Evaluation of the Risk Factors for the Incisional Hernia Occurrence After Robot-Assisted Laparoscopic Radical Prostatectomy.

Objective: Our aim was to evaluate patient-related factors and compare the techniques used for surgical specimen removal [trocar extension (TE) and Pfannenstiel incision (PF)] in terms of incisional hernia (IH) occurrence in patients undergoing robot-assisted laparoscopic radical prostatectomy (RALRP). Materials and Methods: The records of 219 patients who underwent RALRP in our clinic between November 2017 and March 2021 were analyzed retrospectively. Postoperative complication data and functional (continence and potency status) and oncological outcomes were recorded. Hernia type, location, and treatments applied were also noted. Results: After exclusion, complete data were available on 192 patients undergoing RALRP between the specified dates. The TE technique for removing the surgical specimen was performed in 135 patients, and the lower abdominal transverse incision technique (PF) in 57 patients. Preoperative patient- and tumor-related characteristics (age, body mass index [BMI], American Society of Anesthesiologists (ASA) score, T stage, and prostate size) were similar in both surgical groups. IH was detected in 16 patients (14 in the TE group and 2 in the PF group) (P = .156). Thirteen patients underwent surgery for IH, and three were followed up clinically. Conclusion: In our study, no statistically significant demographic or surgical technique-related factors were found to explain the occurrence of IH in patients who underwent RALRP for prostate cancer. It was observed that IH occurred more frequently in the cases where the surgical specimen was removed with the TE technique compared with the PF incision, but this result was not statistically significant. There was also no statistically significant difference between these two groups regarding oncological and functional outcomes in the early postoperative period.

Clinical and histopathological parameters in transrectal ultrasound-guided biopsies associated with tumor upgrading after radical prostatectomy: A comparative analysis of risk groups.

BACKGROUND: Thanks to technological advances, prostate cancer (PCa) can be diagnosed at a younger age. It is known that most of these patients are in the low-intermediate risk group, and the histological grade of the tumor increases in half of those undergoing radical prostatectomy (Rp) compared to their diagnostic biopsies. This is especially important in terms of active surveillance (AS) and/or the timely evaluation of curative treatment options in patients diagnosed at an early age. Our aim was to investigate clinical and histopathological parameters that may be associated with an increase in the histological grade of the tumor in patients with acinar adenocarcinoma who were diagnosed by transrectal ultrasound-guided biopsy (TRUS-Bx) and underwent Rp. METHODS: A total of 205 patients with classical acinar adenocarcinoma diagnosed by TRUS-Bx without metastasis and who underwent Rp were grouped according to the D'Amico risk classification. Age at diagnosis, serum prostate-specific antigen (PSA), PSA density, prostate volume, Prostate Imaging Reporting and Data System (PI-RADS) score, clinical stage, Gleason Grade Group (GGG), high-grade intraepithelial neoplasia in tumor-free cores (HGPIN) (single and ≥2 cores), perineural invasion (PNI), and lymphovascular invasion (LVI) was obtained. Additionally, GGG, pathological stage, lymph node metastasis, surgical margin positivity, and tumor volume obtained from Rp were evaluated. Comparisons were made between the case groups in which the tumor grade increased and remained the same, in terms of age, serum PSA, PSA density, HGPIN in tumor-free cores (single and ≥2 cores), PNI, and LVI in all biopsies (with or without tumors), as well as risk groups. In addition, the relationships of HGPIN in tumor-free cores (single and ≥2 cores), PNI, and LVI on TRUS-Bx with age, serum PSA and PSA density, tumor volume, surgical margin positivity, pathological stage, lymph node metastasis, and risk groups were examined separately. RESULTS: Of the patients, 72 (35.1%) were in the low-risk group, 95 (46.3%) in the intermediate-risk group, and 38 (18.5%) in the high-risk group. Most of the patients with an increased histological grade (n = 38, 48.1%) were in the low-risk group (p < 0.05) and had an advanced median age. HGPIN in single and ≥2 tumor-free cores and PNI were more common in these patients (p < 0.01, p < 0.001, and p < 0.05, respectively). According to the multivariable analysis, advanced age (odds ratio [OR]: 1.087, 95% confidence interval [CI]: 1.029-1.148, p < 0.05), high serum PSA (OR: 1.047, 95% CI: 1.006-1.090, p < 0.05), HGPIN in ≥2 tumor-free cores (OR: 6.346, 95% CI: 3.136-12.912, p < 0.001), and PNI (OR: 3.138, 95% CI: 1.179-8.356, p < 0.05) were independent risk factors for a tumor upgrade. Furthermore, being in the low-risk group was an independent risk factor when compared to the intermediate- and high-risk groups (OR: 0.187, 95% CI: 0.080-0.437, p < 0.001 and OR: 0.054, 95% CI: 0.013-0.230, p < 0.001, respectively). The HGPIN diagnosis was more common in the low- and intermediate-risk groups. Advanced age at diagnosis, high serum PSA and PSA density values were associated with PNI on TRUS-Bx. High serum PSA and PSA density values were associated with LVI on TRUS-Bx. Surgical margin positivity was higher in cases with PNI and LVI detected by TRUS-Bx. HGPIN in ≥2 tumor-free cores, PNI, and LVI on TRUS-Bx were associated with a higher rate of lymph node metastases. CONCLUSIONS: In patients diagnosed with acinar adenocarcinoma, the presence of HGPIN even in a single tumor-free core on TRUS-Bx was found to be significant in terms of showing an increase in the histological tumor grade in Rp. The diagnosis of HGPIN in ≥2 tumor-free cores on TRUS-Bx was determined as an independent risk factor for an increased Gleason score after Rp. Furthermore, an advanced age, a high serum PSA value, being in the low-risk group, and the presence of PNI were associated with a tumor upgrade. HGPIN in ≥2 tumor-free cores, PNI, and LVI were also associated with lymph node metastasis. Therefore, the diagnosis of HGPIN should be signed out on pathological reports.

Evaluation of the mechanical behaviour of the expandable wedge locked nail fixation in retrograde use: A finite element study.

INTRODUCTION: In literature, there have been many studies conducted to research the alternatives of standard interlocking intramedullary nailing. The expandable wedge locked nail fixation, which is thought as a new alternative to the standard interlocking nailing, has been presented in previous numerical studies. The antegrade usage of the wedge locked nail fixation has provided promising results. From this point, the aim of the study is to evaluate mechanical behavior of its retrograde usage on femur models. Additionally, another aim of the study is to investigate the effect of fracture level on mechanical properties of the fixation. MATERIALS AND METHODS: The mechanical behaviors of the wedge locked nail and standard interlocking nail fixations were compared by finite element methods. Sawbones femurs having osteotomies at five different levels to simulate different fractures were fixed with wedge locked nail or interlocking nail by using retrograde approach. With respect to the fracture level, two different nail lengths were used. Axial compression load was applied to fixations. The mechanical behaviors of the fixations were evaluated with respect to stiffness of the fixations and stresses occurred on both implants and bones. RESULTS: Any of the wedge locked nail fixation did not slip at canal. The stress and stiffness results were mostly close with each other for both nail types. The maximum stresses at locking elements or bones contacting these elements increased with decreased distance between the fracture and relevant locking elements. DISCUSSION: The wedge locked nail fixation showed comparable results to the standard interlocking nail fixation with respect to the stiffness and stress. Under axial loading, wedge locked nail provided a secured fixation without any slippage and preserved its position inside the medullary canal. It may be thought as a safe alternative to the standard interlocking nail fixation for retrograde usage. Additionally, according to stress results, it is advised to the surgeons to avoid a close locking to the fracture line.

Efficacy of mono- and multistrain synbiotics supplementation in modifying performance, caecal fermentation, intestinal health, meat and bone quality, and some blood biochemical indices in broilers.

The superiority of synbiotics in terms of their biological effects depends primarily on a suitable combination of both components, pro-biotic and pre-biotic. The present study was conducted to compare the efficacy of mono- and multistrain synbiotics on overall performance, caecal fermentation, intestinal health, meat and bone quality along with some blood biochemical indices in broilers. A total of 231, 1-day-old male Ross 308, broiler chicks were randomly assigned to three experimental groups using 11 replicates each and seven chicks/replicate. The dietary treatments included control group with no synbiotic supplementation, monostrain (Maflor) and multistrain (Maflor plus) synbiotic groups with 1 g/kg of added synbiotics each. Synbiotics feeding significantly improved animal performance with a clear impact on meat quality in terms of low-fat, optimum ultimate pH24, higher water holding capacity, and lower drip and cooking losses. Of the two synbiotics, multistrain seemed to have responded better in modifying small intestinal epithelia and fermentation metabolites, although both synbiotics were comparable in reducing the pathogen load. Load-bearing capacity of both leg bones (femur and tibia) was also enhanced with synbiotics supplementation, which was also reflected in their mineral profile. The blood serum biochemical analysis showed a reduction in circulating cholesterol and triglycerides levels and an increment in IgA and IgG concentrations. In conclusion, the remarkable efficacy of tested synbiotics in providing higher growth, better meat quality in tandem with the optimum gut environment, lower pathogen load, healthy epithelia, immunomodulation, hypocholesterolemic, and hypotriglyceridemic effects affirms their great potential to be used as feed additives in broiler diets. Contrary to our expectations, the effectiveness of a mono-strain in comparison to multistrain synbiotic in improving almost all the features investigated was also notable. Further evaluation under challenging conditions should be explicitly conducted to achieve more comprehensive results.

Mechanical comparison of standard interlocking, clawed, and expandable wedge locked nail fixations: An experimental and numerical study.

INTRODUCTION: Intramedullary nailing has been used as a standard in the treatment of the long bone fractures with its clinical and mechanical advantages. However, using distal locking screws has been associated with longer operative times, higher radiation exposure rates, and complications like breakages of distal screw or nail at the screw hole level. Therefore, attempts to eliminate distal locking screws has been always present for intramedullary nail fixation. With a similar purpose, the present study has been carried out to compare mechanical behaviors of intramedullary nail fixations with different distal locking elements. MATERIALS AND METHODS: In this study, mechanical behaviors of standard interlocking and clawed nail fixations were compared experimentally in the first part. Six fourth generation Sawbones femurs, which have a simulated subtrochanteric fracture, were divided equally and were fixed with standard interlocking and clawed nails. During axial compression tests, experimental strain measurements were taken from all fixations. After validation of numerical models with using experimental strains and stiffnesses, mechanical behaviors of standard interlocking, clawed, and wedge locked nail fixations were compared numerically under axial compression loads. In numerical comparison, the stress-strain distributions were evaluated. RESULTS: Experimental results showed that although that there was no significant difference in stiffnesses, standard nail fixation bore two times higher loads than clawed nail fixations. Under loading, decrease in the distance between fracture surfaces was approximately seven times higher in the clawed nail fixation when compared to standard nail fixations. Numerical results showed that wedge locked nail fixation provided equivalent mechanical behavior to standard interlocking nail. DISCUSSION: In experiments of clawed nail fixation, the high decrease in the distance between fracture surfaces was evidence of the slippage of nail in the medullary canal. For a safe fixation, claws should be deployed when they are completely in contact with the cortical bone, they should be stuck into the bone in a fair amount, and the deployment in the distal third of the femur should be avoided. According to experimentally validated numerical analyses, wedge locked nail fixation may be an alternative for standard interlocking nail fixation if experimental studies support the present results.

Numerical evaluation of the mechanical properties of a novel expandable intramedullary nailing: A new alternative to standard interlocking nailing.

INTRODUCTION: There has been a great effort in preventing the disadvantages of distal locking in intramedullary nailing to date. From this scope, a novel expandable nail fixation eliminating distal locking screws has been designed. The primary aim of this numerical parametric study is to investigate mechanical behavior of expandable nail fixation on the fractured femur model under different contact parameters which are effective in maintaining the nail position and to specify the appropriate values of these contact parameters for a safe fixation. The second aim is to compare mechanical behavior of the expandable nail fixation with the standard interlocking nail fixation. MATERIALS AND METHODS: The expandable nail has three wedges which are responsible for distal fixation by compressing the medullary canal in the radial direction. 4th generation Sawbones femur model was used as bone model. A transverse osteotomy with 20 mm gap was created to simulate a subtrochanteric fracture. The fixations have been examined under axial compression with 1200 N and torsion with 7 Nm. In the parametric study, the tightening torque and static friction coefficient in wedge-canal contact were selected as contact parameters. The outputs were stiffnesses of the fixations, equivalent von-Mises stress distribution on the models, and load sharing between the canal and distal locking elements. RESULTS: The results of the parametric study showed that the model with the tightening torque of 3 Nm and friction coefficient of 0.7 was the safest. The load borne by wedges is generally prone to increase with increased tightening torque and friction coefficient. The both fixations showed close stiffness and stress values. CONCLUSION: The tightening torque of the wedge locking mechanism is directly effective in maintaining the nail position constant in canal, and the safety of the fixation is better ensured with increased tightening torque but stress states on bone must be carefully evaluated. The expandable nail provided comparable results to standard interlocking nails with respect to the fixation stiffness, stress, and contact forces. The expandable nailing may be evaluated as an alternative in the fractures of long bones in the case that the numerical results are supported by future experimental studies.

Methyl methacrylate in external fixation of supracondylar humerus fractures: An experimental study.

Supracondylar humerus fractures are common fractures around the elbow. Open fractures, comminuted metaphyseal fractures and also fractures with bone loss may need to be treated with external fixators. The aim of this study is to compare two different external fixators, tubular external fixators and polymethyl methacrylate with K wires external fixators, with regard to stiffness and stability for metaphyseal-diaphyseal osteotomies of distal humerus close to the joint. Six matched pairs (24 specimens) of second-generation sawbone humerus were prepared in a standard fashion to create a metaphyseal fracture, 5 cm proximal to the distal joint line of humerus and were randomly divided into two groups of 12 specimens each. Each sawbone humerus was osteotomized transversely at the mid-olecranon fossa with a 2-mm oscillating saw to simulate a Gartland type III fracture. The osteotomy was then reduced and stabilized using two different external fixation methods: carbon tubular external fixator with Schanz screws and methyl methacrylate with multiple K wires. Three-point bending and torsion tests were performed on the specimens. Bending and torsional stiffness of specimens were obtained for the fixation methods. According to the results of the study, the methyl methacrylate group has provided higher stiffness than classical tubular fixator with Schanz screws in three-point bending test (7.79 ± 2.33 N/mm vs 3.78 ± 1.18 N/mm, p = 0.006). The methyl methacrylate group also showed better stiffness in torsion test (0.12 ± 0.042 N m/° vs 0.067 ± 0.013 N m/°, p = 0.02). We determined for the first time in literature that external fixation with methyl methacrylate was significantly superior to the classical tubular external fixator with Schanz screws with regard to stiffness and stability under three-point bending and torsional loads. Moreover, methyl methacrylate is inexpensive and easily applied.

Do we need a transforaminal lumbar interbody fusion cage to increase the stability of functional spinal unit when comparing unilateral and bilateral fixation?

Transforaminal lumbar interbody fusion was an alternative to posterior lumbar interbody fusion for decompression surgeries. This study investigates the biomechanical responses of the unilateral and bilateral pedicle screw fixations with/without transforaminal lumbar interbody fusion cages under axial compression, flexion, and torsional loads. Ovine vertebrae were used in this study. Cadavers, randomly divided into five, were intact control group, bilateral pedicle screw fixation group, bilateral pedicle screw fixation group with transforaminal lumbar interbody fusion cage, unilateral pedicle screw fixation group, and unilateral pedicle screw fixation group with transforaminal lumbar interbody fusion cage. Axial compression, flexion, and torsion tests were performed on specimens. All study groups provided higher stiffness and yield load values than control group under axial compression. Addition of transforaminal lumbar interbody fusion cage to bilateral fixation increased the stiffness under axial compression. Moreover, additional use of transforaminal lumbar interbody fusion in unilateral fixation increased the yield load values under axial compression. Control group was the stiffest in flexion test. Placing a transforaminal lumbar interbody fusion cage to both unilateral and bilateral fixations did not significantly change the stiffness values. Additional transforaminal lumbar interbody fusion cage increased the yield moment of the bilateral fixation. In torsion test, control group had the highest stiffness and yield torque. The facet joints are the most important parts of the vertebrae on the stability. When comparing the bilateral and unilateral fixations with transforaminal lumbar interbody fusion addition, the more facet preserving approach has significantly higher stability under axial compression, flexion, and torsion. Unilateral fixation with transforaminal lumbar interbody fusion cage can be said biomechanically stable and advantageous fixation system because of the advantage on the less facet and soft tissue resection compared to bilateral fixation with transforaminal lumbar interbody fusion.

Biomechanical comparison of transdiscal fixation and posterior fixation with and without transforaminal lumbar interbody fusion in the treatment of L5-S1 lumbosacral joint.

Transdiscal screw fixation is generally performed in the treatment of high-grade L5-S1 spondylolisthesis. The main thought of the study is that the biomechanical performances of the transdiscal pedicle screw fixation can be identical to standard posterior pedicle screw fixations with or without transforaminal lumbar interbody fusion cage insertion. Lumbosacral portions and pelvises of 45 healthy lambs' vertebrae were dissected. Animal cadavers were randomly and equally divided into three groups for instrumentation. Three fixation systems, L5-S1 posterior pedicle screw fixation, L5-S1 posterior pedicle screw fixation with transforaminal lumbar interbody fusion cage insertion, and L5-S1 transdiscal pedicle screw fixation, were generated. Axial compression, flexion, and torsion tests were conducted on test samples of each system. In axial compression, L5-S1 transdiscal fixation was less stiff than L5-S1 posterior pedicle screw fixation with transforaminal lumbar interbody fusion cage insertion. There were no significant differences between groups in flexion. Furthermore, L5-S1 posterior fixation was stiffest under torsional loads. When axial compression and flexion loads are taken into consideration, transdiscal fixation can be alternatively used instead of posterior pedicle screw fixation in the treatment of L5-S1 spondylolisthesis because it satisfies enough stability. However, in torsion, posterior fixation is shown as a better option due to its higher stiffness.

Comparison of rigid and semi-rigid instrumentation under acute load on vertebrae treated with posterior lumbar interbody fusion/transforaminal lumbar interbody fusion procedures: An experimental study.

Rigid and semi-rigid fixations are investigated several times in order to compare their biomechanical stability. Interbody fusion techniques are also preferable for maintaining the sagittal balance by protecting the disk height. In this study, the biomechanical comparison of semi-rigid and rigid fixations with posterior lumbar interbody fusion or transforaminal lumbar interbody fusion procedures is conducted under trauma. There were four different test groups to analyze the effect of acute load on treated ovine vertebrae. First and second groups were fixed with polyetheretherketone rods and transforaminal lumbar interbody fusion and posterior lumbar interbody fusion cages, respectively. Third and fourth groups were fixed with titanium rods and posterior lumbar interbody fusion and transforaminal lumbar interbody fusion cages, respectively. The drop tests were conducted with 7 kg weight. There were six samples in each group so the drop test repeated 24 times in total. The test samples were photographed and X-rayed (laterally and anteroposteriorly) before and after drop test. Two fractures were observed on group 1. Conversely, there were no fractures observed for group 2. There were no anterior element fractures for both groups 1 and 2. However, one fracture seen on group 3 was anterior element fracture, whereas the other three were posterior element fractures. All three fractures were anterior element fractures for group 4. Treated vertebrae with polyetheretherketone rods and posterior lumbar interbody fusion cages showed the best durability to the drop tests among the groups. Semi-rigid fixation gave better results than rigid fixation according to failed segments. Posterior lumbar interbody fusion cages seem to be better option for semi-rigid fixation, however mentioned surgical disadvantages must be considered.

Comparison of monoplanar versus biplanar medial opening-wedge high tibial osteotomy techniques for preventing lateral cortex fracture.

PURPOSE: The purpose of this study was to investigate the mechanical strength of both monoplanar and biplanar medial opening-wedge high tibial osteotomy (MOWHTO) procedures and assess the risk of lateral cortex disruption for both techniques. METHODS: Twelve synthetic tibia models with cortical shells were used as test models. Saw cuts for monoplanar MOWHTO and biplanar MOWHTO were generated on the test models in equal numbers (n = 6 for both groups). Wedge opening load and wedge gap distance were evaluated via compressive tests. RESULTS: The mean gap distance just before the lateral cortex fracture in the monoplanar group was 14.7 ± 2.9 mm, which was significantly narrower than that in the biplanar group of 19.1 ± 2.0 mm (p = 0.015). The mean load just before the occurrence of lateral cortex fracture of 32.4 ± 3.2 N in the monoplanar osteotomy group was significantly lower than that in the biplanar osteotomy group of 111.8 ± 9.3 N (p = 0.009). CONCLUSION: Performing a MOWHTO via the biplanar rather than the monoplanar technique allows larger-sized wedges to be opened with less risk of lateral cortical fracture. Thus, larger gaps can be opened and higher angle corrections can be achieved using the biplanar osteotomy procedure. From a clinical viewpoint, the biplanar osteotomy technique reduced the risk of lateral cortical hinge fracture during MOWHTO.

Biomechanical properties of osteoporotic rat femurs after different hormonal treatments: genistein, estradiol, and estradiol/progesterone.

INTRODUCTION: The purpose of the study is to compare the effects of genistein, estradiol, estradiol/progesterone combination on the bone mineral density and biomechanical properties of ovariectomized rats' bone. METHODS: 50 female adult Sprague-Dawley rats were divided into five groups. Bilaterally ovaeriectomy were performed in all groups except the sham-operated group. Groups were a sham-operated group and a control group (water was given), estradiol treated group (17-ß estradiol 0.015 mg/kg per day), genistein treated group (genistein 10 mg/kg per day), and an estradiol/progesterone combination group (17-ß estradiol 0.015 mg/kg plus drosperinone 0.028 mg/kg per day). The water or hormones were implemented in relevant groups for eight weeks by orogasthric catheter. The bone mineral density and biomechanical properties of the femur were analyzed. RESULTS: Genistein, estradiol, and estradiol/progesterone groups increased bone mineral density significantly compared to the control group. In diaphysis and metaphysis bending test, all groups had higher peak load values than the control group. There were statistically significant differences between the estrogen/progesterone group and control group in diaphysis bending with regard to peak load. There were statistically significant differences between the estradiol and control groups in metaphysis bending with regard to peak load. In axial rotation test, all groups had higher peak torque values than the control groups. CONCLUSIONS: Genistein, estradiol and estrogen/progesterone combination improved the biomechanical properties of the ovariectomized rat bone. Genistein which has less side effects may be considered as an alternative in the treatment of postmenopausal osteoporosis.

Experimental Evaluation of the Developmental Mechanism Underlying Fractures at the Adjacent Segment.

BACKGROUND: Compression fractures at adjacent mobile segments have been reported as adjacent segment disease under trauma in several studies. In this study, the occurrence of fractures at the adjacent segment was evaluated experimentally under trauma. METHODS: Static testing of different fixation systems was performed to show their biomechanical performances. The ovine vertebrae fixed with rigid, dynamic, and semirigid systems were used as test samples. The stiffness values of the systems were obtained by testing the vertebrectomy models under compression bending, lateral bending, and torsion tests. In addition, their effects on the adjacent segments were experimentally evaluated within a drop mechanism. A free-fall drop mechanism was designed and manufactured. Next, 3.5-kg, 5-kg, and 7-kg weights were released from 1 m above the test samples to generate compression fractures. The occurrence of compression fractures was observed with the use of radiograph of test samples, which were obtained before and after the drop test. RESULTS: Dynamic and semirigid systems have advantages compared with rigid systems as the result of their lower stiffness values. Radiographs showed that epiphysis fractures occurred at fixed and adjacent mobile segments, which were fixed with semirigid fixation. In addition, dynamic fixation well preserved the fixed and adjacent mobile segments under trauma. CONCLUSIONS: The dynamic system with a polyetheretherketone rod can better preserve both adjacent and fixed segments. However, because of the cantilever beam effect, the semirigid system exhibits a great disadvantage.

Biomechanical comparison of unilateral semi-rigid and dynamic stabilization on ovine vertebrae.

Using the unilateral pedicle screw fixation was thought to decrease the stiffness of the fixed segments. Various prospective, randomized studies were performed to determine whether unilateral pedicle screw fixation provides the necessities of bilateral fixation in one- or two-segment lumbar spinal fusion. In this study, four different unilateral pedicle screw fixation systems were evaluated to determine which one best approximated an intact spine with respect to biomechanics and kinematics. The four groups included an intact group, a unilateral facetectomy group with no fixation, a unilateral semi-rigid pedicle screw fixation group with a poly-ether-ether-ketone rod, and a unilateral dynamic pedicle screw fixation group. The bone mineral densities of all specimens were measured and specimens were matched with groups randomly. Flexion, lateral bending, and axial rotation tests were performed to compare the groups. For the flexion, lateral bending, and axial rotation tests, the best biomechanical outcomes were in the control group. The unilateral facetectomy group had the poorest performance and was not stable enough, compared with the control group. The dynamic and semi-rigid groups showed performance closer to that of the control group. The biomechanical responses of these two groups were also in good agreement, showing no significant statistical differences. Based on these test results, it is concluded that the unilateral dynamic and semi-rigid pedicle screw fixations can be used to provide stability to the vertebrae.

Evaluation of the Effect of Fixation Angle between Polyaxial Pedicle Screw Head and Rod on the Failure of Screw-Rod Connection.

Introduction. Polyaxial screws had been only tested according to the ASTM standards (when they were perpendicularly positioned to the rod). In this study, effects of the pedicle screws angled fixation to the rod on the mechanical properties of fixation were investigated. Materials and Method. 30 vertically fixed screws and 30 screws fixed with angle were used in the study. Screws were used in three different diameters which were 6.5 mm, 7.0 mm, and 7.5 mm, in equal numbers. Axial pull-out and flexion moment tests were performed. Test results compared with each other using appropriate statistical methods. Results. In pull-out test, vertically fixed screws, in 6.5 mm and 7.0 mm diameter, had significantly higher maximum load values than angled fixed screws with the same diameters (P < 0.01). Additionally, vertically fixed screws, in all diameters, had significantly greater stiffness according to corresponding size fixed with angle (P < 0.005). Conclusion. Fixing the pedicle screw to the rod with angle significantly decreased the pull-out stiffness in all diameters. Similarly, pedicle screw instrumentation fixed with angle decreased the minimum sagittal angle between the rod and the screw in all diameters for flexion moment test but the differences were not significant.