Abrogation of LBX1 in skeletal muscle results in hypoplastic limbs and progressive kyphosis in mice.

LBX1 is a gene located near a single-nucleotide polymorphism, rs11190870, which is highly associated with susceptibility to adolescent idiopathic scoliosis. However, the potential involvement of LBX1 in the etiology of this spinal deformity has not been elucidated. In this study, we aimed to determine whether the lack of LBX1 in skeletal muscle results in spinal deformities in mice. We generated mutant mice in which the Lbx1 allele was conditionally excised under the control of a human muscle actin promoter. Mice lacking LBX1 from the skeletal muscle were fertile and available. The mutant mice had hypoplastic forelimbs and weighed less than control animals, but otherwise, there were no overt anomalies. The mice did not exhibit a scoliosis-like spinal deformity; however, they developed moderate kyphosis as they grew old. These observations indicated that LBX1 is involved in limb development and potentially in the maintenance of spinal curvature/alignment in mice.

A Case of Fragility Fracture of the Pelvis Initially Diagnosed as Osteoarthritis of the Hip.

We present the case of a 58-year-old woman who presented with anterior groin pain, initially diagnosed with hip osteoarthritis (OA), scheduled for total hip arthroplasty, and subsequently diagnosed with an occult fragility fracture of the pelvis (FFP) by preoperative computed tomography (CT) examination. We diagnosed the patient with pre-existing hip OA and a bilateral sacrum and left pubic tubercle fracture that exacerbated the groin pain. We operated on the FFP followed by simultaneous bilateral total hip arthroplasty. Given the high prevalence of hip OA and the increasing incidence of FFP, comorbidity of these 2 entities should be ruled out. Even if hip OA is apparent, plain radiographs are insufficient to rule out FFP, necessitating a thorough clinical examination, followed by a CT examination if an FFP is suspected.

Establishment of a suitable combination of serological markers to diagnose surgical site infection following spine surgery: A novel surgical site infection scoring system.

BACKGROUND: The accuracy rates of several effective serological markers of surgical site infection following spine surgery are unclear. We aimed to verify the accuracy of each significant marker and identify the most suitable and effective combination of these markers for the diagnosis of surgical site infection following spine surgery. METHODS: This retrospective study enrolled 329 patients who underwent spine surgery for causes other than infectious spondylitis, including 9 patients with surgical site infection. Complete blood cell count, differential counts, and C-reactive protein levels were measured preoperatively and postoperatively (days 2 and 7). Serological data were compared among non-surgical site infection and surgical site infection cases. Cutoff values for items presenting significant differences were determined using receiver operating characteristic curves. Ratios in each serological factor at each time-point were compared. Combinations of these factors on postoperative day 7 and ratio items were investigated to determine the most suitable combination comprising the least number of items. RESULTS: Significant differences were noted among four factors on postoperative day 7, except for the lymphocyte count. For the ratio items, significant differences were observed among 6 items. The combination of these ten markers was examined; each factor was assigned 1 point. The most suitable combination comprising 4 items, including neutrophil count, neutrophil-to-lymphocyte ratio, lymphocyte count ratio, and C-reactive protein ratio, presented an AUC of 0.95, with a cutoff value, sensitivity, and specificity of 3 points, 0.89, and 0.92, respectively. CONCLUSION: The combination of four markers is the most suitable criterion for the surgical site infection scoring system following spine surgery, where scores of ≥3 points strongly indicate surgical site infection. This criterion may be a strong tool for detecting surgical site infection.

A novel approach for identifying serological markers indicative of surgical-site infection following spine surgery: Postoperative lymphopenia is a risk factor.

BACKGROUND: Postoperative lymphopenia (PL) after spine surgery is reported to be an indicator of surgical-site infection (SSI). PL without SSI is often encountered, resulting in a treatment dilemma. We focused on PL, so as to improve the accuracy of detecting SSI. METHODS: In total, 329 patients underwent spine surgery, including nine patients presenting with SSI. The complete blood cell counts, differential counts, and C-reactive protein (CRP) level were measured pre-surgery and on postoperative days 2, 7, and 14. The relationships between PL and SSI were evaluated, and PL and non-PL conditions were compared among all cases. We then divided the patients into two groups: PL and non-PL, and determined the useful serological markers using receiver operating characteristic curves. RESULTS: Sixty-one patients presented with PL, including four with SSI. However, PL was not directly suggested as a biomarker of SSI (p = 0.067). We revealed PL as a risk factor for SSI (p = 0.004, Odds ratio: 7.54). Among all cases, the lymphocyte count and CRP level differed significantly between the PL and non-PL groups at all perioperative time-points. The white blood cell count, neutrophil count, and CRP levels on postoperative day 7 significantly differed between the SSI and non-SSI cases in the PL group. The area under the curve (AUC) for CRP was greater than that of the other parameters. The neutrophil count was only effective as a marker in the non-PL group. The combination of two cutoff values (CRP: 3.7 mg/dL (PL group) and neutrophil count: 6172/µL (non-PL group)) presented high specificity (87.2%) and sensitivity (88.9%), while only one cutoff value (CRP: 2.9 mg/dL) had a specificity of 77.4% and sensitivity of 77.8%. CONCLUSIONS: Approximately one-fifth of patients developed PL post-surgery, which was a risk factor for SSI, with constant high inflammation. Grouping based on PL and establishing diagnostic cutoff values are more appropriate than establishing only one cutoff value for overall cases.

Impact of Screw Diameter and Length on Pedicle Screw Fixation Strength in Osteoporotic Vertebrae: A Finite Element Analysis.

STUDY DESIGN: Biomechanical study. PURPOSE: To quantitatively investigate the effect of screw size on screw fixation in osteoporotic vertebrae with finite element analysis (FEA). OVERVIEW OF LITERATURE: Osteoporosis poses a challenge in spinal instrumentation; however, the selection of screw size is directly related to fixation and is closely dependent on each surgeon's experience and preference. METHODS: Total 1,200 nonlinear FEA with various screw diameters (4.5-7.5 mm) and lengths (30-50 mm) were performed on 25 patients (seven men and 18 women; mean age, 75.2±10.8 years) with osteoporosis. The axial pullout strength, and the vertebral fixation strength of a paired-screw construct against flexion, extension, lateral bending, and axial rotation were examined. Thereafter, we calculated the equivalent stress of the bone-screw interface during nondestructive loading. Then, using diameter parameters (screw diameter or screw fitness in the pedicle [%fill]), and length parameters (screw length or screw depth in the vertebral body [%length]), multiple regression analyses were performed in order to evaluate the factors affecting various fixations. RESULTS: Larger diameter and longer screws significantly increased the pullout strength and vertebral fixation strength; further, they decreased the equivalent stress around the screws. Multiple regression analyses showed that the actual screw diameter and %length were factors that had a stronger effect on the fixation strength than %fill and the actual screw length. Screw diameter had a greater effect on the resistance to screw pullout and flexion and extension loading (ß =0.38-0.43, p <0.01); while the %length had a greater effect on resistance to lateral bending and axial rotation loading (ß =0.25-0.36, p <0.01) as well as mechanical stress of the bone-screw interface (ß =-0.42, p <0.01). CONCLUSIONS: The screw size should be determined based on the biomechanical behavior of the screws, type of mechanical force applied on the corresponding vertebra, and anatomical limitations.

Feasibility of using tapping torque during lumbar pedicle screw insertion to predict screw fixation strength.

BACKGROUND: Rigid pedicle screw fixation is mandatory for achieving successful spinal fusion; however, there is no reliable method predicting screw fixation before screw insertion. The purpose of the present study was to investigate the efficacy of measurement of tapping torque to predict pedicle screw fixation. METHODS: First, different densities of polyurethane foam were used to measure tapping torque. The insertional torque during pedicle screw insertion and axial pullout strength were measured and compared between under-tapped and same-tapped groups. Next, for in vivo study, the tapping and insertional torque of lumbar pedicle screws using the cortical bone trajectory technique were measured intraoperatively in 45 consecutive patients. Then, correlations between tapping torque, the bone mineral density of the femoral neck and lumbar vertebrae, and insertional torque were investigated. RESULTS: Ex vivo tapping torque significantly correlated with the insertional torque and pullout strength regardless of tapping sizes (r = 0.98, p < 0.001). The mean in vivo tapping and insertional torque were 1.48 ± 0.73 and 2.48 ± 1.25 Nm, respectively (p < 0.001). Insertional torque significantly correlated with tapping torque and two BMD parameters, and the correlation coefficient of tapping torque (r = 0.83, p < 0.001) was higher than those of femoral neck BMD (r = 0.59, p < 0.001) and lumbar BMD (r = 0.39, p < 0.001). CONCLUSIONS: Tapping torque is a reliable predictor of pedicle screw fixation and allows surgeons to improve the integrity of the bone-screw interface by making modification prior to actual screw insertion.

Mobile Spinal Schwannoma with a Completely Cystic Appearance.

BACKGROUND Spinal schwannomas are benign tumors arising from Schwann cells. Although they have been well described, tumor movement in the spinal canal is an extremely rare finding, and entirely cystic spinal schwannomas have rarely been reported. This is the first report of a spinal schwannoma that simultaneously exhibited both these unusual features. CASE REPORT A 48-year-old female presented with dysuria and right leg pain. Initial magnetic resonance imaging (MRI) revealed a well-delineated intradural cystic lesion at the level of L4-S1 vertebrae that was isointense with cerebrospinal fluid on both T1- and T2-weighted images. A follow-up MRI 6 months later showed that the tumor had moved to the level of L2-L4; it also revealed tortuous configuration of nerve roots of the cauda equina. The tumor was resected, and a diagnosis of schwannoma with extensive cystic degeneration was pathologically confirmed. CONCLUSIONS Various possible mechanisms have been suggested for the mobility of extramedullary tumors. In the present case, MRI findings indicated the cause of the tumor movement might be attributed to the laxity of nerve roots. Besides, it is highly atypical for a schwannoma to present an entirely cystic appearance, and the combination of the 2 extraordinary features made preoperative diagnosis difficult. However, 16 out of 22 (73%) of previously reported mobile spinal tumors were schwannomas, so the differential diagnosis for a mobile spinal tumor should include schwannoma, even when the lesion seems entirely cystic on MRI. To minimize the risk of complications and additional surgical dissection, physicians should acknowledge that spinal tumors can migrate.

Comparison of Pedicle Screw Fixation Strength Among Different Transpedicular Trajectories: A Finite Element Study.

STUDY DESIGN: Comparative biomechanical study by finite element (FE) method. OBJECTIVE: To investigate the pullout strength of pedicle screws using different insertional trajectories. SUMMARY OF BACKGROUND DATA: Pedicle screw fixation has become the gold standard for spinal fusion, however, not much has been done to clarify how the fixation strength of pedicle screws are affected by insertional trajectories and bone properties. MATERIALS AND METHODS: Three-dimensional FE models of 20 L4 vertebrae were constructed from the computed tomographic data. Five different transpedicular trajectories were compared: the traditional trajectory, the vertical trajectory, and the 3 lateral trajectories with different sagittal directions (caudal, parallel, cranial). For a valid comparison, screws of the same shape and size were inserted into the same pedicle in each subject, and the pullout strength were compared with nonlinear FE analyses. In addition, the pullout strength was correlated with bone mineral density (BMD). RESULTS: The mean pullout strength showed a 3.9% increase for the vertical trajectory relative to the traditional trajectory, 6.1% for the lateral-caudal trajectory, 21.1% for the lateral-parallel trajectory, and 34.7% for the lateral-cranial trajectory. The lateral-cranial trajectory demonstrated the highest value among all trajectories (P<0.001). In each trajectory, the correlation coefficient between the pullout strength and BMD of the femoral neck (r=0.74-0.83, P<0.01) was higher than the mean BMD of all the lumbar vertebrae (r=0.49-0.75, P<0.01), BMD of the L4 vertebra (r=0.39-0.64, P<0.01), and regional BMD of the L4 pedicle (r=0.53-0.76, P<0.01). CONCLUSIONS: Regional variation in the vertebral bone density and the amount of denser bone-screw interface contribute to the differences of stiffness among different screw trajectories. BMD of the femoral neck is considered to be a better objective predictor of pedicle screw stability than that of the lumbar vertebra.

Cortical Bone Trajectory for Thoracic Pedicle Screws: A Technical Note.

STUDY DESIGN: A morphometric measurement of new thoracic pedicle screw trajectory using computed tomography and a biomechanical study on cadaveric thoracic vertebrae using insertional torque. OBJECTIVE: To introduce a new thoracic pedicle screw trajectory which maximizes engagement with denser bone. SUMMARY OF BACKGROUND DATA: Cortical bone trajectory (CBT) which maximizes the thread contact with cortical bone provides enhanced screw purchase. Despite the increased use of CBT screws in the lumbar spine, no study has yet reported the insertional technique for thoracic CBT. METHODS: First, the computed tomography scans of 50 adults were studied for morphometric measurement of lower thoracic CBT. The starting point was determined to be the intersection of the lateral two thirds of the superior articular process and the inferior border of the transverse process. The trajectory was straight forward in the axial plane angulated cranially targeting the posterior third of the superior endplate. The maximum diameter, length, and the cephalad angle were investigated. Next, the insertional torque of pedicle screws using this new technique was measured and compared with that of the traditional technique on 24 cadaveric thoracic vertebrae. RESULTS: All morphometric parameters of thoracic CBT increased from T9 to T12 (the mean diameter: from 5.8 mm at T9 to 8.5 mm at T12; the length: from 29.7 mm at T9 to 32.0 mm at T12; and the cephalad angle: from 21.4 degrees at T9 to 27.6 degrees at T12). The mean maximum insertional torque of CBT screws and traditional screws were 1.02±0.25 and 0.66±0.15 Nm, respectively. The new technique demonstrated average 53.8% higher torque than the traditional technique (P<0.01). CONCLUSIONS: The detailed morphometric measurement and favorable screw fixation stability of thoracic CBT are reported. The insertional torque using thoracic CBT technique was 53.8% higher than that of the traditional technique.

Factors that regulate spinal cord position after expansive open-door laminoplasty.

INTRODUCTION: Although appropriate dorsal migration of the spinal cord is a desired end point of cervical laminoplasty, it is difficult to predict in advance the spinal cord position after surgery and to control it during surgery. The aim of the present study was to investigate the factors that affect postoperative spinal cord position after cervical laminoplasty using multivariable analysis. MATERIALS AND METHODS: We retrospectively assessed 56 consecutive patients with cervical spondylotic myelopathy treated by open-door laminoplasty. The postoperative anterior space of the spinal cord was measured at 204 levels, and its maximum value was measured at 56 levels within the decompressed area. To identify the factors that regulate the postoperative spinal cord position, we evaluated seven radiological parameters, including the C3-C7 lordosis angle (LA), LA of the decompressed area, C3-C7 spinal cord lordosis angle (SCLA), SCLA of the decompressed area, spinal canal sagittal diameter at C5, number of expanded lamina, and postoperative dural sac diameter. RESULTS: The postoperative anterior space of the spinal cord was 5.5 ± 1.4 mm, and its maximum value was 6.4 ± 1.3 mm. A multiple linear regression analysis revealed that the number of expanded laminae (standardized partial regression coefficient: ß = 0.17, p = 0.009) and dural sac diameter (ß = 0.43, p < 0.001) was significantly associated with anterior space of the spinal cord. Although these parameters were also significantly associated with the maximum value, their relative contributions were reversed; ß = 0.49 (p < 0.001) for the number of expanded laminae and 0.25 (p = 0.029) for the dural sac diameter. CONCLUSIONS: The number of expanded laminae and dural sac diameter was significantly associated with the spinal cord position after laminoplasty. These factors could help to predict spinal cord position following laminoplasty and achieve adequate indirect decompression of the spinal cord.

Biomechanical evaluation of lumbar pedicle screws in spondylolytic vertebrae: comparison of fixation strength between the traditional trajectory and a cortical bone trajectory.

OBJECTIVE In the management of isthmic spondylolisthesis, the pedicle screw system is widely accepted surgical strategy; however, there are few reports on the biomechanical behavior of pedicle screws in spondylolytic vertebrae. The purpose of the present study was to compare fixation strength between pedicle screws inserted through the traditional trajectory (TT) and those inserted through a cortical bone trajectory (CBT) in spondylolytic vertebrae by computational simulation. METHODS Finite element models of spondylolytic and normal vertebrae were created from CT scans of 17 patients with adult isthmic spondylolisthesis (mean age 54.6 years, 10 men and 7 women). Each vertebral model was implanted with pedicle screws using TT and CBT techniques and compared between two groups. First, fixation strength of a single screw was evaluated by measuring axial pullout strength. Next, vertebral fixation strength of a paired-screw construct was examined by applying forces simulating flexion, extension, lateral bending, and axial rotation to vertebrae. RESULTS Fixation strengths of TT screws showed a nonsignificant difference between the spondylolytic and the normal vertebrae (p = 0.31-0.81). Fixation strength of CBT screws in the spondylolytic vertebrae demonstrated a statistically significant decrease in pullout strength (21.4%, p < 0.01), flexion (44.1%, p < 0.01), extension (40.9%, p < 0.01), lateral bending (38.3%, p < 0.01), and axial rotation (28.1%, p < 0.05) compared with those in the normal vertebrae. In the spondylolytic vertebrae, no statistically significant difference was observed for pullout strength between TT and CBT (p = 0.90); however, the CBT construct showed lower vertebral fixation strength in flexion (39.0%, p < 0.01), extension (35.6%, p < 0.01), lateral bending (50.7%, p < 0.01), and axial rotation (59.3%, p < 0.01) compared with the TT construct. CONCLUSIONS CBT screws are less optimal for stabilizing the spondylolytic vertebra due to their lower fixation strength compared with TT screws.

Biomechanical evaluation of fixation strength among different sizes of pedicle screws using the cortical bone trajectory: what is the ideal screw size for optimal fixation?

BACKGROUND: The cortical bone trajectory (CBT) has attracted attention as a new minimally invasive technique for lumbar instrumentation by minimizing soft-tissue dissection. Biomechanical studies have demonstrated the superior fixation capacity of CBT; however, there is little consensus on the selection of screw size, and no biomechanical study has elucidated the most suitable screw size for CBT. The purpose of the present study was to evaluate the effect of screw size on fixation strength and to clarify the ideal size for optimal fixation using CBT. METHOD: A total of 720 analyses on CBT screws with various diameters (4.5-6.5 mm) and lengths (25-40 mm) in simulations of 20 different lumbar vertebrae (mean age: 62.1 ± 20.0 years, 8 males and 12 females) were performed using a finite element method. First, the fixation strength of a single screw was evaluated by measuring the axial pullout strength. Next, the vertebral fixation strength of a paired-screw construct was examined by applying forces simulating flexion, extension, lateral bending, and axial rotation to the vertebra. Lastly, the equivalent stress value of the bone-screw interface was calculated. RESULTS: Larger-diameter screws increased the pullout strength and vertebral fixation strength and decreased the equivalent stress around the screws; however, there were no statistically significant differences between 5.5-mm and 6.5-mm screws. The screw diameter was a factor more strongly affecting the fixation strength of CBT than the screw fit within the pedicle (%fill). Longer screws significantly increased the pullout strength and vertebral fixation strength in axial rotation. The amount of screw length within the vertebral body (%length) was more important than the actual screw length, contributing to the vertebral fixation strength and distribution of stress loaded to the vertebra. CONCLUSIONS: The fixation strength of CBT screws varied depending on screw size. The ideal screw size for CBT is a diameter larger than 5.5 mm and length longer than 35 mm, and the screw should be placed sufficiently deep into the vertebral body.

Incidence and Risk Factors of Adjacent Cranial Facet Joint Violation Following Pedicle Screw Insertion Using Cortical Bone Trajectory Technique.

STUDY DESIGN: Retrospective study evaluating cranial facet joint violation (FJV) by pedicle screws. OBJECTIVE: The aim of the study was to determine the incidence and risk factors of FJV following screw placement via cortical bone trajectory (CBT). SUMMARY OF BACKGROUND DATA: CBT is a new minimally invasive technique for lumbar pedicle screw insertion that minimizes muscle dissection. Inserting a screw from a more caudal entry point can reduce iatrogenic damage to the cranial facet joint; however, no previous reports exist describing the incidence of FJV secondary to the CBT technique. METHODS: We reviewed 202 consecutive patients who underwent lumbar pedicle screw instrumentation using CBT from October 2011 to June 2015. Postoperative CT scans were obtained to determine the degree and incidence of FJV. Clinical and imaging data were analyzed to clarify the risk factors of FJV. The detailed positions of the proximal screws were also investigated and compared between the FJV and non-FJV groups. RESULTS: The incidence of FJV by the proximal screws was 11.8% (48/404), with no occurrence of intra-articular FJV. Multiple logistic regression analysis revealed that age >70 years, vertebral slip >10%, and adjacent facet joint degeneration (Pathria's grade 2 or 3) were independent factors significantly affecting FJV. There were statistically significant differences between the FJV and non-FJV groups in the facet-screw distance (3.2 ±â€Š1.0 vs. 8.1 ±â€Š2.3 mm, P < 0.01), the cranial angle (25.8 ±â€Š6.3° vs. 29.9 ±â€Š7.6°, P < 0.01), and the lamina-screw head distance (5.6 ±â€Š1.6 vs. 6.4 ±â€Š1.9 mm, P < 0.01). CONCLUSION: Lumbar pedicle screw placement via CBT would reduce FJV; however, special care should be taken in patients with age >70 years, vertebral slip >10%, and facet degeneration. LEVEL OF EVIDENCE: 3.

Evaluation of the Fixation Strength of Pedicle Screws Using Cortical Bone Trajectory: What Is the Ideal Trajectory for Optimal Fixation?

STUDY DESIGN: In vivo analysis of insertional torque of pedicle screws using cortical bone trajectory (CBT) technique. OBJECTIVE: To investigate factors contributing to the fixation strength of CBT screws and to clarify the ideal cortical trajectory for lumbar fusion. SUMMARY OF BACKGROUND DATA: CBT has developed as a new minimally invasive technique of lumbar instrumentation. Despite biomechanical studies demonstrating the superior characteristics of CBT, no study has elucidated the most suitable path for optimal fixation or compared the fixation within variations of trajectory. METHODS: The insertional torque of pedicle screws using CBT was measured intraoperatively in 72 consecutive patients. The detailed positions of a total of 268 screws were confirmed using postoperative reconstruction computed tomographic scans and were analyzed to identify factors contributing to the level of insertional torque. Investigated factors were as follows: (1) age, (2) bone mineral density of the femoral neck and lumbar vertebrae by dual-energy x-ray absorptiometry; (3) the pedicle width and height, (4) the length of the implant, (5) total screw length within the vertebra, (6) the screw length within the vertebral body, (7) the screw length within the lamina, (8) the cephalad and lateral angle of the trajectory, and (9) the distance from the long axis of the screw to the inferior and medial borders of the pedicle. RESULTS: Multiple regression analysis showed that bone mineral density of the femoral neck, screw length within the lamina, and cephalad angle were significant independent factors affecting torque. CONCLUSION: The fixation of CBT screws varied depending on technical factors (cephalad angle and screw length within the lamina) as well as the individual patient factor of bone mineral density. The ideal trajectory was directed 25° to 30° cranially along the inferior border of the pedicle so as to obtain maximum contact with the lamina and sufficient length within the vertebral body. LEVEL OF EVIDENCE: 2.

Biomechanical evaluation of the fixation strength of lumbar pedicle screws using cortical bone trajectory: a finite element study.

OBJECT: Cortical bone trajectory (CBT) maximizes thread contact with the cortical bone surface and provides increased fixation strength. Even though the superior stability of axial screw fixation has been demonstrated, little is known about the biomechanical stiffness against multidirectional loading or its characteristics within a unit construct. The purpose of the present study was to quantitatively evaluate the anchorage performance of CBT by the finite element (FE) method. METHODS: Thirty FE models of L-4 vertebrae from human spines (mean age [± SD] 60.9 ± 18.7 years, 14 men and 16 women) were computationally created and pedicle screws were placed using the traditional trajectory (TT) and CBT. The TT screw was 6.5 mm in diameter and 40 mm in length, and the CBT screw was 5.5 mm in diameter and 35 mm in length. To make a valid comparison, the same shape of screw was inserted into the same pedicle in each subject. First, the fixation strength of a single pedicle screw was compared by axial pullout and multidirectional loading tests. Next, vertebral fixation strength within a construct was examined by simulating the motions of flexion, extension, lateral bending, and axial rotation. RESULTS: CBT demonstrated a 26.4% greater mean pullout strength (POS; p = 0.003) than TT, and also showed a mean 27.8% stronger stiffness (p < 0.05) during cephalocaudal loading and 140.2% stronger stiffness (p < 0.001) during mediolateral loading. The CBT construct had superior resistance to flexion and extension loading and inferior resistance to lateral bending and axial rotation. The vertebral fixation strength of the construct was significantly correlated with bone mineral density of the femoral neck and the POS of a single screw. CONCLUSIONS: CBT demonstrated superior fixation strength for each individual screw and sufficient stiffness in flexion and extension within a construct. The TT construct was superior to the CBT construct during lateral bending and axial rotation.

Biomechanical Evaluation of Cross Trajectory Technique for Pedicle Screw Insertion: Combined Use of Traditional Trajectory and Cortical Bone Trajectory.

OBJECTIVE: To introduce a novel double-screw (cross trajectory) technique that combines use of the traditional trajectory (TT) and cortical bone trajectory (CBT) and to investigate its fixation strength quantitatively by finite element (FE) analysis. METHODS: Three-dimensional FE models of 30 osteoporotic L4 vertebrae (patients' mean age: 77.3 ± 7.4 years, 11 men and 19 women) were computationally created. Each vertebral model was implanted with bilateral pedicle screws by TT (using 7.5 mm × 40 mm screws), CBT (using 5.5 mm × 35 mm screws) and cross trajectory (combined use of TT screws of 5.5 mm × 40 mm and CBT screws of 5.5 mm × 35 mm) and compared among three groups. The vertebral fixation strength of a bilateral-screw construct was examined by applying forces simulating flexion, extension, lateral bending, and axial rotation to the vertebrae by non-linear FE analyses. RESULTS: Fixation strength using the cross trajectory was the highest among the three different techniques (P < 0.01). The cross trajectory construct demonstrated 320% higher strength than the TT construct in flexion, 293% higher in extension, 102% higher in lateral bending, and 40% higher in axial rotation (P < 0.01). Similarly, the cross trajectory construct showed 268% higher strength than the CBT construct in flexion, 269% higher in extension, 210% higher in lateral bending, and 178% in axial rotation (P < 0.01). CONCLUSIONS: The cross trajectory technique offered superior fixation strength over the TT and CBT techniques in each plane of motion. This technique may be a valid option for posterior fusion, especially in osteoporotic spine.

Comparison of fusion rates following transforaminal lumbar interbody fusion using polyetheretherketone cages or titanium cages with transpedicular instrumentation.

PURPOSE: Compared to titanium cage, polyetheretherketone (PEEK) cage with pedicle screw fixation has been increasingly used in transforaminal lumbar interbody fusion (TLIF). However, there is insufficient evidence supporting the superiority of PEEK cages over titanium cages as optimal TLIF spacers. The aim of this study was to compare the clinical and radiographic outcomes of patients at a 2-year follow-up after undergoing instrumented TLIF in which either a PEEK cage or a titanium cage was implanted. MATERIALS AND METHODS: We retrospectively analyzed prospectively collected 48 patients who underwent single-level TLIF in which the first 23 patients received a titanium cage and the 25 patients received a PEEK cage. Patient demographics, clinical outcomes, and radiographic imaging were studied. RESULTS: Improvement of clinical outcomes was comparable between the two groups. Based on the criteria using computed tomography, 96 % in the Titanium group and 64 % in the PEEK group showed fusion at 12 months. At 24 months, fusion rate in the Titanium group was increased to 100 %, while PEEK group showed 76 % of fusion rate. In the PEEK group, vertebral osteolysis was noted in 60 % of the cases with nonunion. This abnormal finding was not observed in the Titanium group. Vertebral osteolysis was significantly associated with nonunion. CONCLUSIONS: The superiority of PEEK cages over titanium cages for bony fusion was not demonstrated. Additionally, we found unfavorable radiographic findings in the cases with a PEEK cage, which may lead to nonunion. Improvement in biocompatibility of a PEEK cage will be needed to increase the fusion rate.

Cortical bone trajectory for lumbosacral fixation: penetrating S-1 endplate screw technique: technical note.

OBJECT: A cortical bone trajectory (CBT) is a new pedicle screw trajectory that maximizes the thread contact with cortical bone surface, providing enhanced screw purchase. Despite the increased use of the CBT in the lumbar spine, little is known about the insertion technique for the sacral CBT. The aim of this study was to introduce a novel sacral pedicle screw trajectory. This trajectory engages with denser bone maximally by the screw penetrating the S-1 superior endplate through a more medial entry point than the traditional technique, and also has safety advantages, with the protrusion of the screw tip into the intervertebral disc space carrying no risk of neurovascular injury. METHODS: In this study, the CT scans of 50 adults were studied for morphometric measurement of the new trajectory. The entry point was supposed to be the junction of the center of the superior articular process of S-1 and approximately 3 mm inferior to the most inferior border of the inferior articular process of L-5. The direction was straight forward in the axial plane without convergence, angulated cranially in the sagittal plane penetrating the middle of the sacral endplate. The cephalad angle to the sacral endplate, length of trajectory, and safety of the trajectory were investigated. Next, the insertional torque of pedicle screws using this technique was measured intraoperatively in 19 patients and compared with the traditional technique. RESULTS: The mean cephalad angle in these 50 patients was 30.7° ± 5.1°, and the mean length of trajectory was 31.5 ± 3.5 mm. The CT analysis revealed that the penetrating S-1 endplate technique did not cause any neurovascular injury anteriorly in any case. The new technique demonstrated an average of 141% higher insertional torque than the traditional monocortical technique. CONCLUSIONS: The penetrating S-1 endplate technique through the medial entry point is suitable for the connection of lumbar CBT, has revealed favorable stability for lumbosacral fixation, and has reduced the potential risk of neurovascular injuries.

In vivo analysis of insertional torque during pedicle screwing using cortical bone trajectory technique.

STUDY DESIGN: The insertional torque of pedicle screws using the cortical bone trajectory (CBT) was measured in vivo. OBJECTIVE: To investigate the effectiveness of the CBT technique by measurement of the insertional torque. SUMMARY OF BACKGROUND DATA: The CBT follows a mediolateral and caudocephalad directed path, engaging with cortical bone maximally from the pedicle to the vertebral body. Some biomechanical studies have demonstrated favorable characteristics of the CBT technique in cadaveric lumbar spine. However, no in vivo study has been reported on the mechanical behavior of this new trajectory. METHODS: The insertional torque of pedicle screws using CBT and traditional techniques were measured intraoperatively in 48 consecutive patients. A total of 162 screws using the CBT technique and 36 screws using the traditional technique were compared. In 8 of 48 patients, the side-by-side comparison of 2 different insertional techniques for each vertebra were performed, which formed the H group. In addition, the insertional torque was correlated with bone mineral density. RESULTS: The mean maximum insertional torque of CBT screws and traditional screws were 2.49 ± 0.99 Nm and 1.24 ± 0.54 Nm, respectively. The CBT screws showed 2.01 times higher torque and the difference was significant between the 2 techniques (P < 0.01). In the H group, the insertional torque were 2.71 ± 1.36 Nm in the CBT screws and 1.58 ± 0.44 Nm in the traditional screws. The CBT screws demonstrated 1.71 times higher torque and statistical significance was achieved (P < 0.01). Positive linear correlations between maximum insertional torque and bone mineral density were found in both technique, the correlation coefficient of traditional screws (r = 0.63, P < 0.01) was higher than that of the CBT screws (r = 0.59, P < 0.01). CONCLUSION: The insertional torque using the CBT technique is about 1.7 times higher than the traditional technique. LEVEL OF EVIDENCE: 2.

Morphometric measurement of cortical bone trajectory for lumbar pedicle screw insertion using computed tomography.

STUDY DESIGN: A morphometric measurement of cortical bone trajectory (CBT) for the lumbar pedicle screw insertion using computed tomography (CT). OBJECTIVE: The aim of this study was to conduct a detailed morphometric measurement of the CBT. SUMMARY OF BACKGROUND DATA: The CBT is a novel lumbar pedicle screw trajectory, which follows a caudocephalad path sagittally and a laterally directed path in the transverse plane. The advantage associated with this modified technique is increased cortical bone contact, providing an enhanced screw purchase. However, little is known about the possible screw size or detailed direction of the trajectory. METHODS: The CT scans of 100 adults who underwent examination for spinal problems were studied. A total of 470 lumbar vertebrae excluding spondylosis, malformation, and tumor were observed. In this trajectory, the starting point was supposed to be the junction of the center of the superior articular process and 1 mm inferior to the inferior border of the transverse process. The CT images were analyzed using 3-dimensional reconstruction software. The diameter, length, lateral angle to the vertebral sagittal plane, and cephalad angle to the vertebral horizontal plane of the trajectory were measured. RESULTS: The mean diameter gradually increased from L1 to L5 (from 6.2 mm at L1 to 8.4 mm at L5). The mean length from L1 to L5 were 36.8, 38.2, 39.3, 39.8, and 38.3 mm, respectively. The lateral angle from L1 to L5 were 8.6, 8.5, 9.1, 9.1, and 8.8 degrees, respectively. The cephalad angle from L1 to L5 were 26.2, 25.5, 26.2, 26.0, and 25.8 degrees, respectively. CONCLUSIONS: The morphology of the pedicle, such as shape and pedicle axis angle, differed over the lumbar levels, our measurements demonstrated similar data excluding the diameter of the trajectory. There were no significant differences between each level of the lateral and cephalad angles.