Spinous Process Screw Research Articles

Spinous Process Screw Fixation: A Salvage Technique in Subaxial Cervical Spinal Instrumentation

We sought to evaluate the feasibility and efficacy of spinous process screws in subaxial cervical fixation. A retrospective study was conducted on 7 patients receiving posterior cervical instrumentation for subaxial fracture dislocation or atlantoaxial dislocation from 2014 to 2015. In addition, a biomechanical test was performed on 7 fresh-frozen cadaveric spine samples (from the occiput to C7) from healthy human subjects with no history of spinal trauma. And lastly, the potential trajectories of cervical spinous process screws of 100 adults were measured through axial computed tomography in order to establish the general rule for applicability of this technique. Rigid fixation and solid fusion were achieved in all 7 patients included in the study. Biomechanical test results revealed no significant difference between bilateral lateral mass screw fixation and the hybrid lateral mass and spinous process screw fixation constructs. Measurement of the potential trajectory suggested that spinous process screw fixation was a viable technique in the subaxial cervical spine in the general population. The spinous process screw fixation technique in the subaxial cervical spine is a viable and effective salvage option for patients in whom conventional posterior fixations were not sufficient and salvage, supplementary techniques were required.

Risk of pedicle and spinous process violation during cortical bone trajectory screw placement in the lumbar spine

BackgroundPrevious studies have confirmed the feasibility of the cortical bone trajectory (CBT) technique. However, there are few reports on spinous process violation and screw penetration during the screw insertion. The purpose of this study was to evaluate the incidence of spinous process violation and screw penetration through the pedicle during CBT screw insertion.MethodsComputed tomography (CT) scans with normal lumbar structures were consecutively obtained and three-dimensional (3D) reconstructions of the lumbar spine were created. Bilateral CBT screw placement was simulated on each segment using a screw diameter of 4.5 mm, 5.0 mm, or 5.5 mm. Incidences of these complications were recorded and analyzed.ResultsA total of 90 patients were enrolled. Spinous process violation was observed in 68.3, 53.3, 25.5, 1.7, and 0% from L1 to L5, respectively, using 4.5 mm screws. A significant difference was found among the five segments but this was unconnected to gender or screw diameter. The incidence of screw penetration through the inner wall decreased from L1 to L4; in turn, L1 (16.7–35.5%), L2 (12.7–34.4%), L3 (2.8–23.8%) and L4 (1.1–6.7%). This trend was reversed in L5 (6.7–16.7%). Moreover, screw penetration through the outer wall was rare. The incidence of screw penetration varied with screw size as well as lumbar level, but not with gender.ConclusionsThere are more difficulties of CBT screw fixation in upper lumbar spine. The low rate of screw penetration, using 4.5 mm screws, suggests the safety for CBT fixation in the lumbar spine. Larger screws (5.0 mm or 5.5 mm) are more recommended for use in the lower lumbar spine. Moreover, CBT fixation in L5 deserves greater attention because of the unique morphology of the pedicle.

Outcomes of occipitocervical fixation using a spinous process screw in C2 as a third anchor point for occipitocervical fixation: a case presentation

BackgroundPosterior occipitocervical fixation and fusion are often required to address occipitocervical instability. Safe, stable internal fixation with screws is vital for the success of such surgery. Thus, poor selection of an internal fixation technique may cause fixation and fusion failure, possibly leading to neurovascular injury. Hence, in certain cases, such as in patients with severe instability of an occipitocervical deformity or osteoporosis, we hypothesized that having a third anchor point (a screw in C2) could enhance the stability of the occipitocervical fixation.Case presentationA 31-year-old man with occipitocervical deformity and spinal cord edema underwent a traditional occipitocervical fixation procedure but with the addition of a spinous process screw in C2 as a third anchor point. The procedure included posterior internal fixation and fusion. The occipitocervical fixation was completed by inserting occipital screws, bilateral C2 pedicle screws, C3 lateral mass screws, and a spinous process screw in C2 as a third anchor point. There were no neurovascular complications or incision-site infections. Postoperatively, radiography and computed tomography showed that the occipitocervical reduction and internal fixation had resulted in good spinal alignment, and magnetic resonance imaging showed no obvious spinal cord compression. At 4 months after the surgery, fusion was observed, and the occipitocervical screws remained well positioned. The patient continued to be monitored for 24 months postoperatively. At the 24-month follow-up visit, the muscle strength of the limbs was grade 5, and the patient’s sensation function had improved over his preoperative condition.ConclusionsUse of a C2 spinous process screw as a third anchor point may enhance the stability of occipitocervical fixation. Further biomechanical and clinical studies are needed to validate this result.

C2 Spinous Process Screws

C2 Spinous Process Screws

In Reply to the Letter to the Editor “C2 Spinous Process Screws”

In Reply to the Letter to the Editor “C2 Spinous Process Screws”

The clinical effects of atlantoaxial pedicle screw combined with unilateral axial spinous process and lamina screws for atlantoaxial instability

Objective To investigate the clinical effects of the posterior atlantoaxial pedicle screw fixation combined with unilateral axial spinous process and lamina screws and allogeneic bone graft for atlantoaxial instability. Methods From March 2010 to April 2014, data of 10 patients with atlantoaxial instability who had undergone atlanto-axial vertebral pedicle fixation and interbody fusion combined with posterior atlanto-axial spines lamina nails were retrospectively analyzed. There were 6 males and 4 females with an average age of 39 (range, 16-62) years old. The inclusion criteria was atlantoaxial instability together with unilateral vertebral artery segment high cross deformity (7 patients) or atlantoaxial joint break bad involving unilateral pedicle (7 patients). 3 patients have spinal cord disease symptoms and physical signs, both suffered limited neck mobility and pain. The VAS scores were 1-8, with an average of 3.70±2.11. Preoperative X-ray, CT three-dimensional reconstruction and MRI were collected. X-ray and CT examination were performed 7 d and 1, 3, 6, 12 months after operation to evaluate the internal fixation and bone grafting fusion. Results There's no occurrence of cervical spinal cord and vertebral artery injury. Screws were successfully implanted. 1 case's incision occurred infiltration liquid 3 days after operation. For allograft rejection consideration, we changed the plan, and the infiltrating stopped 5 days later. Other incisions were all primary healing. VAS scores were 1.01±0.89 after operation, which was significantly reduced. X-ray showed good recovery of cervical sequence after the operation, and CT revealed 1 patient with atlas pedicle screw in the medial cortex damage. Spinal canal was without infringing, and the other screw positions were normal. 6 months after operation, X-ray or CT examination both showed bony fusion. Conclusion Atlantoaxial pedicle screw fixation combined with unilateral axial spinous process and lamina screws and allograft bone graft fusion for the treatment of atlantoaxial instability can observe good clinical effects. Key words: Cervical atlas; Axis; Joint instability; Internal fixators

Biomechanical comparison of pedicle screws versus spinous process screws in C2 vertebra: A cadaveric study.

Background:Biomechanical studies have shown C2 pedicle screw to be the most robust in insertional torque and pullout strength. However, C2 pedicle screw placement is still technically challenging. Smaller C2 pedicles or medial localization of the vertebral artery may preclude safe C2 pedicle screw placement in some patients. The purpose of this study was to compare the pullout strength of spinous process screws with pedicle screws in the C2.Materials and Methods:Eight fresh human cadaveric cervical spine specimens (C2) were harvested and subsequently frozen to −20°C. After being thawed to room temperature, each specimen was debrided of remaining soft tissue and labeled. A customs jig as used to clamp each specimen for screw insertion firmly. Screws were inserted into the vertebral body pairs on each side using one of two methods. The pedicle screws were inserted in usual manner as in previous biomechanical studies. The starting point for spinous process screw insertion was located at the junction of the lamina and the spinous process and the direction of the screw was about 0° caudally in the sagittal plane and about 0° medially in the axial plane. Each vertebrae was held in a customs jig, which was attached to material testing machine (Material Testing System Inc., Changchun, China). A coupling device that fit around the head of the screw was used to pull out each screw at a loading rate of 2 mm/min. The uniaxial load to failure was recorded in Newton'st dependent test (for paired samples) was used to test for significance.Results:The mean load to failure was 387 N for the special protection scheme and 465 N for the protection scheme without significant difference (t = −0.862, P = 0.403). In all but three instances (38%), the spinous process pullout values exceeded the values for the pedicle screws. The working distances for the spinous process screws was little shorter than pedicle screws in each C2 specimen.Conclusion:Spinous process screws provide comparable pullout strength to pedicle screws of the C2. Spinous process screws may provide an alternative to pedicle screws fixation, especially with unusual anatomy or stripped screws.

A mechanical comparison of spinous process screwing and pedicle screwing in posterior internal fixation of C2

Objective To compare the pullout strength between spinous process screwing and pedicle screwing in posterior internal fixation of C2. Methods Eight fresh human cadaveric C2 were harvested.Spinous process screws were placed on one side of the C2 and pedicle screws were placed on the other side in a random manner.Cortical bone screws of 4.0 mm in diameter were used.The starting point for spinous process screw insertion was located at the junction of the lamina and the spinous process and the direction of the screw was about 0° caudally in the sagittal plane and about 0° medially in the axial plane.Pedicle screws were placed under direct visualization.After screw placement,each aet of vertebral bodies were mounted in a custom jig for axial pullout testing using a servo-hydraulic testing machine.The load-displacement curves were obtained for each screw pullout. Results The mean pullout strength for the spinous process screws was 387.56 ± 137.73 N,not significantly different from that for the pedicle screws (465.25 ± 214.32 N)( t =-0.862,P =0.403).The working length for the spinous process screws (21.42 ± 1.14 mm) was significanfly shorter than for the pedicle screws (23.16 ± 1.01 mm) ( t =4.368,P ＜0.001). Conclusion Since spinous process screws have similar pullout strength as compared with pedicle screws,they are biomechanically feasible in clinical application. Key words: Axis; Biomechanics; Internal fixators; Screws

An anatomic study of posterior C(2) spinous process laminar screw fixation

To explore the feasibility and the technical parameters in posterior C2 spinous process laminar screw fixation, and discuss the clinic significance of C2 spinous process laminar screws. Twenty cervical cadaveric spines of C2 were dissected, with care taken to expose the lamina and spinous process. After the entrance point of spinous process screw were determined, posterior C2 spinous process laminar screw implantation was performed under visual control. On the morphologic CT scan, the angle and length of the spinous process laminar screw trajectory and the distance between the tip of the screw and the spinal cord and the vertebral artery were measured. The C2 spinous process laminar screws were successfully placed, without impingement of the spinal cord and the vertebral artery. There were little differences between superior and inferior screws in the angle, trajectory length and the distance between the tip of the screw and the spinal cord and the vertebral artery, but without significance (P > 0.05). The placed angles of the screws were 76.8° ± 10.6° in the axial plane. The distance between the tip of the screw and the spinal cord and the vertebral artery was (5.3 ± 1.6) mm and (17.4 ± 3.7) mm respectively. The trajectory length was (23.1 ± 3.2) mm. Posterior C2 spinous process laminar screw fixation is feasible. C2 spinous process laminar screw fixation affords an alternative to standard screw placement for plate fixation and cervical stabilization.

Anatomical considerations for the placement of C₂ spinous process screws

To quantitatively anatomically evaluate the C₂ spinous process, analyze the anatomical feasibility of the C₂ spinous process screws and its clinical significance. To dissect and evaluate 30 cervical cadaveric spines of C₂ which were taken to expose the lamina and spinous process. Anatomic quantitative evaluation of the C₂ spinous process included its height and width. Twenty cervical cadaveric spines of C₂ were chosen to the study of the placement of the C₂ spinous process screws. The starting point for the C₂ spinous process screw insertion was located at the base of the spinous process. After the entrance point of spinous process screws was determined, posterior C₂ spinous process screw implantation was performed bilaterally under direct visualization. On the morphologic CT scan, the width of C₂ spinous process base, the angle and length of the spinous process screw trajectory, and the distance between the tip of the screw and the spinal cord and the vertebral artery were measured. The average height and width of the C₂ spinous process were (12.90 ± 1.30) mm and (18.86 ± 1.17) mm respectively. The C₂ spinous process screws were successfully placed without impingement the spinal cord or the vertebral artery and the breakage of the spinous process. On the CT scan, the average width of the base of C₂ spinous process was (20.7 ± 1.3) mm. The placed angles of the screws were 1.8° ± 1.0° in the axial plane. The distance between the tip of the screw and the spinal cord or the vertebral artery was (8.3 ± 2.6) mm and (20.2 ± 3.1) mm respectively. There were little differences between superior and inferior screws in the angle, the distance between the tip of the screw and the spinal cord or the vertebral artery, but without significance (P > 0.05). The average trajectory length of the C₂ spinous process screws was (19.7 ± 1.1) mm. The average trajectory length of the superior spinous process screws was shorter than that of inferior spinous process screws, with great differences (t = 3.566, P < 0.01). There is the anatomic feasibility of the C₂ spinous process screw fixation which may afford an alternative to standard screw placement for axis fixation. The biomechanical study for the C₂ spinous process screw is also necessary.