A biomechanical cadaveric analysis of polymethylmethacrylate-augmented pedicle screw fixation

Bone Allograft Pedicle Screw Augmentation: A Biomechanical Study

STUDY DESIGN

We performed a comprehensive cadaveric biomechanical study to compare the fixation strength of primary screws, screws augmented with bone allograft, and screws augmented with polymethylmethacrylate cement.

OBJECTIVE

To evaluate a novel technique for screw augmentation using morselized cortico-cancellous bone allograft to fill the widened screw track of failed pedicle screws.

BACKGROUND

To date, there are no known biological methods available for failed pedicle screw augmentation or fixation.

MATERIALS AND METHODS

Biomechanical tests were performed using 2 different testing modalities to quantify fixation strength including axial screw pullout and progressive cyclic displacement tests.

RESULTS

Fifty vertebrae were instrumented with pedicle screws. Our study showed that bone allograft augmentation using the same diameter screw was noninferior to the fixation strength of the initial screw. In the axial pullout test, screws undergoing bone allograft repair failed at 25% lower loads compared with native screws, and screws augmented with cement showed approximately twice as much strength compared with native screws. In the cyclic displacement test, screws fixed with cement resisted loosening the best of all the groups tested. However, screws augmented with bone graft were found to have an equal strength to native screw purchase. our study did not find a correlation with bone mineral density as a predictor for failure in axial pullout or cyclic displacement tests.

CONCLUSION

Bone allograft augmentation for pedicle screw fixation was noninferior to the initial screw purchase in this biomechanical study. This bone allograft technique is a viable option for screw fixation in the revision setting when there is significant bone loss in the screw track.

Cyclic testing of standalone ALIF versus TLIF in lumbosacral spines of low bone mineral density: an ex vivo biomechanical study

PURPOSE

Screwed anterior lumbar interbody fusion (SALIF) alleviates the need for supplemental posterior fixation leading to reduction of perioperative morbidity. Specifically, elderly and multimorbid patients would benefit from shorter operative time and faster recovery but tend to have low bone mineral density (BMD). The current study aimed to compare loosening, defined as increase of ROM and NZ, of SALIF versus transforaminal lumbar interbody fusion (TLIF) under cyclic loading in cadaveric spines with reduced BMD.

METHODS

Twelve human spines (L4-S2; 6 male 6 female donors; age 70.6 ± 19.6; trabecular BMD of L5 84.2 ± 24.4 mgHA/cm3, range 51-119 mgHA/cm3) were assigned to two groups. SALIF or TLIF were instrumented at L5/S1. Range of motion (ROM) and neutral zone (NZ) were assessed before and after axial cyclic loading (0-1150 N, 2000 cycles, 0.5 Hz) in flexion-extension (Flex-Ext), lateral bending, (LB), axial rotation (AR).

RESULTS

ROM of the SALIF specimens increased significantly in all loading directions (p ≤ 0.041), except for left AR (p = 0.053), whereas for TLIF it increased significantly in left LB (p = 0.033) and Flex (p = 0.015). NZ of SALIF showed increase in Flex-Ext and LB, whereas NZ of TLIF did not increase significantly in any motion direction.

CONCLUSIONS

Axial compression loading caused loosening of SALIF in Flex-Ext and LB, but not TLIF at L5/S1 in low BMD specimens. Nevertheless, Post-cyclic ROM and NZ of SALIF is comparable to TLIF. This suggests that, neither construct is optimal for the use in patients with reduced BMD.

A Dual-Screw Technique for Vertebral Compression Fractures via Robotic Navigation in the Osteopenic Lumbar Spine: An In-Vitro Biomechanical Analysis

STUDY DESIGN

Biomechanical cadaveric study.

OBJECTIVES

Multi-rod constructs maximize posterior fixation, but most use a single pedicle screw (PS) anchor point to support multiple rods. Robotic navigation allows for insertion of PS and cortical screw (CS) within the same pedicle, providing 4 points of bony fixation per vertebra. Recent studies demonstrated radiographic feasibility for dual-screw constructs for posterior lumbar spinal fixation; however, biomechanical characterization of this technique is lacking.

METHODS

Fourteen cadaveric lumbar specimens (L1-L5) were divided into 2 groups (n = 7): PS, and PS + CS. VCF was simulated at L3. Bilateral posterior screws were placed from L2-L4. Load control (±7.5Nm) testing performed in flexion-extension (FE), lateral bending (LB), axial rotation (AR) to measure ROM of: (1) intact; (2) 2-rod construct; (3) 4-rod construct. Static compression testing of 4-rod construct performed at 5 mm/min to measure failure load, axial stiffness.

RESULTS

Four-rod construct was more rigid than 2-rod in FE (P < .001), LB (P < .001), AR (P < .001). Screw technique had no significant effect on FE (P = .516), LB (P = .477), or AR (P = .452). PS + CS 4-rod construct was significantly more stable than PS group (P = .032). Stiffness of PS + CS group (445.8 ± 79.3 N/mm) was significantly greater (P = .019) than PS (317.8 ± 79.8 N/mm). Similarly, failure load of PS + CS group (1824.9 ± 352.2 N) was significantly greater (P = .001) than PS (913.4 ± 309.8 N).

CONCLUSIONS

Dual-screw, 4-rod construct may be more stable than traditional rod-to-rod connectors, especially in axial rotation. Axial stiffness and ultimate strength of 4-rod, dual-screw construct were significantly greater than rod-to-rod. In this study, 4-rod construct was found to have potential biomechanical benefits of increased strength, stiffness, stability.

Pedicle screw pull-out testing in polyurethane foam blocks: Effect of block orientation and density

Synthetic bone models such as polyurethane (PU) foam are a well-established substitute to cadaveric bone for screw pull-out testing; however, little attention has been given to the effect of PU foam anisotropy on orthopaedic implant testing. Compressive and screw pull-out performance in three PU foam densities; 0.16 g/cm3 (PCF 10), 0.32 g/cm3 (PCF 20) and 0.64 g/cm3 (PCF 40) were performed in each of the X, Y or Z orientations. The maximum compressive force, stiffness in the linear region, maximum stress and modulus were determined for all compression tests. Pedicle screws were inserted and pulled out axially to determine maximum pull-out force, energy to failure and stiffness. One-way ANOVA and post hoc tests were used to compare outcome variables between PU foam densities and orientations, respectively. Compression tests demonstrated the maximum force was significantly different between all orientations for PCF 20 (X, Y and Z) while stiffness and maximum stress were different between X versus Y and X versus Z. Maximum pull-out force was significantly different between all orientations for PCF 10 foam. No significant differences were noted for other foam densities. There is potential for screw pull-out testing results to be significantly affected by orientation in lower density PU foams. It is recommended that a single, known orientation of the PU foam block be used for experimental testing.

High Rate of Pulmonary Cement Embolism after Cement-Augmented Pedicle Screw Fixation: A 12-Year Single-Center Study

BACKGROUND

 The global trend toward increased life expectancy because of remarkable improvements in health care quality has drawn increased attention to osteoporotic fractures and degenerative spine diseases. Cement-augmented pedicle screw fixation has been established as the mainstay treatment for patients with poor bone quality. This study aimed to determine the number of patients with cement leakage and pulmonary cement embolism (PCE) as detected on thoracic computed tomography (CT), and to assess the potential risk factors for PCE.

METHODS

 Patients undergoing cement-augmented pedicle screw placement in our institution between May 2008 and December 2020 were included. Data regarding baseline characteristics, complications, and cement leakage rates were collected. Indications for the performance of a postoperative thoracic CT due to the suspicion of PCE were intra- or postoperative complications, or postoperative oxygen supplementation. Moreover, PCE was accidently diagnosed because the thoracic CT was performed for medical reasons other than the suspicion of PCE (tumor staging, severe pneumonia, or exacerbated chronic pulmonary obstructive disease).

RESULTS

 A total of 104 patients with a mean age of 72.8 years (standard deviation of 6.7) were included. Of 802 screws, 573 were cement augmented. Of the 104 patients, 44 (42.3%) underwent thoracic CT scans to diagnose PCE; additionally, 67 (64.4%) demonstrated cement leakage, of whom 27 developed PCE and 4 were symptomatic. Cement-augmented thoracic screws were a risk factor for PCE (odds ratio: 1.5; 95% confidence interval: 1.2-2.1; p = 0.004).

CONCLUSIONS

 This study showed a high prevalence of cement leakage after cement-augmented pedicle screw insertion, with a relatively frequent incidence of PCE, as tracked by thoracic CT scans. Cement-augmented thoracic screw placement was a unique risk factor for PCE.

Percutaneous Juxtapedicular Cement Salvage of Failed Spinal Instrumentation? Institutional Experience and Cadaveric Biomechanical Study

BACKGROUND AND OBJECTIVES

Instrumented spinal fusion constructs sometimes fail because of fatigue loading, frequently necessitating open revision surgery. Favorable outcomes after percutaneous juxtapedicular cement salvage (perc-cement salvage) of failing instrumentation have been described; however, this approach is not widely known among spine surgeons , and its biomechanical properties have not been evaluated. We report our institutional experience with perc-cement salvage and investigate the relative biomechanical strength of this technique as compared with 3 other common open revision techniques.

METHODS

A retrospective chart review of patients who underwent perc-cement salvage was conducted. Biomechanical characterization of revision techniques was performed in a cadaveric model of critical pedicle screw failure. Three revision cohorts involved removal and replacement of hardware: (1) screw upsizing, (2) vertebroplasty, and (3) fenestrated screw with cement augmentation. These were compared with a cohort with perc-cement salvage performed using a juxtapedicular trajectory with the failed primary screw remaining engaged in the vertebral body.

RESULTS

Ten patients underwent perc-cement salvage from 2018 to 2022 to address screw haloing and/or endplate fracture threatening construct integrity. Pain palliation was reported by 8/10 patients. Open revision surgery was required in 4/10 patients, an average of 8.9 months after the salvage procedure (range 6.2-14.7 months). Only one revision was due to progressive hardware dislodgement. The remainder avoided open revision surgery through an average of 1.9 years of follow-up. In the cadaveric study, there were no significant differences in pedicle screw pullout strength among any of the revision cohorts.

CONCLUSION

Perc-cement salvage of failing instrumentation is reasonably efficacious. The technique is biomechanically noninferior to other revision strategies that require open surgery for removal and replacement of hardware. Open revision surgery may be avoided by perc-cement salvage in select cases.

A Novel Semi-Cannulated Screw Enhanced Bone Cement Augmentation and Pullout Strength in Posterior Cervical Lateral Mass Screw Fixations: An In Vitro Biomechanical and Morphological Study

OBJECTIVE

To develop a novel semi-cannulated lateral mass screw (SC-LMS) for cervical posterior fixations and compare the fixation stability and safety of SC-LMS with regular solid lateral mass screw (S-LMS) in bone cement augmentation and pullout strength using fresh cadaveric cervical vertebrae.

METHODS

The conventional multiaxial screw for cervical lateral mass fixation was modified to a cannulated screw with two lateral holes, used for bone cement injection in situ. Eight fresh human cervical vertebrae (C3, C4, and C5) were collected and used. μCT scan was performed to evaluate the bone quality of the lateral masses, including bone mineral density (BMD), trabecular thickness (Tb.Th), and trabecular separation (Tb.Sp). SCLMS or S-LMS were randomly inserted into the paired cervical vertebrae and pulled out as a screw loosening model. These screws were reinserted in with bone cement augmentation, scanned by μCT to obtain the bone cement distribution along the screws, and pulled out to test the screw purchase strength.

RESULTS

Fmax values exhibited strong positive correlations with the local BMD (𝑟 = 0.8640, p < 0.0001) and Tb.Th (𝑟 = 0.6795, p = 0.0038), whereas a negative correlation with Tb.Sp (𝑟 = -0.5567, p = 0.0251). A significant difference was observed between the Fmax before and after PMMA injection on the SC-LMS side (p = 0.019). The SC-LMS exhibited lower risk of cement leakage than S-LMS after PMMA injection, and a positive correlation was observed between 𝐹max and the distribution volumes on the SC-LMS side.

CONCLUSION

The novel SC-LMS provides more robust fixation stability and is safer than the S-LMS for PMMA augmentation, which may be related to the cement-screw-cement-bone complex formation.

Cement Augmentation of Pedicle Screw Instrumentation: A Literature Review

This literature review aimed to review the current understanding, indications, and limitations of pedicle screw instrumentation cement augmentation. Since they were first reported in the 1980s, pedicle screw cement augmentation rates have been increasing. Several studies have been published to date that describe various surgical techniques and the biomechanical changes that occur when cement is introduced through the screw-bone interface. This article provides a concise review of the uses, biomechanical properties, cost analysis, complications, and surgical techniques used for pedicle screw cement augmentation to help guide physician practices. A comprehensive review of the current literature was conducted, with key studies, and contributions from throughout history being highlighted. Patients with low bone mineral density are the most well-studied indication for pedicle screw cement augmentation. Many studies show that cement augmentation can improve pullout strength in patients with low bone mineral density; however, the benefit varies inversely with pathology severity and directly with technique. The various screw types are discussed, with each having its own mechanical advantages. Cement distribution is largely dependent on the filling method and volume of cement used. Cement composition and timing of cement use after mixing are critical considerations in practice because they can significantly alter the bone-cement and screw-cement interfaces. Overall, studies have shown that pedicle screw cement augmentation has a low complication rate and increased pullout strength, justifying its universal use in patients with a suboptimal bone-implant interface.

[Osteoporotic vertebral body fractures]

The number of osteoporotic fractures of the spine is increasing. These fractures are associated with elevated morbidity and mortality. This article provides an overview of the special features of these fractures, the diagnostic procedure, their classification, and the conservative and surgical treatment options. For the mostly elderly patients, it is important to treat the underlying disease and to address associated problems such as frailty and sarcopenia. To meet this growing medical and socio-economic challenge, a holistic interdisciplinary and interprofessional treatment approach is required.

Screw Osteointegration-Increasing Biomechanical Resistance to Pull-Out Effect

Spinal disorders cover a broad spectrum of pathologies and are among the most prevalent medical conditions. The management of these health issues was noted to be increasingly based on surgical interventions. Spinal fixation devices are often employed to improve surgery outcomes, increasing spinal stability, restoring structural integrity, and ensuring functionality. However, most of the currently used fixation tools are fabricated from materials with very different mechanical properties to native bone that are prone to pull-out effects or fail over time, requiring revision procedures. Solutions to these problems presently exploited in practice include the optimal selection of screw shape and size, modification of insertion trajectory, and utilization of bone cement to reinforce fixation constructs. Nevertheless, none of these methods are without risks and limitations. An alternative option to increasing biomechanical resistance to the pull-out effect is to tackle bone regenerative capacity and focus on screw osteointegration properties. Osteointegration was reportedly enhanced through various optimization strategies, including use of novel materials, surface modification techniques (e.g., application of coatings and topological optimization), and utilization of composites that allow synergistic effects between constituents. In this context, this paper takes a comprehensive path, starting with a brief presentation of spinal fixation devices, moving further to observations on how the pull-out strength can be enhanced with existing methods, and further focusing on techniques for implant osteointegration improvement.

Cement Augmented Pedicle Screw Instrumentation in Pediatric Spine Surgery

BACKGROUND

Osteoporosis in pediatric patients is rare. Osteomalacia and osteoporosis are known to develop in syndromic or neuromuscular scoliosis children. Spinal deformity surgery for pediatric patients with osteoporosis is challenging, associated with pedicle screw (PS) failure and compression fractures. Cement augmentation of PS is one several measures to prevent screw failure. It provides additional pull-out strength to the PS in the osteoporotic vertebra.

METHODS

In 2010-2020, an analysis of pediatric patients who had cement augmentation of PS with a minimum follow-up of 2 years was performed. Radiological and clinical evaluations were analyzed.

RESULTS

The study included 7 patients (4 girls, 3 boys) with a mean age of 13 years (range, 10-14 years) and mean follow-up of 3 years (range, 2-3 years). Only 2 patients underwent revision surgery. Total number of cement augmented PSs was 52 with an average of 7 per patient. Only 1 patient had lower instrumented vertebra vertebroplasty. There was no PS pull-out in the cement augmented levels, and there were no neurological deficits or pulmonary cement embolisms. One patient developed a PS pull-out in uncemented levels. Two patients developed compression fractures, one, with osteogenesis imperfecta, in the supra-adjacent levels (upper instrumented vertebra + 1 and upper instrumented vertebra + 2), and the other, with neuromuscular scoliosis, in the uncemented segments.

CONCLUSIONS

In this study, all cement augmented PSs provided satisfactory radiological outcomes without PS pull-out and adjacent vertebral compression fracture. In pediatric spine surgery, in osteoporotic patients with a poor bone purchase, cement augmentation may be used, especially in high-risk patients with osteogenesis imperfecta, neuromuscular scoliosis, and syndromic scoliosis.

Pedicle screw augmentation in posterior constructs of the thoracolumbar spine: How many pedicle screws should be augmented?

BACKGROUNDS

To evaluate the effects of different pedicle screw augmentation strategies on screw loosening and adjacent segment collapse at the proximal end of long-segment instrumentation.

METHODS

Eighteen osteoporotic (9 male, 9 female donors; mean age: 74.7 ± 10.9 [SD] years) thoracolumbar multi-segmental motion segments (Th11 - L1) were assigned as follows: control, one-level augmented screws (marginally), and two-level augmented screws (fully augmented) groups (3 × 6). Pedicle screw placement was performed in Th12 and L1. Cyclic loading in flexion started with 100-500 N (4 Hz) and was increased by 5 N every 500 cycles. Standardized lateral fluoroscopy images with 7.5 Nm loading were obtained periodically during loading. The global alignment angle was measured to evaluate the overall alignment and proximal junctional kyphosis. The intra-instrumental angle was used to evaluate screw fixation.

FINDINGS

Considering screw fixation as a failure criterion, the failure loads of the control (683 N), and marginally (858 N) and fully augmented (1050 N) constructs were significantly different (ANOVA p = 0.032).Taking the overall specimen alignment as failure criteria, failure loads of the three groups (control 933 ± 271.4 N, marginally 858 N ± 196 N, and full 933 ± 246.3 N were in the same range and did not show any significance (p = 0.825).

INTERPRETATION

Global failure loads were comparable among the three groups and unchanged with augmentation because the adjacent segment and not the instrumentation failed first. Augmentation of all screws showed significant improved in screw anchorage.

Second-generation bone cement-injectable cannulated pedicle screws for osteoporosis: biomechanical and finite element analyses

BACKGROUND

Biomechanical and finite element analyses were performed to investigate the efficacy of second-generation bone cement-injectable cannulated pedicle screws (CICPS) in osteoporosis.

METHODS

This study used the biomechanical test module of polyurethane to simulate osteoporotic cancellous bone. Polymethylmethacrylate (PMMA) bone cement was used to anchor the pedicle screws in the module. The specimens were divided into two groups for the mechanical tests: the experimental group (second-generation CICPS) and control group (first-generation CICPS). Safety was evaluated using maximum shear force, static bending, and dynamic bending tests. Biomechanical stability evaluations included the maximum axial pullout force and rotary torque tests. X-ray imaging and computed tomography were used to evaluate the distribution of bone cement 24 h after PMMA injection, and stress distribution at the screw fracture and screw-cement-bone interface was assessed using finite element analysis.

RESULTS

Mechanical testing revealed that the experimental group (349.8 ± 28.6 N) had a higher maximum axial pullout force than the control group (277.3 ± 8.6 N; P < 0.05). The bending moments of the experimental group (128.5 ± 9.08 N) were comparable to those of the control group (113.4 ± 20.9 N; P > 0.05). The screw-in and spin-out torques of the experimental group were higher than those of the control group (spin-in, 0.793 ± 0.015 vs. 0.577 ± 0.062 N, P < 0.01; spin-out, 0.764 ± 0.027 vs. 0.612 ± 0.049 N, P < 0.01). Bone cement was mainly distributed at the front three-fifths of the screw in both groups, but the distribution was more uniform in the experimental group than in the control group. After pullout, the bone cement was closely connected to the screw, without loosening or fragmentation. In the finite element analysis, stress on the second-generation CICPS was concentrated at the proximal screw outlet, whereas stress on the first-generation CICPS was concentrated at the screw neck, and the screw-bone cement-bone interface stress of the experimental group was smaller than that of the control group.

CONCLUSION

These findings suggest that second-generation CICPS have higher safety and stability than first-generation CICPS and may be a superior choice for the treatment of osteoporosis.

Posterior instrumentation for osteoporotic fractures in the thoracic or lumbar spine: Cement-augmented pedicle screws vs hybrid constructs

BACKGROUND

Cement-augmented pedicle screws (CPS) and hybrid construct (HC), consisting of pedicle screws and additional hooks, are common fixation methods for osteoporotic spine fracture. No study has compared surgical results of CPS and HC for treating osteoporotic spine fracture. The aim of the study was to compare surgical results using CPS or HC for osteoporotic fractures of the thoracic or lumbar spine.

METHODS

This retrospective cohort study included 84 patients who received surgical treatment with CPS (n = 43) or HC (n = 41) for osteoporotic spine fractures from January 2011 to December 2015, with a mean follow-up of 67 months. Sixty-five patients with neurological deficits received long posterior instrumentation, short posterior decompression, and posterolateral fusion. The 19 patients without neurologic deficits received long posterior instrumentation without posterior decompression and fusion. Radiographic, clinical, and neurologic outcomes were evaluated.

RESULTS

The HC group had significantly shorter operative times (231 vs 258 minutes), greater blood loss (497 vs 427 mL), better immediate postoperative kyphosis reduction (10.6° vs 9.1°), and greater final reduction loss (9.8° vs 7.1°) than the CPS group. In both groups, significant loss of the kyphotic angle was apparent during follow-up. Improved ambulation after surgery occurred in 51.2% and 58.5% of patients in the CPS and HC groups, respectively. Neurologic function after surgery improved 0.5 and 0.7 grades in the CPS and HC groups, respectively. Implants failed in 2.3% and 2.4% of patients in the CPS and HC groups, respectively. The incidence of cement leakage from screw augmentation was 38.9%.

CONCLUSION

The CPS and HC techniques for treating osteoporotic fractures of the thoracic or lumbar spine did not differ statistically in terms of improved radiologic and clinical outcomes, final neurologic and ambulatory function, or implant failure rates, making them equally comparable alternatives.

Impaction grafting of lumbar pedicle defects: a biomechanical study of a novel technique for pedicle screw revision

OBJECTIVE

The two most common revision options available for the management of loose pedicle screws are larger-diameter screws and cement augmentation into the vertebral body for secondary fixation. An alternative revision method is impaction grafting (pedicoplasty) of the failed pedicle screw track. This technique uses the impaction of corticocancellous bone into the pedicle and vertebral body through a series of custom funnels to reconstitute a new pedicle wall and a neomedullary canal. The goal of this study was to compare the biomechanics of screws inserted after pedicoplasty (impaction grafting) of a pedicle defect to those of an upsized screw and a cement-augmented screw.

METHODS

For this biomechanical cadaveric study the investigators used 10 vertebral bodies (L1-5) that were free of metastatic disease or primary bone disease. Following initial screw insertion, each screw was subjected to a pullout force that was applied axially along the screw trajectory at 5 mm per minute until failure. Each specimen was instrumented with a pedicoplasty revision using the original screw diameter, and on the contralateral side either a fenestrated screw with cement augmentation or a screw upsized by 1 mm was inserted in a randomized fashion. These revisions were then pulled out using the previously mentioned methods.

RESULTS

Initial screw pullout values for the paired upsized screw and pedicoplasty were 717 ± 511 N and 774 ± 414 N, respectively (p = 0.747) (n = 14). Revised pullout values for the paired upsized screw and pedicoplasty were 775 ± 461 N and 762 ± 320 N, respectively (p = 0.932). Initial pullout values for the paired cement augmentation and pedicoplasty were 792 ± 434 N and 880 ± 558 N, respectively (p = 0.649). Revised pullout values for the paired cement augmentation and pedicoplasty were 1159 ± 300 N and 687 ± 213 N, respectively (p < 0.001).

CONCLUSIONS

Pedicle defects are difficult to manage. Reconstitution of the pedicle and creation of a neomedullary canal appears to be possible through the use of pedicoplasty. Biomechanically, screws that have been used in pedicoplasty have equivalent pullout strength to an upsized screw, and have greater insertional torques than those with the same diameter that have not been used in pedicoplasty, yet they are not superior to cement augmentation. This study suggests that although cement augmentation appears to have superior pullout force, the novel pedicoplasty technique offers promise as a viable biological revision option for the management of failed pedicle screws compared with the option of standard upsized screws in a cadaveric model. These findings will ultimately need to be further assessed in a clinical setting.

Reversed windshield-wiper effect leads to failure of cement-augmented pedicle screw: Biomechanical mechanism analysis by finite element experiment

The failure mode of cement-augmented pedicle screw (CAPS) was different from common pedicle screw. No biomechanical study of this failure mode named as "reversed windshield-wiper effect" was reported. To investigate the mechanisms underlying this failure mode, a series of finite element models of CAPS and PS were modified on L4 osseous model. Nine models were created according to the cement volume at 0.5 mL interval (range: 1-5 mL). Pullout load and cranio-caudal loads were applied on the screws. Stress and instantaneous rotation center (IRC) of the vertebra were observed. Under cranio-caudal load, the stress concentrated on the screw tip and pedicle region. The maximal stress (MS) at the screw tip region was +2.143 MPa higher than pedicle region. With cement volume increasing, the maximal stress (MS) at the screw tip region decreased dramatically, while MS at pedicle region was not obviously affected. As dose increased to 1.5 mL, the MS at pedicle region became higher than screw tip region and the maximal stress difference was observed at 3.5 mL. IRC of the vertebra located at the facet joint region in PS model. While IRC in CAPS models shifted anteriorly closer to the vertebral body with the increasing of cement volume. Under axial pull-out load, the maximal stress (MS) of cancellous bone in CAPS models was 29.53-50.04% lower than that 2.228 MPa in PS model. MS in the screw-bone interface did not change significantly with cement volume increasing. Therefore, the possible mechanism is that anterior shift of IRC and the negative difference value of MS between screw tip and pedicle region due to cement augmentation, leading to the screw rotate around the cement-screw complex as the fulcrum point.

Comparison of pedicle screw fixation with or without cement augmentation for treating single-segment isthmic spondylolisthesis in the osteoporotic spine

The present study examined the necessity of cement-augmented pedicle screw fixation in osteoporotic patients with single-segment isthmic spondylolisthesis.Fifty-nine cases were reviewed retrospectively. Thirty-three cases were in the polymethylmethacrylate-augmented pedicle screw (PMMA-PS) group, and the other 26 cases were in the conventional pedicle screw (CPS) group. Evaluation data included operation time, intraoperative blood loss, hospitalization cost, hospitalization days, rates of fusion, screw loosening, bone cement leakage, visual analogue scale (VAS) scores, Oswestry disability index (ODI), lumbar lordosis (LL), pelvic tilt (PT) and sacral slope (SS).The operation time and blood loss in the CPS group decreased significantly compared to those in the PMMA-PS group. The average hospitalization cost of the PMMA-PS group was significantly higher than that of the CPS group. There was no significant difference in the average hospital stay between the 2 groups. The initial and last follow-up postoperative VAS and ODI scores improved significantly in the two groups. There were no significant differences in VAS and ODI between the 2 groups at each time point. The last postoperative spine-pelvic parameters were significantly improved compared with those preoperatively. In the PMMA-PS group, the fusion rate was 100%. The fusion rate was 96.15% in the CPS group. No significant difference was found between the two groups for the fusion rate. Nine patients in the PMMA-PS group had bone cement leakage. There was no screw loosening in the PMMA-PS group. There were 2 cases of screw loosening in the CPS group. There were no significant differences in screw loosening, postoperative adjacent segment fractures, postoperative infection or postoperative revision between the 2 groups. The use of PMMA-PS on a regular basis is not recommended in posterior lumbar interbody fusion for the treatment of single-segment isthmic spondylolisthesis with osteoporosis.

Time to revisit contraindications of vertebroplasty- A retrospective study of osteoporotic burst fracture operated with vertebroplasty and short segment fixation

Background

Methods

Results

Conclusions

[Cement augmentation in spinal surgery]

Bone cement has been used in spinal surgery for as long as 50 years. In contemporary spinal surgery, cement augmentation of fractured osteoporotic vertebrae in the form of vertebroplasty/kyphoplasty as well as cement augmentation of pedicle screws in instrumented procedures of any etiology are established as standard procedures. Both procedures are very effective, although the benefits of vertebroplasty/kyphoplasty procedures have been controversially discussed in the past. Overall, complications rarely occur. The most relevant complication is cement leakage, which is asymptomatic in the majority of cases but in the worst case might lead to neurological deficits, embolic events and even circulatory collapse. Prevention of cement leakage is therefore crucial. Risk factors for cement leakage and preventive measures are presented in a comprehensive review based on the available literature.

Hydroxyapatite Use in Spine Surgery—Molecular and Clinical Aspect

Hydroxyapatite possesses desirable properties as a scaffold in tissue engineering: it is biocompatible at a site of implantation, and it is degradable to non-toxic products. Moreover, its porosity enables infiltration of cells, nutrients and waste products. The outcome of hydroxyapatite implantation highly depends on the extent of the host immune response. Authors emphasise major roles of the chemical, morphological and physical properties of the surface of biomaterial used. A number of techniques have been applied to transform the theoretical osteoconductive features of HAp into spinal fusion systems—from integration of HAp with autograft to synthetic intervertebral implants. The most popular uses of HAp in spine surgery include implants (ACDF), bone grafts in posterolateral lumbar fusion and transpedicular screws coating. In the past, autologous bone graft has been used as an intervertebral cage in ACDF. Due to the morbidity related to autograft harvesting from the iliac bone, a synthetic cage with osteoconductive material such as hydroxyapatite seems to be a good alternative. Regarding posterolateral lumbar fusion, it requires the graft to induce new bone growth and reinforce fusion between the vertebrae. Hydroxyapatite formulations have shown good results in that field. Moreover, the HAp coating has proven to be an efficient method of increasing screw fixation strength. It can decrease the risk of complications such as screw loosening after pedicle screw fixation in osteoporotic patients. The purpose of this literature review is to describe in vivo reaction to HAp implants and to summarise its current application in spine surgery.

Outcomes of the use of cement-augmented cannulated pedicle screws in lumbar spinal fusion

BACKGROUND CONTEXT

There are few studies of the radio-clinical outcomes of cement-augmented cannulated pedicle screw (CPS) fixation in osteoporotic patients.

PURPOSE

To compare the radiological and clinical outcomes between groups receiving cement-augmented CPS and solid pedicle screws (SPS) in lumbar fusion surgery.

STUDY DESIGN/SETTING

Retrospective comparative study PATIENT SAMPLE: A total of 187 patients who underwent lumbar fusion surgery for degenerative spinal stenosis or spondylolisthesis from 2014 to 2019.

OUTCOME MEASURES

Radiological evaluation included screw failure, cage failure, rod breakage, and fusion grade at postoperative 6 months and 1 year. Pre- and postoperative visual analog scales for back pain (VAS-BP), leg pain (VAS-LP), Korean Oswestry disability index (K-ODI), and postoperative complications were also compared.

METHODS

Outcomes of patients with high risk factors for implant failure [old age, osteoporosis, autoimmune disease or chronic kidney disease (CKD)] who underwent open transforaminal lumbar interbody fusion with cement-augmented CPS fixation (Group C, n=55) or SPS fixation (Group S, n=132) were compared.

RESULTS

324 pedicle screws in Group C and 775 pedicle screws in Group S were analyzed. Group C had a significantly higher average age and lower T-score, and included more patients with autoimmune disease and CKD than group S (all p<.05). Clear zones, screw migration and loss of correction were significantly less frequent in Group C (all p<.05). Thirteen screw breakages were observed; they were only in Group C (4.0%) and all were in the proximal of the two holes. Interbody and posterolateral fusion rates were not significantly different. At last follow-up, all clinical parameters including VAS-BP, VAS-LP, and K-ODI scores had improved significantly in both groups. Postoperative complications were not significantly different in the two groups.

CONCLUSION

In lumbar fusion surgery, using cement-augmented CPS in high-risk groups for implant failure could be a useful technical option for reducing acute radiological complications and obtaining clinical results comparable to those obtained using SPS in patients with low risk of implant failure.

LEVEL OF EVIDENCE

Level 4.

Pull-out strength evaluation of cement augmented iliac screws in osteoporotic spino-pelvic fixation

INTRODUCTION

Spino-pelvic fixation has been widely accepted for surgical treatment of sacral tumor, scoliosis surgery and pelvic fractures. Cement augmentation of screws is an option to improve implant stability in osteoporotic bone quality. Aim of the present study is to compare iliac screw fixation without cement fixation and two cement application options in a biomechanical testing.

HYPOTHESIS

Cement augmentation of iliac screws leads to superior pull-out strength.

MATERIAL AND METHODS

Thirty female and osteoporotic human iliac bones were used. Three operation treatment groups were generated: Screw fixation (cannulated screws) without cement augmentation [Operation treatment (OT) A], screw fixation with cement augmentation before screw placement (cannulated screws) (OT B) and screw fixation with perforated screws and cement augmentation after screw placement (OTC). Pull-out tests were performed with a rate of 6mm/min. A load versus displacement curve was generated. Maximum pull-out force (N) was measured in the load-displacement curve.

RESULTS

Paired group 1 (OT A vs. OT B): Screw fixation without cement augmentation: 592.6N±335.07 and screw fixation with cement augmentation before screw placement: 996N±287.43 (p=0.0042). Paired group 2 (OT A vs. OT C): screw fixation without cement augmentation: 716.2N±385.86 and fenestrated screw fixation with cement augmentation after screw placement: 1324.88N±398.76 (p=0.0489). Paired group 3 (OT B vs. OT C): Screw fixation with cement augmentation before screw placement: 1077.2±486.66 and fenestrated screw fixation with cement augmentation after screw placement: 1298.2N±726.19 (p=0.3286).

DISCUSSION

Regarding iliac screw fixation for spino-pelvic ostesynthesis in osteoporotic bone, cement augmentation is significantly superior to solid iliac screw fixation respecting pull-out-strength. Nevertheless, further biomechanical studies are needed to verify these findings.

LEVEL OF EVIDENCE

Not applicable; biomechanical cadaver study.

The Influence of Different Injection Hole Designs of Augmented Pedicle Screws on Bone Cement Leakage and Distribution Patterns in Osteoporotic Patients

OBJECTIVE

To compare cement distribution and leakage for 2 bone cement-augmented screws with different designs of injection holes in patients and the impact of screw locations and bone mineral density (BMD) on the results.

METHODS

This study recruited 40 patients who underwent instrumentation with cement-augmented screws. Screw holes of group A were 4 holes located in the distal one third of screws, while screw holes of group B were 6 holes located in distal, middle, and proximal sites. Postoperative computed tomography images were obtained to evaluate the rate and type of cement leakage and the distribution pattern of cement. The lateral or center position of screw tip, BMD, and T-score were also analyzed for their influence on the results.

RESULTS

Of 192 screws, 80 (41.7%) exhibited cement leakage on postoperative computed tomography. The incidence of cement distribution in the posterior half and type B leakage in group B was significantly higher compared with group A. In group A, the probability of cement distribution in the posterior half was significantly increased when the screw was laterally inserted. For both groups, the higher incidence of cement distribution in the posterior half was correlated with lower BMD and T-score.

CONCLUSIONS

Our results showed that screws with injection holes closer to the screw tip had higher incidences of distribution in the anterior half of the body and lower incidences of type B leakage. Patients with lower BMD and T-scores should be closely monitored, and a more centered position is recommended for screw insertion.

Cement-Augmented Carbon Fiber-Reinforced Pedicle Screw Instrumentation for Spinal Metastases: Safety and Efficacy

OBJECTIVE

To investigate the complication rates and long-term implant failure rates in a monocentric study of a consecutive cohort of patients with thoracolumbar spinal metastases after posterior instrumentation with a fenestrated carbon fiber-reinforced poly-ether-ether-ketone (CFRP) pedicle screw system.

METHODS

We retrospectively reviewed demographics, Karnofsky Performance Status Scale scores, complications, and implant failure rates.

RESULTS

Between June 2016 and November 2019, 51 consecutive patients underwent cement-augmented CFRP pedicle screw instrumentation at our institution. Mean age was 68 years (standard deviation 10.5), the median preoperative Karnofsky Performance Status Scale of 80 increased to 90 postoperatively (P = 0.471). Most common primary entities were breast (25.5%), lung (15.7%), and prostate (13.7%) cancers. Of 428 placed screws, 293 (68.5%) were augmented with polymethylmethacrylate, a mean 6 per patient (standard deviation ±2). Screws were inserted via a minimally invasive system technique in 54.9% of cases. In total, 11.8% of patients had immediate postoperative sequelae related to the cement. Pulmonary cement embolisms were noted in 3 patients, 2 had paravertebral extravasation, and 1 had an embolism into a segmental artery. Of these 6, 2 patients with pulmonary embolisms reported related symptoms. Follow-up was available for 80.4%. After a mean 9.8 months, screw loosening was noted in 11.8% of cases on computed tomography, although it was asymptomatic in all but 1 patient. Screw pull-out did not occur. Neither cement-related (P = 0.353) nor general complication rates (P = 0.507) differed significantly between open and minimally invasive system techniques.

CONCLUSIONS

Percutaneous cement-augmented CFRP pedicle screw instrumentation facilitates artifact-reduced postoperative imaging, while maintaining a risk profile and implant failure rates comparable to conventional metallic instrumentation.

Fenestrated pedicle screws for thoracolumbar instrumentation in patients with poor bone quality: Case series and systematic review of the literature

OBJECTIVE

To describe the results of a single-surgeon series and systematically review the literature on cement-augmented instrumented fusion with fenestrated pedicle screws.

METHODS

All patients treated by the senior surgeon using fenestrated screws between 2017 and 2019 with a minimum of 6-months of clinical and radiographic follow-up were included. For the systematic review, we used PRISMA guidelines to identify all prior descriptions of cement-augmented instrumented fusion with fenestrated pedicle screws in the English literature. Endpoints of interest included hardware loosening, cement leakage, and pulmonary cement embolism (PCE).

RESULTS

Our series included 38 patients (mean follow-up 14.8 months) who underwent cement-augmented instrumentation for tumor (47.3%), deformity/degenerative disease (39.5%), or osteoporotic fracture (13.2%). Asymptomatic screw lucency was seen in 2.6%, cement leakage in 445, and pulmonary cement embolism (PCE) in 5.2%. Our literature review identified 23 studies (n = 1526 patients), with low reported rates of hardware loosening (0.2%) and symptomatic PCE (1.0%). Cement leakage, while common (55.6%), produced symptoms in fewer than 1% of patients. Indications for cement-augmentation in this cohort included: spine metastasis with or without pathologic fracture (n = 18; 47.3%), degenerative spine disease or fixed deformity with poor underlying bone quality (n = 15; 39.5%), and osteoporotic fracture (n = 5; 13.2%).

CONCLUSION

Cement-augmented fusion with fenestrated screws appears to be a safe, effective means of treating patients with poor underlying bone quality secondary to tumor or osteoporosis. High-quality evidence with direct comparisons to non-augmented patients is needed.

Comparison of three different screw trajectories in osteoporotic vertebrae: a biomechanical investigation

BACKGROUND

Pedicle screw insertion in osteoporotic patients is challenging. Achieving more screw-cortical bone purchase and invasiveness minimization, the cortical bone trajectory and the midline cortical techniques represent alternatives to traditional pedicle screws. This study compares the fatigue behavior and fixation strength of the cement-augmented traditional trajectory (TT), the cortical bone trajectory (CBT), and the midline cortical (MC).

METHODS

Ten human cadaveric spine specimens (L1 - L5) were examined. The average age was 86.3 ± 7.2 years. CT scans were provided for preoperative planning. CBT and MC were implanted by using the patient-specific 3D-printed placement guide (MySpine®, Medacta International), TT were implanted freehand. All ten cadaveric specimens were randomized to group A (CBT vs. MC) or group B (MC vs. TT). Each screw was loaded for 10,000 cycles. The failure criterion was doubling of the initial screw displacement resulting from the compressive force (60 N) at the first cycle, the stop criterion was a doubling of the initial screw displacement. After dynamic testing, screws were pulled out axially at 5 mm/min to determine their remaining fixation strength.

RESULTS

The mean pull-out forces did not differ significantly. Concerning the fatigue performance, only one out of ten MC of group A failed prematurely due to loosening after 1500 cycles (L3). Five CBT already loosened during the first 500 cycles. The mean displacement was always lower in the MC. In group B, all TT showed no signs of failure or loosening. Three MC failed already after 26 cycles, 1510 cycles or 2144 cycles. The TT showed always a lower mean displacement. In the subsequent pull-out tests, the remaining mean fixation strength of the MC (449.6 ± 298.9 N) was slightly higher compared to the mean pull-out force of the CBT (401.2 ± 261.4 N). However, MC (714.5 ± 488.0 N) were inferior to TT (990.2 ± 451.9 N).

CONCLUSION

The current study demonstrated that cement-augmented TT have the best fatigue and pull-out characteristics in osteoporotic lumbar vertebrae, followed by the MC and CBT. MC represent a promising alternative in osteoporotic bone if cement augmentation should be avoided. Using the patient-specific placement guide contributes to the improvement of screws' biomechanical properties.

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.

Safety and efficacy of cement augmentation with fenestrated pedicle screws for tumor-related spinal instability

OBJECTIVE

Achieving rigid spinal fixation can be challenging in patients with cancer-related instability, as factors such as osteopenia, radiation, and immunosuppression adversely affect bone quality. Augmenting pedicle screws with cement is a strategy to overcome construct failure. This study aimed to assess the safety and efficacy of cement augmentation with fenestrated pedicle screws in patients undergoing posterior, open thoracolumbar surgery for spinal metastases.

METHODS

A retrospective review was performed for patients who underwent surgery for cancer-related spine instability from 2016 to 2019 at the Massachusetts General Hospital. Patient demographics, surgical details, radiographic characteristics, patterns of cement extravasation, complications, and prospectively collected Patient-Reported Outcomes Measurement Information System Pain Interference and Pain Intensity scores were analyzed using descriptive statistics. Logistic regression was performed to determine factors associated with cement extravasation.

RESULTS

Sixty-nine patients underwent open posterior surgery with a total of 502 cement-augmented screws (mean 7.8 screws per construct). The median follow-up period for those who survived past 90 days was 25.3 months (IQR 10.8-34.6 months). Thirteen patients (18.8%) either died within 90 days or were lost to follow-up. Postoperative CT was performed to assess the instrumentation and patterns of cement extravasation. There was no screw loosening, pullout, or failure. The rate of cement extravasation was 28.9% (145/502), most commonly through the segmental veins (77/145, 53.1%). Screws breaching the lateral border of the pedicle but with fenestrations within the vertebral body were associated with a higher risk of leakage through the segmental veins compared with screws without any breach (OR 8.77, 95% CI 2.84-29.79; p < 0.001). Cement extravasation did not cause symptoms except in 1 patient who developed a symptomatic thoracic radiculopathy requiring decompression. There was 1 case of asymptomatic pulmonary cement embolism. Patients experienced significant pain improvement at the 3-month follow-up, with decreases in Pain Interference (mean change 15.8, 95% CI 14.5-17.1; p < 0.001) and Pain Intensity (mean change 28.5, 95% CI 26.7-30.4; p < 0.001).

CONCLUSIONS

Cement augmentation through fenestrated pedicle screws is a safe and effective option for spine stabilization in the cancer population. The risk of clinically significant adverse events from cement extravasation is very low.

Strategies for posterior-only minimally invasive surgery in thoracolumbar metastatic epidural spinal cord compression

Background:

Metastatic epidural spinal cord compression (MESCC) is a debilitating sequela of cancer. Here, we evaluated various subtypes of posterior-only minimally invasive spinal (MIS) procedures utilized to address different cancers.

Methods:

Within this retrospective review, we analyzed the treatment of thoracolumbar MESCC treated with three MIS techniques: decompression and fusion (Subgroup A), partial corpectomy (Subgroup B), and full corpectomy (Subgroup C).

Results:

There were 51 patients included in the study; they averaged 58.7 years of age, and 51% were females. Most tumors were in the thoracic spine (51%). The average preoperative Frankel grade was D (62.7%); 69% (35) improved postoperatively. The patients were divided as follows: subgroup A (15 patients = 29.4%), B (19 patients = 37.3%), and C (17 patients = 33.3%). The length of hospitalization was similar (~5.4 days) for all groups. The overall complication rate was 31%, while blood loss was lower in Subgroups A and B versus C.

Conclusion:

Different MIS surgical techniques were utilized in patients with thoracic and/or lumbar MESCC. Interestingly, clinical outcomes were similar between MIS subgroups, in this study, with a trend toward higher complications and greater blood loss associated with those undergoing more aggressive MIS procedures (e.g., full corpectomy and fusion).

[Polymethylmethacrylate-augmented screw fixation in treatment of senile thoracolumbar tuberculosis combined with severe osteoporosis]

OBJECTIVE

To explore the safety and effectiveness of polymethylmethacrylate-augmented screw fixation (PASF) in the treatment of elderly thoracolumbar tuberculosis combined with severe osteoporosis.

METHODS

The clinical data of 20 elderly patients with thoracolumbar tuberculosis and severe osteoporosis who underwent PASF after anterior or posterior debridement and bone grafting and met the selection criteria between December 2012 and December 2014 were retrospectively analyzed. There were 8 males and 12 females with an average age of 68.5 years (range, 65-72 years). T value of bone mineral density was -4.2 to -3.6, with an average of -3.9. There were 12 cases of thoracic tuberculosis, 3 cases of thoracolumbar tuberculosis, and 5 cases of lumbar tuberculosis. The diseased segments involved T 3-L 4, including 11 cases of single-segment disease, 6 cases of double-segment disease, and 3 cases of multi-segment disease. The disease duration was 3-9 months, with an average of 6 months. The preoperative spinal nerve function of the patients was evaluated by the American Spinal Injury Association (ASIA) grading. There were 2 cases of grade A, 5 cases of grade B, 6 cases of grade C, 4 cases of grade D, and 3 cases of grade E. Postoperative imaging examination was used to evaluate the bone graft fusion and paravertebral abscess absorption, and to measure the Cobb angle of the segment to evaluate the improvement of kyphosis. The levels of erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) were tested. The visual analogue scale (VAS) score, Oswestry disability index (ODI), and ASIA grading were used to evaluate the effectivreness before operation, at 1 month after operation, and at last follow-up. The clinical cure of tuberculosis was also evaluated.

RESULTS

All operation successfully completed. The operation time was 154-250 minutes, with an average of 202 minutes; the intraoperative blood loss was 368-656 mL, with an average of 512 mL. All 20 patients were followed up 18-42 months, with an average of 26.8 months. The postoperative pain and symptoms of tuberculosis in all patients relieved, and the paravertebral abscess was absorbed, reaching the cure standard for spinal tuberculosis. All bone grafts fusion achieved within 1 year after operation. Only 1 case had asymptomatic bone cement leakage into the paravertebral veins, and the remaining patients had no serious complications such as bone cement leakage in the spinal canal, pulmonary embolism, and neurovascular injury. At last follow-up, spinal cord nerve function significantly improved when compared with preoperative one. Among them, ASIA grading were 7 cases of grade C, 8 cases of grade D, and 5 cases of grade E, showing significant difference when compared with preoperative one ( Z=2.139, P=0.000). VAS score, ODI score, segmental Cobb angle, ESR, and CRP at 1 month after operation and at last follow-up were significantly improved when compared with preoperative ones ( P<0.05); there was no significant difference between 1 month after operation and last follow-up ( P>0.05). During the follow-up, no complications such as failure of internal fixation, proximal junctional kyphosis, or tuberculosis recurrence occurred.

CONCLUSION

For elderly patients with thoracolumbar tuberculosis and severe osteoporosis, PASF treatment is safe and effective.

[Minimally invasive stabilization of thoracolumbar osteoporotic fractures]

BACKGROUND

Minimally invasive stabilization of thoracolumbar osteoporotic fractures (OF) in neurologically intact patients is well established. Various posterior and anterior surgical techniques are available. The OF classification and OF score are helpful for defining the indications and choice of operative technique.

OBJECTIVE

This article gives an overview of the minimally invasive stabilization techniques, typical complications and outcome.

MATERIAL AND METHODS

Selective literature search and description of surgical techniques and outcome.

RESULTS

Vertebral body augmentation alone can be indicated in painful but stable fractures of types OF 1 and OF 2 and to some extent for type OF 3. Kyphoplasty has proven to be an effective and safe procedure with a favorable clinical outcome. Unstable fractures and kyphotic deformities (types OF 3-5) should be percutaneously stabilized from posterior. The length of the pedicle screw construct depends on the extent of instability and deformity. Bone cement augmentation of the pedicle screws is indicated in severe osteoporosis but increases the complication rate. Restoration of stability of the anterior column can be achieved through additional vertebral body augmentation or rarely by anterior stabilization. Clinical and radiological short and mid-term results of the stabilization techniques are promising; however, the more invasive the surgery, the more complications occur.

CONCLUSION

Minimally invasive stabilization techniques are safe and effective. The specific indications for the individual procedures are guided by the OF classification and the individual clinical situation of the patient.

Minimally invasive spinal fixation in an aging population with osteoporosis: clinical and radiological outcomes and safety of expandable screws versus fenestrated screws augmented with polymethylmethacrylate

OBJECTIVE

The goal of this study was to compare the clinical and radiological outcomes between fenestrated pedicle screws augmented with cement and expandable pedicle screws in percutaneous vertebral fixation surgical procedures for the treatment of degenerative and traumatic spinal diseases in aging patients with osteoporosis.

METHODS

This was a prospective, single-center study. Twenty patients each in the expandable and cement-augmented screw groups were recruited. Clinical outcomes included visual analog scale (VAS), Oswestry Disability Index (ODI), and satisfaction rates. Radiographic outcomes comprised radiological measurements on the vertebral motion segment of the treated levels. Intraoperative data including complications were collected. All patients completed the clinical and radiological outcomes. Outcomes were compared preoperatively and postoperatively.

RESULTS

An average shorter operative time was found in procedures in which expandable screws were used versus those in which cement-augmented screws were used (p < 0.001). No differences resulted in perioperative blood loss between the 2 groups. VAS and ODI scores were significantly improved in both groups after surgery. There was no significant difference between the 2 groups with respect to baseline VAS or ODI scores. The satisfaction rate of both groups was more than 85%. Radiographic outcomes also showed no significant difference in segment stability between the 2 groups. No major complications after surgery were seen. There were 4 cases (20%) of approach-related complications, all in fenestrated screw procedures in which asymptomatic cement extravasations were observed. In 1 case the authors detected a radiologically evident osteolysis around a cement-augmented screw 36 months after surgery. In another case they identified a minor loosening of an expandable screw causing local back discomfort at the 3-year follow-up.

CONCLUSIONS

Expandable pedicle screws and polymethylmethacrylate augmentation of fenestrated screws are both safe and effective techniques to increase the pullout strength of screws placed in osteoporotic spine. In this series, clinical and radiological outcomes were equivalent between the 2 groups. To the authors’ knowledge, this is the first report comparing the cement augmentation technique versus expandable screws in the treatment of aging patients with osteoporosis.

Biomechanical Comparison of Pull-out Strength of Different Cementation and Pedicle Screw Placement Techniques in a Calf Spine Model

BACKGROUND

We hypothesized that an entire pedicle screw tract cement augmentation has greater strength than traditional techniques.

METHOD

Twenty-four fresh frozen calf lumbar spines were randomized into three study groups, each having eight vertebrae: (1) screw cemented after vertebroplasty; (2) fenestrated cemented screw; and (3) cementation of the entire pedicle screw tract. For the right side screws, two pedicle screws were inserted in each vertebra with the standard position in the sagittal plane, whereas the left side screws were placed at a 30° angle craniocaudal plane. From the recorded force-displacement curves, the maximum peak load (failure load) of each screw was determined. The mode of failure was screw stripping at all levels tested.

RESULTS

The pull-out strength for standard screw replacement at the sagittal plane was 1843.3 N, 1707.45 N, and 5365.1 N consecutively. The failure load value in the standard position in the sagittal plane in the cementation of the entire pedicle screw tract group was significantly higher than that in the fenestrated cemented screw group and screw cemented after vertebroplasty (p < 0.001 and p < 0.001, respectively). The standard pedicle screw position in the sagittal plane showed a significant pull-out strength than the others (p < 0.001).

CONCLUSION

The pull-out strength of the cementation of the entire pedicle screw tract was 2.5 times higher than the others. The pull-out strength of the pedicle screws in malposition obtained the same strength to the standard positions after the augmentation procedure in our study.

The effect of two types of resorbable augmentation materials - a cement and an adhesive - on the screw pullout pullout resistance in human trabecular bone

Augmentation materials, such as ceramic and polymeric bone cements, have been frequently used to improve the physical engagement of screws inserted into bone. While ceramic, degradable cements may ultimately improve fixation stability, reports regarding their effect on early fixation stability have been inconsistent. On the other hand, a newly developed degradable ceramic adhesive that can bond with tissues surrounding the screw, may improve the pullout performance, ensure early stability, and subsequent bony integration. The aim of this study was to investigate failure mechanisms of screw/trabecular bone constructs by comparing non-augmented screws with screws augmented with a calcium phosphate cement or an adhesive, i.e. a phosphoserine-modified calcium phosphate. Pullout tests were performed on screws inserted into trabecular cylinders extracted from human femoral bone. Continuous and stepwise pullout loading was applied with and without real-time imaging in a synchrotron radiation micro-computed tomograph, respectively. Statistical analysis that took the bone morphology into account confirmed that augmentation with the adhesive supported significantly higher pullout loads compared to cement-augmented, or non-augmented screws. However, the adhesive also allowed for a higher injection volume compared to the cement. In-situ imaging showed cracks in the vicinity of the screw threads in all groups, and detachment of the augmentation materials from the trabecular bone in the augmented specimens. Additional cracks at the periphery of the augmentation and the bone-material interfaces were only observed in the adhesive-augmented specimen, indicating a contribution of surface bonding to the pullout resistance. An adhesive that has potential for bonding with tissues, displayed superior pullout resistance, compared to a brushite cement, and may be a promising material for cementation or augmentation of implants.

Biomechanical study of space frame structure based on bone cement screw

Stability of space frame structures with bone cement screw reinforcement by biomechanical testing was analyzed. Seven complete human spine specimens with osteoporosis were selected. Three specimens were separated into 18 vertebral bodies. Nine vertebral bodies were randomly selected and bone cement screws were implanted on both sides. Bone cement was used to form a bridge at the front end of the two screws (single vertebral group A). The other nine vertebral bodies were implanted with cement screws on both sides, but the front ends of the two screws were not bridged (single vertebral group B). The remaining spine specimens were used for biomechanical testing of the overall stability of the three-dimensional frame. The four specimens were osteotomized, and then two specimens were randomly selected. Bone cement screws were implanted on both sides of the vertebral body, and a bone cement bridge was formed at the front end of the two screws to establish a three-dimensional frame structure (multi-vertebral group A). The other two spine specimens were implanted with cement screws on both sides of the vertebral body, but the front ends of the two screws were not bridged (multi-vertebral group B). A statistical difference was found between the extractive force of bridged and non-bridged specimens. Group B showed some loosening of screws after the test. The stability of the triangle structure screw, which was formed after the bridge was established at the front end of the single-vertebral bone cement screw, was significantly enhanced. Moreover, the stability was significantly improved after the three-dimensional frame structure was established in the multi-vertebral body group, providing a new method for clinical improvement of the stability and reliability of internal fixation in patients with severe osteoporosis and spinal disease.

Clinical Effects and Complications of Pedicle Screw Augmentation with Bone Cement: Comparison of Fenestrated Screw Augmentation and Vertebroplasty Augmentation

Background

Pedicle screw augmentation with bone cement has been experimentally demonstrated to increase the pullout strength. However, the mechanisms of screw loosening are complicated and interacting. Although vertebroplasty augmentation and fenestrated screw augmentation have been compared in many studies, there has been no comparative study on their clinical effects and complications in real clinical settings. We investigated clinical effects of bone cement augmentation of a pedicle screw and differences according to augmentation methods.

Methods

Of the total 241 patients who had osteoporosis and underwent posterior pedicle screw fixation without anterior bone graft between January 2010 and December 2016, 132 patients with ≥2 years of radiological follow-up were included in this retrospective study. The patients were divided into group I (unaugmented) and group II (bone cement augmented). Group II was subdivided into II-S group (solid screw augmented) and II-F group (fenestrated screw augmented). The incidence of screw loosening was compared between groups I and II. Cement leakage, screw loosening, and screw fractures were investigated in the subgroups.

Results

In total, 36 of 71 (52%, group I) unaugmented cases and 96 of 170 (56%, group II) augmented cases were followed up for ≥2 years. Of the total 78 solid screw augmented cases, 42 (56%) were in II-S group; 54 of the total 92 (59%) fenestrated screw augmented cases were in II-F group. Groups I and II were homogenous regarding demographic characteristics; II-S and II-F groups were also homogenous. The incidence of screw loosening was 50.0% (18/36) in group I and 7.3% (7/96) in group II (p < 0.001). Cement leakage developed in 2 of 42 (4.8%) cases in II-S group and in 5 of 54 (9.3%) cases in II-F group (p = 0.462). Screw loosening developed in 6 of 42 (14.3%) cases in II-S group and in 1 of 54 cases (1.9%) in II-F group (p = 0.041). Screw fracture developed in none of 42 cases in II-S group and in 3 of 54 cases (5.6%) in II-F group (p = 0.254).

Conclusions

In osteoporotic patients, bone cement augmentation of a pedicle screw decreased the incidence of screw loosening, and fenestrated screw augmentation was more effective than vertebroplasty augmentation.

Complex biomechanical properties of non-augmented and augmented pedicle screws in human vertebrae with reduced bone density

Background

In osteoporotic bone, the quality of the bone-to-implant interface is decreased, which may lead to early implant failure. Screw anchorage can be improved by augmentation. This effect is mainly investigated with a pull-out test. To our knowledge, the effect of cement augmentation in an in vivo physiological setup focusing on screw movement has not been investigated to date. The aim of this work was to investigate and compare augmented and native screw behavior in a physiologically related setup.

Methods

Twelve fresh-frozen human lumbar vertebrae were divided into two groups. Each vertebra was bilaterally instrumented with either non-augmented or augmented pedicle screw systems and loaded in a recently developed test setup that provided cyclic conditions comparable to a physiological gait. The cyclic loading should test the primary implant stability, comparable to the postoperative period of two months in a worst-case scenario in the absence of osseous remodeling. Screws were tracked optically, and screw movement and failure patterns were observed.

Results

Mutual influence between the left and right sides resulted in a successive, rather than simultaneous, failure. Augmentation of the screws in vertebrae with poor bone quality reduced screw subsidence and thus improved the rigidity of the screw-to-implant interface by up to six-fold. The non-augmented condition was significantly related to early screw failure.

Conclusions

Pedicle screw system failure involves a complex bilateral-coupled mechanism. The cyclic loading based on physiological conditions during walking has allowed the postoperative conditions and clinical failure mechanisms to be simulated in vitro and clarified. Future implant systems should be investigated with a physiologically related setup.

Advancements in osteoporotic spine fixation

With the global rise in the population of elderly along with other risk factors, spine surgeons have to encounter osteoporotic spine more often. Osteoporotic spine, however, causes problems in management, particularly where instrumentation is involved, resulting in screw loosening, pull out, pseudoarthroses or adjacent segment kyphosis. Osteoporosis alters the bio mechanics at the bone implant interface resulting in various degrees of fixation failure. Various advancements have been made in this field to deal with such issues in addition to modification of basic surgical techniques such as increasing the diameter and length of the screw, smaller pilot hole, under tapping, longer constructs, supplemental anterior fixation, sublaminar wires or laminar hooks, use of transverse connectors and triangulation techniques, among others. They include novel surgical techniques such as cortical bone trajectory, superior cortical trajectory, double screw technique, cross trajectory technique, bicortical screw technique or prophylactic vertebroplasty. Advances in the screw design include expandable screws, fenestrated screws, conical screws and coated screws. In addition to PMMA cement augmentation, other biodegradable cements have been introduced to mitigate the side effects of PMMA such as calcium phosphate, calcium apatite and hydroxyapatite. Pharmacotherapy with teriparatide can aid fusion and lower the rate of pedicle screw loosening. Many of these strategies have only bio mechanical evidence and require well designed clinical trials to establish their clinical efficacy. Though no single technique is fool proof, little modifications in the existing techniques or utilizing a combination of techniques without adding to the cost of the surgery may help to achieve a near-ideal result. Surgeons have to equip their armamentarium with all the recent advances, and should be open to novel thoughts and techniques.

Ultrasound melted polymer sleeve for improved primary pedicle screw anchorage: A novel augmentation technique

BACKGROUND

Cement augmentation of pedicle screws to prevent screw loosening is associated with significant complications, such as cement leakage or bone necrosis. Therefore, an alternative strategy to improve pedicle screw anchorage has been recently developed: Polymer reinforcement of pedicle screws uses an in situ melted polymer sleeve in order to enhance screw anchorage. This biomechanical study evaluated the effect of polymer-reinforcement by comparing polymer-reinforced pedicle screws to non-augmented as well as cement-augmented screws under cyclic loading.

METHODS

For each of the two comparisons (polymer-reinforced vs. non-augmented screws and polymer-reinforced vs. cement-augmented screws), polymer-reinforced screws and control screws were placed into the left and right pedicle of seven vertebrae (mean age: 74.0 (SD 9.3) years) to allow for pairwise left-right comparisons. Each screw was subjected to cyclic cranio-caudal loading with an initial load ranging from -50 N to +50 N and with stepwise increasing compressive loads (5 N every 100 cycles) until screw loosening.

FINDINGS

Polymer-reinforced pedicle screws resisted a higher number of load cycles until loosening than the contralateral non-augmented control screws (4300 SD 2018 vs. 2457 SD 1116 load cycles, p = 0.015). Screw anchorage of polymer-reinforced pedicle screws was comparable to that of cement augmented control screws (3857 (SD2085) vs. 4300 (SD1257) load cycles until failure, p = 0.64).

INTERPRETATION

Our findings indicate that polymer-reinforcement significantly enhances pedicle screw anchorage in low quality bone and that its effect is similar in size than that of cement augmentation.

Complex spine deformities in young patients with severe osteogenesis imperfecta: current concepts review

The severity of osteogenesis imperfecta (OI), the associated reduced quality and quantity of collagen type I, the degree of bone fragility, ligamentous laxity, vertebral fractures and multilevel vertebral deformities all impair the mechanical integrity of the whole spinal architecture and relate to the high prevalence of progressive kyphoscoliotic deformities during growth. Bisphosphonate therapy may at best slow down curve progression but does not seem to lower the prevalence of deformities or the incidence of surgery. Brace treatment is problematic due to pre-existing chest wall deformities, stiffness of the curve and the brittleness of the ribs which limit transfer of corrective forces from the brace shell to the spine. Progressive curves entail loss of balance, chest deformities, pain and compromise of pulmonary function and eventually require surgical stabilization, usually around puberty. Severe vertebral deformities including deformed, small pedicles, highly brittle bones and chest deformities, short deformed trunks and associated issues like C-spine and cranial base abnormalities (basilar impressions, cervical kyphosis) as well as deformed lower and upper extremities are posing multiple peri- and intraoperative challenges. Hence, an early multidisciplinary approach (anaesthetist, pulmonologist, paediatric orthopaedic spine surgeon) is mandatory. This paper was written under the guidance of the Spine Study Group of the European Paediatric Orthopaedic Society. It highlights the most pertinent information given in the current literature and various practical aspects on surgical care of spine deformities in young OI patients based on the personal experience of the contributing authors.

Early term effects of rhBMP-2 on pedicle screw fixation in a sheep model: histomorphometric and biomechanical analyses

Background

The effects of recombinant human bone morphogenetic protein-2 (rhBMP-2) on pedicle screw pullout force and its potential to improve spinal fixation have not previously been investigated. rhBMP-2 on an absorbable collagen sponge (ACS) carrier was delivered in and around cannulated and fenestrated pedicle screws in a sheep lumbar spine instability model. Two control groups (empty screw and ACS with buffer) were also evaluated. We hypothesized that rhBMP-2 could stimulate bone growth in and around the cannulated and fenestrated pedicle screws to improve early bone purchase.

Methods

Eight skeletally mature sheep underwent destabilizing laminectomies at L2-L3 and L4-L5 followed by stabilization with pedicle screw and rod constructs. An ACS carrier was used to deliver 0.15 mg of rhBMP-2 within and around the cannulated and fenestrated titanium pedicle screws. Biomechanics and histomorphometry were used to evaluate the early term results at 6 and 12 postoperative weeks.

Results

rhBMP-2 was unable to improve bony purchase of the cannulated and fenestrated pedicle screws compared to both control groups. Although rhBMP-2 groups had pullout forces that were less than both control groups, both rhBMP-2 groups had pullout force values exceeding 2,000 N, which was comparable to previously published results for unmodified pedicle screws. Significant differences in the percentages of bone in peri-screw tissues was not observed amongst the four treatment groups. Microradiography and quantitative histomorphometry showed that at 6 weeks, rhBMP-2 induced peri-screw remodeling regions containing peri-implant bone which was hypodense with respect to surrounding native trabeculae. A moderate correlation between biomechanical pullout variables and histomorphometry data was observed.

Conclusions

The design of the cannulated and fenestrated pedicle screw was able to facilitate new bone formation to achieve high pullout forces. However, delivery of rhBMP-2 should be carefully controlled to prevent excessive bone remodeling which could cause early screw loosening.

Biomechanical study of injectable hollow pedicle screws for PMMA augmentation in severely osteoporotic lumbar vertebrae: effect of PMMA distribution and volume on screw stability

OBJECTIVEThe purpose of this study was to compare stability of injectable hollow pedicle screws with different numbers of holes using different volumes of polymethylmethacrylate (PMMA) in severely osteoporotic lumbar vertebrae and analyze the relationship between screw stability and distribution and volume of PMMA.METHODSForty-eight severely osteoporotic cadaveric lumbar vertebrae were randomly divided into 3 groups-groups A, B, and C (16 vertebrae per group). The screws used in group A had 4 holes (2 pairs of holes, with the second hole of each pair placed 180° further along the thread than the first). The screws used in group B had 6 holes (3 pairs of holes, placed with the same 180° difference in position). Unmodified conventional screws were used in group C. Each group was randomly divided into subgroups 0, 1, 2, and 3, with different volumes of PMMA used in each subgroup. Type A and B pedicle screws were directly inserted into the vertebrae in groups A and B, respectively, and then different volumes of PMMA were injected through the screws into the vertebrae in subgroups 0, 1, 2, and 3. The pilot hole was filled with different volumes of PMMA followed by insertion of screws in groups C0, C1, C2, and C3. Distributions of PMMA were evaluated radiographically, and axial pull-out tests were performed to measure the maximum axial pullout strength (Fmax).RESULTSRadiographic examination revealed that PMMA surrounded the anterior third of the screws in the vertebral bodies (VBs) in groups A1, A2, and A3; the middle third of screws in the junction area of the vertebral body (VB) and pedicle in groups B1, B2, and B3; and the full length of screws evenly in both VB and pedicle in groups C1, C2, and C3. In addition, in groups A3 and B3, PMMA from each of the screws (left and right) was in contact with PMMA from the other screw and the PMMA was closer to the posterior wall and pedicle than in groups A1, A2, B1, and B2. One instance of PMMA leakage was found (in group B3). Two-way analysis of variance revealed that 2 factors-distribution and volume of PMMA-significantly influenced Fmax (p < 0.05) but that they were not significantly correlated (p = 0.078). The Fmax values in groups in which screws were augmented with PMMA were significantly better than those in groups in which no PMMA was used (p < 0.05).CONCLUSIONSPMMA can significantly improve stability of different injectable pedicle screws in severely osteoporotic lumbar vertebrae, and screw stability is significantly correlated with distribution and volume of PMMA. The closer the PMMA is to the pedicle and the greater the quantity of injected PMMA used, the greater the pedicle screw stability is. Injection of 3.0 mL PMMA through screws with 4 holes (2 pair of holes, with the screws in each pair placed on opposite sides of the screw) produces optimal stability in severely osteoporotic lumbar vertebrae.

Risk Factors for Adjacent Fractures After Cement-Augmented Thoracolumbar Pedicle Screw Instrumentation

Background

The aim of our study was to identify factors that influence the occurrence of adjacent fractures in patients with cement-augmented pedicle screw instrumentation.

Methods

Data were retrospectively collected from medical charts and operative reports for every surgery in which cement-augmented instrumentation was used in our hospital of 4 consecutive years. A total of 93 operations were included and examined for gender, age, T-score, number of fused segments, number of implanted screws, broken screws, loosening of screws, leakage and distribution pattern of cement, pre- and postoperative kyphosis angle, revision surgery and adjacent fractures in follow-up. Categorical data were compared using the χ² test or by Fisher's exact test, as appropriate. Continuous variables conforming to a normal distribution were compared using Student's t test. Otherwise the Mann-Whitney U test was applied. A P-value of <.05 was considered statistically significant. A trend was defined as a P < .2.

Results

The mean age was 68.1 years with a mean T-score of -3.12. Nineteen adjacent fractures occurred during follow-up and the median follow-up was 12 months (range, 1-27). Patients showed a higher risk for adjacent fractures following revision surgery (P = .016). Most fractures occurred superior to the instrumented level (P = .013) and in the first 12 months. Difference of T-score between the group "no adjacent fracture" and the group "adjacent fracture" was 0.7 (P = .138). Another trends were found in greater age (P = .119) and long instrumentations (P = .199).

Conclusions and Clinical Relevance

Revision surgeries are associated with a higher risk of adjacent fractures. In these cases, prophylactic kyphoplasty of the superior vertebra should be considered. This study is a retrospective, nonrandomized cohort/follow-up study.

Level of Evidence

3.

Biomechanical comparative study of the stability of injectable pedicle screws with different lateral holes augmented with different volumes of polymethylmethacrylate in osteoporotic lumbar vertebrae

BACKGROUND CONTEXT

Polymethylmethacrylate (PMMA) is widely used for pedicle screw augmentation in osteoporosis. Until now, there had been no studies of the relationship between screw stability and the distribution and volume of PMMA.

PURPOSE

The objective of this study was to analyze the relationship between screw stability and the distribution pattern and injected volume of PMMA.

STUDY DESIGN

This is a biomechanical comparison of injectable pedicle screws with different lateral holes augmented with different volumes of PMMA in cadaveric osteoporotic lumbar vertebrae.

METHODS

Forty-eight osteoporotic lumbar vertebrae were randomly divided into Groups A, B, and C with different pedicle screws (16 vertebrae in each group), and then each group was randomly divided into Subgroups 0, 1, 2, and 3 with different volumes of PMMA (four vertebra with eight pedicles in each subgroup). A pilot hole was prepared in advance using the same method in all samples. Type A and type B pedicle screws were directly inserted into vertebrae in Groups A and B, respectively, and then different volumes of PMMA (0, 1.0, 1.5, and 2.0 mL) were injected through the screws and into vertebrae in Subgroups 0, 1, 2, and 3. The pilot holes were filled with different volumes of PMMA (0, 1.0, 1.5, and 2.0 mL), and then the screws were inserted in Groups C0, C1, C2, and C3. Screw position and distribution of PMMA were evaluated radiographically, and axial pullout tests were performed to measure maximum axial pullout strength (F_max).

RESULTS

Polymethylmethacrylate surrounded the anterior one-third of screws in the vertebral body in Groups A1, A2, and A3; the middle one-third of screws in the junction area of the vertebral body and the pedicle in Groups B1, B2, and B3; and the full length of screws evenly in both the vertebral body and the pedicle in Groups C1, C2, and C3. There was no malpositioning of screws or leakage of PMMA in any sample. Two-way analysis of variance revealed that two factors-distribution and volume of PMMA-significantly influenced F_max (p<.05) but that they were not significantly correlated (p=.088). F_max values in groups using augmentation with PMMA values significantly improved compared with those in groups without PMMA (p<.05).

CONCLUSIONS

Polymethylmethacrylate can significantly enhance the stability of different injectable pedicle screws in osteoporotic lumbar vertebrae, and screw stability is significantly correlated with the distribution pattern and the injected volume of PMMA. The closer the PMMA to the pedicle and the greater the quantity of injected PMMA, the greater is the pedicle screw stability. Injection of 2.0 mL of PMMA through screws with four lateral 180° holes or of 1.0 mL of PMMA through screws with six lateral 180° holes increases the stability of pedicle screws.

Anterior Lumbar Interbody Fusion With Cement Augmentation Without Posterior Fixation to Treat Isthmic Spondylolisthesis in an Osteopenic Patient-A Surgical Technique

Background

Anterior lumbar interbody fusion (ALIF) has been well established as an effective surgical intervention for chronic back pain due to osteoporotic vertebral collapse. Historically, ALIF has consisted of an anterior approach to disc height restoration with a subsequent posterior pedicle screw fixation. Although the applications of cement augmentation with posterior fixation have been previously reported, treatment of patients with both isthmic spondylolisthesis and decreased bone mineral density using a stand-alone ALIF is controversial because of concerns for decreased fusion rates and increased subsidence risk, respectively. We report a case of stand-alone ALIF used to treat a low-grade isthmic spondylolisthesis in the setting of idiopathic thoraco-lumbar scoliosis in a patient with secondary degenerative changes and discuss the benefits of this surgical technique in a patient with several comorbidities.

Methods

An osteopenic 66-year-old woman with multiple medical comorbidities and 2 years of left radicular leg pain was found to have a Myerding grade I isthmic spondylolisthesis in the setting of idiopathic thoraco-lumbar scoliosis with secondary changes. The patient underwent an L5-S1 stand-alone ALIF with anterior cement augmentation without posterior pedicle screw fixation.

Results

The patient experienced immediate relief of radicular leg pain postoperatively and had an uneventful course. At 2 years follow-up, she remained symptom free, and radiographs showed excellent fusion and maintenance of intervertebral disc height.

Conclusions

The use of stand-alone ALIF with anterior cement augmentation of the vertebral bodies is a surgical technique that could produce excellent improvement in patients with low-grade isthmic spondylolisthesis in the setting of osteopenia. The use of the all-anterior approach in similar patients with multiple medical comorbidities can also be a useful technique, as it decreases associated morbidity of surgery and complication risks associated with prolonged operative times.

Novel Placement of Cortical Bone Trajectory Screws in the Lumbar Spine: A Radiographic and Cadaveric Study

STUDY DESIGN

This is a radiographic and cadaveric study.

OBJECTIVE

The aim of this study was to conduct a detailed comparison about the parameters between the ideal cortical bone trajectory (CBT) and practical CBT screw.

SUMMARY OF BACKGROUND DATA

CBT screws have recently become popular in spinal surgery, mainly because of their improved fixation while minimizing soft tissue dissection. However, to our knowledge, no previous study has provided a detailed comparison on the parameters between the ideal CBT and practical CBT screws.

MATERIALS AND METHODS

The 3-dimensional computed tomography scans of 126 spinal vertebrae separated from 40 lumbar spines were studied. After determining the CBT, the maximal screw length, maximal screw diameter, lateral angle (LA), and cephalad angle (CA) were calculated. Thereafter, CBT screws were inserted into these cadaveric lumbar spines. Subsequently, the lateral angle of screw (LAs) and cephalad angle of screw (CAs) of the screws were measured using 3-dimensional computed tomography.

RESULTS

As for the ideal CBT, the maximal screw length gradually increased from L1 (32.0 mm) to L4 (35.3 mm) and then decreased at L5 (34.8 mm). Moreover, the maximal screw diameter increased from L1 (4.5 mm) to L5 (7.5 mm). The LA from L1 to L5 were 9.2, 9.4, 9.9, 11.2, and 12.0 degrees, respectively. The CA from L1 to L5 were 25.8, 25.8, 26.3, 26.8, and 26.0 degrees, respectively. As for the actual CBT screw, the LAs from L1 to L5 were 12.7, 14.1, 13.2, 12.4, and 13.0 degrees, respectively. The CAs from L1 to L5 were 25.4, 27.5, 29.2, 30.1, and 30.5 degrees, respectively. Significant differences were observed between the angles of the ideal trajectory and the actual screw.

CONCLUSIONS

Parameters of the actual CBT screw are slightly larger than the optimal trajectory measurements. The CAs and LAs are ∼25-30 and 10-16 degrees, respectively. L1 and L2 should be given considerable attention when using the CBT technique. And the trajectory measurements can only be used as a guide in clinical practice.