Lumbar pedicle screw fixation with cortical bone trajectory: A review from anatomical and biomechanical standpoints

Cortical Trajectory versus Traditional Pedicle Screw Trajectory in Open Transforaminal Lumbar Interbody Fusion: Meta-Analysis of Complications and Clinical Outcomes

BACKGROUND

Lumbar degenerative disease imposes a substantial burden on global health care expenditures. Transforaminal lumbar interbody fusion (TLIF) using either traditional trajectory (TT) pedicle screws or cortical bone trajectory (CBT) pedicle screws has become increasingly common. This meta-analysis evaluated outcomes and safety of open TLIF with TT compared with CBT.

METHODS

PubMed, Cochrane, and Google Scholar were searched up to April 2024. The studied outcomes included complications, revision surgeries, operating room time, estimated blood loss, length of hospital stay (LOS), incision length, Visual Analog Scale, Oswestry Disability Index, and Japanese Orthopedic Association.

RESULTS

This meta-analysis included 5 studies; 770 patients undergoing TLIF were included, with 415 in the CBT group and 355 in the TT group. No statistically significant differences were found in the rate of overall complications, including specific complications, rate of revision surgeries, patient-reported outcome measures, operating room time, and estimated blood loss. However, the CBT group demonstrated shorter LOS (P = 0.05) and shorter incision lengths (P < 0.001) compared with the TT group.

CONCLUSIONS

TT and CBT in TLIF procedures demonstrated comparable rates of complications, reoperations, and patient-reported outcome measures. Despite similar operating room times and estimated blood loss, the CBT group exhibited shorter incision lengths and shorter LOS than the TT group. Both CBT and TT pedicle screws are safe and effective options for TLIF. There are potential benefits to CBT such as shorter incision and LOS, although TT remains an essential tool for spinal instrumentation techniques.

A 3D-CT Study of the Cortical Bone Trajectory Screw Placement Parameters Based on Lumbar CT

OBJECTIVE

The cortical bone trajectory (CBT) technology is an effective substitute for traditional pedicle screw (PS) technology. However, there is still controversy about the CBT screw technology placement strategy. The objective of this study was to simulate cortical screw placement with the help of three-dimensional (3D) software, to discuss the differences in screws between genders and vertebral segments, and to explore a safer and more efficient strategy for cortical screw placement.

METHODS

Mimics Medical software was used to construct a 3D model of the lumbar spine, and the placement of CBT screws was simulated. The volume of each vertebral body from L1 to L5, the pedicle isthmus height (IH), the pedicle isthmus width (IW), and the sagittal vertebral distance (SAVD) were measured. The transverse distance (TD) and the longitudinal distance (LD) between the ideal starting point (SP) and the clinical SP (the intersection Q of the midline of the superior articular process and the horizontal line 1 mm below the transverse process) were measured. The cephalad angle (CA), lateral angle (LA), maximum screw diameter (MSD), maximum screw length (MSL) of each trajectory of the L1 to L5 vertebral bodies, and the percentage of the screw insertion depth (PSID) into the vertebral body were measured. Data were statistically analyzed using Student's t-test, one-way analysis of variance (ANOVA), and Tukey's test.

RESULTS

Vertebral anatomical parameters and CBT screw parameters differed between males and females. Female patients had lower IH, IW, SAVD, CA, LA, MSD, and MSL than males. IH was greatest in L1 (male, 17.81 mm; female, 16.12 mm) and the smallest in L5 (male, 14.11 mm; female, 13.05 mm). IW was smallest in L1 (male, 8.89 mm; female, 7.37 mm) and greatest in L5 (male, 16.59 mm; female, 15.43 mm). The MSD of males was smallest in L1 (6.05 mm) and greatest in L3 (7.06 mm); the MSD of females was smallest in L1 (5.13 mm) and greatest in L4 (6.64 mm). MSL was greatest at L3 (male, 33.63 mm; female, 32.28 mm) and smallest at L5 (male, 31.25 mm; female, 29.97 mm). CA was smallest in L1 (male, 22.80°; female, 21.92°) and greatest in L3 (male, 25.29°; female, 24.33°). LA was smallest in L1 (male 12.37°, female 11.27°) and greatest in L5 (male 13.56°, female 12.96°). Among the males, TD was smallest at L1 (-0.51 mm) and greatest at L5 (1.37 mm), while LD was greatest at L2 (3.46 mm) and smallest at L5 (2.40 mm). In females, TD was greatest at L1 (0.12 mm) and smallest at L3 (-0.51 mm), while LD was greatest at L1 (3.69 mm) and smallest at L5 (2.08 mm). In the overall sample, the incidence of SAVD and PSID gradually increased from L1 to L5.

CONCLUSION

The optimal screw placement strategy for CBT screws varies significantly according to sex and vertebral body segments, particularly noting the specificity of screw placement at L5. The optimal screw placement strategy should be selected based on the patient's sex and segment characteristics before surgery to maximize the safety and accuracy of CBT screw placement.

Comparison of No Tap (two-step) and tapping robotic assisted cortical bone trajectory screw insertion

Workflow for cortical bone trajectory (CBT) screws includes tapping line-to-line or under tapping by 1 mm. We describe a non-tapping, two-step workflow for CBT screw placement, and compare the safety profile and time savings to the Tap (three-step) workflow. Patients undergoing robotic assisted 1-3 level posterior fusion with CBT screws for degenerative conditions were identified and separated into either a No-Tap or Tap workflow. Number of total screws, screw-related complications, estimated blood loss, operative time, robotic time, and return to the operating room were collected and analyzed. There were 91 cases (458 screws) in the No-Tap and 88 cases (466 screws) in the Tap groups, with no difference in demographics, revision status, ASA grade, approach, number of levels fused or diagnosis between cohorts. Total robotic time was lower in the No-Tap (26.7 min) versus the Tap group (30.3 min, p = 0.053). There was no difference in the number of malpositioned screws identified intraoperatively (10 vs 6, p = 0.427), screws converted to freehand (3 vs 3, p = 0.699), or screws abandoned (3 vs 2, p = 1.000). No pedicle/pars fracture or fixation failure was seen in the No-Tap cohort and one in the Tap cohort (p = 1.00). No patients in either cohort were returned to OR for malpositioned screws. This study showed that the No-Tap screw insertion workflow for robot-assisted CBT reduces robotic time without increasing complications.

Radiation Exposure During Lumbar Interbody Fusion Surgery Can Be Reduced by Using a Three-Dimensional Patient-Specific Template Guide

BACKGROUND

The use of posterior lumber interbody fusion (PLIF) using cortical bone trajectory (CBT) with a patient-specific 3D template guide is increasingly widespread. To our knowledge, no studies have extensively evaluated the reduction of radiation exposure when using patient-specific drill template guides. The purpose of this study is to compare the intra-operative radiation dose and surgeon's exposure to radiation in CBT-PLIF when using a patient-specific drill guide with that in traditional minimally invasive (MIS)-PLIF.

METHODS

In this observational study, we retrospectively compared data from five patients who were treated with single-level CBT-PLIF using a patient-specific drill guide (G group) and five patients who were treated with single-level traditional MIS-PLIF (M group). We compared the surgical time, surgeon's exposure to radiation, and intra-operative radiation time and dose between the two groups of patients.

RESULTS

The mean age of the patients was 67.0 years in the M group and 74.2 years in the G group. The average surgical time was 242.8 min in the M group and 189.6 min in the G group (p = 0.020). The surgeon's exposure to radiation was 373.7 µSv in the M group and 81.75 µSv in the G group at chest level outside the protector (p = 0.00092); 42.0 µSv (M group) and 3.6 µSv (G group) at chest level inside the protector (p = 0.0000062); and 4.33 µSv (M group) and 1.20 µSv (G group) at the buttocks of the surgeon (p = 0.0013). Radiation time was 269.8 s (M group) and 56.6 s (G group) (p = 0.0097), and radiation dose was 153.7 mGy (M group) and 30.42 mGy (G group) (p = 0.00057).

CONCLUSION

The patient-specific drill template guide is an invaluable tool that facilitates the safe insertion of CBT screws with a low radiation dose from the outset.

Biportal endoscopic-assisted cortical bone trajectory screw placement and lumbar interbody fusion

BACKGROUND

Endoscopically assisted screw fixation with lumbar interbody fusion is rarely performed. We succeeded in implanting the cortical bone trajectory (CBT) screws under the guidance of unilateral biportal endoscopy (UBE).

METHOD

We attempted endoscopically assisted screw fixation in a patient with degenerative spondylolisthesis. Through a third portal, ipsilateral CBT screws were implanted without complications.

CONCLUSIONS

We successfully performed unilateral biportal endoscopic lumbar interbody fusion (ULIF) with CBT and reversed CBT screws. Compared with percutaneous pedicle screw (PPS) placement, this procedure is a minimally invasive, endoscopic alternative that allows precise screw placement.

Comparison of safety and efficacy of posterior lumbar interbody fusion (PLIF) and modified transforaminal lumbar interbody fusion (M-TLIF) in the treatment of single-segment lumbar degenerative diseases

OBJECTIVE

To compare modified transforaminal lumbar interbody fusion (M-TLIF) with posterior lumbar interbody fusion (PLIF) in the treatment of single-segment lumbar degenerative disorders in order to assess its safety and effectiveness.

METHODS

From January 2016 to January 2021, 74 patients who received single-segment M-TLIF were examined. A total of 74 patients having single-segment PLIF during the same time period were included in a retrospective controlled study using the same inclusion and exclusion criteria. The two groups were compared in terms of the fusion rate, the Oswestry disability index (ODI), the visual analogue scale of low back pain (VAS), the perioperative condition, the postoperative complications, and the postoperative neighbouring segment degeneration.

RESULTS

All patients had surgery satisfactorily and were monitored for at least a year afterwards. The baseline values for the two groups did not significantly differ. The interbody fusion rate between PLIF (98.65%) and M-TLIF (97.30%) was not significantly different. In the follow-up, the M-TLIF group's VAS score for low back and leg pain was lower than that of the PLIF group. The ODI score of the M-TLIF group was lower than that of the PLIF group at 7 days and 3 months following surgery. Both groups' post-op VAS and ODI scores for low back and leg pain were much lower than those from before the procedure. In M-TLIF group, the operation time, drainage tube extraction time, postoperative bed rest time and hospital stay time were shorter, and the amount of intraoperative blood loss was less. Compared with those before operation, the height of intervertebral space and intervertebral foramen were significantly increased in both groups during postoperative follow-up (P < 0.05). The postoperative complications and adjacent segment degeneration of M-TLIF were significantly lower than those of PLIF.

CONCLUSIONS

M-TLIF is a safe and effective treatment for lumbar degenerative disorders, with a high fusion rate and no significant difference between M-TLIF and PLIF. M-TLIF's efficacy and safety are comparable to that of PLIF, particularly in terms of early relief of low back pain and improvement in quality of life following surgery. Therefore, M-TLIF technology can be popularized and applied in clinic.

The Cortical Bone Trajectory Screw Technique Assisted by the Mazor Renaissance Robotic System as a Salvage Strategy for Failed Lumbar Spine Surgery: Technical Note and Case Series

Purpose

The objective of this study was to describe the Mazor Renaissance robotic system-assisted CBT (cortical bone trajectory) screw technique as a salvage strategy for failed lumbar spine surgery.

Patients and Methods

Between January 2018 and June 2022, 7 patients underwent salvage surgery with the CBT screw fixation technique assisted by the Mazor Renaissance robot system in our institution. Intraoperative observations were recorded for blood loss, duration of operation, and fluoroscopy time. Complications related to CBT screws were also recorded. The accuracy of CBT screws was recorded in accordance with the modified Gertzbein-Robbins classification. The JOA (Japanese Orthopedic Association) score for low back pain was used to evaluate surgical outcomes.

Results

A total of 26 CBT screws were placed in 7 patients, including 4 females and 3 males. Three patients underwent ASD (adjacent segment disease) and four patients underwent lumbar union failure with loose or compromised PSs (pedicle screws). The mean operation time was 129.29 ± 32.97 minutes, the mean blood loss was 180 ± 52.60 mL, and the mean intraoperative fluoroscopy time was 14.29 ± 3.15 s. All screws were clinically acceptable according to the Gertzbein-Robbins classification. There were no complications related to CBT screws in any of the cases. The JOA scores for low back pain of all patients were significantly improved at the final follow-up.

Conclusion

The CBT screw fixation technique supplemented the traditional PS fixation technique, which can be performed as a salvage strategy for failed lumbar spine surgery and achieved good clinical results. The spinal robot was very helpful in evaluating pedicle size and determining CBT screw direction, especially in a previously instrumented lumbar pedicle.

Multi-rod fixation in spinal neuroarthropathy: a novel surgical technique

Spinal cord injury (SCI) leads to compromised biomechanical stability due to impaired neuroprotection. This may trigger deformity and destruction of multiple segments of the spine which is known as spinal neuroarthropathy (SNA) or Charcot arthropathy. Surgical treatment of SNA is highly demanding in terms of reconstruction, realignment, and stabilization. In particular, construct failure due to the combination of high shear forces and reduced bone mineral density in the lumbosacral transition zone is a frequent complication in SNA. Notably, up to 75% of SNA patients need multiple revisions within the first year after surgery in order to achieve successful bony fusion. The purpose of this technical report is to present a novel surgical approach with higher overall construct stability to efficiently treat SNA and avoiding repetitive revisions. The new technique of triple rod stabilisation of the lumbosacral transition zone in combination with the introduction of tricortical laminovertebral (TLV) screws is demonstrated in three patients with complete SCI of the thoracic spinal cord. After surgery all patients reported an improvement of the Spinal Cord Independence Measure III (SCIM III) and none of the reported cases showed construct failure within an at least 9 months follow up period. Although TLV screws violate the integrity of the spinal canal, there were no complications with regard to cerebral spinal fluid fistulas and/or arachnopathies so far. The new concept of triple rod stabilization in combination with TLV screws provides improved construct stability in patients with SNA and thus could help to reduce revision and complications rates and improve patient outcome in this disabling degenerative disease.

Biomechanical Analysis of Cortical Bone Trajectory Screw Versus Bone Cement Screw for Fixation in Porcine Spinal Low Bone Mass Model

STUDY DESIGN

A prospective study of in vitro animal.

OBJECTION

To compare the biomechanics of cortical bone trajectory screw (CBT) and bone cement screw (BC) in an isolated porcine spinal low bone mass model.

SUMMARY OF BACKGROUND DATA

The choice of spinal fixation in patients with osteoporosis remains controversial. Is CBT better than BC? Research on this issue is lacking.

METHODS

Ten porcine spines with 3 segments were treated with EDTA decalcification. After 8 weeks, all the models met the criteria of low bone mass. Ten specimens were randomly divided into groups, group was implanted with CBT screw (CBT group) and the other group was implanted with bone cement screw (BC group). The biomechanical material testing machine was used to compare the porcine spine activities of the two groups in flexion, extension, bending, and axial rotation, and then insertional torque, pull-out force, and anti-compression force of the 2 groups were compared. Independent sample t test was used for comparison between groups.

RESULTS

Ten 3 segments of porcine spine models with low bone mass were established, and the bone mineral density of all models was lower than 0.75 g/cm 2 . There is no difference between the CBT and BC groups in flexion, extension, bending, and axial rotation angle, P >0.05. However, there were significant differences between the 2 groups and the control group, with P ＜0.01. The 2 groups significantly differed between the insertional torque ( P =0.03) and the screw pull-out force ( P =0.021). The anti-compression forces between the 2 groups have no significant difference between the two groups ( P =0.946).

CONCLUSIONS

The insertional torque and pull-out force of the CBT were higher than those of the BC in the isolated low bone porcine spine model. The range of motion and anti-compression ability of the model was similar between the 2 fixation methods.

Residual motion of cortical versus pedicle screw constructs after decompression, interbody fusion and cross-link augmentation

PURPOSE

To compare the residual range of motion (ROM) of cortical screw (CS) versus pedicle screw (PS) instrumented lumbar segments and the additional effect of transforaminal interbody fusion (TLIF) and cross-link (CL) augmentation.

METHODS

ROM of thirty-five human cadaver lumbar segments in flexion/extension (FE), lateral bending (LB), lateral shear (LS), anterior shear (AS), axial rotation (AR), and axial compression (AC) was recorded. After instrumenting the segments with PS (n = 17) and CS (n = 18), ROM in relation to the uninstrumented segments was evaluated without and with CL augmentation before and after decompression and TLIF.

RESULTS

CS and PS instrumentations both significantly reduced ROM in all loading directions, except AC. In undecompressed segments, a significantly lower relative (and absolute) reduction of motion in LB was found with CS 61% (absolute 3.3°) as compared to PS 71% (4.0°; p = 0.048). FE, AR, AS, LS, and AC values were similar between CS and PS instrumented segments without interbody fusion. After decompression and TLIF insertion, no difference between CS and PS was found in LB and neither in any other loading direction. CL augmentation did not diminish differences in LB between CS and PS in the undecompressed state but led to an additional small AR reduction of 11% (0.15°) in CS and 7% (0.05°) in PS instrumentation.

CONCLUSION

Similar residual motion is found with CS and PS instrumentation, except of slightly, but significantly inferior reduction of ROM in LB with CS. Differences between CS and PS in diminish with TLIF but not with CL augmentation.

Residual motion of different posterior instrumentation and interbody fusion constructs

PURPOSE

To elucidate residual motion of cortical screw (CS) and pedicle screw (PS) constructs with unilateral posterior lumbar interbody fusion (ul-PLIF), bilateral PLIF (bl-PLIF), facet-sparing transforaminal lumbar interbody fusion (fs-TLIF), and facet-resecting TLIF (fr-TLIF).

METHODS

A total of 35 human cadaver lumbar segments were instrumented with PS (n = 18) and CS (n = 17). Range of motion (ROM) and relative ROM changes were recorded in flexion/extension (FE), lateral bending (LB), axial rotation (AR), lateral shear (LS), anterior shear (AS), and axial compression (AC) in five instrumentational states: without interbody fusion (wo-IF), ul-PLIF, bl-PLIF, fs-TLIF, and fr-TLIF.

RESULTS

Whereas FE, LB, AR, and AC noticeably differed between the instrumentational states, AS and LS were less prominently affected. Compared to wo-IF, ul-PLIF caused a significant increase in ROM with PS (FE + 42%, LB + 24%, AR + 34%, and AC + 77%), however, such changes were non-significant with CS. ROM was similar between wo-IF and all other interbody fusion techniques. Insertion of a second PLIF (bl-PLIF) significantly decreased ROM with CS (FE -17%, LB -26%, AR -20%, AC -51%) and PS (FE - 23%, LB - 14%, AR - 20%, AC - 45%,). Facet removal in TLIF significantly increased ROM with CS (FE + 6%, LB + 9%, AR + 17%, AC of + 23%) and PS (FE + 7%, AR + 12%, AC + 13%).

CONCLUSION

bl-PLIF and TLIF show similarly low residual motion in both PS and CS constructs, but ul-PLIF results in increased motion. The fs-TLIF technique is able to further decrease motion compared to fr-TLIF in both the CS and PS constructs.

Percutaneous cortical bone trajectory screw fixation versus traditional open pedicle screw fixation for type A thoracolumbar fractures without neurological deficit

Retrospective matched-cohort comparative study. Cortical bone trajectory screw (CBT) technique is a new insertion technique in terms of fixation strength and less invasiveness. The purposes of this study were to compare the clinical and radiological outcomes of percutaneous CBT fixation (PCBT) with traditional open posterior pedicle screw fixation (OPPS) technique. Between September 2019 and October 2020, patients undergoing posterior stabilization were matched for age, sex, diagnosis, fractured level, and AO classification. 24 control patients with OPPS were identified and appropriately matched to 24 consecutive patients with PCBT technique. Clinical outcomes and radiographic assessments including vertebral wedge angle (VWA) and sagittal index were recorded and compared between the two groups. Incision length, intraoperative blood loss and hospital stay in the PCBT group were significantly better than the OPPS group (P < 0.05). The VAS scores 5 days after operation for PCBT patients were significantly lower than those for OPPS patients (P = 0.003), but these differences lost significance at last follow-up. There was no significant difference in VWA and sagittal index between OPPS and PCBT group (P > 0.05). While no complications were noted in the PCBT group, there were four cases with complications in the traditional OPPS group. The present study showed that PCBT is a safe and feasible method for the treatment of thoracolumbar fractures without neurological deficits. This new surgical treatment was more minimally invasive, yet yielded equivalent or superior clinical and radiographic outcomes compared to the traditional open pedicle screw fixation surgery.

Application of the cortical bone trajectory technique in posterior lumbar fixation

The cortical bone trajectory (CBT) is a novel technique in lumbar fixation and fusion. The unique caudocephalad and medial-lateral screw trajectories endow it with excellent screw purchase for vertebral fixation via a minimally invasive method. The combined use of CBT screws with transforaminal or posterior lumbar interbody fusion can treat a variety of lumbar diseases, including spondylolisthesis or stenosis, and can also be used as a remedy for revision surgery when the pedicle screw fails. CBT has obvious advantages in terms of surgical trauma, postoperative recovery, prevention and treatment of adjacent vertebral disease, and the surgical treatment of obese and osteoporosis patients. However, the concept of CBT internal fixation technology appeared relatively recently; consequently, there are few relevant clinical studies, and the long-term clinical efficacy and related complications have not been reported. Therefore, large sample and prospective studies are needed to further reveal the long-term complications and fusion rate. As a supplement to the traditional pedicle trajectory fixation technique, the CBT technique is a good choice for the treatment of lumbar diseases with accurate screw placement and strict indications and is thus deserving of clinical recommendation.

Cortical Bone Trajectory Pedicle Screw Fixation in Surgical Treatment of Monosegmental Pyogenic Lumbar Spondylodiskitis

BACKGROUND AND STUDY OBJECT

 Pedicle screw fixation has been widely used in surgical treatment for infective lumbar spondylodiskitis to prevent instability and deformity. The cortical bone trajectory pedicle screw (CBTPS) fixation is a minimally invasive posterior spinal fixation system that runs from the pedicle's entry point of the caudiomedial region toward the cephalad-divergent direction. Successful results with CBTPS fixation have been reported to treat degenerative and osteoporotic spinal diseases. This study aims to investigate the clinical feasibility of CBTPS in the surgical treatment of pyogenic lumbar spondylodiskitis.

PATIENT AND METHODS

 We retrospectively retrieved 20 consecutive patients from two academic centers who were surgically treated for monosegmental lumbar pyogenic spondylodiskitis. The primary surgical treatment was the anterior lumbar interbody fusion with decompression, debridement, and reconstruction using an autogenous iliac strut bone graft. One to 2 weeks after the primary surgery, patients underwent a second surgery for posterior instrumentation using conventional pedicle screws (CPS; group I) and CBTPS (group II). Radiographic parameters of the deformity angle at the fusion segment and clinical parameter of visual analog scale (VAS) scores were assessed preoperatively, postoperatively, and at the last follow-up.

RESULTS

 There were 10 patients in each group. The mean follow-up periods of groups I and II were 51.10 ± 6.95 and 28.60 ± 9.31 months, respectively. Intergroup analysis indicated the two groups area age-matched (p = 0.38), but initial C-reactive protein (CRP; mg/dL, p = 0.04), CRP normalization (months, p = 0.00), and follow-up duration (months, p = 0.00) were heterogeneous. Meanwhile, deformity angles (segmental lordosis) between the two groups were not significantly different preoperatively (p = 0.25), postoperatively (p = 0.13), and at last follow-up (p = 0.38). The intragroup analysis indicated a significant postoperative increase of lordosis in both group I and II (p = 0.00 and 0.04, respectively) with subsequent subsidence. Lordosis remained increased at the last follow-up with or without significance (group I, p = 0.02; group II, p = 0.62). Both groups showed significant improvement in VAS scores (group I, p = 0.00; group II, p = 0.00).

CONCLUSION

 In monosegmental lumbar spondylodiskitis, posterior stabilization of the anterior strut bone graft by CBTPS and CPS was comparable via the radiographic parameter of segmental lordosis or deformity angle. Our observation suggests the clinical feasibility of CBTPS in the treatment of relatively mild monosegmental pyogenic lumbar spondylodiskitis.

Radiological and clinical outcomes of midline lumbar fusion on sagittal lumbar-pelvic parameters for degenerative lumbar diseases

BACKGROUND

Improving the sagittal lumbar-pelvic parameters after fusion surgery is important for improving clinical outcomes. The impact of midline lumbar fusion (MIDLF) on sagittal lumbar-pelvic alignment for the management of degenerative lumbar diseases is still unknown.

AIM

To analyze the effects of short-segment MIDLF and minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) on sagittal lumbar-pelvic parameters.

METHODS

We retrospectively analyzed 63 patients with degenerative lumbar diseases who underwent single-segment MIDLF or MIS-TLIF. The imaging data of patients were collected before surgery and at the final follow-up. The radiological sagittal parameters included the lumbar lordosis (LL), lower LL, L4 slope (L4S), L5 slope (L5S), L5 incidence (L5I), L1 axis and S1 distance (LASD), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), and PI-LL mismatch (PI-LL). Additionally, the clinical outcomes, including lower back and leg pain visual analog scale (VAS) and Oswestry disability index (ODI) scores, were also analyzed.

RESULTS

In both groups, LL and Lower LL significantly increased, while L5I and LASD significantly decreased at the final follow-up compared to that recorded prior to operation (P < 0.05). In the MIDLF group, L4S significantly decreased compared to that recorded prior to operation (P < 0.05), while the mean SS significantly increased and the PT significantly decreased compared to that recorded prior to operation (P < 0.05). In the MIS-TLIF group, SS slightly increased and the mean PT value decreased compared to that recorded prior to operation, but without a statistically significant difference (P > 0.05). However, the PI-LL in both groups was significantly reduced compared to that recorded prior to operation (P < 0.05). There was no significant difference in the sagittal lumbar-pelvic parameters between the two groups prior to operation and at the final follow-up (P > 0.05). In addition, the change in sagittal lumbar-pelvic parameters did not differ significantly, except for ΔLASD within the two groups (P > 0.05). The mean lower back and leg pain VAS and ODI scores in both groups were significantly improved three months after surgery and at the final follow-up. Though the mean ODI score in the MIDLF group three months after surgery was slightly higher than that in the MIS-TLIF group, there was no significant difference between the two groups at the final follow-up.

CONCLUSION

Short-segment MIDLF and MIS-TLIF can equally improve sagittal lumbar parameters such as LL, Lower LL, L5I, and LASD in the treatment of lumbar degenerative diseases. However, MIDLF had a larger impact on pelvic parameters than MIS-TLIF.

A nomogram for predicting screw loosening after single-level posterior lumbar interbody fusion utilizing cortical bone trajectory screw: A minimum 2-year follow-up study

Purpose

This study aims to investigate the risk factors for screw loosening after single-level posterior lumbar interbody fusion (PLIF) utilizing cortical bone trajectory (CBT) screw and establish a nomogram for predicting screw loosening.

Methods

A total of 79 patients (316 screws) who underwent single-level PLIF with CBT screw were included in the study. Preoperative, postoperative, and final follow-up demographic data, surgical data, and radiographic parameters were documented and analyzed to identify risk factors, and a predictive nomogram was established for screw loosening. The nomogram was assessed by concordance index (C-index), calibration plot, decision curve analysis (DCA), and internal validation.

Results

The incidence of screw loosening was 26.6% in 79 patients and 11.4% in 316 screws. Multifactorial regression analysis confirmed that fixed to S1 (FS1, OR = 3.82, 95% CI 1.12-12.71, P = 0.029), the coronal angle of the screw (CA, OR = 1.07, 95% CI 1.01-1.14, P = 0.039), and cortical bone contacted layers (CBCLs, OR = 0.17, 95% CI 0.10-0.29, P < 0.001) were risk factors and incorporated in the nomogram for predicting screw loosening after single-level PLIF with a CBT screw. The C-index of the nomogram was 0.877 (95% CI 0.818-0.936), which demonstrated good predictive accuracy. The calibration plot indicated an acceptable calibration of the nomogram that also had a positive benefit in guiding treatment decisions.

Conclusion

FS1, CA, and CBCLs are identified to be significant risk factors for screw loosening after single-level PLIF with the CBT technique. The nomogram we have established can be used to predict screw loosening and contribute to surgical decisions.

A Novel Calcium Phosphate-Based Nanocomposite for Augmentation of Cortical Bone Trajectory Screw Fixation

Purpose

To evaluate the effect of cement augmentation of cortical bone trajectory (CBT) screws using a novel calcium phosphate–based nanocomposite (CPN).

Material and Methods

CBT screws were placed into cadaveric lumbar vertebrae. Depending on the material used for augmentation, they were divided into the following three groups: CPN, polymethylmethacrylate (PMMA), and control. Radiological imaging was used to evaluate the cement dispersion. Biomechanical tests were conducted to measure the stability of CBT screws. A rat cranial defect model was used to evaluate biodegradation and osseointegration of the CPN.

Results

After cement augmentation, the CPN tended to disperse into the distal part of the screws, whereas PMMA remained limited to the proximal part of the screws (P < 0.05). As for cement morphology, the CPN tended to form a concentrated mass, whereas PMMA arranged itself as a scattered cement cloud, but the difference was not significant (P > 0.05). The axial pullout test showed that the average maximal pullout force (Fmax) of CPN-augmented CBT screws was similar to that of the PMMA group (CPN, 1639.56 ± 358.21 N vs PMMA, 1778.45 ± 399.83 N; P = 0.745) and was significantly greater than that of the control group (1019.01 ± 371.98 N; P < 0.05). The average torque value in the CPN group was higher than that in the control group (CPN, 1.51 ± 0.78 N∙m vs control, 0.97 ± 0.58 N∙m) and lower than that in the PMMA group (1.93 ± 0.81 N∙m), but there were no statistically significant differences (P > 0.05). The CPN could be biodegraded and gradually replaced by newly formed bone tissue after 12 weeks in a rat cranial defect model.

Conclusion

The biocompatible CPN could be a valuable augmentation material to enhance CBT screw stability.

A parametric investigation on traditional and cortical bone trajectory screws for transpedicular fixation

Background

Many studies have been conducted to compare traditional trajectory (TT) and cortical bone trajectory (CBT) screws; however, how screw parameters affect the biomechanical properties of TT and CBT screws, and so their efficacy remains to be investigated.

Methods

A finite element model was used to simulate screws with different trajectories, diameters, and lengths. Responses for implant and tissues at the adjacent and fixed segments were used as the comparison indices. The contact lengths and spanning areas of the inserted screws were defined and compared across the varieties.

Results

The trajectory and diameter had a greater impact on the responses from the implant and tissues than the length. The CBT has shorter length than the TT; however, the contact length and supporting area of the CBT within the cortical bone were 19.6%. and 14.5% higher than those of the TT, respectively. Overall, the TT and CBT were equally effective at stabilizing the instrumented segment, except for bending and rotation. The CBT experienced less adjacent segment compensations than the TT. With the same diameter and length, the TT was considerably less stressed than the CBT, especially for flexion and extension.

Conclusions

The CBT may provide less stress at adjacent segments compared with the TT. The CBT may provide more stiffer in osteoporotic segments than the TT due to greater contact with cortical bone and a wider supporting base between the paired screws. However, both entry point and insertion trajectory of the CBT should be carefully executed to avoid vertebral breach and ensure a stable cone-screw purchase.

Comparative outcomes of cortical bone trajectory screw fixation and traditional pedicle screws in lumbar fusion: A meta-analysis

BACKGROUND

Pedicular screws (PS) is often used in lumbar fusion. Cortical bone trajectory (CBT) is a novel technology in lumbar fusion with less clinical outcomes evidence. So we conduct a meta-analysis to compare the efficacy and safety between cortical bone trajectory screw fixation and traditional pedicle screws in lumbar fusion surgery.

METHODS

Multiple databases were searched for the articles about comparison of cortical bone trajectory (CBT) and traditional pedicle screws (PS) in lumbar fusion surgeries. The Meta-analysis was conducted by Revman 5.3 software. The following indicators were abstracted: visual analog scale (VAS) scores for back and leg pain, Oswestry Disability Index (ODI), Japanese Orthopedic Association (JOA), surgical duration, complications, and blood loss. The quality of the articles was assessed by the Newcastle-Ottawa Scale or Cochrane Handbook.

RESULTS

25 studies were included involving a total of 1735 patients. There is no difference in preoperative VAS scores, JOA, ODI, postoperative VAS scores and fusion rates. Besides, postoperative JOA(MD = 0.78, P = 0.02), ODI (MD = -2.09, P＝0.03), surgical duration(MD = -26.90, P = 0.02), complications(MD = 0.70, P = 0.03), and blood loss(MD = -85.27, P＝0.0009) showed greater improvement trends in CBT group than PS group with significant difference.

CONCLUSION

CBT reduced the rate of complications, surgical duration, blood loss, postoperative ODI and JOA scores. CBT technique with better postoperative outcomes achieved similar fusion rates compared with PS technique.

Finite element analysis of human lumbar vertebrae in internal fixation system model with different bone density trajectories

PURPOSE

To evaluate the biomechanics effect of modified cortical bone screw technique (MCBT) with other traditional internal fixation systems on lumbar osteoporotic wet specimen.

METHODS

Four different finite element models were established using CT data: (1) lumbar osteoporosis model without internal fixation system; (2) traditional pedicle screw technology (TT) model; (3) traditional cortical bone screw technology (CBT) model; (4) MCBT model. The changes of global displacement, intervertebral disc displacement of all models and internal fixation system Von Mises stress among the three models were compared under the same physiological load.

RESULTS

Compared with the other three models, the total displacement of the modified CBT screw model was the smallest, with the maximum displacement of 0.216 mm; The intervertebral disc displacement of the modified CBT screw model was the smallest, with the maximum displacement of 0.149 mm; the internal fixation system Von Mises stress of the modified CBT screw technique model was the largest compared with the other three models, The maximum Von Mises stress is 232.73 MPa.

CONCLUSION

Compared to traditional pedicle screw and traditional CBT, MCBT has better mechanical stability, and it is of certain clinical application value.

RELATIONSHIP BETWEEN VERTEBRAL VESSELS AND CORTICAL PATH SCREWS IN CORTICAL TRANSFIXATION

ABSTRACT Introduction: This study aims to evaluate the safety of using the cortical path screw with transfixation of the second cortical bone in relation to the vascular structures. Methods: This retrospective observational study (level of evidence: III, study of non-consecutive patients) analyzed data from the medical records of patients who underwent computed angiotomography scans of the abdomen at Hospital Mater Dei, measuring, in millimeters, the distance between the point of the lumbar vertebra considered the anatomical reference for the transfixation of the second cortical bone and the vascular structures adjacent to the spine (abdominal aorta, inferior vena cava, iliac vessels, segmental lumbar arteries). Results: Forty-eight patients were evaluated, with a mean age of 60 years (±8 years, 41-75), of whom 52% were male and 48% female. The measurements obtained between the pre-vertebral vessels and the possible screw exit points did not demonstrate contact in any of the vertebrae studied. Conclusions: The measurements obtained suggest the safety of using the cortical path screw transfixing the second cortical bone. Knowing the position of the vessels is essential to reduce intra- and postoperative complications related to spinal instrumentation. Level of evidence III; Study of non-consecutive patients.

Placement of Unilateral Cortical Bone Trajectory Screws in Previously Instrumented Pedicle without Removal of Existing Hardware for Adjacent Segment Disease

Adjacent segment disease (ASD) in the lumbar spine is a possible consequence in segments adjacent to a fusion. As the number of lumbar fusions in the United States increases, the rates of ASD will continue to climb. There are several treatment options for ASD with open decompression and extension of the fusion being common. However, need for exposure and removal of existing instrumentation can lead to increased operative times resulting in increasing blood loss and infection risk. The purpose of this paper is to describe a case report for unilateral cortical trajectory screw instrumentation, allowing for posterior instrumentation without having to remove the existing pedicle screws in the setting of ASD. Our technique can be done with standard c-arm fluoroscopy without the need for navigation.

Alternatives to Traditional Pedicle Screws for Posterior Fixation of the Degenerative Lumbar Spine

BACKGROUND

Traditional pedicle screws are currently the gold standard to achieve stable 3-column fixation of the degenerative lumbar spine. However, there are cases in which pedicle screw fixation may not be ideal. Due to their starting point lateral to the pars interarticularis, pedicle screws require a relatively wide dissection along with a medialized trajectory directed toward the centrally located neural elements and prevertebral vasculature. In addition, low bone mineral density remains a major risk factor for pedicle screw loosening, pullout, and pseudarthrosis. The purpose of this article is to review the indications, advantages, disadvantages, and complications associated with posterior fixation techniques of the degenerative lumbar spine beyond the traditional pedicle screws.

METHODS

Comprehensive literature searches of the PubMed, Scopus, and Web of Science databases were performed for 5 methods of posterior spinal fixation, including (1) cortical bone trajectory (CBT) screws, (2) transfacet screws, (3) translaminar screws, (4) spinous process plates, and (5) fusion mass screws and hooks. Articles that had been published between January 1, 1990, and January 1, 2020, were considered. Non-English-language articles and studies involving fixation of the cervical or thoracic spine were excluded from our review.

RESULTS

After reviewing over 1,700 articles pertaining to CBT and non-pedicular fixation techniques, a total of 284 articles met our inclusion criteria. CBT and transfacet screws require less-extensive exposure and paraspinal muscle dissection compared with traditional pedicle screws and may therefore reduce blood loss, postoperative pain, and length of hospital stay. In addition, several methods of non-pedicular fixation such as translaminar and fusion mass screws have trajectories that are directed away from or posterior to the spinal canal, potentially decreasing the risk of neurologic injury. CBT, transfacet, and fusion mass screws can also be used as salvage techniques when traditional pedicle screw constructs fail.

CONCLUSIONS

CBT and non-pedicular fixation may be preferred in certain lumbar degenerative cases, particularly among patients with osteoporosis. Limitations of non-pedicular techniques include their reliance on intact posterior elements and the lack of 3-column fixation of the spine. As a result, transfacet and translaminar screws are infrequently used as the primary method of fixation. CBT, transfacet, and translaminar screws are effective in augmenting interbody fixation and have been shown to significantly improve fusion rates and clinical outcomes compared with stand-alone anterior lumbar interbody fusion.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Pedicle screws versus cortical screws in posterior lumbar interbody fusion surgery for degenerative spondylolisthesis: a systematic review and meta-analysis

BACKGROUND CONTEXT

A few meta-analyses have compared conventional pedicle screws (PS) with cortical bone trajectory-pedicle screws (cortical screw [CS]) in posterior lumbar fusion surgery. However, these studies did not control for diagnosis, which has been shown to impact surgical outcomes.

PURPOSE

To compare PS with CS as a posterior fixation technique in posterior lumbar interbody fusion (PLIF) for degenerative spondylolisthesis (DS).

STUDY DESIGN

Systematic review and meta-analysis.

METHODS

We searched the Cochrane, Embase, and Medline databases for articles that compared postoperative outcomes between PS and CS for posterior stabilization in PLIF for DS with November 11, 2020, as the publication cutoff. The differences in primary and secondary outcome measures were calculated and analyzed for significance (p<.05). All the reported means were pooled.

RESULTS

A total of 916 publications were assessed; 5 studies met all the study criteria. The fusion rates between PS and CS groups were not significantly different (p=.41). Blood loss and operative time were significantly less in the CS group than the PS group (p=.04 and 0.02, respectively), but the length of stay was not significantly different (p=.08). The total complication rate was significantly less in CS group than that in PS group (p=.002). The rates of adjacent segment pathology (ASP) and operation for ASP in the CS group were significantly less than the PS group (p=.03 and .04, respectively).

CONCLUSIONS

Though CS and PS appear to have similar 1-year fusion rates and length of stay, there appears to lower blood loss and operative time with CS. Though encouraging, these findings were based on low-quality evidence from a small number of retrospective studies that are prone to bias.

Cortical Trajectory Screw Fixation in Lumbar Spine Surgery: A Review of the Existing Literature

Posterior lumbar fusion is a safe and effective surgical method for diseases, such as lumbar stenosis, spondylolisthesis, lumbar instability, spinal deformity, and tumor. Pedicle screw (PS) fixation was first introduced by Bouche and has been adopted as the gold standard for posterior lumbar fusion. Santoni and colleagues introduced a new methodological screw insertion technique that uses a cortical bone trajectory (CBT), described as that from a medial to lateral path in the transverse axial plane and caudal to the cephalad path in the sagittal plane through the pedicle for maximum contact of the screw with the cortical bone. Owing to the lower invasiveness, superior cortical bone contact, and reduced neurovascular injury incidence, the CBT technique has been widely used in posterior lumbar fusion; however, these advantages have not been proven in clinical/radiological and biomechanical studies. We designed the present study to review the existing evidence and evaluate the merit of CBT screw fixation. Six electronic databases were searched for relevant articles published in August 2020 using the search terms "cortical bone trajectory," "CBT spine," "CBT fixation," "cortical pedicle screws," and "cortical screws." Studies were analyzed and divided into the following groups: "biomechanics investigation," "surgical technique," and "clinical/radiological studies." Most studies compared CBT and PS fixation, and the CBT screw fixation method showed better or similar outcomes.

Head-mounted display augmented reality to guide pedicle screw placement utilizing computed tomography

PURPOSE

Augmented reality has potential to enhance surgical navigation and visualization. We determined whether head-mounted display augmented reality (HMD-AR) with superimposed computed tomography (CT) data could allow the wearer to percutaneously guide pedicle screw placement in an opaque lumbar model with no real-time fluoroscopic guidance.

METHODS

CT imaging was obtained of a phantom composed of L1-L3 Sawbones vertebrae in opaque silicone. Preprocedural planning was performed by creating virtual trajectories of appropriate angle and depth for ideal approach into the pedicle, and these data were integrated into the Microsoft HoloLens using the Novarad OpenSight application allowing the user to view the virtual trajectory guides and CT images superimposed on the phantom in two and three dimensions. Spinal needles were inserted following the virtual trajectories to the point of contact with bone. Repeat CT revealed actual needle trajectory, allowing comparison with the ideal preprocedural paths.

RESULTS

Registration of AR to phantom showed a roughly circular deviation with maximum average radius of 2.5 mm. Users took an average of 200 s to place a needle. Extrapolation of needle trajectory into the pedicle showed that of 36 needles placed, 35 (97%) would have remained within the pedicles. Needles placed approximated a mean distance of 4.69 mm in the mediolateral direction and 4.48 mm in the craniocaudal direction from pedicle bone edge.

CONCLUSION

To our knowledge, this is the first peer-reviewed report and evaluation of HMD-AR with superimposed 3D guidance utilizing CT for spinal pedicle guide placement for the purpose of cannulation without the use of fluoroscopy.