Sacral Screw Research Articles

3D-Printed Prosthesis with an Articular Interface for Anatomical Acetabular Reconstruction After Type I + II (+ III) Internal Hemipelvectomy

Background: Pelvic reconstruction after type I + II (or type I + II + III) internal hemipelvectomy with extensive ilium removal is a great challenge. In an attempt to anatomically reconstruct the hip rotation center (HRC) and achieve a low mechanical failure rate, a custom-made, 3D-printed prosthesis with a porous articular interface was developed. The aim of this study was to investigate the clinical outcomes of patients treated with this prosthesis. Methods: This retrospective cohort study included 28 patients with type I + II (+ III) internal hemipelvectomy through the articular interface of the sacroiliac joint and managed with a prosthesis at a single center between August 2016 and August 2021. Complications and oncological outcomes were analyzed. The position of the reconstructed HRC was assessed and lower-limb function was evaluated. Biomechanical analyses of different fixation modes of the prosthesis were conducted using finite element analysis. Results: The displacement distance of the HRC from preoperatively to postoperatively was a mean (and standard deviation) of 14.12 ± 8.75 mm. The rate of implant-related complications was 14.3% (4 of 28) for prosthetic breakage, 14.3% (4 of 28) for aseptic loosening, 7.1% (2 of 28) for dislocation, and 7.1% (2 of 28) for deep infection. The mean Musculoskeletal Tumor Society (MSTS)-93 score was 18.2. The aseptic loosening rate was significantly greater for prostheses fixed with 3 sacral screws (4 of 10, 40.0%) than for those fixed with 4 (0 of 10, 0%) or 5 screws (0 of 8, 0%) (p = 0.024). The prosthetic breakage rate was lower in patients who underwent lumbosacral fixation (0 of 13, 0%) than in those who did not (4 of 15, 26.7%), although the difference did not reach significance (p = 0.102). Biomechanical analyses suggested that the addition of lumbosacral fixation or increasing the number of sacral screws from 3 to 4 or 5 visibly reduced the peak stress of the sacral screws. Conclusions: The use of a 3D-printed prosthesis with an articular interface for pelvic reconstruction demonstrated stable prosthetic fixation, anatomical acetabular reconstruction, and acceptable early functional outcomes. Level of Evidence: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Optimizing sacral screw fixation in patients with caudal regression syndrome.

The aim of this study is to evaluate and compare techniques and outcomes associated with two different technique of pelvic screw insertion in patients with caudal spine absence. A cohort of patients with varying degrees of caudal structural regression, serves as the focal point of this investigation. Pelvic configurations were classified based on established criteria to facilitate comparative analysis. Each patient underwent spinal surgical interventions, with a follow-up period extending beyond 2years. The primary surgical interventions predominantly involved spinal stabilization coupled with correction of scoliosis and kyphosis through one or two pairs of pelvic screws. In this study, we investigated a cohort of 22 patients with caudal spine absence, encompassing diverse conditions, such as lumbo-sacral aplasia, hemisacrum, and lumbar absence, with preserved sacrum. Following spinal surgery, notable improvements were observed in scoliosis and pathological lumbar kyphosis, with several patients achieving significant functional milestones such as independent ambulation. There were no significant differences in short-term complications between patients undergoing single versus double pair pelvic screw implantation. Long-term complications, primarily non-fusion, were notably more prevalent in patients undergoing fixation with a single pair of pelvic screws. Surgical intervention, particularly spinopelvic fixation, demonstrated promising outcomes in terms of improving spinal deformities. The implantation of two pairs of pelvic screws demonstrates greater reliability compared to the insertion of a single pair, diminishing the risk of non-fusion.

Finite-element analysis of different fixation types after Enneking II + III pelvic tumor resection

The current primary treatment approach for malignant pelvic tumors involves hemipelvic prosthesis reconstruction following tumor resection. In cases of Enneking type II + III pelvic tumors, the prosthesis necessitates fixation to the remaining iliac bone. Prevailing methods for prosthesis fixation include the saddle prosthesis, ice cream prosthesis, modular hemipelvic prosthesis, and personalized prosthetics using three-dimensional printing. To prevent failure of hemipelvic arthroplasty protheses, a novel fixation method was designed and finite element analysis was conducted. In clinical cases, the third and fourth sacral screws broke, a phenomenon also observed in the results of finite element analysis. Based on the original surgical model, designs were created for auxiliary dorsal iliac, auxiliary iliac bottom, auxiliary sacral screw, and auxiliary pubic ramus fixation. A nonlinear quasi-static finite element analysis was then performed under the maximum load of the gait cycle, and the results indicated that assisted sacral dorsal fixation significantly reduces stress on the sacral screws and relative micromotion exceeding 28 μm. The fixation of the pubic ramus further increased the initial stability of the prosthesis and its interface osseointegration ability. Therefore, for hemipelvic prostheses, incorporating pubic ramus support and iliac back fixation is advisable, as it provides new options for the application of hemipelvic tumor prostheses.

The classification of sacral foramina in a South African sample using cadaveric and osteological remains

Sacroiliac (SI) joint fixation is a technique used for SI joint fractures, SI joint dislocations and sacral fractures. Sacral screws can be placed either into the S1 or the S2 vertebrae if S1 is insufficient. Malpositioning of the screws is a common surgical complication as sacral variations exists amongst populations. Complications associated with the misposition of screws can lead to injury of the sacral venous plexus, iliac vessels, or sacral nerve roots. Therefore, this study aimed to evaluate sacral variations in a South African sample by determining distances between the first and second sacral foramina and classifying the common types of sacra found.A quantitative cross-sectional comparative study was conducted. One hundred and twenty (n = 120) dry human sacra and 11 formalin-fixed cadavers were measured to determine the linear distances between the first two anterior and posterior sacral foramina. Additionally, the dry human sacra were classified according to Mahato's classification system. A cadaver SI joint fixation simulation was performed by an orthopaedic surgeon.The mean sacral promontory height was found to be 31.81 mm and 37.52 mm in osteological and cadaver specimens, respectively. The mean anterior pedicle height was significantly different for the left (18.81 mm) and right (21.67 mm) side measurements. A statistically significant difference was found between cadavers and osteological samples for all measurements taken. In the osteological sample, ancestry and age mostly influenced the variations noted.Using Mahato's classification system, sacra with five sacral segments, auricular surfaces extending from the superior part of S1 to the middle of S3 and no accessory L5/S1 articulations had the highest prevalence of 59.17 %.The South African sample exhibited similarities but did not fully compare to other populations. The results in this study should be considered as a reference for surgeries involving the SI joint and sacral foramina. However, where possible, the exact anatomy with possible variations of the patient should be evaluated preoperatively using X-rays and angiograms.

Clinical study on freehand of bicortical sacral screw fixation with the assistance of torque measurement device

BackgroundSacral screw loosening is a typical complication after internal fixation surgery through the vertebral arch system. Bicortical fixation can successfully prevent screw loosening, and how improving the rate of bicortical fixation is a challenging clinical investigation.ObjectiveTo investigate the feasibility of improving the double corticality of sacral screws and the optimal fixation depth to achieve double cortical fixation by combining the torque measurement method with bare hands.MethodsNinety-seven cases of posterior lumbar internal fixation with pedicle root system were included in this study. Based on the tactile feedback of the surgeon indicating the expected penetration of the screw into the contralateral cortex of the sacrum, the screws were further rotated by 180°, 360°, or 720°, categorized into the bicortical 180° group, bicortical 360° group, and bicortical 720° group, respectively. Intraoperatively, the torque during screw insertion was recorded. Postoperatively, the rate of double-cortex engagement was evaluated at 7 days, and screw loosening was assessed at 1 year follow-up.ResultsThe bicortical rates of the 180° group, 360° group, and 720° group were 66.13%, 91.18% and 93.75%, respectively. There were statistically significant differences between the 180° group and both the 360° and 720° groups (P < 0.05). However, there was no statistically significant difference between the 360° group and the 720° group (P > 0.05).The rates of loosening of sacral screws in the 180° group, 360° group, and 720° group were 20.97%, 7.35% and 7.81%, respectively. There were statistically significant differences between the 180° group and both the 360° and 720° groups (P < 0.05). However, there was no statistically significant difference between the 360° group and the 720° group (P > 0.05). The bicortical 360° group achieved a relatively satisfactory rate of dual cortical purchase while maintaining a lower rate of screw loosening.ConclusionManual insertion of sacral screws with the assistance of a torque measurement device can achieve a relatively satisfactory dual cortical purchase rate while reducing patient hospitalization costs.

Pelvic Ring Fractures: A Biomechanical Comparison of Sacral and Lumbopelvic Fixation Techniques.

Pelvic ring fractures are becoming more common in the aging population and can prove to be fatal, having mortality rates between 10% and 16%. Stabilization of these fractures is challenging and often require immediate internal fixation. Therefore, it is necessary to have a biomechanical understanding of the different fixation techniques for pelvic ring fractures. A previously validated three-dimensional finite element model of the lumbar spine, pelvis, and femur was used for this study. A unilateral pelvic ring fracture was simulated by resecting the left side of the sacrum and pelvis. Five different fixation techniques were used to stabilize the fracture. A compressive follower load and pure moment was applied to compare different biomechanical parameters including range of motion (contralateral sacroiliac joint, L1-S1 segment, L5-S1 segment), and stresses (L5-S1 nucleus stresses, instrument stresses) between different fixation techniques. Trans-iliac-trans-sacral screw fixation at S1 and S2 showed the highest stabilization for horizontal and vertical displacement at the sacral fracture site and reduction of contralateral sacroiliac joint for bending and flexion range of motion by 165% and 121%, respectively. DTSF (Double transiliac rod and screw fixation) model showed highest stabilization in horizontal displacement at the pubic rami fracture site, while the L5_PF_W_CC (L5-Ilium posterior screw fixation with cross connectors) and L5_PF_WO_CC (L5-Ilium posterior screw fixation without cross connectors) showed higher rod stresses, reduced L1-S1 (approximately 28%), and L5-S1 (approximately 90%) range of motion. Longer sacral screw fixations were superior in stabilizing sacral and contralateral sacroiliac joint range of motion. Lumbopelvic fixations displayed a higher degree of stabilization in the horizontal displacement compared to vertical displacement of pubic rami fracture, while also indicating the highest rod stresses. When determining the surgical approach for pelvic ring fractures, patient-specific factors should be accounted for to weigh the advantages and disadvantages for each technique.

Variables Associated With Loss of Fixation of Retrograde Rami Screws in Minimally Displaced Lateral Compression Type 1 Pelvic Ring Injuries.

To evaluate variables associated with loss of fixation of retrograde rami screws in the treatment of stress-positive minimally displaced lateral compression type 1 (LC1) injuries. Retrospective comparative study. Level 1 trauma center. Stress-positive minimally displaced (<1 cm) LC1 pelvic ring injuries treated with retrograde rami screws. Loss of fixation, defined as >5 mm of pelvic fracture displacement based on the radiographic tear-drop distance or >5 mm of implant displacement on follow-up radiographs; revision surgery for loss of fixation. Thirty-eight patients with 40 retrograde rami screws were analyzed. Median patient age was 64 years (interquartile range 42.5-73.3 years), 71.1% (n = 27/38) were female, and 52.6% (n = 20/38) of injuries were secondary to low-energy mechanisms. Loss of fixation occurred in 17.5% (n = 7/40) of screws with 10% (n = 4/40) requiring revision surgery. On univariate analysis, patients who had a loss of fixation were more likely to have greater dynamic displacement on stress radiographs (22.0 vs. 15.2 mm; median difference 5.6 mm, confidence interval [CI] -19.2 to 10.3; P = 0.04), unicortical rami screws (71.4% vs. 9.1%; proportional difference 62.3%, CI 8.8%-22.6%; P = 0.001), and partially threaded rami screws (71.4% vs. 21.2%; proportional difference 50.2%, CI 10.0%-77.6%; P = 0.01). The remaining variables had no observed association ( P ≥ 0.05) with loss of fixation, including age, sex, body mass index, energy of injury mechanism, tobacco use, American Society of Anesthesiologist score, sacral fracture type, distal rami fractures, rami comminution, number of sacral screws, fully threaded sacral screws, transsacral screws, or rami screw diameter. On multivariate analysis, only unicortical rami screws ( P = 0.01) remained associated with loss of fixation. Retrograde rami screws had a high rate of loss of fixation in minimally displaced LC1 pelvic ring injuries, and this was associated with unicortical screws. These screws should be avoided when possible. Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Feasibility analysis and nail planning ofS2 iliac crest screw placement in children

To evaluate the feasibility of S2 alar iliac screw insertion in Chinese children using computerized three-dimension reconstruction and simulated screw placement technique, and to optimize the measurement of screw parameters. A total of 83 pelvic CT data of children who underwent pelvic CT scan December 2018 to December 2020 were retrospectively analyzed, excluding fractures, deformities, and tumors. There were 44 boys and 39 girls, with an average age of (10.66±3.52) years, and were divided into 4 groups based on age (group A:5 to 7 years old;group B:8 to 10 years old;group C:11-13 years old;group D:14 to 16 years old). The original CT data obtained were imported into Mimics software, and the bony structure of the pelvis was reconstructed, and the maximum and minimum cranial angles of the screws were simulated in the three-dimensional view with the placement of 6.5 mm diameter S2 alar iliac screws. Subsequently, the coronal angle, sagittal angle, transverse angle, total length of the screw, length of the screw in the sacrum, width of the iliac, and distance of the entry point from the skin were measured in 3-Matic software at the maximum and minimum head tilt angles, respectively. The differences among the screw parameters of S2 alar iliac screws in children of different ages and the differences between gender and side were compared and analyzed. In all 83 children, 6.5 mm diameter S2 iliac screws could be placed. There was no significant difference between the side of each screw placement parameter. The 5 to 7 years old children had a significantly smaller screw coronal angle than other age groups, but in the screw sagittal angle, the difference was more mixed. The 5 to 7 years old children could obtain a larger angle at the maximum head tilt angle of the screw, but at the minimum cranial angle, the larger angle was obtained in the age group of 11 to 13 years old. There were no significant differences among the age groups. The coronal angle and sagittal angle under maximum cephalic angle and minimum cranial angle of 5 to 7 years old male were (40.91±2.91)° and (51.85±3.75)° respectively, which were significantly greater than in female. The coronal angle under minimum cranial angle was significantly greater in girls aged 8-10 years old than in boys. For the remaining screw placement angle parameters, there were no significant differences between gender. The differences in the minimum iliac width, the screw length, and the length of the sacral screws showed an increasing trend with age in all age groups. The distance from the screw entry point to the skin in boys were significantly smaller than that of girls. The minimum width of the iliac in boys at 14 to 16 years of age were significantly wider than that in girls at the same stage. In contrast, in girls aged 5 to 7 years and 11 to 13 years, the screw length was significantly longer than that of boys at the same stage. The pelvis of children aged 5 to 16 years can safely accommodate the placement of 6.5 mm diameter S2 alar iliac screws, but the bony structures of the pelvis are developing and growing in children, precise assessment is needed to plan a reasonable screw trajectory and select the appropriate screw length.

A retrospective CT based comparative analysis of available screw pathways to determine optimal iliac screw trajectory

&lt;b&gt;Introduction:&lt;/b&gt; The lumbo-sacral stabilization using iliac screw is gaining popularity in such cases of long multi segment lumbar constructs. Iliac screws help to achieve strong spinopelvic fixation, augments and protects sacral screws. However, there is a great variability found in literature for iliac screw fixation in terms of trajectory, screw length and screw diameter. Also, to the best of our knowledge, there is lacunae in current literature regarding the optimal pathway, screw length and screw diameter in the Indian population. Hence, we planned the study with the aim to analyze the available screw pathways to determine optimal iliac screw trajectory, screw length and diameter for the Indian population.&lt;br /&gt; &lt;b&gt;Material and methods:&lt;/b&gt; This was a tertiary center-based retrospective study. One hundred pelvic CT scans of patients in 18-70 years age, who underwent abdominal CT on Siemens 256-slice dual source CT scanner for various indications were evaluated. Subsequently, 4 iliac screw trajectories were assessed by connecting the points given below using double oblique reformats on which the lengths and narrowest zones of these trajectories were measured. Path A: Posterior Superior Iliac Spine (PSIS) to Anterior Superior Iliac Spine (AIIS); Path B: point between PSIS and posterior inferior iliac spine (PIIS) to Anterior Inferior iliac spine&amp;nbsp; (AIIS); Path C: iliac crest intersection point (CLIC) point to Upper acetabulum; Path D: CLIC point to acetabular center.&lt;br /&gt; [p1]&amp;nbsp;&lt;b&gt;[a2]&amp;nbsp;Results:&lt;/b&gt; Statistically significant difference was found in the lengths of various pathways. Path A (PSIS to AIIS) was found to be the longest (mean 13 cm). The second longest path in our study was path C (CLIC point to Upper acetabulum). The narrowest widths of each path were not found to have any statistically significant difference.&lt;br /&gt; &lt;b&gt;Conclusion:&lt;/b&gt; Iliac screw fixation is of paramount importance for lumbosacral stabilization. Of the studied paths, trajectory from posterior-superior iliac spine to Antero-inferior iliac spine has the longest passage length and is the most optimal path for the Indian population. In case additional screws are required, the trajectory from CLIC point to Upper acetabulum provides the second largest screw passage.

Percutaneous sacral screw fixation alone sufficient for mildly displaced U-type sacral fractures with preserved osseous fixation pathways

PurposeTo describe U-type sacral fracture characteristics amenable to percutaneous sacral screw fixation.MethodsU-type sacral fractures were identified from a trauma registry at a level 1 trauma center from 2014 to 2020. Patient demographics, injury mechanism, fracture characteristics, and fixation construct were retrospectively retrieved. Associations between fracture pattern and surgical fixation were identified.Results82 U-type sacral fractures were reviewed. Six treated with lumbopelvic fixation (LPF) and 76 were treated with percutaneous sacral screws (PSS) alone. Patients receiving LBF had greater sacral fracture displacement in coronal, sagittal, and axial planes compared to patients receiving PSS alone (P < 0.05), negating osseous fixation pathways. All patients went onto sacral union and there were no implant failures or unplanned reoperations for either group.ConclusionIf osseous fixation pathways are present, U-type sacral fractures can be successfully treated with percutaneous sacral screws. LPF may be indicated in more displaced fractures with loss of spinopelvic alignment. Both techniques for U-type sacral fractures result in reliable fixation and healing without reoperations.

Kyphectomy in myelomeningocele revisited: risk factors for failure.

Lumbar kyphosis occurs in approximately 8-20% of patients with myelomeningocele (MMC). The purpose of this article is to analyze the risks and benefits of vertebrectomy and spinal stabilization in MMC children with severe lumbar kyphosis and to establish treatment guidelines. This is an IRB-approved retrospective analysis of 59 patients with MMC who underwent kyphectomy and posterior instrumentation in three centers. Average age at surgery was 7.9years (2weeks-17years). Sitting trunk position, skin status, kyphosis angle, and thoracic lordosis were analyzed preoperatively, postoperatively, and at an average follow-up of 8.2years (range 2.5-16). The correction was maintained by applying a short posterior instrumentation in 6 patients, and extending to the pelvis in 53 cases. Pelvic fixation was achieved using the Warner and Fackler technique in 24 patients, the Dunn-McCarthy in 8, Luque-Galveston in 8, sacral screws in 2, and ilio-sacral screws in 11. Sitting position improved postoperatively in 47 of the 53 patients who underwent pelvic fixation and only in one patient with short instrumentation. All 6 patients with long instrumentation and poor postoperative sitting balance were in the Dunn-McCarthy fixation group. Skin sores at the apex of the deformity disappeared postoperatively in all patients but recurred in two patients with short instrumentations. Kyphosis angle improved from 109° (45°-170°) preoperatively to 10° (0°-45°) postoperatively and 21° (0°-55°) at last follow-up. The best results were seen in cases where a cross-k-wire fixation of the kyphectomy site was used, augmented with a long thoraco-pelvic instrumentation consisting of Luque sublaminar wires in the thoracic region and a Warner-Fackler type of pelvic fixation. Good results were also found with the bipolar technique and ilio-sacral screw fixation. Six over 24 patients with the Warner and Fackler technique showed gradual dislodgment or hardware failure, with subsequent nonunion of the kyphectomy site in four. Infection, with or without wound dehiscence and/or hardware exposure, occurred in 17 cases, necessitating hardware removal in 9 patients. Lumbar kyphosis in MMC children is best managed by resection of enough vertebrae from the apex to produce a flat lumbar spine, with perfect bone-to-bone contact and long thoraco-pelvic instrumentation using the Warner and Fackler technique through the S1 foramina or the bipolar technique with ilio-sacral screw fixation. Additional local fixation of the osteotomy site using cross-wires with or without cerclage increases the stability of the construct. The majority of complications occurred in patients with short instrumentations or where residual kyphosis persisted postoperatively regardless of the type of pelvic fixation or hardware density. The Dunn-McCarthy technique for pelvic fixation following kyphectomy in MMC was less successful in producing stable pelvic fixation and should not be considered in this patient category.

Navigated, percutaneous, three-step technique for lumbar and sacral screw placement: a novel, minimally invasive, and maximally safe strategy

BackgroundMinimally invasive spine surgery is a field of active and intense research. Image-guided percutaneous pedicle screw (PPS) placement is a valid alternative to the standard free-hand technique, thanks to technological advancements that provide potential improvement in accuracy and safety. Herein, we describe the clinical results of a surgical technique exploiting integration of neuronavigation and intraoperative neurophysiological monitoring (IONM) for minimally invasive PPS.Materials and MethodsAn intraoperative-computed tomography (CT)-based neuronavigation system was combined with IONM in a three-step technique for PPS. Clinical and radiological data were collected to evaluate the safety and efficacy of the procedure. The accuracy of PPS placement was classified according to the Gertzbein–Robbins scale.ResultsA total of 230 screws were placed in 49 patients. Only two screws were misplaced (0.8%); nevertheless, no clinical sign of radiculopathy was experienced by these patients. The majority of the screws (221, 96.1%) were classified as grade A according to Gertzbein–Robbins scale, seven screws were classified as grade B, one screw was classified as grade D, and one last screw was classified as grade E.ConclusionsThe proposed three-step, navigated, percutaneous procedure offers a safe and accurate alternative to traditional techniques for lumbar and sacral pedicle screw placement.Level of Evidence Level 3.Trial registration Not applicable.

Rod Attachment Induces Significant Strain in Lumbosacral Fixation.

This was a laboratory investigation. Rod attachment can induce significant pedicle screw-and-rod pre- strain that may predispose the instrumentation to failure. This study investigated how in vitro L5-S1 rod strain and S1 screw strain during rod-screw attachment (pre-strain) compared with strains recorded during pure-moment bending ( test- strain). The lumbosacral junction is highly vulnerable to construct failure due to rod fatigue fracture, sacral screw pull-out, and screw fatigue fracture. Twelve cadaveric specimens were instrumented with L2-ilium pedicle screws and rod. Strain gauges on contoured rods and sacral screws recorded strains during sequential rod-to-screw tightening (pre-strains). The same instrumented constructs were immediately tested in a 6-degree-of-freedom apparatus under continuous loading to 7.5Nm in multidirectional bending while recording instrumentation test-strains. Rod and screw pre-strains and test-strains were compared using 1-way repeated-measures analysis of variance followed by Holm-Šidák paired analysis (significant at P <0.05). The mean first (171±192µE) and second (322±269µE) rod attachment pre-strains were comparable to mean test-strains during flexion (265±109µE) and extension (315±125µE, P ≥0.13). The mean rod attachment pre-strain was significantly greater than mean test-strains during bidirectional lateral bending (40±32µE ipsilateral and 39±32µE contralateral, P <0.001) and axial rotation (72±60µE ipsilateral and 60±57µE contralateral, P <0.001). The mean first and second sacral screw pre-strains during rod attachment (1.03±0.66 and 1.39±1.00Nm, respectively) did not differ significantly ( P =0.41); however, the mean sacral screw pre-strain during final (second) rod attachment was significantly greater than screw test-strains during all directions of movement (≤0.81Nm, P ≤0.03). Instrumentation pre-strains imposed during in vitro rod-screw attachment of seemingly well-contoured rods in L2-ilium fixation are comparable to, and at times greater than, strains experienced during in vitro bending. Spine surgeons should be aware of the biomechanical consequences of rod contouring and attachment on construct vulnerability.

Reconstruction with 3D-printed prostheses after type I + II + III internal hemipelvectomy: Finite element analysis and preliminary outcomes.

Background: Prosthetic reconstruction after type I + II+ III internal hemipelvectomy remains challenging due to the lack of osseointegration and presence of giant shear force at the sacroiliac joint. The purpose of this study was to evaluate the biomechanical properties of the novel 3D-printed, custom-made prosthesis with pedicle screw-rod system and sacral tray using finite element analysis. Methods: Four models that included one intact pelvis were established for validation. Forces of 500N and 2,000N were applied, respectively, to simulate static bipedal standing and the most loaded condition during a gait cycle. Biomechanical analysis was performed, and the results were compared; the preliminary outcomes of four patients were recorded. Results: For the reconstructed hemipelvis, stress was mainly concentrated on the sacral screws, bone-prosthesis interface, and upper endplate of the L5 vertebra. The optimization of the design with the sacral tray structure could decrease the peak stress of the sacral screws by 18.6%, while the maximal stress of the prosthesis increased by 60.7%. The addition of the lumbosacral pedicle-rod system further alleviated stress of the sacral screws and prosthesis by 30.2% and 19.4%, respectively. The site of peak stress was contemporaneously transferred to the connecting rods within an elastic range. In the retrospective clinical study, four patients who had undergone prosthetic reconstruction were included. During a follow-up of 16.6 ± 7.5months, the walking ability was found preserved in all patients who are still alive and no prosthesis-related complications had occurred except for one hip dislocation. The Musculoskeletal Tumor Society (MSTS) score was found to be 19.5 ± 2.9. Conclusion: The novel reconstructive system yielded favorable biomechanical characteristics and demonstrated promising preliminary outcomes. The method can be used as a reference for reconstruction after type I + II + III hemipelvectomy.

The effect of bone density measurement with computed tomography on lumbosacral fusion and orientation of the sacral screw

The effect of bone density measurement with computed tomography on lumbosacral fusion and orientation of the sacral screw

Surgical management of high-grade lumbar spondylolisthesis associated with Hajdu-Cheney syndrome: illustrative case.

Hajdu-Cheney syndrome (HCS) is a rare connective tissue disorder characterized by severe bone demineralization. In the spine, it is associated with the early onset of severe osteoporosis and can cause spondylolisthesis. Spinal instrumentation in the setting of severe osteoporosis is challenging because of poor resistance of vertebrae to biomechanical stress. A 59-year-old woman with known idiopathic HCS presented with a grade 4 L5-S1 spondylolisthesis and right L5 pedicle fracture associated with a left L5 pars fracture, causing a progressive L5 radiculopathy that was worse on the left side than the right side and bilateral foot drop. The authors performed decompressive lumbar surgery, which included a complete L5 laminectomy and resection of the left L5 pedicle. This was followed by multilevel lumbosacral instrumentation using cement-augmented fenestrated pedicle screws as well as transdiscal sacral screws and bilateral alar-iliac fixation. Postoperatively, the radicular pain resolved, and the left foot drop partially recovered. Stabilization of high-grade spondylolisthesis in the setting of bone demineralization disorders is challenging. The use of different instrumentation techniques is important because it increases biomechanical stability of the overall instrumentation construct.

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

Objective To find a preoperative computed tomography-based method to predict the incidence of sacral screw loosening and assist surgical planning. Methods Surgically treated patients for degenerative lumbosacral disorders with rigid pedicle screw fixation of patients with L5-S1 vertebra in our center from January 2016 to January 2021 were retrospectively included in the current study. CT scan attenuation of the horizontal plane of the sacrum was measured with Hounsfield units (HU). Postoperative X-ray tests were used to diagnose screw loosening. The data was analyzed by independent sample t-tests, X2 analysis, Pearson correlation analysis, and ROC curve analysis. Results A total of 162 (114 male, 48 female, average age 63.7 ± 7.3 years) patients were included in the final analysis. Significant differences were found between the screw loosening group and nonloosening group concerning the HU value of the sacrum at the horizontal plane (P < 0.01). In ROC curve analysis, AUC was 0.674 (95% CI: 0.592-0.756). A cutoff of 200 HU provided 64.8% sensitivity and 62.4% specificity, and a cutoff of 150 HU provided 90.2% sensitivity. Conclusions Analyzing 162 patients with at least 12 months of follow-up, we propose cutoff CT attenuation values of 200 HU and 150 HU to take moderate and radical measures of screw augmentation to prevent screw loosening in the sacral bone.

Anatomy of the L5 nerve root in the pelvis for safe sacral screw placement: a cadaveric study.

Previous reports have focused on the complications of L5 nerve root injury caused by anterolateral misplacement of the S1 pedicle screws. Anatomical knowledge of the L5 nerve root in the pelvis is essential for safe and effective placement of the sacral screw. This cadaveric study aimed to investigate the course of the L5 nerve root in the pelvis and to clarify a safe zone for inserting the sacral screw. Fifty-four L5 nerve roots located bilaterally in 27 formalin-fixed cadavers were studied. The ventral rami of the L5 nerve roots were dissected along their courses from the intervertebral foramina to the lesser pelvis. The running angles of the L5 nerve roots from the centerline were measured in the coronal plane. In addition, the distances from the ala of the sacrum to the L5 nerve roots were measured in the sagittal plane. The authors found that the running angles of the L5 nerve roots changed at the most anterior surface of the ala of the sacrum. The angles of the bilateral L5 nerve roots from the right and left L5 intervertebral foramina to their inflection points were 13.77° ± 5.01° and 14.65° ± 4.71°, respectively. The angles of the bilateral L5 nerve roots from the right and left inflection points to the lesser pelvis were 19.66° ± 6.40° and 20.58° ± 5.78°, respectively. There were no significant differences between the angles measured in the right and left nerve roots. The majority of the L5 nerves coursed outward after changing their angles at the inflection point. The distances from the ala of the sacrum to the L5 nerve roots in the sagittal plane were less than 1 mm in all cases, which indicated that the L5 nerve roots were positioned close to the ala of the sacrum and had poor mobility. All of the L5 nerve roots coursed outward after exiting the intervertebral foramina and never inward. To prevent iatrogenic L5 nerve root injury, surgeons should insert the S1 pedicle screw medially with an angle > 0° toward the inside of the S1 anterior foramina and the sacral alar screw laterally with an angle > 30°.

Pedicle Subtraction Osteotomy Construct Optimization: A Cadaveric Study of Various Multirod and Interbody Configurations.

Fourteen cadaveric specimens were separated into two groups: (1) L3 pedicle subtraction osteotomy (PSO) with transforaminal lumbar interbody fusion (TLIF) or (2) lateral lumbar interbody fusion (LLIF). A 2-rod configuration (2R) was compared with two supplemental rod configurations: 4-rod (4R) with accessory rods (ARs) using connectors or 4R with satellite rods (SRs) without connectors. Compare PSO constructs with different rod configurations and adjacent-level interbody support. Supplemental rods and anterior column support enhance biomechanical performance. Pure moments were applied in (1) intact, (2) pedicle screws and rods, (3) PSO + 2R, (4) 4R AR, and (5) 4R SR conditions. Primary and supplemental rods had strain gauges across the index level. Sacral screw bending moments and range of motion (ROM) were recorded. For TLIF, AR decreased ROM during flexion (P = 0.02) and extension (P < 0.001) versus 2R. For LLIF, AR and SR decreased motion versus 2R during left (AR: P = 0.03; SR: P = 0.04) and right (AR: P = 0.002; SR: P = 0.01) axial rotation. For LLIF, sacral screw strain increased with SR compared with AR in compression and right lateral bending (P ≤ 0.03). During lateral bending, rod strain increased with PSO+TLIF+SR versus PSO+LLIF+2R and PSO+LLIF+AR (P ≤ 0.02). For LLIF, SR configuration increased rod strain versus AR during flexion, extension, and lateral bending (P≤ 0.01); for TLIF, rod strain increased with SR versus AR during extension (P = 0.03). For LLIF, AR configuration increased posterior supplemental rod strain versus SR during flexion (P = 0.02) and lateral bending (P < 0.001). Both supplemental rod configurations reduced motion in both groups. Constructs with the SR configuration increased the primary rod strain and the sacral screw bending moment compared with AR constructs, which can share strain. Deep-seated SRs, which have become increasingly popular, may be more vulnerable to failure than ARs. LLIF provided more stability in sagittal plane. Protective effect of supplemental rods on rod strain was more effective with TLIF.Level of Evidence: NA.

Computed Tomographic Evaluation of the Accuracy of Minimally Invasive Sacroiliac Screw Fixation in Cats.

The aim of this study was to report the use of computed tomography (CT) for postoperative evaluation of the accuracy of sacroiliac reduction and minimally invasive screw fixation in a series of five cats. Medical records between January 2016 and March 2017 of cats presenting to the author's institution were reviewed. Included were cats that had undergone minimally invasive sacroiliac screw fixation with a complete medical record and pre- and postoperative radiographs. Screw size was obtained from the medical records. CT images were acquired prospectively and evaluated to assess joint reduction, relative screw size and screw positioning. Six sacroiliac luxations and 6 screws were available. Fixation was achieved with either a 2.4 (n = 1) or 2.7 mm (n = 5), 316L stainless steel, cortical bone screw. Mean screw size as a proportion of sacral diameter was 47.7%. Sacroiliac reduction >90% in the craniocaudal plane and sacral screw purchase >60% of the sacral width were achieved in 3/5 cases. Mean dorsoventral screw angulation was 1.6 degrees (range: -9.7 to 11.7 degrees) and craniocaudal angulation was -4.5 degrees (range: -16.6 to 6.6 degrees). Complications included screw loosening in the one case of bilateral repair and penetration of the neural canal in one case which was not detected with postoperative radiographic evaluation. CT evaluation provides a useful method for the assessment of sacroiliac reduction and the accuracy of screw placement.