Screw Position Research Articles

Nozzle Pressure- and Screw Position-Based CAE Scientific Process Parameter Setup for Injection Molding Process

This study developed a scientific process parameter setup based on nozzle pressure and screw position, with the process parameter search sequence being injection speed, V/P switchover position, packing pressure, and packing time. Unlike previous studies, this study focuses on the scientific process parameter setup of experiments and simulations, as well as on the implementation of calibration. Experiments and simulations had the same trend of results in the scientific process parameter setup. Although the experiments and simulations had the same trend, the machine response caused parameter errors. After setting the time constant of the simulations, injection speed profiles from the experiments and simulations became closely aligned. The simulation results for the injection speed and V/P switchover position became closer to the experiment results than the results of the uncalibrated simulation. The error between the simulated and experimental injection speed was reduced from 20% to 6% after applying time constant calibration. The V/P switchover point error was also reduced from 11% to 5%, highlighting the effectiveness of the time constant to calibrate the simulation.

Biomechanical insights into anterolateral vertebral screw fixation in osteoporotic spines: a comparative study of fixation methods and positions using porcine vertebrae

ObjectiveCombining oblique lumbar interbody fusion (OLIF) with posterior pedicle screw fixation (PPSF) has been proposed to reduce cage subsidence, especially in osteoporotic spines. Recently, anterolateral screw-rod fixation has gained interest as it allows direct pathology observation and avoids a posterior approach. However, controversies exist between anterolateral screw fixation systems and traditional PPSF due to variations in osteoporotic vertebral mineral density, screw fixation positions, and fixation methods (bicortical vs. unicortical). This study aimed to investigate the biomechanical impact of fixation position and method in osteoporotic spine.MethodsSeventy-two fresh‑frozen porcine vertebrae (L1–6) were decalcified using 0.5 M EDTA and divided into two groups based on fixation method: bicortical or unicortical. Six groups for each method were created according to the screw position in the lateral vertebral body, with six specimens in each group: anterior, central, and posterior in the middle body and para-endplate regions. Correlations among screw position, fixation method and axial pullout strength were analyzed.ResultsA 4-week decalcification process, bone mineral density in the porcine vertebrae decreased to approximately 48% (p < 0.05) of the original value, categorizing them as osteoporotic. Bicortical fixation showed significantly greater pullout forces than unicortical fixation, with differences ranging from 82 to 273%. Notably, central or posterior screws outperformed anterior screws in pullout strength.ConclusionBicortical fixation exhibited significantly greater pullout forces than unicortical fixation. We suggest positioning screws in the central or posterior region of the middle body with bicortical fixation in osteoporotic vertebrae.

Increased Lag-Screw Slide and All-Cause Revision in a New-Generation Cephalomedullary Nail after Treatment of Geriatric Intertrochanteric Femoral Fractures.

To compare lag-screw slide and revision surgery rate between two generations of the Stryker Gamma cephalomedullary nail (Stryker, Kalamazoo, MI). Design: Retrospective chart review. Single academic, Level-1 Trauma Center. All geriatric patients (65-years and older) who underwent fixation of an intertrochanteric femoral fracture (AO/OTA type 31A1/2/3) by a single surgeon with the Stryker Gamma System from 2020-2024 with at least 3-month follow-up. The Gamma3 system was utilized until the Gamma4 became available in September 2022. Patients were grouped based on the implant utilized for fixation: Gamma3 (G3) or Gamma4 (G4) and sub-grouped based on the centrum-collum-diaphyseal (CCD) angle of the implant (125° versus 130°). The main outcome was sliding of the lag screw. Slide distance was calculated from the difference between the screw position immediately post-operatively and at 6 and 12 weeks post-operatively. The secondary outcome variables were revision surgery for any reason, tip-apex distance (TAD), and reduction quality. Fifty-one patients (40 female) with a mean age of 83 years (range 65-99) were in the G3 group compared to 46 patients (31 female) with a mean age of 79 years (range 65-96) in the G4 group. The average BMI of the G3 group was 24 kg/m2 (15-35 kg/m2) compared to 27 kg/m2 in the G4 group (17-41 kg/m2) (p = 0.004). There were no significant differences when comparing diabetes, smoking status, or mechanism of injury between groups (p>0.05). There was no significant difference when comparing the average TAD between the G3 (10 mm) and G4 (9.5 mm) (p = 0.39). There was no significant difference in reduction quality between the G3 (46 good reductions) and the G4 (42 good reductions) groups (p = 0,85).At 6 weeks, the G4 (5 mm) had significantly greater lag screw slide compared to the G3 (3 mm) (p = 0.016). At 12 weeks, the G4 (7 mm) also had significantly greater lag screw slide when compared to the G3 (4 mm) (p = 0.004). There was no significant difference in lag screw slide for the 125° implant between the G3 and G4 groups at 6-weeks (3 mm versus 5 mm, p = 0.44) or 12 weeks (4mm versus 6 mm, p = 0.14). Regarding the 130° implant, the G4 had significantly greater slide compared to the G3 at both at 6-weeks (5 mm versus 3mm, p =0.03; 95% CI -6.07 to -0.41) and 12-weeks (8 mm versus 4 mm, p = 0.03; 95% CI -5.65 to -0.26). The G4 group had 7 revision procedures performed (3 lag screw exchanges for iliotibial band irritation and 4 revision arthroplasties for lag screw slide, fracture shortening, iliotibial band irritation, abductor malfunction, and leg length discrepancy) compared to 1 revision procedure (lag screw exchange for iliotibial band irritation) in the G3 group (p = 0.04). The 130° Gamma4 demonstrated increased lag screw slide and all-cause revision surgery when compared to the 130° Gamma3 when utilized in the treatment of geriatric IT femoral fractures. Given the high incidence of increased slide and the significantly higher revision surgery rate, this implant should undergo further investigation.

An overview of patients with intertrochanteric femoral fractures treated with proximal femoral nail fixation using important criteria

BackgroundThis study aimed to assess important criteria, including osteoporosis, fracture type, implant position within the bone, fracture reduction, and radiographic union, in patients with intertrochanteric femoral fractures treated with proximal femoral nail (PFN) fixation and to show their effect on clinical outcomes.MethodsPFN fixation was applied in 73 patients (41 females, 32 males; mean age: 64.5 ± 6.2). The T score, fracture type according to the AO Foundation and Orthopedic Trauma Association (AO/OTA), implant-related complications (IRCs), Harris hip score (HHS), Jensen social function (JSF) score, and Parker-Palmer mobility score (PPMS), postoperative reduction classification, screw position according to the Cleveland zone, Radiographic Union Scale for the Hip (RUSH) score, and tip-apex distance (TAD) were recorded.ResultsMost screws were in central-central (n = 42) and inferior-central (n = 11) positions. IRCs were seen mostly in cases of screws placed in peripheral zones (n = 10) and were not observed in almost any patient with a TAD ≤ 25 mm (n = 52) (p < 0.001). Most of the patients with acceptable or good fracture reduction did not have IRCs (n = 11 and 50, respectively) (p < 0.001). Half of type 3A1 (n = 13) and most type 3A2 (n = 20) fractures showed radiographic union at 3 months, and most type 3A3 (n = 9) fractures showed radiographic union at 5 months (p < 0.05). At 12 months, type 3A2 fractures had the highest HHS (79.2 ± 5.3) and PPMS (3.9 ± 1.5), while type 3A3 fractures had the lowest HHS (70.3 ± 4.6) and PPMS (0.6 ± 2.8) (p < 0.05). At 12 and 24 months, type 3A3 fractures had higher JSF scores (2.8 ± 0.4 and 3.5 ± 0.5, respectively); at 3 months, type 3A1 fractures had higher JSF scores (3.1 ± 0.3) (p < 0.05). The radiographic bone union time was prolonged in patients with a T score ≤ -2.5 standard deviation (SD) (p < 0.05). The HHS and PPMS increased while the RUSH score, considered as the radiographic union, was going towards the 4th month and decreased after the 4th month (p < 0.05).ConclusionsConsidering the criteria (osteoporosis, fracture type, implant position within the bone, fracture reduction, and radiographic union) examined in this study, satisfactory results can be obtained with PFN fixation in the treatment of patients with intertrochanteric femoral fractures.

Biomechanical Evaluation of Clival Screw Fixation for Occipitocervical Instablity: A Finite Element Analysis.

The clivus is trapezoidal in shape with uneven bone structure, the optimal number and position of screws for clival fixation are not clear. Therefore, this study aims to explore the optimization clival screw fixation method for occipitocervical instability using finite element analysis. Seven finite element models were developed to evaluate biomechanical properties of clival screw fixation for treating occipitocervical stability, including (i) one clival screw fixation A1 and A2 models; (ii) two clival screws fixation B1 and B2 models; (iii) three clival screws fixation C1 and C2 models; (iv) four clival screws fixation D1 model. Loads of 1.5 Nm were applied to the model fRoM different directions to induce flexion, extension, lateral bending, and axial rotation movements. The regular triangle C1 type three clival screws fixation exhibited great stability, with RoM of 4.20° in flexion, 5.80° in extension, 0.85° in lateral bending, and 1.60° in axial rotation. The peak stress on the internal fixation devices were relatively low, with maximum screw stress of 194 MPa in flexion, 276 MPa in extension, 180 MPa in lateral bending, and 213 MPa in axial rotation; the maximum plate stress were 126, 554, 426, and 378 MPa, respectively. The areas with higher stress were mainly concentrated at the robust neck section of the plate. The triangular configuration of three clival screws fixation represented the optimized anterior occipitocervical fixation method through the clivus, offering superior biomechanical stability, lower stress on the devices and dispersed stress distribution in the occipitocervical region.

Does Position of Pedicle Screws Correlate With Adjacent Segment Degeneration? An Average 6-Year Follow-Up Retrospective Study.

Retrospective case serie. Assess the correlation between pedicle screw (PS) position of the first instrumented vertebra (FIV) with proximal adjacent segment degeneration (ASD) development or progression. Patients ≥55years who have undergone lumbar fusion with a minimum 2-year follow-up were included. Radiographic PS position was assessed by the angle between the first PS and the upper vertebral endplate (VE) and by the PS tip-VE distance. Radiographic parameters of ASD included: disc height, disc angle, and vertebral listhesis. ASD magnetic resonance imaging (MRI) parameters included: disc degeneration and lumbar stenosis. ROC curve analysis was performed to identify the best cut-off points in correlation with lumbar stenosis. Forty-eight patients were included with an average follow-up of 6years. All 48 included patients developed some degree of ASD whether on radiographic or MRI parameters. PS tip-VE distance and PS-VE angle were both positively correlated with: (1) Delta (Δ) lumbar stenosis; (2) Δ Disc degeneration; and (3) Δ Disc height. ROC curve analysis correlating PS tip-VE distance and PS-VE angle with an increase in the canal stenosis severity ≥2° resulted in a cut-off point of 36% and 9.5°, respectively. The cranial orientation (PS-VE angle) of the pedicle screw in the first instrumented vertebra, along with a shorter pedicle screw tip-vertebral endplate distance (PS tip-VE), positively correlated with ASD progression at an average 6-year follow-up. Protective values against lumbar stenosis were identified as a PS tip-VE distance ≥36% of the first instrumented vertebra height and a PS-VE angle ≤9.5° relative to the upper vertebral endplate.

Evaluation of Pedicle Screw Position on Computerized Tomography Using Three-Dimensional Reconstruction Software.

Background and Objectives: Recent advances in intraoperative navigation systems have improved the accuracy of pedicle screw placement in spine surgery. However, many hospitals have limited access to these advanced technologies due to resource constraints. In such settings, postoperative computed tomography (CT) evaluation remains crucial for assessing screw placement and related potential complications. Metal artifacts in CT scans often compromise the diagnostic accuracy. This study aimed to develop and validate three-dimensional (3-D) reconstruction software to enhance screw localization accuracy and facilitate its practical clinical application. Materials and Methods: This study included two phases: 3-D software development utilizing specific threshold values of Hounsfield units for titanium screws followed by internal validation. For validation, fifty pedicle screws were inserted into porcine lumbar vertebrae with random violation (superior, inferior, medial, or lateral). Three fellowship-trained surgeons evaluated screw positions using both conventional CT bone window settings and the developed software. Additional clinical validation involving 386 pedicle screws from cervical to lumbar spine was performed by two surgeons. Results: The software demonstrated significantly higher specificity (83% vs. 63%) and positive predictive value (96% vs. 91%) compared to conventional CT bone window settings, while maintaining 100% sensitivity and negative predictive value. Interobserver reliability was excellent for both methods (0.961 for bone window vs. 0.990 for software). In clinical validation, the software showed superior intraobserver (0.83 vs. 0.74) and interobserver reliability (0.855 vs. 0.513) compared to picture archiving and communication system (PACS) workstation evaluation. Conclusions: The developed software provides improved accuracy and reliability in pedicle screw position evaluation through distinct screw outline visualization and metal artifact reduction. Its equipment-independent nature and cost-effectiveness make it particularly valuable for clinical implementation.

Surgical treatment of a case of avulsion of the lateral head of the gastrocnemius muscle in a cat

AbstractAvulsion of the origin of the gastrocnemius muscle is a rare condition typically resulting from an acute, low‐grade local muscle injury: it usually presents as a weight‐bearing lameness with a tarsal hyperflexion. Surgical reattachment of the avulsed portion of the muscle is considered the treatment of choice. Overall, this pathology carries a good prognosis when a positive surgical outcome is achieved. A 9‐year‐old, female, neutered, domestic shorthair cat presented with an acute‐onset, weight‐bearing lameness and a plantigrade stance in the right hindlimb. Clinical and radiographic findings lead to a diagnosis of avulsion of the lateral origin of the gastrocnemius muscle: this was surgically anchored as close as possible to its anatomical origin, the tarsocrural joint was then locked in extension using a calcaneo‐tibial cortical positional screw for 5 weeks, and the leg was splinted for 7 weeks post‐operatively. At the 4‐month post‐surgical follow‐up, the cat showed a satisfactory limb function.

Effect of screw placement order on range of proximal tibial fragment rotation adjustment and osteotomy gap formation when using manual reduction during tibial plateau levelling osteotomy (TPLO)

AimTo determine the optimal first proximal screw position which permits proximal tibial fragment rotation adjustment while minimising osteotomy gap formation when a manual reduction technique is used for TPLO in dogs.MethodsTPLOs were performed on bone models using Synthes 3.5‐mm TPLO implants with a jig but without the use of an anti‐rotational pin. The osteotomy was held in manual reduction with pointed reduction forceps placed across the proximal tibial fragment while the first three screws were applied. The first two screws were placed in the non‐locking holes of the distal stem of the plate as per manufacturer's screw placement order guidelines. The third screw was placed in one of the three locking screw positions in the head of the plate, denoted as the ‘cranial’, ‘proximal’ and ‘caudal’ screw positions. After the first three screws were placed, the range of possible proximal tibial fragment rotation change (up to 6 mm in each direction) and the resultant cranial and caudal osteotomy gaps were measured.ResultsThe proximal screw position minimises cranial osteotomy gap formation with negative rotation changes to the proximal tibial fragment. The caudal screw position minimises caudal osteotomy gap formation with positive rotation changes to the proximal tibial fragment. Rotation change had a greater effect on cranial osteotomy gaps compared to caudal osteotomy gaps. The cranial screw position had the most limited osteotomy rotation change.ConclusionThe proximal screw position should be placed first in the head of the plate to allow proximal tibial fragment rotation adjustment while minimising osteotomy gap formation when using a manual reduction technique when performing a TPLO.

Biomechanical comparison of Gofried positive support reduction of Pauwels type III femoral neck fractures: A finite elements analysis

ObjectiveThis study aims to investigate the biomechanical characteristics of non-anatomical reduction and different screw positions on the stability of Pauwels type III femoral neck fractures. MethodsThree-dimensional finite element models of femoral neck fractures were constructed using CT images. Four types of internal fixation methods were simulated, including biplane double-supported screw fixation (BDSF), three inverted triangular parallel cannulated screws (3CS), new parallel cannulated screws with posterior screws moving down (New 3CS), and two parallel cannulated screws (2CS). von Mises stress and total displacement were compared between the fracture models after the femoral head was subjected to an axial load of 2100 N. Stress and displacement data for the implants and the femur were recorded for each fixation method and compared. ResultsThe results demonstrated that positive reduction of a Pauwels type III femoral neck fracture provided greater stability than neutral or negative reduction. Specifically, the BDSF group showed the lowest maximum von Mises stress in the femur (17.66 MPa) in positive reduction, compared to 3CS (21.08 MPa), New 3CS (22.14 MPa), and 2CS (36.57 MPa). The total displacement of positive reduction in the BDSF group was 0.3143 mm, which was lower than in the 3CS (0.3498 mm), New 3CS (0.3343 mm), and 2CS (0.4533 mm) groups. The stress distribution in the positive support reduction group was lower than that of the other groups, indicating better load distribution. Among the three-screw fixation methods, the New 3CS system exhibited the highest stress in the screws (with a peak of 28.62 MPa), while the 2CS group displayed the highest stresses overall, both in the femur and the screws. ConclusionFor Pauwels type III femoral neck fractures, a positive support reduction with BDSF fixation exhibited superior biomechanical performance than negative reduction. Based on the finite element analysis conducted in this study, the positive support reduction with BDSF fixation can enhance fixation stability, suggesting that non-anatomical reduction is recommended.

Accuracy of percutaneous pedicle screw placement using modified single anterior-posterior fluoroscopy with the C-arm for the treatment of traumatic thoracic and lumbar fractures

We aimed to assess percutaneous pedicle screw (PPS) placement accuracy, fluoroscopy shot number, and operation time using a modified single anterior-posterior (AP) fluoroscopy with a C-arm in treating traumatic thoracic and lumbar vertebral fractures. In total, 164 patients with single-level traumatic thoracic or lumbar fracture who underwent 6 PPS placements between April 2018 and September 2020 were divided into 2 groups. Conventional AP combined lateral fluoroscopy was used in Group A, whereas modified single AP fluoroscopy was used in Group B. The accuracy of the PPS placement, number of fluoroscopy shots, and operation time were compared. All patients underwent computed tomography 2-4 days after surgery to evaluate screw position. Pedicle breach was divided into 4 grades based on postoperative computed tomography. Our study included 984 implanted pedicle screws, of which 36 (3.7%) were malpositioned. The breach rate was 3.5% (grade 1, 3.1%; grade 2, 0.4%) in Group A and 3.7% (grade 1, 3.0%; grade 2, 0.8%) in Group B. The median number of fluoroscopy shots during PPS placement was 21.9 in Group A and 8.4 in Group B. The median operation time was 76.07 ± 6.86 minutes in Group A and 55.78 ± 7.21 minutes in Group B. The PPS placement method using modified single AP fluoroscopy for treating traumatic thoracic and lumbar spine fractures was fairly accurate and reduced the number of fluoroscopy shots and operation time. This technique requires only a C-arm for assistance and can be easily mastered by spinal surgeons across hospitals of various levels.

Positional Screw Effect in the Treatment of Humeral Shaft Fractures Using a Minimally Invasive Plate Osteosynthesis Technique.

This study compares the difference in the clinical and radiologic outcomes when minimally invasive plate osteosynthesis (MIPO) technique is performed with or without using a positional screw in the treatment of humeral shaft fractures. From January 2010 to January 2021, a retrospective study was conducted on a total of 63 patients who underwent the MIPO technique for the treatment of humeral shaft fractures. We divided these patients into 2 groups: in group I, patients underwent MIPO without a positional screw; in group II, patients underwent MIPO with a positional screw. We compared functional outcomes including the American Shoulder and Elbow Surgeons score, University of California at Los Angeles score, Simple Shoulder Test, range of motion before and after surgery, operation time, blood loss, and complications. And we compared radiologic outcomes including pre- and postoperative anteroposterior (AP) and lateral displacement of the fracture and union time on plain radiographs. The average patient age was 64.6 ± 15.1 years (range, 25-88 years). Group I consisted of 30 patients (10 men and 20 women), and group II consisted of 33 patients (11 men and 22 women). Between the 2 groups, there was no statistically significant difference in sex, body mass index, functional scores, AP and lateral displacement of the fracture on postoperative x-ray, operation time, and blood loss. In group II, a faster bony union was obtained than that in group I (4.6 vs. 6.4 months). Complications included 2 cases of transient radial nerve palsy in both groups and metallic failures (2 in group I and 1 in group II). When performing MIPO for humeral shaft fractures, adding a positional screw could be more stabilizing than bridge plating without a positional screw, leading to faster bony union. A positional screw might help control interfragmentary movement without inhibiting essential interfragmentary movement for fracture healing.

A novel method to judge the safe position of C2 lamina screw with double holes

BackgroundTo evaluate the feasibility of C2 laminar screw (C2LS) fixation assisted by double holes and to explore a novel method for judging its safe positioning.MethodsThe Digital Imaging in Communications format data of 25 C2 vertebrae specimens were obtained by computed tomography thin-slice scanning, and the data were imported into Mimics software for three-dimensional reconstruction. The bone cortex was removed at the starting and terminal midpoints of the lamina as the observation holes. Points A, M, and P represented the three different entry points of the C2LS. Point M was designated as the central entry point, point A was 1 mm from the extension surface of point M to the ventral side, and point P was 1 mm from the extension surface of point M to the dorsal side. Further classified into groups A, M, and P based on the screw path correlation parameters at each entry point. The distance between holes 1 and 2 (D1 and D2) was measured at the maximum safe inclination, parallel, and maximum safe extroversion positions when the screw-insertion points of C2LS were at the center points A, M, and P, respectively. The data of D1 and D2 of the three groups (A, M, P) in different screw directions were analyzed and compared.ResultsTwenty-five specimens were measured in the parallel, maximum safe inclination, and maximum safe extroversion groups. In the parallel relationship, there were significant differences in the D1 and D2 data between the M and P groups. In the introversion relationship, there were significant differences in the D1 and D2 data between the M and P groups. In the extroversion relationship, there were significant differences in the D1 and D2 data among the A, M, and P groups, respectively.ConclusionUse of the C2LS assisted by double holes was able to determine the safe position of the screw in operation. When D1 is greater than D2, the screw position can be considered relatively safe, with the intraoperative visual manifestation of a deep screw in hole 1 and a shallow screw in hole 2. If D1 is close to D2, it is necessary to ensure that the screws in both holes 1 and 2 are shallow, then the screw position is safe. If the screw in hole 1 is observed to be shallower than in hole 2 during surgery, regardless of the entry point position, there is a significant risk of ventral cortical perforation. Especially when the entry point is more anterior, even when inserting the screw parallel to the lamina, caution must be taken against the risk of ventral cortical perforation.

Robot-assisted technique can achieve accurate screw placement in four-corner fusion and reduce operative difficulty: a cadaver study

BackgroundThe purpose of this study is to explore the feasibility and accuracy of a robot-assisted technique in four-corner fusion compared with traditional freehand operation.MethodsTwenty cadaver specimens were randomly assigned to the robot-assisted group and freehand groups. Three screws were placed percutaneously to fix the capitate-lunate joint, lunate-triquetrum joint, and triquetrum-hamate-capitate joint in each specimen by robot-assisted or freehand technique. The offset between the actual and planned screw positions was determined by merging the images of intraoperative and postoperative CT scans in the robot-assisted group. The centrality of the screw, time-consuming, drilling attempts, and radiation exposure were compared between the two groups.ResultsThe mean offset between the actual and planned screw position was 1.09 (SD: 0.56) mm. The offset at the start point of the screw was significantly lower than that at the endpoint. There was no significant difference in the centrality of the screws, surgical time between the two groups. The number of drilling attempts and the radiation dose received by surgeons were significantly lower in the robot-assisted group.ConclusionsAlthough there was no significant difference in screw centrality between the two groups, the slight offset between the actual and planned screw positions confirmed the feasibility of the robot-assisted technique in four-corner fusion. The robot-assisted technique has advantages in reducing the difficulty of surgery and protecting the surgeon from exposure to large doses of radiation.

Evaluation of cortical bone thickness at the nasomaxillary and zygomaticomaxillary buttresses using cone-beam computed tomography imaging for Le Fort I osteotomy

Background/PurposeStudies have indicated that 50%–55% of the population have malocclusion, and approximately 5%–10% require orthognathic surgery to correct this condition. Optimal placement of plates and screws significantly affects the success rate of the surgery and postoperative stability. This study evaluates the cortical thickness of the maxillary bone in the nasomaxillary and zygomaticomaxillary buttress regions in Taiwanese patients based on cone-beam computed tomography (CBCT) images. Materials and methods128 Patients undergoing Le Fort I osteotomy were selected for this study. Their CBCT images were input into medical imaging software to simulate the placement of titanium screws and plates. The cortical bone thickness at these positions was measured to assess the thickness in the nasomaxillary buttress (surrounding the nasal opening) and the zygomaticomaxillary buttress (surrounding the maxillary zygomatic process). Associations of these thicknesses with gender, age, and screw position were analyzed. ResultsIn the nasomaxillary region, cortical bone was thicker on the upper and lower vertical regions, with men generally having thicker bone. The zygomaticomaxillary region had increased thickness near the zygomatic end and distal region. Younger adults had significantly greater bone thickness in certain areas than those over 30 years. ConclusionThe nasomaxillary region's upper and lower vertical regions and the zygomatic end in the zygomaticomaxillary region provide optimal screw placement sites. Bone thickness differences by gender and age suggest occlusal force and age-related bone resorption as influencing factors.

Robotic pedicle screw placement with 3D MRI registration: moving towards radiation free robotic spine surgery

BACKGROUND CONTEXTPreoperative imaging for lumbar spine surgery often includes magnetic resonance imaging (MRI) for soft tissues and computer tomography (CT) for bony detail. While CT scans expose patients to ionizing radiation, whereas MRI scans do not. Emerging MRI techniques allow CT-like 3-dimensional (3D) visualization of bony structures, potentially removing the need for ionizing radiation from CT scans. PURPOSEThis study aims to explore the accuracy of robot-assisted lumbar pedicle screw placement based on preoperative CT-like 3D MRI as the data source for robotic registration. STUDY DESIGNHuman cadaveric study. METHODSCT-like 3D MRI scans of the lumbar spine were acquired in ten human cadavers. A robotic navigation platform was used to plan and navigate pedicle screw placement based on the CT-like 3D MRI. Postoperative CT scans assessed the accuracy of screw positioning compared to preoperative planning based on the Gertzbein-Robbins scale (GRS) and by direct measurement (mm). RESULTSA total of 100 lumbar pedicle screws were robotically placed in ten cadavers (L1 through L5 bilaterally) based on CT-like 3D MRI. On postoperative CT evaluation, 99.0% of the positioned screws achieved an acceptable grade on the GRS (Grade A: n=89 or Grade B: n=10), with 89.0% classified as Grade A and 10.0% as Grade B. Meaning that 89.0% of screws were fully contained within the pedicle (GRS A), and 10% had a minor cortical breach <2 mm (GRS B). The median deviation from the planned trajectory was 0.2 mm (axial IQR: 0.1 to 0.5 mm; sagittal: IQR: 0.1 to 0.4 mm), in both axial and sagittal planes. CONCLUSIONThis study showed that image registration of CT-like 3D MRI for robotic-assisted spine surgery is technically feasible and that accurate pedicle screw placement can be achieved without preoperative CT. Each CT-like 3D MRI was successfully registered for robotic navigation. CLINICAL SIGNIFICANCEThe results suggest that CT-like 3D MRI has the potential to be a radiation-free alternative for preoperative planning and navigation in lumbar spine instrumentation procedures.

Robotic assistance for upper cervical instrumentation: report on accuracy and safety.

This study aims to evaluate the accuracy and safety of C1 lateral mass and upper cervical pedicle screw placement assisted by the TiRobot II system. Ten patients who underwent cervical spine surgery assisted by the TiRobot II system were included. Screw accuracy was assessed using the Gertzbein-Robbins scale and by comparing the final screw positions with pre-planned trajectories. Deviations in screw tip, tail, and angle were recorded. Clinical data, including symptoms, surgical outcomes, and postoperative follow-up, were collected. Neurological improvement was evaluated using pre- and post-operative mJOA scores, with recovery rates calculated by Hirabayashi's method to assess outcomes 3months after surgery. A total of 30 screws were placed in 10 patients. All screws (30/30) were within the clinically acceptable range, with 93.33% (28 screws) classified as Grade A and 6.67% (2 screws) as Grade B. In the sagittal plane, the average tip deviation was 1.82 ± 0.79mm, tail deviation 1.64 ± 0.60mm, and angular deviation 1.92 ± 1.39°. In the axial plane, tip deviation was 1.96 ± 0.87mm, tail deviation 1.92 ± 0.65mm, and angular deviation 2.01 ± 1.07°. The average surgery time was 318.80 ± 66.07min, with a mean EBL of 205.00 ± 55.03mL. Postoperative mJOA scores significantly improved from 8.10 ± 1.97 to 12.60 ± 1.78 (p < 0.05), with a 52 ± 14% recovery rate. All patients showed significant symptom improvement. The TiRobot II system demonstrates the capability to precisely execute pre-planned trajectories and improves the accuracy and safety of C1 lateral mass and upper cervical screw placement.

Three-Dimensional Fluoroscopic System to Assess Robotically Placed Pedicle Screws: Should We Confirm Robotic Pedicle Screw Placement With Advanced Imaging?

Retrospective cohort study. The purpose of this study is to determine the utility of advanced imaging to confirm the placement of robotic pedicle screws. With increasing robotic adoption, certain institutions and surgeons have developed protocols for obtaining 3D intraoperative imaging after robotic pedicle screw placement to ensure proper hardware placement. No studies have assessed the utility of these protocols relative to the potential risks of increased radiation exposure and operative time. The purpose of this study is to determine if we should be obtaining advanced imaging to confirm the placement of robotic pedicle screws. This is a single institution retrospective cohort study of patients from May 2022 to July 2023 who underwent lumbar spinal fusion by a high-volume orthopedic spine surgeon at a level 1 metropolitan hospital. All cases used combined robotics and navigation systems for pedicle screw placement and intraoperative 3D imaging for evaluation of screw position. Pedicle screw accuracy was assessed using the Gertzbein and Robbins system (GRS). Acceptable pedicle screw position was defined as GRS A or B. Seventy patients with 354 robotically placed pedicle screws were assessed with intraoperative 3D fluoroscopy. All pedicle screws were placed in either a GRS type A or type B position. Three hundred fifty-one were placed in a GRS A classification (99.2%, 351/354), and 3 were placed in a GRS B classification (0.08% 3/354). No patients had screw-related complications. The average radiation dosage of 3D imaging was 289.7±164.6mGy. The robotic system places pedicle screws accurately without 3D intraoperative imaging. Given the increased radiation and operative time associated with 3D imaging protocols 3D imaging scans should only be obtained in cases with heightened clinical concern. Level IV.

Beyond 25 millimetres makes the difference: a prospective study on tip apex distance in dynamic hip screw treatment of intertrochanteric fractures

Background: The tip apex distance (TAD) is a key indicator of screw cut-out risk in dynamic hip screw (DHS) treatment for intertrochanteric fractures. This study sought to assess the prognostic significance of TAD in intertrochanteric fractures managed with DHS. Methods: This prospective observational study encompassed 50 patients with intertrochanteric fractures who had DHS fixing treatment. TAD was measured on postoperative radiographs. Patients were followed clinically and radiologically for a minimum of 3 months. The primary outcome was screw cut-out. Results: The mean TAD was 25.5 mm, with a range of 10 to 47 mm. Four screw cut-outs were seen, all in patients with TAD exceeding 35 mm. The mean TAD was 24.18 mm for successfully treated fractures, in contrast to 40.89 mm for those who experienced cut-out. No cut-outs were seen with TAD &lt;25 mm. The inferior-central region of the femoral head was the predominant site for screw placement, occurring in 30% of cases. Conclusions: TAD is a dependable predictor of screw cut-out risk in DHS fixation of intertrochanteric fractures. Maintaining a TAD &lt;25 mm and screw position in the inferior-central zone of the femoral head may help minimize cut-out risk. Surgeons should aim for proper screw placement and consider TAD when treating these fractures.

Efficacy comparison of robot-assisted versus freehand fluoroscopy-assisted minimally invasive transforaminal lumbar interbody fusion for degenerative lumbar spinal diseases

Objective: To compare the clinical and radiographic outcomes between robot-assisted minimally invasive transforaminal lumbar interbody fusion (RA MIS-TLIF) and fluoroscopy-assisted MIS-TLIF (FA MIS-TLIF) in patients with degenerative lumbar spinal diseases. Methods: The clinical data of 114 patients with lumbar degenerative diseases who underwent MIS-TLIF in Qilu Hospital of Shandong University from January 2019 to March 2022 were analyzed retrospectively. Fifty-eight patients underwent RA MIS-TLIF (robot group) and 56 patients received FA MIS-TLIF (freehand group). There were 16 males and 42 females in the robot group, with a mean age of (56.7±8.1) years. And there were 19 males and 37 females in the freehand group, with a mean age of (57.2±8.6) years. The clinical outcome parameters were the visual analog scale (VAS) of pain, Oswestry Disability Index (ODI) score, operative time, number of intraoperative fluoroscopies, blood loss, postoperative hospital stay and complications. The radiographic change measures were the accuracy of screw placement, facet joint violation (FJV), fusion status, and change in disc height at the proximal adjacent segment. All the patients were followed-up for 2-5 years. Results: There was no significant differences in the VAS and ODI scores, blood loss, or postoperative hospital stay between the two groups (all P>0.05). The operative time was longer in robot group than freehand group [(158.5±12.1) min vs (146.4±15.4) min, P<0.001]. There was no significant difference in the number of intraoperative fluoroscopies for patients between robot group and freehand group (P>0.05). The number of intraoperative fluoroscopies for the surgeon was significantly lower in robot group than freehand group (13.8±3.9 vs 74.7±6.8, P<0.001). The rate of a perfect screw position (grade A) was higher in robot group than freehand group [87.5%(203/232) vs 70.1%(157/224), P<0.001]. However, there was no significant difference in the proportion of clinically acceptable screws (grades A and B) between the two groups [98.3%(228/232) vs 96.9%(217/224), P=0.330]. The FJV grade was significantly higher in freehand group than robot group (0.43±0.68 vs 0.13±0.43, P<0.001). During at 2-year postoperative follow-up, there was no significant difference in the fusion status between the two groups (P>0.05); however, the decrease in disc height at the proximal adjacent segment was significantly less in robot group than freehand group [(0.63±0.38) mm vs (0.92±0.35) mm, P=0.001]. In the robotic group, a pedicle screw penetrated the outer wall of the vertebral pedicle in one patient, which was adjusted during surgery. In the freehand group, two screws were inserted too deeply and penetrated the anterior cortex, resulting in mild abdominal discomfort postoperatively, which resolved by the third day after surgery. Conclusions: Robot-assisted percutaneous pedicle screw placement is a safer and more accurate alternative to conventional freehand fluoroscopy-assisted pedicle screw insertion in MIS-TLIF. Compared with freehand MIS-TLIF, robot-assisted MIS-TLIF increases the operation time, but the accuracy of screw placement is higher, and the intraoperative radiation dose and the degree of adjacent segment degeneration are reduced.