the screw/rod technique and appears to be more useful in very unstable cases.

scholarly journals Biomechanical Comparison of Posterior Fixation Combinations with an Allograft Spacer between the Lateral Mass and Pedicle Screws

2020 ◽  
Vol 10 (20) ◽  
pp. 7291
Author(s):  
Soo-Bin Lee ◽  
Hwan-Mo Lee ◽  
Tae-Hyun Park ◽  
Sung Lee ◽  
Young-Woo Kwon ◽  
...  
Keyword(s):  
Pedicle Screws ◽  
Element Model ◽  
Axial Rotation ◽  
Posterior Fixation ◽  
Hybrid Technique ◽  
Lateral Mass ◽  
Lateral Bending ◽  
Flexion Extension ◽  
Hybrid Motion ◽  
Biomechanical Comparison

Background: There are a few biomechanical studies that describe posterior fixation methods with pedicle screws (PS) and lateral mass screws (LMS); the combination of both screw types and their effect on an allograft spacer in a surgically treated cervical segment is unknown. Methods: Finite element model (FEM) analyses were used to investigate the effects of a hybrid technique using posterior PS and LMS. Stress distribution and subsidence risk from a combination of screws under hybrid motion control conditions, including flexion, extension, axial rotation, and lateral bending, were investigated to evaluate the biomechanical characteristics of different six-screw combinations. Findings: The load sharing on the allograft spacer in flexion mode was highest in the LMS model (74.6%) and lowest in the PS model (35.1%). The likelihood of subsidence of allograft spacer on C6 was highest in the screws from the distal LMS (type 5) model during flexion and extension (4.902 MPa, 30.1% and 2.189 MPa, 13.4%). In lateral bending, the left unilateral LMS (type 4) model screws on C5 (3.726 MPa, 22.9%) and C6 (2.994 MPa, 18.4%) yielded the greatest subsidence risks, because the lateral bending forces were supported by the LMS. In counterclockwise axial rotation, the left unilateral LMS (type 4) model screws on C5 (3.092 MPa, 19.0%) and C6 (3.076 MPa, 18.9%) demonstrated the highest subsidence risks. Conclusion: The asymmetrical ipsilateral use of LMS and posterior PS in lateral bending and axial rotation demonstrated the lowest stability and greatest subsidence risk. We recommend bilateral symmetrical insertion of LMS or posterior PS and posterior PS on distal vertebrae for increased stability and reduced risk of allograft spacer subsidence.

Restabilization of the Occipitocervical Junction After a Complete Unilateral Condylectomy: A Biomechanical Comparison of Unilateral and Bilateral Fixation Techniques

2019 ◽  
Vol 19 (2) ◽  
pp. 157-164 ◽  
Author(s):  
Ilyas M Eli ◽  
Michael Karsy ◽  
Darrel S Brodke ◽  
Kent N Bachus ◽  
William T Couldwell ◽  
...  
Keyword(s):  
Biomechanical Testing ◽  
Axial Rotation ◽  
Neurological Injury ◽  
Occipital Condyle ◽  
Posterior Fixation ◽  
Lateral Bending ◽  
Flexion Extension ◽  
Fixation Techniques ◽  
The Difference ◽  
Biomechanical Comparison

Abstract BACKGROUND Occipitocervical instability may result from transcondylar resection of the occipital condyle. Initially, patients may be able to maintain a neutral alignment but severe occipitoatlantal subluxation may subsequently occur, with cranial settling, spinal cord kinking, and neurological injury. OBJECTIVE To evaluate the ability of posterior fixation constructs to prevent progression to severe deformity after radical unilateral condylectomy. METHODS Eight human cadaveric specimens (Oc-C2) underwent biomechanical testing to compare stiffness under physiological loads (1.5 N m). A complete unilateral condylectomy was performed to destabilize one Oc-C1 joint, and the contralateral joint was left intact. Unilateral Oc-C1 or Oc-C2 constructs on the resected side and bilateral Oc-C1 or Oc-C2 constructs were tested. RESULTS The bilateral Oc-C2 construct provided the greatest stiffness, but the difference was only statistically significant in certain planes of motion. The unilateral constructs had similar stiffness in lateral bending, but the unilateral Oc-C1 construct was less stiff in axial rotation and flexion-extension than the unilateral Oc-C2 construct. The bilateral Oc-C2 construct was stiffer than the unilateral Oc-C2 construct in axial rotation and lateral bending, but there was no difference between these constructs in flexion-extension. CONCLUSION Patients who undergo a complete unilateral condylectomy require close surveillance for occipitocervical instability. A bilateral Oc-C2 construct provides suitable biomechanical strength, which is superior to other constructs. A unilateral construct decreases abnormal motion but lacks the stiffness of a bilateral construct. However, given that most patients undergo a partial condylectomy and only a small proportion of patients develop instability, there may be scenarios in which a unilateral construct may be appropriate, such as for temporary internal stabilization.

scholarly journals Unilateral C-1 posterior arch screws and C-2 laminar screws combined with a 1-side C1–2 pedicle screw system as salvage fixation for atlantoaxial instability

2016 ◽  
Vol 24 (2) ◽  
pp. 315-320 ◽  
Author(s):  
Jin Guo-Xin ◽  
Wang Huan
Keyword(s):  
Biomechanical Testing ◽  
Pedicle Screws ◽  
Atlantoaxial Instability ◽  
Posterior Arch ◽  
Lateral Bending ◽  
Significant Difference ◽  
Flexion Extension ◽  
Intact Condition ◽  
Atlantoaxial Fixation ◽  
Group B

OBJECT Atlantoaxial instability often requires surgery, and the current methods for fixation pose some risk to vascular and neurological tissues. Thus, new effective and safer methods are needed for salvage operations. This study sought to assess unilateral C-1 posterior arch screws (PASs) and C-2 laminar screws (LSs) combined with 1-side C1–2 pedicle screws (PSs) for posterior C1–2 fixation using biomechanical testing with bilateral C1–2 PSs in a cadaveric model. METHODS Six fresh ligamentous human cervical spines were evaluated for their biomechanics. The cadaveric specimens were tested in their intact condition, stabilization after injury, and after injury at 1.5 Nm of pure moment in 6 directions. The 3 groups tested were bilateral C1–2 PSs (Group A); left side C1–2 PSs with an ipsilateral C-1 PAS + C-2 laminar screw (Group B); and left side C1–2 PSs with a contralateral C-1 PAS + C-2 LS (Group C). During the testing, angular motion was measured using a motion capture platform. Data were recorded, and statistical analyses were performed. RESULTS Biomechanical testing showed that there was no significant difference among the stabilities of these fixation systems in flexion-extension and rotation control. In left lateral bending, the bilateral C1–2 PS group decreased flexibility by 71.9% compared with the intact condition, the unilateral C1–2 PS and ipsilateral PAS+LS group decreased flexibility by 77.6%, and the unilateral C1–2 PS and contralateral PAS+LS group by 70.0%. Each method significantly decreased C1–2 movements in right lateral bending compared with the intact condition, and the bilateral C1–2 PS system was more stable than the C1–2 PS and contralateral PAS+LS system (p = 0.036). CONCLUSIONS A unilateral C-1 PAS + C-2 LS combined with 1-side C-1 PSs provided the same acute stability as the PS, and no statistically significant difference in acute stability was found between the 2 screw techniques. These methods may constitute an alternative method for posterior atlantoaxial fixation.

Biomechanical studies of an artificial disc implant in the human cadaveric spine

2005 ◽  
Vol 2 (3) ◽  
pp. 339-343 ◽  
Author(s):  
Patrick W. Hitchon ◽  
Kurt Eichholz ◽  
Christopher Barry ◽  
Paige Rubenbauer ◽  
Aditya Ingalhalikar ◽  
...  
Keyword(s):  
Biomechanical Testing ◽  
Axial Rotation ◽  
Load Testing ◽  
Artificial Disc ◽  
Lateral Bending ◽  
Content Type ◽  
Intact State ◽  
Flexion Extension ◽  
Fine Print

Object. The authors compared the biomechanical performance of the human cadaveric spine implanted with a metallic ball-and-cup artificial disc at L4–5 with the spine's intact state and after anterior discectomy. Methods. Seven human L2—S1 cadaveric spines were mounted on a biomechanical testing frame. Pure moments of 0, 1.5, 3.0, 4.5, and 6.0 Nm were applied to the spine at L-2 in six degrees of motion (flexion, extension, right and left lateral bending, and right and left axial rotation). The spines were tested in the intact state as well as after anterior L4–5 discectomy. The Maverick disc was implanted in the discectomy defect, and load testing was repeated. The artificial disc created greater rigidity for the spine than was present after discectomy, and the spine performed biomechanically in a manner comparable with the intact state. Conclusions. The results indicate that in an in vitro setting, this model of artificial disc stabilizes the spine after discectomy, restoring motion comparable with that of the intact state.

Biomechanical Effect of the C2 Laminar Decortication on the Stability of C2 Intralaminar Screw Construct and Biomechanical Comparison of C2 Intralaminar Screw and C2 Pars Screw

2011 ◽  
Vol 69 (suppl_1) ◽  
pp. ons1-ons7 ◽  
Author(s):  
Jae Taek Hong ◽  
Tomoyuki Takigawa ◽  
Ranjith Udayakunmar ◽  
Hun Kyu Shin ◽  
Peter Simon ◽  
...  
Keyword(s):  
Axial Rotation ◽  
Insertion Torque ◽  
Lateral Mass ◽  
Pullout Strength ◽  
Lateral Bending ◽  
Biomechanical Stability ◽  
Laminar Screw ◽  
Flexion Extension ◽  
The Stability ◽  
C2 Laminar Screw

Abstract BACKGROUND: There have been no reports of biomechanical stability of C1-2 constructs after decortication of the C2 lamina. In addition, few studies have compared the stability of C2 laminar screw and pars screw constructs. OBJECTIVE: To compare the biomechanical stability of 3 different C1-2 construct conditions (C2 pars screw, C2 intralaminar screw, C2 intralaminar construct with C2 laminar decortication). METHODS: Fourteen fresh-frozen cadaveric cervical specimens (C1-3) were used. In 7 specimens, pure moments of 1.5 Nm were applied in flexion/extension, lateral bending, and axial rotation. Each specimen was tested in the normal state, in the destabilized state (after odontoidectomy and resection of transverse atlantal ligament), and after application of constructs. After kinematic study, these 7 specimens underwent axial pullout strength testing of pars screw and 50% decorticated C2 intralaminar screws. In another 7 specimens, insertion torque and pullout strength were measured to compare the pars screw and intact C2 intralaminar screw. RESULTS: There were no statistically significant differences between the intact C2 intralaminar and 50% decorticated C2 intralaminar screw constructs in terms of range-of-motion limitations. The C2 pars screw construct was significantly superior to the C2 laminar screw construct in lateral bending (P &lt; .01) and axial rotation (P &lt; .01) and equivalent to the C2 laminar screw construct in flexion/extension (P = .42). There was no significant pullout strength difference between the 3 kinds of C2 screw. CONCLUSION: The C1 lateral mass-C2 pars screws construct was stronger than the C1 lateral mass-C2 intralaminar screw construct. Decortication of C2 laminar (up to 50%) did not affect the immediate stability of the C1-2 construct.

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