The use of pedicle-screw internal fixation for the operative treatment of spinal disorders

Cost-effectiveness Analysis of Existing Pedicle Screws Reusing Technique in Extension Revision Operation for Adjacent Segmental Stenosis After Lumbar Posterolateral Fusion

STUDY DESIGN

Retrospective case-control study.

OBJECTIVE

A cost-effectiveness analysis was performed by comparing patients who received extension revision operations for adjacent segment disease (ASD) reusing the pedicle screws extracted from fused segments with patients who received conventional surgery.

SUMMARY OF BACKGROUND DATA

ASD often required extension revision surgery, and during extension surgery, pedicle screws may be reused by extracting from the fused segments of primary surgery.

METHODS

Study examined 37 patients who received extension revision surgery for ASD from January 2003 to December 2013. For the fixation of extended segments during revision operation, in 16 cases the pedicle screws extracted from fused segments were reused (group R), and in 21 cases new pedicle screws were used (group C) as a conventional method. Clinical outcomes were evaluated by means of visual analog scale scores for lumbago and leg pain, and the Korean Oswestry Disability Index. Radiologic outcomes were evaluated from the extent of bone union. The total operating costs in the two groups were compared.

RESULTS

Visual analog scale scores for lumbago and leg pain, and the Korean Oswestry Disability Index measured at final follow-up averaged 3.6 and 3.8, and 19.9 in group R, and 3.8 and 3.1, and 21.1 in group C, respectively (P = 0.280, P = 0.387, P = 0.751). For radiologic outcomes, there was one case of nonunion in each group. The cost of surgery was 5332 US dollars in group R, and 6109 US dollars in group C, respectively (P = 0.036).

CONCLUSION

Reusing pedicle screws extracted from the fused segments during extension revision operation for ASD can reduce the cost of surgery, and achieves clinical and radiological results similar to those of the conventional operation.

LEVEL OF EVIDENCE

4.

Comparative Analysis of Effect of Density, Insertion Angle and Reinsertion on Pull-Out Strength of Single and Two Pedicle Screw Constructs Using Synthetic Bone Model

STUDY DESIGN

Biomechanical study.

PURPOSE

To determine the effect of density, insertion angle and reinsertion on pull-out strength of pedicle screw in single and two screw-rod configurations.

OVERVIEW OF LITERATURE

Pedicle screw pull-out studies have involved single screw construct, whereas two screws and rod constructs are always used in spine fusions. Extrapolation of results using the single screw construct may lead to using expensive implants or increasing the fusion levels specifically in osteoporotic bones.

METHODS

Single screw and two screw pull-out strength tests were carried out according to American Society for Testing and Materials F 543-07 on foam models to test the effect of density, insertion angle and reinsertion using poly axial pedicle screws.

RESULTS

Bone density was the most significant factor deciding the pull-out strength in both single and two screw constructs. The difference in pull-out strength between single screw and two screw configurations in extremely osteoporotic bone model (80 kg/m(3)) was 78%, whereas in the normal bone model it was 48%. Axial pull-out value was highest for the single screw configuration; in the two screw configuration the highest pull-out strength was at 10°-15°. There was an 18% reduction in pull-out strength due to reinsertion in single screw configuration. The reinsertion effect was insignificant in the two screw configuration.

CONCLUSIONS

A significant difference in response of various factors on holding power of pedicle screw between single and two-screw configurations is evident. The percentage increase in pull-out strength between single and two screw constructs is higher for osteoporotic bone when compared to normal bone. Reinsertion has no significant effect on pull-out strength in the two screw rod configuration.

LEVEL OF EVIDENCE IN THE PLACEMENT OF TRANSPEDICULAR SCREWS IN SUBAXIAL CERVICAL SPINE

ABSTRACT The high-energy trauma mainly involves vertebral lesions and 6% occur in the cervical region. This poses a challenge to spine surgeons in surgical decision-making, both in terms of approach as the instrumentation. International recommendations establish that the procedures performed are reproducible, safe, and effective. The techniques for placement of pedicle screws are complicated and have been based on intraoperative navigation (limited by cost) and fluoroscopy (greater exposure of health care professionals and patients to radiation). Therefore, the freehand technique is an option. The goal was to identify the level of evidence and grade of recommendation in the medical literature regarding the safety and efficacy of pedicle screw instrumentation with freehand technique in subaxial cervical spine. To this end, we carried out a systematic review with the following MeSH terms: safety, efficacy, vertebral artery. Articles were evaluated twice in a standardized and blind way by two observers skilled in systematic analysis, after CLEIS 3401 authorization in November 2014. Due to the nature of the study and the variables, articles with a high level of evidence and grade of recommendation were not found. Level of Evidence obtained on safety and efficacy in the placement of pedicle screws in subaxial column with freehand technique: 2b. Degree of Recommendation obtained on safety and efficacy in the placement of pedicle screws in subaxial column with freehand technique: B, favorable recommendation.

Biomechanical Comparison of Spinal Fusion Methods Using Interspinous Process Compressor and Pedicle Screw Fixation System Based on Finite Element Method

Objective

To investigate the biomechanical effects of a newly proposed Interspinous Process Compressor (IPC) and compare with pedicle screw fixation at surgical and adjacent levels of lumbar spine.

Methods

A three dimensional finite element model of intact lumbar spine was constructed and two spinal fusion models using pedicle screw fixation system and a new type of interspinous devices, IPC, were developed. The biomechanical effects such as range of motion (ROM) and facet contact force were analyzed at surgical level (L3/4) and adjacent levels (L2/3, L4/5). In addition, the stress in adjacent intervertebral discs (D2, D4) was investigated.

Results

The entire results show biomechanical parameters such as ROM, facet contact force, and stress in adjacent intervertebral discs were similar between PLIF and IPC models in all motions based on the assumption that the implants were perfectly fused with the spine.

Conclusion

The newly proposed fusion device, IPC, had similar fusion effect at surgical level, and biomechanical effects at adjacent levels were also similar with those of pedicle screw fixation system. However, for clinical applications, real fusion effect between spinous process and hooks, duration of fusion, and influence on spinous process need to be investigated through clinical study.

The feasibility of transpedicular screw fixation of the subaxial cervical spine in the Arab population: a computed tomography-based morphometric study

Background

Transpedicular screw fixation of the cervical spine provides excellent biomechanical stability. The feasibility of inserting a 3.5-mm screw in the pedicle requires a minimum pedicle diameter of 4.5 mm. This diameter allows at least 0.5 mm bony bridge medially and laterally in order to avoid pedicle violation which can result in neurovascular complications. We aim to evaluate the feasibility of this technique in Arab people since no data are available about this population.

Materials and methods

This cross-sectional study involved a retrospective review of computed tomography scans of normal cervical spines of 99 Arab adults. Ten morphometric measurements were obtained. Data were analyzed using a p value of ≤0.05 as the cut-off level of statistical significance.

Results

Our sample included 63 (63.6 %) males and 36 (36.4 %) females, with a mean age of 35.5 ± 16.5 years. The morphometric parameters of C3–C7 spine pedicles were larger in males than in females. The outer pedicle width (OPW) was <4.5 mm in >25 % of all subjects at C3–C6 vertebrae. Statistically significant differences in the OPW between males and females were noted at C3 (p = 0.032) and C6 (p = 0.004).

Conclusions

Inserting pedicle screws in the subaxial cervical spine is feasible among the majority of Arab people.

Level of evidence

Level 3.

Patient-Based Surgical Outcomes of Posterior Lumbar Interbody Fusion: Patient Satisfaction Analysis

STUDY DESIGN

A retrospective study.

OBJECTIVE

The purpose of this study was to investigate: (1) patient-based surgical outcomes of posterior lumbar interbody fusion (PLIF); (2) correlations between patient-based surgical outcomes and surgeon-based surgical outcomes; (3) factors associated with patient satisfaction.

SUMMARY OF BACKGROUND DATA

There have been no reports of patient-based surgical outcomes of PLIF for lumbar spondylolisthesis.

METHODS

Patients who underwent PLIF for L4 degenerative spondylolisthesis between 2006 and 2009 were reviewed (n = 121). Surgical outcomes were assessed 5 years after primary surgery using a questionnaire, a numerical rating scale (NRS) of pain, the 36-Item Short Form Health Survey (SF-36), the Japanese Orthopedic Association score (JOA score), and the recovery rate. The original questionnaire consisted of 5 categories, with scoring out of 100 points for surgery, satisfaction, improvement, recommendation to others, and willingness to undergo repeat surgery. Patient-based outcomes were divided into 3 groups according to the questionnaire responses as positive, intermediate, and negative and were compared with the JOA scores.

RESULTS

A total of 103 patients responded, for a response rate of 85%. The average patient-evaluated score for surgery was 82 points. The positive response rate in each category was 78% for satisfaction, 88% for improvement, 74% for recommendation, and 71% for repeat. The average pre- and postoperative JOA scores were 11.2 and 23.2, respectively. The average recovery rate was 68.5%. There were significant correlations between patient-based surgical outcomes and the JOA score. Furthermore, there were significant correlations between patient-based surgical outcomes and the NRS and physical component scores of the SF-36. Postoperative permanent motor loss was a major factor related to a negative response.

CONCLUSION

The patient-evaluated score for surgery was 82 points. More than 70% of patients gave positive responses in all sections of the questionnaire. There were significant correlations between patient-based and surgeon-based surgical outcomes.

LEVEL OF EVIDENCE

2.

Finite Element Analysis of a New Pedicle Screw-Plate System for Minimally Invasive Transforaminal Lumbar Interbody Fusion

PURPOSE

Minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) is increasingly popular for the surgical treatment of degenerative lumbar disc diseases. The constructs intended for segmental stability are varied in MI-TLIF. We adopted finite element (FE) analysis to compare the stability after different construct fixations using interbody cage with posterior pedicle screw-rod or pedicle screw-plate instrumentation system.

METHODS

A L3-S1 FE model was modified to simulate decompression and fusion at L4-L5 segment. Fixation modes included unilateral plate (UP), unilateral rod (UR), bilateral plate (BP), bilateral rod (BR) and UP+UR fixation. The inferior surface of the S1 vertebra remained immobilized throughout the load simulation, and a bending moment of 7.5 Nm with 400N pre-load was applied on the L3 vertebra to recreate flexion, extension, lateral bending, and axial rotation. Range of motion (ROM) and Von Mises stress were evaluated for intact and instrumentation models in all loading planes.

RESULTS

All reconstructive conditions displayed decreased motion at L4-L5. The pedicle screw-plate system offered equal ROM to pedicle screw-rod system in unilateral or bilateral fixation modes respectively. Pedicle screw stresses for plate system were 2.2 times greater than those for rod system in left lateral bending under unilateral fixation. Stresses for plate were 3.1 times greater than those for rod in right axial rotation under bilateral fixation. Stresses on intervertebral graft for plate system were similar to rod system in unilateral and bilateral fixation modes respectively. Increased ROM and posterior instrumentation stresses were observed in all loading modes with unilateral fixation compared with bilateral fixation in both systems.

CONCLUSIONS

Transforaminal lumbar interbody fusion augmentation with pedicle screw-plate system fixation increases fusion construct stability equally to the pedicle screw-rod system. Increased posterior instrumentation stresses are observed in all loading modes with plate fixation, and bilateral fixation could reduce stress concentration.

Comparison between percutaneous fluoroscopic-guided and conventional open pedicle screw placement techniques for the thoracic spine

Percutaneous placement of pedicle screws is a well-established technique, however, no studies have compared percutaneous and open placement of screws in the thoracic spine. The aim of this cadaveric study was to compare the accuracy and safety of these techniques at the thoracic spinal level. A total of 288 screws were inserted in 16 (eight cadavers, 144 screws in percutaneous and eight cadavers, 144 screws in open). Pedicle perforations and fractures were documented subsequent to wide laminectomy followed by skeletalisation of the vertebrae. The perforations were classified as grade 0: no perforation, grade 1: < 2 mm perforation, grade 2: 2 mm to 4 mm perforation and grade 3: > 4 mm perforation. In the percutaneous group, the perforation rate was 11.1% with 15 (10.4%) grade 1 and one (0.7%) grade 2 perforations. In the open group, the perforation rate was 8.3% (12 screws) and all were grade 1. This difference was not significant (p = 0.45). There were 19 (13.2%) pedicle fractures in the percutaneous group and 21 (14.6%) in the open group (p = 0.73). In summary, the safety of percutaneous fluoroscopy-guided pedicle screw placement in the thoracic spine between T4 and T12 is similar to that of the conventional open technique.

Cite this article: Bone Joint J 2015;97-B:1555–61.

Unskilled unawareness and the learning curve in robotic spine surgery

BACKGROUND

Robotic assistance for the placement of pedicle screws has been established as a safe technique. Nonetheless rare instances of screw misplacement have been reported.The aim of the present retrospective study is to assess whether experience and time affect the accuracy of screws placed with the help of the SpineAssist™ robot system.

METHODS

Postoperative computed tomography (CT) scans of 258 patients requiring thoracolumbar pedicle screw instrumentation from 2008 to 2013 were reviewed. Overall, 13 surgeons performed the surgeries. A pedicle breach of >3 mm was graded as a misplacement. Surgeons were dichotomised into an early and experienced period in increments of five surgeries.

RESULTS

In 258 surgeries, 1,265 pedicle screws were placed with the aid of the robot system. Overall, 1,217 screws (96.2 %) were graded as acceptable. When displayed by surgeon, the development of percent misplacement rates peaked between 5 and 25 surgeries in 12 of 13 surgeons. The overall misplacement rate in the first five surgeries was 2.4 % (6/245). The misplacement rate rose to 6.3 % between 11 and 15 surgeries (10/158; p = 0.20), and reached a significant peak between 16 and 20 surgeries with a rate of 7.1 % (8/112; p = 0.03). Afterwards, misplacement rates declined.

CONCLUSIONS

A major peak in screw inaccuracies occurred between cases 10 and 20, and a second, smaller one at about 40 surgeries. One potential explanation could be a transition from decreased supervision (unskilled but aware) to increased confidence of a surgeon (unskilled but unaware) who adopts this new technique prior to mastering it (skilled). We therefore advocate ensuring competent supervision for new surgeons at least during the first 25 procedures of robotic spine surgery to optimise the accuracy of robot-assisted pedicle screws.

A comparison of feasibility and safety of percutaneous fluoroscopic guided thoracic pedicle screws between Europeans and Asians: is there any difference?

PURPOSE

To directly compare the safety of fluoroscopic guided percutaneous thoracic pedicle screw placement between Caucasians and Asians.

METHODS

This was a retrospective computerized tomography (CT) evaluation study of 880 fluoroscopic guided percutaneous pedicle screws. 440 screws were inserted in 73 European patients and 440 screws were inserted in 75 Asian patients. Screw perforations were classified into Grade 0: no violation; Grade 1: <2 mm perforation; Grade 2: 2-4 mm perforation; and Grade 3: >4 mm perforation. For anterior perforations, the pedicle perforations were classified into Grade 0: no violation, Grade 1: <4 mm perforation; Grade 2: 4-6 mm perforation; and Grade 3: >6 mm perforation.

RESULTS

The inter-rater reliability was adequate with a kappa value of 0.83. The mean age of the study group was 58.3 ± 15.6 years. The indications for surgery were tumor (70.3 %), infection (18.2 %), trauma (6.8 %), osteoporotic fracture (2.7 %) and degenerative diseases (2.0 %). The overall screw perforation rate was 9.7 %, in Europeans 9.1 % and in Asians 10.2 % (p > 0.05). Grade 1 perforation rate was 8.4 %, Grade 2 was 1.2 % and Grade 3 was 0.1 % with no difference in the grade of perforations between Europeans and Asians (p > 0.05). The perforation rate was the highest in T1 (33.3 %), followed by T6 (14.5 %) and T4 (14.0 %). Majority of perforations occurred medially (43.5 %), followed by laterally (25.9 %), and anteriorly (23.5 %). There was no statistical significant difference (p > 0.05) in the perforation rates between right-sided pedicle screws and left-sided pedicle screws (R: 10.0 %, L: 9.3 %).

CONCLUSIONS

There were no statistical significant differences in the overall perforation rates, grades of perforations, direction of perforations for implantation of percutaneous thoracic pedicle screws insertion using fluoroscopic guidance between Europeans and Asians. The safety profile for this technique was comparable to the current reported perforation rates for conventional open pedicle screw technique.

Is It Beneficial to Remove the Pedicle Screw Instrument After Successful Posterior Fusion of Thoracolumbar Burst Fractures?

STUDY DESIGN

Case-control study.

OBJECTIVE

To investigate the clinical and radiological outcomes of pedicle screw removal after successful fusion of thoracolumbar burst fractures.

SUMMARY OF BACKGROUND DATA

Implant removal is a common procedure in orthopedic surgery, although the benefits of and indications for removal remain controversial. Previous studies on pedicle screw removal have reported conflicting outcomes, because the study subjects and surgical goals were heterogeneous in nature.

METHODS

We studied 45 consecutive patients who underwent implant removal and a control cohort of 45 age- and sex-matched patients who retained their spinal implants after successful posterior fusion of thoracolumbar burst fractures using pedicle screw instrument. In most cases, long-segment instrumentation with short-segment posterior fusion was performed. The mean elapsed period prior to implant removal after index fracture surgery was 18.3 ± 17.6 months. A visual analogue scale for back pain was applied, the Oswestry disability index calculated, and radiological parameters derived at the time of implant removal and 1 and 2 years postoperatively obtained. These data were compared with those of the control group evaluated at the same times after index fracture surgery.

RESULTS

Patient demographics, mechanisms of injury, fracture morphologies, and the outcomes of index fracture surgery were similar between the 2 groups. The mean visual analogue scale and Oswestry disability index scores were better at both the 1- and 2-year follow-ups in the implant removal group than in the control group (all P values = 0.000). The segmental motion angle of the implant removal group was 1.6° ± 1.5° at the time of implant removal, and increased significantly to 5.8° ± 3.9° at 1-year follow-up (P = 0.000), and was maintained at this level at the 2-year follow-up (5.9° ± 4.1°) (P = 0.000).

CONCLUSION

In patients treated successfully for thoracolumbar burst fractures, pedicle screw removal is beneficial because it alleviates pain and disability. Restoration of the segmental motion angle after implant removal may contribute to the clinical improvement.

LEVEL OF EVIDENCE

3.

Radiographic comparison of cross-sectional lumbar pedicle fill when placing screws with navigation versus free-hand technique

BACKGROUND

Pedicle screws are often used for spinal fixation. Increasing the percentage of pedicle that is filled with the screw presumably yields greater fixation. It has not been shown whether spinal navigation helps surgeons more completely fill their instrumented pedicles.

METHODS

Fifty consecutive patients from each arm (navigated and free-hand) were retrospectively reviewed. The cross-sectional area of each instrumented lumbar pedicle and screw were measured using an automatic area calculation tool. The coronal images and measurements were blinded to the surgeons.

RESULTS

The instrumented pedicles in the navigated patients were significantly more filled by screws than the pedicles in the non-navigated patients (P < 0.001).

CONCLUSION

Obtaining a higher cross-sectional percentage fill of the pedicle with a screw is expected to provide greater spinal fixation in instrumented fusion surgery. This study shows that utilizing spinal navigation helps to more completely fill the pedicles that are being instrumented. Copyright © 2015 John Wiley & Sons, Ltd.

Pedicle screw placement in the lumbar spine: effect of trajectory and screw design on acute biomechanical purchase

OBJECT

Low bone mineral density in patients undergoing lumbar spinal surgery with screws is an especially difficult challenge because poor bone quality can severely compromise the maximum achievable purchase of the screws. A relatively new technique, the cortical bone screw trajectory, utilizes a medialized trajectory in the caudocephalad direction to engage a greater amount of cortical bone within the pars interarticularis and pedicle. The objectives of this cadaveric biomechanical study were to 1) evaluate a cortical screw system and compare its mechanical performance to the traditional pedicle screw system; 2) determine differences in bone quality associated with the cortical screw trajectory versus the normal pedicle screw insertion technique; 3) determine the cortical wall breach rate with both the cortical and traditional screw trajectories; and 4) determine the performance of the traditional screw in the cortical screw trajectory.

METHODS

Fourteen fresh frozen human lumbar spine sections (L1–5) were used in this study (mean age 57 ± 19 years). The experimental plan involved drilling and tapping screw holes for 2 trajectories under navigation (a traditional pedicle screw and a cortical screw) in both high-and low-quality vertebrae, measuring the bone quality associated with these trajectories, placing screws in the trajectories, and evaluating the competence of the screw purchase via 2 mechanical tests (pullout and toggle). The 3 experimental variants were 1) traditional pedicle screws placed in the traditional pedicle screw trajectory, 2) traditional pedicle screws placed in the cortical screw trajectory, and 3) cortical screws placed in the cortical screw trajectory.

RESULTS

A statistically significant increase in bone quality was observed for the cortical trajectories with a cortical screw (42%; p < 0.001) and traditional pedicle screw (48%; p < 0.001) when compared to the traditional trajectory with a traditional pedicle screw within the high-quality bone group. These significant differences were also found in the lowquality bone cohort. All mechanical parameter comparisons (screw type and trajectory) between high-quality and lowquality samples were significant (p < 0.01), and these data were all linearly correlated (r ≥ 0.65) to bone mineral density. Not all mechanical parameters determined from pullout and toggle testing were statistically significant between the 3 screw/trajectory combinations. The incidence of cortical wall breach with the cortical or traditional pedicle screw trajectories was not significantly different.

CONCLUSIONS

The data demonstrated that the cortical trajectory provides denser bone that allows for utilization of smaller screws to obtain mechanical purchase that is equivalent to long pedicle screws placed in traditional pedicle screw trajectories for both normal- and low-quality bone. Overall, this biomechanical study in cadavers provides evidence that the cortical screw trajectory represents a good option to obtain fixation for the lumbar spine with low-quality bone.

Toward a better understanding of direct vertebral rotation for AIS surgery: development of a multisegmental biomechanical model and factors affecting correction

BACKGROUND CONTEXT

The direct vertebral rotation (DVR) technique involves vertebral manipulation by the application of force in the transverse plane using a pedicle screw as the anchor point. The biomechanics of this technique has not been well studied, and the applied derotation force may affect cosmetic outcome and potential complications.

PURPOSE

The purpose of the study was to develop an in vitro biomechanical model replicating DVR and examine the effects of screw placement, derotation direction, and segmental versus en bloc rotation on correction.

STUDY DESIGN

This study is based on a cadaveric spine model examining the biomechanics of DVR.

METHODS

Short three vertebral segments were dissected from thoracolumbar cadaveric spines (T5-L4). Each pedicle of the central vertebra received a unicortical, bicortical, or in-out-in screw. Unconstrained biomechanical tests were performed in an axial rotation (medial and lateral directions) mimicking DVR surgery. Nondestructive tests were performed examining peak force and rotational stiffness with/without a contralateral rod. A destructive failure test was performed on each pedicle screw with a contralateral rod connecting via the contralateral pedicle screw. Repeated-measures analysis of variance and post hoc Student t tests were used to detect significance with screw placement and loading direction as main factors.

RESULTS

Without the contralateral rod, the rotation direction was significant (p=.004, medial stiffness more than lateral). With the contralateral rod, in-out-in placement demonstrated lower stiffness than unicortical or bicortical screws (p=.009), and the rotation direction was significant (p=.003, medial stiffness more than lateral). There was no interaction effect between main factors. Peak force with and without a contralateral rod resulted in a similar pattern of significance as stiffness. Destructive failure tests showed that the placement was significant (p<.02) with in-out-in resulting in lower stiffness than unicortical- and bicortical-placed screws. In-out-in (25±6 N) and unicortical (35±16 N) placements resulted in lower peak load (p<.001) than bicortical (48±17 N) screws.

CONCLUSIONS

The biomechanical characteristics of DVR are dependent on the derotation direction and screw placement. Correction for adolescent idiopathic scoliosis can be attempted irrespective of the type of pedicle screw placement, more efficiently if performing derotation maneuvers en bloc on bicortical screws in the medial direction.

Percutaneous “K-wireless” pedicle screw fixation technique: an evaluation of the initial experience of 100 screws with assessment of accuracy, radiation exposure, and procedure time

OBJECT

Percutaneous pedicle screws are used to provide rigid internal fixation in minimally invasive spinal procedures and generally require the use of Kirchner wires (or K-wires) as a guide for screw insertion. K-wires can bend, break, advance, or pull out during the steps of pedicle preparation and screw insertion. This can lead to increased fluoroscopic and surgical times and potentially cause neurological, vascular, or visceral injury. The authors present their experience with a novel “K-wireless” percutaneous pedicle screw system that eliminates the inherent risks of K-wire use.

METHODS

A total of 100 screws were placed in 28 patients using the K-wireless percutaneous screw system. Postoperative dedicated spinal CT scans were performed in 25 patients to assess the accuracy of screw placement. Screw placement was graded A through D by 2 independent radiologists: A = within pedicle, B = breach < 2 mm, C = breach of 2–4 mm, and D = breach > 4 mm. Screw insertion and fluoroscopy times were also recorded in each case. Clinical complications associated with screw insertion were documented.

RESULTS

A total of 100 K-wireless percutaneous pedicle screws were placed into the lumbosacral spine in 28 patients. Postoperative CT was performed in 25 patients, thus the placement of only 90 screws was assessed. Eighty-seven screws were placed within the pedicle confines (Grade A), and 3 violated the pedicle (2 Grade B [1 lateral, 1 medial] and 1 Grade D [medial]) for an overall accuracy rate of 96.7%. One patient required reoperation for screw repositioning due to a postoperative L-5 radiculopathy secondary to a Grade D medial breach at L-5. This patient experienced improvement of the radiculopathy after reoperation. Average screw insertion and fluoroscopy times were 6.92 minutes and 22.7 seconds per screw, respectively.

CONCLUSIONS

The results of this study demonstrate that the placement of K-wireless percutaneous pedicle screws is technically feasible and can be performed accurately and safely with short procedure and fluoroscopy times.

The evolution of image-guided lumbosacral spine surgery

Techniques and approaches of spinal fusion have considerably evolved since their first description in the early 1900s. The incorporation of pedicle screw constructs into lumbosacral spine surgery is among the most significant advances in the field, offering immediate stability and decreased rates of pseudarthrosis compared to previously described methods. However, early studies describing pedicle screw fixation and numerous studies thereafter have demonstrated clinically significant sequelae of inaccurate surgical fusion hardware placement. A number of image guidance systems have been developed to reduce morbidity from hardware malposition in increasingly complex spine surgeries. Advanced image guidance systems such as intraoperative stereotaxis improve the accuracy of pedicle screw placement using a variety of surgical approaches, however their clinical indications and clinical impact remain debated. Beginning with intraoperative fluoroscopy, this article describes the evolution of image guided lumbosacral spinal fusion, emphasizing two-dimensional (2D) and three-dimensional (3D) navigational methods.

Novel pedicle screw and plate system provides superior stability in unilateral fixation for minimally invasive transforaminal lumbar interbody fusion: an in vitro biomechanical study

Purpose

This study aims to compare the biomechanical properties of the novel pedicle screw and plate system with the traditional rod system in asymmetrical posterior stabilization for minimally invasive transforaminal lumbar interbody fusion (MI-TLIF). We compared the immediate stabilizing effects of fusion segment and the strain distribution on the vertebral body.

Methods

Seven fresh calf lumbar spines (L3-L6) were tested. Flexion/extension, lateral bending, and axial rotation were induced by pure moments of ± 5.0 Nm and the range of motion (ROM) was recorded. Strain gauges were instrumented at L4 and L5 vertebral body to record the strain distribution under flexion and lateral bending (LB). After intact kinematic analysis, a right sided TLIF was performed at L4-L5. Then each specimen was tested for the following constructs: unilateral pedicle screw and rod (UR); unilateral pedicle screw and plate (UP); UR and transfacet pedicle screw (TFS); UP and TFS; UP and UR.

Results

All instrumented constructs significantly reduced ROM in all motion compared with the intact specimen, except the UR construct in axial rotation. Unilateral fixation (UR or UP) reduced ROM less compared with the bilateral fixation (UP/UR+TFS, UP+UR). The plate system resulted in more reduction in ROM compared with the rod system, especially in axial rotation. UP construct provided more stability in axial rotation compared with UR construct. The strain distribution on the left and right side of L4 vertebral body was significantly different from UR and UR+TFS construct under flexion motion. The strain distribution on L4 vertebral body was significantly influenced by different fixation constructs.

Conclusions

The novel plate could provide sufficient segmental stability in axial rotation. The UR construct exhibits weak stability and asymmetrical strain distribution in fusion segment, while the UP construct is a good alternative choice for unilateral posterior fixation of MI-TLIF.

Unilateral versus bilateral pedicle screw fixation for degenerative lumbar diseases: a meta-analysis of 10 randomized controlled trials

Background

The common and effective treatment for degenerative lumbar diseases is lumbar spinal fusion. Controversy still exists on the choice for instrumentation with spinal fusion procedures. Therefore, we conducted this meta-analysis exclusively of RCTs to compare the clinical outcomes of patients receiving bilateral versus unilateral pedicle screw fixation (PSF).

Material/Methods

After systematic review of published and unpublished literature, a meta-analysis was conducted to compare the 2 treatment strategies. The methodological quality of the literature was assessed using the PEDro critical appraisal tool.

Results

Data synthesis showed less blood loss (P<0.001) and shorter operative time (P<0.001) in patients receiving unilateral PSF compared to bilateral PSF. However, there was no significant difference in fusion rates and functional outcomes between the 2 groups.

Conclusions

The meta-analysis indicated no significant difference in fusion rates and functional outcomes between the 2 treatment procedures, but unilateral PS fixation reduced blood loss and operative time.

Robotic assisted surgeries for the treatment of spine tumors

Background

Surgery plays an important role in the treatment of patients with metastatic or primary spine tumors. In recent years, various new techniques, such as robotic assisted spine surgery have been developed which has shown some promising results by improving the accuracy of spinal instrumentation and reducing potential complications. The purpose of this study was to evaluate our early experience using robotic guidance in the treatment of spinal tumors.

Methods

Data were collected from medical records for each surgery in which the robotic system was used to assist with biopsy, pedicle screw placement and/or vertebral augmentation in the treatment of spinal tumors. Patient's age, gender, diagnosis and surgical procedure were documented. The surgical time, estimated blood loss, peri-operative and post-operative complications were obtained. The visual analog scale (VAS) for back pain and leg pain were also recorded.

Results

A total of 9 consecutive patients (7 female, 2 male) were included in this study, beginning with the first case experience. The mean age of the patients was 60 years (range 47-69). All patients presented with thoracic or lumbar vertebral collapse and/or myelopathy. Robotic assisted posterior instrumentation was successfully performed in all patients. Robotic assisted vertebral augmentation was performed in 4 patients. The average number of levels instrumented was 5. The average surgery time (skin to skin) was 4 hours and 24 minutes and the mean blood loss was 319 ml. There were no complications perioperatively or through the latest follow-up. Seven of the 9 patients reported improved back pain and/or leg pain at the latest follow-up and the data were not available in two patients.

Conclusions

The published complication rates of spinal tumor surgeries range between 5.3% and 19%. With robotic assistance, the surgical complication rate appears improved over the historical figures. Our study shows that the robotic system was safe and performed as desired in the treatment of metastatic and primary spine tumors. These results support that further evaluation in a larger series of patients.

Balancing rigidity and safety of pedicle screw fixation via a novel expansion mechanism in a severely osteoporotic model

Many successful attempts to increase pullout strength of pedicle screws in osteoporotic bone have been accompanied with an increased risk of catastrophic damage to the patient. To avoid this, a single-armed expansive pedicle screw was designed to increase fixation strength while controlling postfailure damage away from the nerves surrounding the pedicle. The screw was then subsequently tested in two severely osteoporotic models: one representing trabecular bone (with and without the presence of polymethylmethacrylate) and the other representing a combination of trabecular and cortical bone. Maximum pullout strength, stiffness, energy to failure, energy to removal, and size of the resulting block damage were statistically compared among conditions. While expandable pedicle screws produced maximum pullout forces less than or comparable to standard screws, they required a higher amount of energy to be fully removed from both models. Furthermore, damage to the cortical layer in the composite test blocks was smaller in all measured directions for tests involving expandable pedicle screws than those involving standard pedicle screws. This indicates that while initial fixation may not differ in the presence of cortical bone, the expandable pedicle screw offers an increased level of postfailure stability and safety to patients awaiting revision surgery.

The effect of lateral wall perforation on screw pull-out strength: a cadaveric study

BACKGROUND

Lateral pedicle wall perforations occur frequently during pedicle screw insertion. Although it is known that such an occurrence decreases the screw pull-out strength, the effect has not been quantified biomechanically.

MATERIALS AND METHODS

Twenty fresh cadaveric lumbar vertebrae were harvested, and the bone mineral density (BMD) of each was evaluated with dual-energy radiography absorptiometry (DEXA). Twenty matched, 6.5-mm pedicle screws were inserted in two different manners in two groups, the control group and the experimental group. In the control group, the pedicle screw was inserted in a standard fashion taking adequate precaution to ensure there was no perforation of the wall. In the experimental group, the pedicle screw was inserted such that its trajectory perforated the lateral wall. Group assignments were done randomly, and the maximal fixation strength was recorded for each screw pull-out test with a material-testing system (MTS 858 II).

RESULTS

The average BMD for both groups was 0.850 g/cm(2) (0.788-0.912 g/cm(2)). The average (and standard deviation) maximal pull-out forces were 1,015.8 ± 249.40 N for the experimental group and 1,326.0 ± 320.50 N for the control group. According to a paired t-test, the difference between the two groups was statistically significant (P < 0.001).

CONCLUSION

The results of this study confirm that the maximal pull-out strength of pedicle screws decreases by approximately 23.4% when the lateral wall is perforated.

Mid-term results of computer-assisted cervical pedicle screw fixation

Study Design

A retrospective study.

Purpose

The present study aimed to evaluate mid-term results of cervical pedicle screw (CPS) fixation for cervical instability.

Overview of Literature

CPS fixation has widely used in the treatment of cervical spinal instability from various causes; however, there are few reports on mid-term surgical results of CPS fixation.

Methods

Record of 19 patients who underwent cervical and/or upper thoracic (C2-T1) pedicle screw fixation for cervical instability was reviewed. The mean observation period was 90.2 months. Evaluated items included Japanese Orthopaedic Association (JOA) score and C2-7 lordotic angle before surgery and at 5 years after surgery. Postoperative computerized tomography was used to determine the accuracy of screw placement. Visual analog scale (VAS) for neck pain and radiological evidence of adjacent segment degeneration (ASD) at the 5-year follow-up were also evaluated.

Results

Mean JOA score was significantly improved from 9.0 points before surgery to 12.8 at 5 years after surgery (p=0.001). The C2-7 lordotic angle of the neutral position improved from 6.4° to 7.8° at 5 years after surgery, but this was not significant. The major perforation rate was 5.0%. There were no clinically significant complications such as vertebral artery injury, spinal cord injury, or nerve root injury caused by any screw perforation. Mean VAS for neck pain was 49.4 at 5 years after surgery. The rate of ASD was 21.1%.

Conclusions

Our mid-term results showed that CPS fixation was useful for treating cervical instability. Severe complications were prevented with the assistance of a computed tomography-based navigation system.

[Postoperative spine]

Approximately 15-30 % of surgical procedures involving the lumbar spine are associated with complications that require further diagnostic work-up. The choice of imaging modality for postoperative complications depends on the extent, pattern and temporal evolution of the postoperative neurological signs and symptoms as well as on the preoperative clinical status, the surgical procedure itself and the underlying pathology. The interpretation of imaging findings, in particular the distinction between postoperative complications and normally expected nonspecific postoperative imaging alterations can be challenging and requires the integration of clinical neurological information and the results of laboratory tests. The combination of different imaging techniques might help in cases of equivocal imaging results.

Navigated pedicle screw placement using computed tomographic data in dorsolumbar fractures

BACKGROUND

Computed tomographic (CT) based navigation is a technique to improve the accuracy of pedicle screw placement. It is believed to enhance accuracy of pedicle screw placement, potentially avoiding complications arising due to pedicle wall breach. This study aims to assess the results of dorsolumbar fractures operated by this technique.

MATERIALS AND METHODS

Thirty consecutive skeletally mature patients of fractures of dorsolumbar spine (T9-L5) were subjected to an optoelectronic navigation system. All patients were thoroughly examined for neurological deficit. The criterion for instability were either a tricolumnar injury or presence of neurological deficit or both. Patients with multilevel fractures and distorted spine were excluded from study. Time taken for insertion of each pedicle screw was recorded and placement assessed with a postoperative CT scan using Laine's grading system.

RESULTS

Only one screw out of a total of 118 screws was misplaced with a Laine's Grade 5 placement, showing a misplacement rate of 0.847%. Average time for matching was 7.8 min (range 5-12 min). Average time taken for insertion of a single screw was 4.19 min (range 2-8 min) and total time for all screws after exposure was 34.23 min (range 24-45 min) for a four screw construct. No neurovascular complications were seen in any of the patients postoperatively and in subsequent followup of 1-year duration.

CONCLUSION

CT-based navigation is effective in improving accuracy of pedicle screw placement in traumatic injuries of dorsolumbar spine (T9-L5), however additional cost of procuring CT scan to the patient and cost of equipment is of significant concern in developing countries. Reduced radiation exposure and lowered ergonomic constraints around the operation table are its additional benefits.

A novel anchoring system for use in a nonfusion scoliosis correction device

BACKGROUND CONTEXT

Insertion of a pedicle screw in the mid- and high thoracic regions has a serious risk of facet joint damage. Because flexible implant systems require intact facet joints, we developed an enhanced fixation that is less destructive to spinal structures. The XSFIX is a posterior fixation system that uses cables that are attached to the transverse processes of a vertebra.

PURPOSE

To determine whether a fixation to the transverse process using the XSFIX is strong enough to withstand the loads applied by the XSLATOR (a novel, highly flexible nonfusion implant system) and thus, whether it is a suitable alternative for pedicle screw fixation.

STUDY DESIGN

The strength of a novel fixation system using transverse process cables was determined and compared with the strength of a similar fixation using polyaxial pedicle screws on different vertebral levels.

METHODS

Each of the 58 vertebrae, isolated from four adult human cadavers, was instrumented with either a pedicle screw anchor (PSA) system or a prototype of the XSFIX. The PSA consisted of two polyaxial pedicle screws and a 5 mm diameter rod. The XSFIX prototype consisted of two bodies that were fixed to the transverse processes, interconnected with a similar rod. Each fixation system was subjected to a lateral or an axial torque.

RESULTS

The PSA demonstrated fixation strength in lateral loading and torsion higher than required for use in the XSLATOR. The XSFIX demonstrated high enough fixation strength (in both lateral loading and torsion), only in the high and midthoracic regions (T10-T12).

CONCLUSIONS

This experiment showed that the fixation strength of XSFIX is sufficient for use with the XSLATOR only in mid- and high thoracic regions. For the low thoracic and lumbar region, the PSA is a more rigid fixation. Because the performance of the new fixation system appears to be favorable in the high and midthoracic regions, a clinical study is the next challenge.

The 100 most cited papers in spinal deformity surgery: a bibliometric analysis

Spinal deformity is a condition that has been recognized for many millennia. There have been major advances in the treatment of spinal deformity in recent years and studies outlining new ideas can inspire others to further advance the speciality. The number of citations a paper receives may indicate the influence of that paper. It is therefore important that we evaluate and analyze the most cited works in our field. The aim of this study is to identify the 100 most cited papers relevant to spinal deformity surgery in the literature. A search through the Thomson Reuters Web of Science™ for citations related to spinal deformity surgery was performed. The number of citations, mean citation number (total number citations/years since publication), journal, authors, year of publication and country of origin of the top 100 papers was recorded. The top 100 papers were cited a combined 17,646 times, ranging from 453 to 112. The majority of papers originated from the United States (71) and were published in 20 different journals. The decade 1990-1999 was the most prolific, with 36 of the 100 papers published during this time. Papers pertaining to the management of scoliosis (49) were the most common. This study identifies the top 100 most cited papers in the field of spinal deformity surgery. While citation is not a specific marker of the scientific quality of a paper, it is a surrogate for the influence a paper has had on the orthopedic community. This list of papers provides an invaluable resource for both those in training and those actively practicing and involved in the further development of spinal deformity surgery.

ASTM F1717 standard for the preclinical evaluation of posterior spinal fixators: Can we improve it?

Preclinical evaluation of spinal implants is a necessary step to ensure their reliability and safety before implantation. The American Society for Testing and Materials reapproved F1717 standard for the assessment of mechanical properties of posterior spinal fixators, which simulates a vertebrectomy model and recommends mimicking vertebral bodies using polyethylene blocks. This set-up should represent the clinical use, but available data in the literature are few. Anatomical parameters depending on the spinal level were compared to published data or measurements on biplanar stereoradiography on 13 patients. Other mechanical variables, describing implant design were considered, and all parameters were investigated using a numerical parametric finite element model. Stress values were calculated by considering either the combination of the average values for each parameter or their worst-case combination depending on the spinal level. The standard set-up represents quite well the anatomy of an instrumented average thoracolumbar segment. The stress on the pedicular screw is significantly influenced by the lever arm of the applied load, the unsupported screw length, the position of the centre of rotation of the functional spine unit and the pedicular inclination with respect to the sagittal plane. The worst-case combination of parameters demonstrates that devices implanted below T5 could potentially undergo higher stresses than those described in the standard suggestions (maximum increase of 22.2% at L1). We propose to revise F1717 in order to describe the anatomical worst case condition we found at L1 level: this will guarantee higher safety of the implant for a wider population of patients.

Pathophysiological effects of lumbar instrumentation surgery on lumbosacral nerve roots in the vertebral foramen: measurement of local pressure of intervertebral foramen

STUDY DESIGN

Measurement of local pressure of the intervertebral foramina.

OBJECTIVE

To evaluate the pathophysiological effects of lumbar instrumentation surgery on lumbosacral nerve roots in the vertebral foramen.

SUMMARY OF BACKGROUND DATA

The physiological states of lumbosacral nerve roots in the vertebral foramen remain controversial.

METHODS

From 2000 to 2012, 11 of 710 patients with L4 degenerative spondylolisthesis failed to develop postoperative radiculopathy because of intraoperative pedicle screw malposition (L5: 10, L4: 1). We prospectively evaluated the local pressure at the L4-L5 and L5-LS vertebral foramina in 18 patients with L4 degenerative spondylolisthesis. All patients underwent L4-L5 posterolateral fusion (PLF) with L3-L4-L5 laminotomy. Intraoperatively, local pressure of the intervertebral foramen was measured using a catheter pressure transducer while changing the lumbar spine posture, and the measurement was performed before and after L4-L5 PLF.

RESULTS

The local pressures at the L4-L5 vertebral foramen were 29.74 ± 16.26 and 51.57 ± 23.18 mm Hg (before fixation), and 39.13 ± 17.69 and 41.71 ± 17.94 mm Hg (after fixation) in the lumbar spine neutral and extension postures, respectively. The local pressure before fixation increased significantly during lumbar spine extension (P < 0.001), although the value after fixation was almost identical. The local pressures at the L5-LS vertebral foramen were 26.91 ± 18.16 and 54.36 ± 26.67 mm Hg (before fixation), and 24.82 ± 17.1 and 58.46 ± 32.78 mm Hg (after fixation) in the lumbar spine neutral and extension postures, respectively. The local pressure before and after fixation increased significantly during lumbar spine extension (P < 0.001), and the values after fixation were higher than those before fixation.

CONCLUSION

The local pressure at the L4-L5 vertebral foramen did not change during lumbar extension after L4-L5 PLF, whereas the local pressure at the L5-LS vertebral foramen was significantly increased during lumbar extension after L4-L5 PLF. Our results suggested that the nerve roots caudal to the fixed segments may be exposed to higher external dynamic stresses after lumbar instrumentation surgery.

LEVEL OF EVIDENCE

4.

Pedicle morphometry of upper thoracic vertebrae: an anatomic study of 503 cadaveric specimens

STUDY DESIGN

An anatomic study of pedicle dimensions was performed for upper thoracic vertebrae from American human subjects.

OBJECTIVE

To quantify the dimensions of the upper thoracic pedicles and to better define the demographic factors that could ultimately govern the caliber selection of pedicle screws.

SUMMARY OF BACKGROUND DATA

Transpedicular screw fixation allows for segmental instrumentation into multiple vertebrae across multilevel fusion area, offering considerable biomechanical advantage over the conventional hook and lateral mass fixation. Large variations in morphology from previous studies may be related to differences in demographics, sample size, and methodology.

METHODS

For this study, T1-T6 vertebrae from 503 American human cadavers were directly measured with a digital caliper. Examiner measured each vertebra to determine medial-lateral pedicle width and cranial-caudal pedicle height. Demographic information regarding age, sex, and race, as well as body height and weight, was available for all 503 subjects.

RESULTS

Pedicle height generally increased in size caudally down the upper thoracic spine, but the highest pedicle height was at the T3 level with a mean of 12.25 mm. Pedicle width displayed a narrowing pattern moving down. The widest pedicle width was at the T1 level with a mean of 8.66 mm. The 2 older age groups had larger pedicles than the 2 younger age groups. Males have larger pedicles than females for all upper thoracic levels. The tallest and heaviest groups had larger pedicles than the shorter and lighter groups, respectively. Race was not a significant factor in affecting pedicle dimension.

CONCLUSION

Our large-scale study of American specimens characterized the relationship between pedicle dimensions and a variety of demographic factors such as age, sex, body height, and weight. With substantial statistical power, this study showed that male, older, taller, and heavier individuals had larger pedicles.

LEVEL OF EVIDENCE

N/A.

Pedicle screw reinsertion using previous pilot hole and trajectory does not reduce fixation strength

STUDY DESIGN

Fresh-frozen human cadaveric biomechanical study.

OBJECTIVE

To evaluate the biomechanical consequence of pedicle screw reinsertion in the thoracic spine.

SUMMARY OF BACKGROUND DATA

During pedicle screw instrumentation, abnormal appearance on fluoroscopic imaging or low current reading with intraoperatively evoked electromyographic stimulation of a pedicle screw warrants complete removal to reassess for pedicle wall violation or screw malposition. However, screw fixation strength has never been evaluated biomechanically after reinsertion using a previous pilot hole and trajectory.

METHODS

Thirty-one thoracic individual fresh-frozen human cadaveric vertebral levels were instrumented bilaterally with 5.5-mm titanium polyaxial pedicle screws, and insertional torque (IT) was measured with each revolution. A paired comparison was performed for each level. Screw reinsertion was performed by completely removing the pedicle screw, palpating the tract, and then reinserting along the same trajectory. Screws were tensile loaded to failure "in-line" with the screw axis.

RESULTS

There was no significant difference for pedicle screw pullout strength (POS) between reinserted and control screws (732 ± 307 N vs. 742 ± 320 N, respectively; P = 0.78). There was no significant difference in IT between initial insertion for the test group (INI) (0.82 ± 0.40 N·m) and control (0.87 ± 0.50 N·m) (P = 0.33). IT for reinserted screws (0.58 ± 0.47 N·m) had significantly decreased compared with INI and control screws (29% decrease, P = 0.00; 33% decrease, P = 0.00, respectively). The test group screws in the thoracic spine had significant correlations between initial IT and POS (r = 0.79, P = 0.00), and moderate correlations between reinsertion IT and POS in the thoracic spine (r = 0.56, P = 0.00).

CONCLUSION

Despite a significant reduction in pedicle screw IT, there was no significant difference in pedicle screw POS with reinsertion. Therefore, when surgeons must completely remove a pedicle screw for tract inspection, reinsertion along the same trajectory may be performed without significantly compromising fixation strength.

LEVEL OF EVIDENCE

N/A.

Outcomes and complications following posterior long lumbar fusions exceeding three levels

The outcomes and complications of posterior-only lumbar instrumented long fusions exceeding three segments with selective segmental transforaminal lumbar interbody fusion for the treatment of degenerative lumbar scoliosis, kyphosis, or both combined with spondylolisthesis were analyzed to investigate risk factors associated with surgical instrumentation failure. Fifteen consecutive patients with degenerative lumbar scoliosis, kyphosis, or both combined with spondylolisthesis were studied retrospectively. There were 5 male and 10 female patients, with a mean age of 71.8 years. All the patients were followed for a mean duration of 19.4 months postoperatively. Radiographic evaluation included coronal Cobb angle, lumbar lordosis (LL) angle, pelvic incidence (PI), and pelvic tilt (PT). The clinical outcomes were assessed by means of Japanese Orthopedic Association (JOA) score. Patients were divided into two groups: group 1—7 patients with surgical complications; group 2—8 patients without complications. The preoperative and postoperative coronal Cobb's angle were not significantly different between groups 1 and 2. The LL highly correlated with developing surgical complications. There were statistically significant differences in preoperative and postoperative LL and the mean difference between PI and the LL (PI–LL) between groups 1 and 2. Linear correlation and regression analysis showed that there was no correlation between JOA score and the coronal Cobb angle in degenerative scoliosis patients. However, we found a positive correlation between JOA and LL. Our series of long lumbar fusions had a high complication and instrumentation failure. Creating adequate LL angle in harmony with PI was a key to prevent surgical complications and attain neurological improvement.

Biomechanical evaluation of the Facet Wedge: a refined technique for facet fixation

PURPOSE

Purpose of this paper is to evaluate the primary stability of a new approach for facet fixation the so-called Facet Wedge (FW) in comparison with established posterior fixation techniques like pedicle screws (PS) and translaminar facet screws (TLS) with and without anterior cage interposition.

METHODS

Twenty-four monosegmental fresh frozen non-osteoporotic human motion segments (L2-L3 and L4-L5) were tested in a two-arm biomechanical study using a robot-based spine tester. Facet Wedge was compared with pedicle screws and translaminar screws as a stand-alone device and in combination with an anterior fusion cage.

RESULTS

Pedicle screws, FW and translaminar screws could stabilize an intact motion segment effectively. Facet Wedge was comparable to PS for lateral bending, extension and flexion and slightly superior for axial rotation. Facet Wedge showed a superior kinematic capacity compared to translaminar screws.

CONCLUSIONS

Facet Wedge offers a novel posterior approach in achieving primary stability in lumbar spinal fixation. The results of the present study showed that the Facet Wedge has a comparable primary stability to pedicle screws and potential advantages over translaminar screws.

Influence of the screw augmentation technique and a diameter increase on pedicle screw fixation in the osteoporotic spine: pullout versus fatigue testing

PURPOSE

For posterior spinal stabilization, loosening of pedicle screws at the bone-screw interface is a clinical complication, especially in the osteoporotic population. Axial pullout testing is the standard pre-clinical testing method for new screw designs although it has questioned clinical relevance. The aim of this study was to determine the fixation strength of three current osteoporotic fixation techniques and to investigate whether or not pullout testing results can directly relate to those of the more physiologic fatigue testing.

METHODS

Thirty-nine osteoporotic, human lumbar vertebrae were instrumented with pedicle screws according to four treatment groups: (1) screw only (control), (2) prefilled augmentation, (3) screw injected augmentation, and (4) unaugmented screws with an increased diameter. Toggle testing was first performed on one pedicle, using a cranial-caudal sinusoidal, cyclic (1.0 Hz) fatigue loading applied at the screw head. The initial compressive forces ranged from 25 to 75 N. Peak force increased stepwise by 25 N every 250 cycles until a 5.4-mm screw head displacement. The contralateral screw then underwent pure axial pullout (5 mm/min).

RESULTS

When compared to the control group, screw injected augmentation increased fatigue force (27 %, p = 0.045) while prefilled augmentation reduced fatigue force (-7 %, p = 0.73). Both augmentation techniques increased pullout force compared to the control (ps < 0.04). Increasing the screw diameter by 1 mm increased pullout force (24 %, p = 0.19), fatigue force (5 %, p = 0.73), and induced the least stiffness loss (-29 %) from control.

CONCLUSIONS

For the osteoporotic spine, screw injected augmentation showed the best biomechanical stability. Although pullout testing was more sensitive, the differences observed were not reflected in the more physiological fatigue testing, thus casting further doubt on the clinical relevance of pullout testing.

The Benefits of Cement Augmentation of Pedicle Screw Fixation Are Increased in Osteoporotic Bone: A Finite Element Analysis

STUDY DESIGN

Biomechanical study using a finite element model of a normal and osteoporotic lumbar vertebrae comparing resistance with axial pullout and bending forces on polymethylmethacrylate-augmented and non-augmented pedicle screws.

OBJECTIVE

To compare the effect of cement augmentation of pedicle screw fixation in normal and osteoporotic bone with 2 different techniques of cement delivery.

SUMMARY OF BACKGROUND DATA

Various clinical and biomechanical studies have addressed the benefits of cement augmentation of pedicle screws, but none have evaluated whether this effect is similar, magnified, or attenuated in osteoporotic bone compared with normal bone. In addition, no study has compared the biomechanical strength of augmented pedicle screws using cement delivery through the pedicle screw with delivery through a pilot hole.

METHODS

This study was funded by a grant from DePuy Synthes Spine. Normal and osteoporotic lumbar vertebrae with pedicle screws were simulated. The models were tested for screw pullout strength with and without cement augmentation. Two methods of cement delivery were also tested. Both methods were tested using 1 and 2.5 cm³ volume of cement infiltrated in normal and osteoporotic bone.

RESULTS

The increase in screw pullout force was proportionally greater in osteoporotic bone with equivalent volumes of cement delivered. The researchers found that 1 and 2.5 cm³ of cement infiltrated bone volume resulted in an increase in pullout force by about 50% and 120% in normal bone, and by about 64% and 156% in osteoporotic bone, respectively. The delivery method had only a minimal effect on pullout force when 2.5 cm³ of cement was injected (<4% difference).

CONCLUSIONS

Cement augmentation increases the fixation strength of pedicle screws, and this effect is proportionately greater in osteoporotic bone. Cement delivery through fenestrated screws and delivery through a pilot hole result in comparable pullout strength at higher cement volumes.

Accuracy of Pedicle Screw Placement in Scoliosis Surgery: A Comparison between Conventional Computed Tomography-Based and O-Arm-Based Navigation Techniques

Study Design

Retrospective study.

Purpose

We compared the accuracy of O-arm-based navigation with computed tomography (CT)-based navigation in scoliotic surgery.

Overview of Literature

No previous reports comparing the results of O-arm-based navigation with conventional CT-based navigation in scoliotic surgery have been published.

Methods

A total of 222 pedicle screws were implanted in 29 patients using CT-based navigation (group C) and 416 screws were implanted in 32 patients using O-arm-based navigation (group O). Postoperative CT was performed to assess the screw accuracy, using the established Neo classification (grade 0: no perforation, grade 1: perforation <2 mm, grade 2: perforation ≥2 and <4, and grade 3: perforation ≥4 mm).

Results

In group C, 188 (84.7%) of the 222 pedicle screw placements were categorized as grade 0, 23 (10.4%) were grade 1, 11 (5.0%) were grade 2, and 0 were grade 3. In group O, 351 (84.4%) of the 416 pedicle screw placements were categorized as grade 0, 52 (12.5%) were grade 1, 13 (3.1%) were grade 2, and 0 were grade 3. Statistical analysis showed no significant difference in the prevalence of grade 2.3 perforations between groups C and O. The time to position one screw, including registration, was 10.9±3.2 minutes in group C, but was significantly decreased to 5.4±1.1 minutes in group O.

Conclusions

O-arm-based navigation facilitates pedicle screw insertion as accurately as conventional CT-based navigation. The use of O-arm-based navigation successfully reduced the time, demonstrating advantages in the safety and accuracy of pedicle screw placement for scoliotic surgery.

Biomechanical study of expandable pedicle screw fixation in severe osteoporotic bone comparing with conventional and cement-augmented pedicle screws

Pedicle screws are widely utilized to treat the unstable thoracolumbar spine. The superior biomechanical strength of pedicle screws could increase fusion rates and provide accurate corrections of complex deformities. However, osteoporosis and revision cases of pedicle screw substantially reduce screw holding strength and cause loosening. Pedicle screw fixation becomes a challenge for spine surgeons in those scenarios. The purpose of this study was to determine if an expandable pedicle screw design could be used to improve biomechanical fixation in osteoporotic bone. Axial mechanical pull-out test was performed on the expandable, conventional and augmented pedicle screws placed in a commercial synthetic bone block which mimicked a human bone with severe osteoporosis. Results revealed that the pull-out strength and failure energy of expandable pedicle screws were similar with conventional pedicle screws augmented with bone cement by 2 ml. The pull-out strength was 5-fold greater than conventional pedicle screws and the failure energy was about 2-fold greater. Besides, the pull-out strength of expandable screw was reinforced by the expandable mechanism without cement augmentation, indicated that the risks of cement leakage from vertebral body would potentially be avoided. Comparing with the biomechanical performances of conventional screw with or without cement augmentation, the expandable screws are recommended to be applied for the osteoporotic vertebrae.

Safety and accuracy of robot-assisted versus fluoroscopy-guided pedicle screw insertion for degenerative diseases of the lumbar spine: a matched cohort comparison

Object

Recent years have been marked by efforts to improve the quality and safety of pedicle screw placement in spinal instrumentation. The aim of the present study is to compare the accuracy of the SpineAssist robot system with conventional fluoroscopy-guided pedicle screw placement.

Methods

Ninety-five patients suffering from degenerative disease and requiring elective lumbar instrumentation were included in the study. The robot cohort (Group I; 55 patients, 244 screws) consisted of an initial open robot-assisted subgroup (Subgroup IA; 17 patients, 83 screws) and a percutaneous cohort (Subgroup IB, 38 patients, 161 screws). In these groups, pedicle screws were placed under robotic guidance and lateral fluoroscopic control. In the fluoroscopy-guided cohort (Group II; 40 patients, 163 screws) screws were inserted using anatomical landmarks and lateral fluoroscopic guidance. The primary outcome measure was accuracy of screw placement on the Gertzbein-Robbins scale (Grade A to E and R [revised]). Secondary parameters were duration of surgery, blood loss, cumulative morphine, and length of stay.

Results

In the robot group (Group I), a perfect trajectory (A) was observed in 204 screws (83.6%). The remaining screws were graded B (n = 19 [7.8%]), C (n = 9 [3.7%]), D (n = 4 [1.6%]), E (n = 2 [0.8%]), and R (n = 6 [2.5%]). In the fluoroscopy-guided group (Group II), a completely intrapedicular course graded A was found in 79.8% (n = 130). The remaining screws were graded B (n = 12 [7.4%]), C (n = 10 [6.1%]), D (n = 6 [3.7%]), and E (n = 5 [3.1%]). The comparison of “clinically acceptable” (that is, A and B screws) was neither different between groups (I vs II [p = 0.19]) nor subgroups (Subgroup IA vs IB [p = 0.81]; Subgroup IA vs Group II [p = 0.53]; Subgroup IB vs Group II [p = 0.20]). Blood loss was lower in the robot-assisted group than in the fluoroscopy-guided group, while duration of surgery, length of stay, and cumulative morphine dose were not statistically different.

Conclusions

Robot-guided pedicle screw placement is a safe and useful tool for assisting spine surgeons in degenerative spine cases. Nonetheless, technical difficulties remain and fluoroscopy backup is advocated.

What is the learning curve for robotic-assisted pedicle screw placement in spine surgery?

BACKGROUND

Some early studies with robotic-assisted pedicle screw implantation have suggested these systems increase accuracy of screw placement. However, the relationship between the success rate of screw placement and the learning curve of this new technique has not been evaluated.

QUESTIONS/PURPOSES

We determined whether, as a function of surgeon experience, (1) the success rate of robotic-assisted pedicle screw placement improved, (2) the frequency of conversion from robotic to manual screw placement decreased, and (3) the frequency of malpositioned screws decreased.

METHODS

Between June 2010 and August 2012, the senior surgeon (IHL) performed 174 posterior spinal procedures using pedicle screws, 162 of which were attempted with robotic assistance. The use of the robotic system was aborted in 12 of the 162 procedures due to technical issues (registration failure, software crash, etc). The robotic system was successfully used in the remaining 150 procedures. These were the first procedures performed with the robot by the senior surgeon, and in this study, we divided the early learning curve into five groups: Group 1 (Patients 1-30), Group 2 (Patients 31-60), Group 3 (Patients 61-90), Group 4 (Patients 91-120), and Group 5 (Patients 121-150). One hundred twelve patients (75%) had spinal deformity and 80 patients (53%) had previous spine surgery. The accuracy of screw placement in the groups was assessed based on intraoperative biplanar fluoroscopy and postoperative radiographs. The results from these five groups were compared to determine the effect on the learning curve. The numbers of attempted pedicle screw placements were 359, 312, 349, 359, and 320 in Groups 1 to 5, respectively.

RESULTS

The rates of successfully placed screws using robotic guidance were 82%, 93%, 91%, 95%, and 93% in Groups 1 to 5. The rates of screws converted to manual placement were 17%, 7%, 8%, 4%, and 7%. Of the robotically placed screws, the screw malposition rates were 0.8%, 0.3%, 1.4%, 0.8%, and 0%.

CONCLUSIONS

The rate of successfully placed pedicle screws improved with increasing experience. The rate of the screws that were converted to manual placement decreased with increasing experience. The frequency of screw malposition was similar over the learning curve at 0% to 1.4%. Future studies will need to determine whether this finding is generalizable to others.

LEVEL OF EVIDENCE

Level III, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.

Lumbar transpedicular implant failure: a clinical and surgical challenge and its radiological assessment

STUDY DESIGN

It is a multicenter, controlled case study review of a big scale of pedicle-screw procedures from January 2000 to June 2010. The outcomes were compared to those with no implant failure.

PURPOSE

The purpose of this study was to review retrospectively the outcome of 100 patients with implant failure in comparison to 100 control-patients, and to study the causes of failure and its prevention.

OVERVIEW OF LITERATURE

Transpedicular fixation is associated with risks of hardware failure, such as screw/rod breakage and/or loosening at the screw-rod interface and difficulties in the system assembly, which remain a significant clinical problem. Removal or revision of the spinal hardware is often required.

METHODS

Two hundred patients (88 women, 112 men) were divided into 2 major groups, with 100 patients in group I (implant failure group G1) and 100 patients in group II (successful fusion, control group G2). We subdivided the study groups into two subgroups: subgroup a (single-level instrumented group) and subgroup b (multilevel instrumented group). The implant status was assessed based on intraoperative and follow-up radiographs.

RESULTS

Implant failure in general was present in 36% in G1a, and in 64% in G1b, and types of implant failure included screw fracture (34%), rod fracture (24%), rod loosening (22%), screw loosening (16%), and failure of both rod and screw (4%). Most of the failures (90%) occurred within 6 months after surgery, with no reported cases 1 year postoperatively.

CONCLUSIONS

We tried to address the problem and study the causes of failure, and proposed solutions for its prevention.

CT provides precise size assessment of implanted titanium alloy pedicle screws

BACKGROUND

After performing instrumented spinal fusion with pedicle screws, postoperative imaging using CT to assess screw position may be necessary. Stainless steel implants produce significant metal artifact on CT, and the degree of distortion is at least partially dependent on the cross-sectional area of the implanted device. If the same effect occurs with titanium alloy implants, ability to precisely measure proximity of screws to adjacent structures may be adversely affected as screw size increases.

QUESTIONS/PURPOSES

We therefore asked whether (1) CT provides precise measurements of true screw widths; and (2) precision degrades based on the size of the titanium implant imaged.

METHODS

CT scans performed on 20 patients after instrumented spinal fusion for scoliosis were reviewed. The sizes of 151 titanium alloy pedicle screws were measured and compared with known screw size. The amount of metal bloom artifact was determined for each of the four screw sizes. ANOVA with Tukey's post hoc test were performed to evaluate differences in scatter, and Spearman's rho coefficient was used to measure relationship between screw size and scatter.

RESULTS

All screws measured larger than their known size, but even with larger 7-mm screws the size differential was less than 1 mm. The four different screw sizes produced scatter amounts that were different from each other (p < 0.001).The amount of metal bloom artifact produced does increase as the size of the screw increases (rho = 0.962, p < 0.001).

CONCLUSIONS

CT of titanium alloy pedicle screws produces minimal artifact, thus making this the preferred imaging modality to assess screw position after surgery. Although the amount of artifact increases with the volume of titanium present, the degree of distortion is minimal and is usually less than 1 mm.

Radiographic evaluation of the use of transverse traction device in vertebral arthrodesis for degenerative diseases

OBJECTIVE: Perform radiographic analysis of the use of Transverse Traction Device (DTT) with respect to fusion rate in patients submitted to vertebral arthrodesis for degenerative lumbar diseases. METHODS: We selected x-ray images on anteroposterior, lateral and oblique views and with maximum flexion and extension dynamics of 23 patients submitted to posterolateral arthrodesis of the lumbar spine with a minimum follow-up period of six months. The images were evaluated and classified by the Linovitz's system by two spine surgeons. RESULTS: We evaluated the radiographs of 23 patients after the minimum postoperative period of 6 months and of these, 11 have used DTT. With regard to the consolidation rate, seven patients (63.6%) in the group of DTT were classified as fusion as well as six patients (50%) who were not submitted to the treatment. There was no statistical difference between the groups regarding the consolidation rate. CONCLUSION: The use of transverse traction device in this study showed no significant difference in the rate of consolidation in radiographic evaluation. Studies on the effective participation of this device in the stability of pedicle fixation systems are still lacking in the literature.

Comparison study of the pullout strength of conventional spinal pedicle screws and a novel design in full and backed-out insertions using mechanical tests

Recently, new pedicle screw designs have been developed. However, these designs’ performances are still unclear, especially when backed out after insertion. The objective of this study was to investigate the performances of different screw designs when backed out from full insertion. Seven conventional designs of the pedicle screw and one novel design were inserted into polyurethane foam (0.32 g/cm3). All screws were first fully inserted (43 mm) and were backed out 360°. Axial pullout tests were performed and the reaction force was measured. The results showed that the conical screw of type 1 with a small inner diameter provided the highest pullout strength in both full insertion and backed-out insertion (2401.85 and 2169.82 N, respectively). However, this screw’s pullout strength significantly decreased (9.7%) when backed out from full insertion. There was no significant difference between the conical screw of type 1 with a small inner diameter and double duo core screw ( p > 0.01) in backed-out insertion. The cylindrical screw with a small diameter, dual inner core screw and double dual core screw also provided good results in both full insertion (2115.44, 2182.99 and 2226.93 N, respectively) and backed-out conditions (2065.80, 2014.28 and 1941.29 N, respectively). The increased pullout strength of the conical design could be due to the effect of bone compaction. However, the screw exhibited less consistent pullout strength when backed out when compared with the other designs. The conical screw should be inserted to the precise position without turning back, especially in osteoporosis patients. The dual inner core screw and double dual core screw could provide greater stability in both conditions. Care should be taken when using both the cylindrical screw with a small thread depth and the dual outer core screw.

Clinical evaluation of the polymethylmethacrylate-augmented thoracic and lumbar pedicle screw fixation guided by the three-dimensional navigation for the osteoporosis patients

PURPOSE

To evaluate the safety and efficacy of three-dimensional (3D) navigation-guided polymethylmethacrylate (PMMA)-augmented thoracic and lumbar pedicle screw fixation for the osteoporotic patients.

METHODS

27 consecutive osteoporosis patients with a variety of spinal disorders who underwent 3D navigation-guided PMMA-augmented pedicle screw fixation were evaluated clinically and radiologically in the perioperative and 1-year follow-up period. The improvement of Japanese Orthopaedic Association (JOA) scores was analyzed. PMMA leakage and other complications were inspected intraoperatively and postoperatively. Screw loosening and bone fusion were evaluated radiographically during follow-up.

RESULTS

8 patients had thoracic and lumbar fractures; 18 patients had degenerative spinal disorders; one patient had revision surgery. One patient died of postoperative pneumonia. Each of the other 26 patients was followed up regularly at 3, 6, 12 and 18 months postoperatively. The mean therapeutic improvement rate is 39.6% evaluated by JOA scores. 2 patients (7.4%) had leakage into the spinal canal in front of the posterior longitudinal ligament and two patients (7.4%) had leakage into the prevertebral soft tissue inspected by the postoperative CT scans. No pedicle cortex breach and cement leakage surrounding pedicle cortex were observed. None of patients complained of dyspnoea and showed evidence of pulmonary embolism. Bone fusions were found in 20 patients (bony fusion rate 76.9%) at the 12-month follow-up and no screw loosening occurs.

CONCLUSION

The results show favorable outcome using 3D navigation-guided PMMA-augmented thoracic and lumbar pedicle screw fixation for the osteoporosis patients both clinically and radiologically.