Clinical evaluation of a bone cement-injectable cannulated pedicle screw augmented with polymethylmethacrylate: 128 osteoporotic patients with 42 months of follow-up

Micro-Computed Tomography Analysis and Histological Observation of the Screw-Bone Interface of Novel Porous Scaffold Core Pedicle Screws and Hollow Lateral Hole Pedicle Screws: A Comparative Study in Bama Pigs

OBJECTIVE

Screw loosening is a common complication of pedicle screw internal fixation surgery. This study aimed to investigate whether the application of a porous scaffold structure can increase the contact area between screws and bone tissue by comparing the bone ingrowth and screw-bone interface of porous scaffold core pedicle screws (PSCPSs) and hollow lateral hole pedicle screws (HLHPSs) in the lumbar spine of Bama pigs.

METHODS

Sixteen pedicle screws of both types were implanted into the bilateral pedicles of the L1-4 vertebrae of 2 Bama pigs. All Bama pigs were sacrificed and the lumbar spine was freed into individual vertebrae at 16 weeks postoperatively. After the vertebrae were made into screw-centered specimens, micro-computed tomography analysis and histological observation were performed to assess the screw-bone interface and bone growth around and within the screws.

RESULTS

We found that the bone condition around PSCPSs and HLHPSs did not show significant differences on micro-computed tomography three-dimensional reconstruction images. CT transverse views showed different bone growth inside the 2 screws. In PSCPSs, bone tissue was seen to fill the internal pores and was evenly distributed around each strut. Inside HLHPSs, bone growth was confined to 1 side of the screw and did not fill the entire cavity. Osteometric analysis showed that bone volume fraction and trabecular number, the parameters representing bone mass, were higher in PSCPSs than in HLHPSs. These differences were not statistically significant (P > 0.05). Histological observations visualized that the osseointegration within PSCPSs was superior to that of HLHPSs, and the tight integration of bone tissue with the porous scaffold resulted in a larger screw-bone integration area in PSCPSs than in HLHPSs.

CONCLUSIONS

Compared with HLHPSs, PSCPSs possessing a porous scaffold core could promote bone ingrowth and osseointegration, resulting in an effective enhancement of the combined area of the screw-bone interface.

Is there a risk of further displacement of the fractured fragment into the spinal canal in osteoporotic vertebral burst fractures after unilateral PKP? A prospective study

BACKGROUND CONTEXT

The optimal treatment for osteoporotic vertebral burst fracture (OVBF) without neurological symptoms is still a matter of debate.

PURPOSE

To evaluate the safety and efficacy of percutaneous kyphoplasty (PKP) for OVBF.

STUDY DESIGN

The study is a prospective study and is registered in the China Clinical Trials Registry with the registration number ChiCTR-OOC-17013227.

PATIENT SAMPLE

The study involved 119 patients with 137 fractured vertebrae who underwent unilateral PKP for OVBF.

OUTCOME MEASURES

The measurements were carried out independently by two physicians and measured with picture archiving and communication system (PACS) and ImageJ software (National Institutes of Health, Bethesda, MD, USA).

METHODS

The change in the spinal canal area and posterior wall protrusions (PWP) were measured before and after surgery via three-dimensional computed tomographic imaging (CT). Preoperative, postoperative, and final follow-up standing X-rays were used to measure the height of the anterior wall (HAW), height of the posterior wall (HPW), and local kyphotic angle (LKA). Additionally, visual analogue scale (VAS) and the Oswestry Disability Index (ODI) were also determined.

RESULTS

Among the 137 vertebrae assessed, 79 exhibited an increased postoperative canal area, while 57 showed a decrease, with mean values of 8.28±6.871 mm² and -9.04±5.991 mm², respectively. Notably, no significant change in postoperative canal area was identified on the entire dataset (p>.01). There was a significant decrease between median preoperative (3.9 [IQ1-IQ3=3.3-4.8] mm) and postoperative (3.7 [IQ1-IQ3=3.0-4.4] mm) PWP (p<.01). Preoperative and postoperative HAW measurements were 19.4±6.1 mm and 23.2±5.2 mm, respectively (p<.01). However, at the final follow-up, the HAW was lower than the postoperative value. The HPW was also significantly improved after surgery (p<.01), but at the final follow-up, it was significantly decreased compared with the postoperative measurement. Following surgery, KA was significantly corrected (p<.01); however, at the final follow-up, relapse was detected (average KA: 18.4±10.3°). At the final follow-up, both VAS and ODI were significantly improved compared with the preoperative period (p<.01). As for complications, 50 patients experienced cement leakage, and 16 patients experienced vertebral refracture. All patients did not develop neurological symptoms during the follow-up.

CONCLUSIONS

OVBF without neurological deficits showed significant improvement in symptoms during the postoperative period after PKP. There was no notable alteration in the spinal canal area, but a significant decrease in PWP was observed. Consequently, we posit that PKP stands as a secure and efficacious surgical intervention for treating OVBF cases devoid of neurological symptoms.

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.

Cardiopulmonary Cement Embolism Following Cement-Augmented Pedicle Screw Fixation: A Narrative Review

Fixation using cement-augmented pedicle screws (CAPS) is being increasingly performed. However, CAPS-associated cement leakage is a critical problem that can lead to cardiopulmonary cement embolism (CPCE). This narrative review aimed to explore the incidence of and risk factors and treatment strategies for CPCE and cement leakage-related complications after CAPS fixation. Data were extracted from each article, including characteristics of CPCE after CAPS fixation (incidence, location, diagnostic method and criteria, treatment, and outcome and prognosis). Overall, 28 case series and 14 case reports that met the inclusion criteria were included. Of the 1974 cases included in the review, CPCE was noted in 123, symptomatic CPCE in 35, and death in six, respectively. The frequencies of PCE and symptomatic PCE after CAPS fixation were 6% (range: 0-28.6%) and 1.3% (range: 0-26%), respectively. The range of frequencies of PCE and symptomatic PCE after CAPS fixation may have been wide because the definition of CPCE and data collection methods differed among the reports analyzed. Since PCE due to large cement emboli may be primarily related to the surgical technique, improved technique, such as minimizing the number of CAPSs by injecting low-volume high-viscosity cement at low velocity and pressure, and careful observation of cement leakage during CAPS insertion may reduce PCE associated with cement leakage. Spinal surgeons should pay more attention to the occurrence of CPCE during and after CAPS insertion, which can cause serious complications in some patients.

Is 3D-printed prosthesis stable and economic enough for anterior spinal column reconstruction after spinal tumor resection? A retrospective comparative study between 3D-printed off-the-shelf prosthesis and titanium mesh cage

OBJECT

To investigate the stability and cost-effectiveness of the three-dimensional-printed (3DP) off-the-shelf (OTS) prosthesis in the reconstruction of the anterior column of the thoracic/lumbar spine after tumor resection.

METHODS

Thirty-five patients (26 with primary malignant tumors and nine with metastatic malignant tumors) who underwent tumor resection and anterior column reconstruction between January 2014 and January 2019 were included in a single institute. Patients were divided into the 3DP OTS prosthesis (3DP) group (n = 14) and the titanium mesh cage (TMC) group (n = 21) by the type of implant. The operation time, intraoperative blood loss, hospital stay, history of radiotherapy, surgical level and total cost were collected and compared between the two groups. Mechanical complications and radiological parameters including mean vertebral height, subsidence, fixation failure(nonunion, migration, screw loosening, rod breakage) rate were recorded at preoperation, 1 week, 3 months, 6 months, 12 months after surgery then at 1 year interval or stop until the end of survival. The follow-up patients were also sent with short form-36 to assess their health-related quality of life (HRQoL) and questions about the current condition of their disease.

RESULTS

The mean overall follow-up was 24.6 months. Of the 35 patients involved, six patients died and six were lost to follow-up. The differences between the two groups in operative time, intraoperative blood loss, and hospital stay were not statistically significant (p > 0.05). The differences in fixation failure and the subsidence rate between the two groups were not statistical significant (p > 0.05). The difference of subsidence rate between the cases with and without osteoporosis, cases with and without radiotherapy was statistically significant within each group (p < 0.05). However, the difference of subsidence rate between the surgical level above or below T10 was not statistically significant (p > 0.05). The response rate of the questionnaire among the survived patients was 100% (23/23 patients). The results of the Short Form- (SF-)36 between the two groups were similar (p > 0.05). The total cost was higher in the 3DP group (p < 0.05) with its higher graft cost (p < 0.05), but the differences in internal fixation cost and other cost were not statistically significant between groups (p > 0.05).

CONCLUSION

Compared to TMC, the 3DP OTS prosthesis achieved similar clinical and radiological results in spinal anterior spinal column reconstruction of thoracic/lumbar spinal tumor resection. However, the 3DP OTS prosthesis was more expansive than TMC.

Results of in situ fixation of Andersson lesion by posterior approach in 35 cases

STUDY OBJECTIVE

Due to the rarity of the Andersson lesion (AL), the literature is ambiguous regarding the type of surgical fixation, need for debridement and deformity correction. The purpose of this retrospective study is to evaluate the efficacy, feasibility and functional outcome of posterior fixation in AL.

MATERIALS AND METHODS

This study included 35 patients having thoracolumbar AL operated for in situ fixation and fusion with minimum of 24-month follow-up. VAS (Visual Analogue Score) back pain, ODI (Oswestry Disability Index), Frankel's grade were compared and analyzed. Union status was noted with complications.

RESULTS

The mean age of 35 patients was 56.34(± 11.3) years with average follow-up of 51.49 months. Two patients had AL at two levels. 27/37 AL were at discal level. Average estimated blood loss (EBL) was 276.43 ml and duration of surgery was 130.43 min. On an average, operated segments needed 7.77 screws. There were ten minor complications without long-term sequel. Neurological improvement was noted in 30 patients. Average preoperative VAS score improved from 8.69 to 3.14, ODI score improved from 68.76 to 18.77 at final follow-up which were significant (p < 0.05). There was significant improvement in Frankel's grading (Z = - 4.354, P = 0.00).

CONCLUSIONS

Surgical management of AL by posterior approach and posterior stabilization can give satisfactory results without the need of extensive anterior reconstruction, bone grafting or deformity correction procedures without added morbidity and complications.

Location of pedicle screw hold in relation to bone quality and loads

Introduction: Sufficient screw hold is an indispensable requirement for successful spinal fusion, but pedicle screw loosening is a highly prevalent burden. The aim of this study was to quantify the contribution of the pedicle and corpus region in relation to bone quality and loading amplitude of pedicle screws with traditional trajectories.

Methods: After CT examination to classify bone quality, 14 pedicle screws were inserted into seven L5. Subsequently, Micro-CT images were acquired to analyze the screw’s location and the vertebrae were split in the midsagittal plane and horizontally along the screw’s axis to allow imprint tests with 6 mm long sections of the pedicle screws in a caudal direction perpendicular to the screw’s surface. Force-displacement curves in combination with the micro-CT data were used to reconstruct the resistance of the pedicle and corpus region at different loading amplitudes.

Results: Bone quality was classified as normal in three specimens, as moderate in two and as bad in two specimens, resulting in six, four, and four pedicle screws per group. The screw length in the pedicle region in relation to the inserted screw length was measured at an average of 63%, 62%, and 52% for the three groups, respectively. At a calculated 100 N axial load acting on the whole pedicle screw, the pedicle region contributed an average of 55%, 58%, and 58% resistance for the normal, moderate, and bad bone quality specimens, respectively. With 500 N load, these values were measured at 59%, 63%, and 73% and with 1000 N load, they were quantified at 71%, 75%, and 81%.

Conclusion: At lower loading amplitudes, the contribution of the pedicle and corpus region on pedicle screw hold are largely balanced and independent of bone quality. With increasing loading amplitudes, the contribution of the pedicle region increases disproportionally, and this increase is even more pronounced in situations with reduced bone quality. These results demonstrate the importance of the pedicle region for screw hold, especially for reduced bone quality.

Prediction of Sacral Screw Loosening after Lumbosacral Surgeries Involving Rigid Fixation of Sacral Bone Using Preoperative Computed Tomography Scans

Objective

To find a preoperative computed tomography-based method to predict the incidence of sacral screw loosening and assist surgical planning.

Methods

Surgically treated patients for degenerative lumbosacral disorders with rigid pedicle screw fixation of patients with L5-S1 vertebra in our center from January 2016 to January 2021 were retrospectively included in the current study. CT scan attenuation of the horizontal plane of the sacrum was measured with Hounsfield units (HU). Postoperative X-ray tests were used to diagnose screw loosening. The data was analyzed by independent sample t-tests, X² analysis, Pearson correlation analysis, and ROC curve analysis.

Results

A total of 162 (114 male, 48 female, average age 63.7 ± 7.3 years) patients were included in the final analysis. Significant differences were found between the screw loosening group and nonloosening group concerning the HU value of the sacrum at the horizontal plane (P < 0.01). In ROC curve analysis, AUC was 0.674 (95% CI: 0.592-0.756). A cutoff of 200 HU provided 64.8% sensitivity and 62.4% specificity, and a cutoff of 150 HU provided 90.2% sensitivity.

Conclusions

Analyzing 162 patients with at least 12 months of follow-up, we propose cutoff CT attenuation values of 200 HU and 150 HU to take moderate and radical measures of screw augmentation to prevent screw loosening in the sacral bone.

Decompression and fusion surgery for osteoporotic vertebral fractures: WFNS Spine Committee Recommendations

INTODUCTION

Osteoporotic vertebral fractures (OVF) are common due to aging populations. Their clinical management remains controversial. Although conservative approaches are sufficient in most cases, there are certain conditions where decompression or fusion surgery are necessary. This manuscript aims to clarify the indications and types of surgeries for OVF.

EVIDENCE ACQUISITION

A Medline and Pubmed search spanning the period between 2010 and 2020 was performed using the keywords "osteoporotic vertebral fractures and decompression surgery" and "osteoporotic vertebral fractures and fusion surgery". In addition, we reviewed up-to-date information on decompression and fusion in osteoporotic vertebral fracture (OVF) to reach an agreement in two consensus meetings of the World Federation of Neurosurgical Societies (WFNS) Spine Committee that was held in January and February 2021. The Delphi method was utilized to improve the validity of the questionnaire.

EVIDENCE SYNTHESIS

A total of 19 studies examining decompression and fusion surgery in OVF were reviewed. Literature supports the statement that decompression and fusion surgery are necessary for progressive neurological deficits after OVF. The Spine Section of the German Society for Orthopedics and Trauma (DGOU) classification revealed that it might help make surgical decisions. We also noted that in patients planning to undergo surgery to correct significant kyphosis after OVF, several techniques, including multilevel fixation, cement augmentation, preservation of sagittal balance, and avoiding termination at the apex of kyphosis are necessary to prevent complications. Additionally, it became clear that there is no consensus to choose the type of open surgery (anterior, posterior, combined, using cement or bone or vertebral body cage, the levels, and kind of instrumentation). The current literature indicated that implant failure in the osteoporotic spine is a common complication, and many techniques have been described to prevent implant failure in the osteoporotic spine. However, the superiority of one method over another is unclear.

CONCLUSIONS

Open surgery for osteoporotic vertebral fractures should be considered if neurologic deficits and significant painful kyphosis. The apparent indications of surgery and most ideal surgical technique for OVF remain unclear in the literature; therefore, the decision must be individualized.

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.

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.

Biomechanical design and analysis of auxetic pedicle screw to resist loosening

BACKGROUND

Pedicle screws are widely used in fusion surgery, while screw loosening often occurrs. An auxetic structures based pedicle screw was proposed to improve the bone-screw fixation by radial expansion of the screw body under tensile force to resist pulling out. It was optimized to obtain excellent anti-pullout ability for a particular bone based on the biomechanical interaction between screw and surrounding bone.

METHODS

The screw was designed based on re-entrant unit cells. The mechanical properties of it were adjusted by the wall thickness (t) and re-entrant angle (θ) of the unit cell, and characterized using finite element (FE) method. The designed screws were manufactured using 3D-printing, and Ti6Al4V as the materials. Subsequently, the pullout FE models were established, and verified by pulling the fabricated screws out of Sawbone blocks. The pulling out processes of screws from bone were simulated to explore the optimizing design of the screw.

RESULTS

The mechanical properties of the screw could be adjusted in a wide range. The biomechanical interaction between the screw and bone can affect the anti-pullout performance of the screw. With an identical elastic modulus (E), better auxiticity of the screw, resulted in a better anti-pullout performance; while an appropriate E is the necessary condition for its excellent anti-pullout performance for a particular bone.

CONCLUSION

Appropriate mechanical properties are necessary for the auxetic pedicle screw with excellent screw-bone fixation performance for a particular bone, which can be obtained by rationally designing the wall thickness and re-entrant angle of the unit cells.

Comparison of unilateral and bilateral polymethylmethacrylate-augmented cannulated pedicle screw fixation for the management of lumbar spondylolisthesis with osteoporosis

Background

Cannulated pedicle screw (CPS) augmented by polymethylmethacrylate (PMMA) can achieve satisfactory clinical efficacy in the treatment of lumbar spondylolisthesis with osteoporosis. However, accurate application of CPSs will help to avoid the difficulty of screw revision and reduce the incidence of PMMA-related complications. This study aimed to investigate the mid-term efficacy of CPS compared to unilateral and bilateral applications in this common lumbar degenerative disease.

Methods

May 2011 and May 2018, 50 patients with lumbar spondylolisthesis with osteoporosis who underwent posterior fixation and fusion using traditional pedicle screws or CPSs were included in the study. Patients were divided into two groups based on the application: the unilateral PMMA-augmented CPS group (UC, n = 29) and the bilateral PMMA-augmented CPS group (BC, n = 21). Operation time, blood loss, average hospitalization time, PMMA leakage, and other complications were recorded. The visual analog scale (VAS) and Oswestry disability index (ODI) scores were used to evaluate symptom recovery. Radiographic results were compared for intervertebral fusion and screw loosening.

Results

There were no significant differences in the baseline data of the two groups.

The VAS and ODI scores improved significantly after surgery (P < 0.05), with no significant differences between the groups (P > 0.05). The operation time and blood loss in the UC group were significantly lower than those in the BC group (P < 0.05). However, the loss of intervertebral disk height and Taillard index did not differ significantly between the groups. The rates of PMMA leakage in the UC and BC groups were 7.0% and 11.9%, respectively (P < 0.05). Bony fusion was achieved in all groups without screw loosening at the last follow-up. Only one patient experienced superficial infection in both groups, while cerebrospinal fluid leakage was observed in two patients in the BC group.

Conclusions

Unilateral application of PMMA-augmented CPS may provide adequate clinical safety and effectiveness in the surgical treatment of lumbar spondylolisthesis with osteoporosis.

Effect of Fenestrated Pedicle Screws with Cement Augmentation in Osteoporotic Patients Undergoing Spinal Fusion

OBJECTIVE

Osteoporosis is a well-known risk factor for instrumentation failure and subsequent pseudoarthrosis after spinal fusion. In the present systematic review, we analyzed the biomechanical properties, clinical efficacy, and complications of cement augmentation via fenestrated pedicle screws in spinal fusion.

METHODS

We conducted a systematic review in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Reports appearing in the PubMed database up to March 31, 2020 were queried using the key words "cement," "pedicle screw," and "osteoporosis." We excluded non-English language studies, studies reported before 2000, studies that had involved use of cement without fenestrated pedicle screws, nonhuman studies, technical reports, and individual case reports.

RESULTS

Twenty-five studies met the inclusion criteria. Eleven studies had tested the biomechanics of cement-augmented fenestrated pedicle screws. The magnitude of improvement achieved by cement augmentation of pedicle screws increased with the degree of osteoporosis. The cement-augmented fenestrated pedicle screw was superior biomechanically to the alternative "solid-fill" technique. Fourteen studies had evaluated complications. Cement extravasation with fenestrated screw usage was highly variable, ranging from 0% to 79.7%. However, cement extravasation was largely asymptomatic. Thirteen studies had assessed the outcomes. The use of cement-augmented fenestrated pedicles decreased screw pull out and improved fusion rates; however, the clinical outcomes were similar to those with traditional pedicle screw placement.

CONCLUSIONS

The use of cement-augmented fenestrated pedicle screws can be an effective strategy for achieving improved pedicle screw fixation in patients with osteoporosis. A potential risk is cement extravasation; however, this complication will typically be asymptomatic. Larger comparative studies are needed to better delineate the clinical efficacy.

Ceramic Biologics for Bony Fusion-a Journey from First to Third Generations

PURPOSE OF REVIEW

To provide information on characteristics and use of various ceramics in spine fusion and future directions.

RECENT FINDINGS

In most recent years, focus has been shifted to the use of ceramics in minimally invasive surgeries or implementation of nanostructured surface modification features to promote osteoinductive properties. In addition, effort has been placed on the development of bioactive synthetics. Core characteristic of bioactive synthetics is that they undergo change to simulate a beneficial response within the bone. This change is based on chemical reaction and various chemical elements present in the bioactive ceramics. Recently, a synthetic 15-amino acid polypeptide bound to an anorganic bone material which mimics the cell-binding domain of type-I collagen opened a possibility for osteogenic and osteoinductive roles of this hybrid graft material. Ceramics have been present in the spine fusion arena for several decades; however, their use has been limited. The major obstacle in published literature is small sample size resulting in low evidence and a potential for bias. In addition, different physical and chemical properties of various ceramics further contribute to the limited evidence. Although ceramics have several disadvantages, they still hold a great promise as a value-based graft material with being easily available, relatively inexpensive, and non-immunogenic.

Pre-Clinical Evaluation of Biological Bone Substitute Materials for Application in Highly Loaded Skeletal Sites

The development of bone substitute materials (BSMs) intended for load-bearing bone defects is highly complicated, as biological and mechanical requirements are often contradictory. In recent years, biological BSMs have been developed which allow for a more efficient integration of the material with the surrounding osseous environment and, hence, a higher mechanical stability of the treated defect. However, while these materials are promising, they are still far from ideal. Consequently, extensive preclinical experimentation is still required. The current review provides a comprehensive overview of biomechanical considerations relevant for the design of biological BSMs. Further, the preclinical evaluation of biological BSMs intended for application in highly loaded skeletal sites is discussed. The selected animal models and implantation site should mimic the pathophysiology and biomechanical loading patterns of human bone as closely as possible. In general, sheep are among the most frequently selected animal models for the evaluation of biomaterials intended for highly loaded skeletal sites. Regarding the anatomical sites, segmental bone defects created in the limbs and spinal column are suggested as the most suitable. Furthermore, the outcome measurements used to assess biological BSMs for regeneration of defects in heavily loaded bone should be relevant and straightforward. The quantitative evaluation of bone defect healing through ex vivo biomechanical tests is a valuable addition to conventional in vivo tests, as it determines the functional efficacy of BSM-induced bone healing. Finally, we conclude that further standardization of preclinical studies is essential for reliable evaluation of biological BSMs in highly loaded skeletal sites.