Percutaneous screw fixation of the iliosacral joint: optimal screw pathways are frequently not completely intraosseous

Chronic pelvic insufficiency fractures and their treatment

Fragility and insufficiency fractures of the pelvis (FFP) and sacrum (SIF) are increasingly prevalent, particularly among the elderly, due to weakened bone structure and low-energy trauma. Chronic instability from these fractures causes persistent pain, limited mobility, and significant reductions in quality of life. Hospitalization is often required, with substantial risks of loss of independence (64-89%) and high mortality rates (13-27%). While conservative treatment is possible, surgical intervention is preferred for unstable or progressive fractures. FFP and SIF are primarily associated with osteoporosis, with 71% of patients not receiving adequate secondary fracture prevention. Imaging modalities play a crucial role in diagnosis. Conventional radiography often misses sacral fractures, while computed tomography (CT) is the gold standard for evaluating fracture morphology. Magnetic resonance imaging (MRI) offers the highest sensitivity (99%), essential for detecting complex fractures and assessing bone edema. Advanced techniques like dual-energy CT and SPECT/CT provide further diagnostic value. Rommens and Hofmann's classification system categorizes FFP based on anterior and posterior pelvic ring involvement, guiding treatment strategies. Progression from stable fractures (FFP I-II) to highly unstable patterns (FFP IV) is common and influenced by factors like pelvic morphology, bone density, and sarcopenia. Treatment varies based on fracture type and stability. Non-displaced posterior fractures can be managed with sacroplasty or screw fixation, while displaced or unstable patterns often require more invasive methods, such as triangular lumbopelvic fixation or transsacral bar osteosynthesis. Sacroplasty provides significant pain relief but has limited stabilizing capacity, while screw augmentation with polymethylmethacrylate improves fixation in osteoporotic bones. Anterior ring fractures may be treated with retrograde transpubic screws or symphyseal plating, with biomechanical stability and long-term outcomes depending on fixation techniques. FFP and SIF management requires a multidisciplinary approach to ensure stability, pain relief, and functional recovery, emphasizing early diagnosis, tailored surgical strategies, and secondary prevention of osteoporotic fractures.

Evaluation of the true lateral fluoroscopic projection for the relation of the S1 recess/foramen to safe corridors in transiliac-transsacral screw placement in human cadaveric pelves

INTRODUCTION

Percutaneous screw fixation is a widely used treatment for posterior pelvic ring injuries. Transiliac-transsacral screw fixation has demonstrated superior biomechanical properties over bilateral sacroiliac screws, particularly in the minimally displaced bilateral sacral fractures. Screw placement under fluoroscopic control is still common, while CT navigation is gaining popularity. However, the accurate placement of screws within a safe zone is essential to avoid neurovascular complications.

METHODS

An anatomical study using human cadaveric pelves was conducted to assess radiological landmarks and determine a safe zone in relation to the S1 recess/foramen for transiliac-transsacral screw placement.

RESULTS

Fourteen pelves were evaluated. Ten pelves were classified as having a satisfactory corridor for screw placement, while four were deemed to have an impossible or high-risk corridor. A safe zone was defined based on the diagonal bisector of the S1 vertebral body, ICD and anterior cortex.

DISCUSSION

The study findings suggest that lateral fluoroscopic projection can determine a safe entry point for screw placement. Understanding the anatomy and landmarks on lateral fluoroscopic images is crucial for successful screw placement and avoiding complications.

CONCLUSION

The S1 body diagonal is consistently located anterior to the S1 recess in lateral fluoroscopic projections, providing a potential safe corridor for transiliac-transsacral screw placement at the S1 level in nondysmorphic pelves. Further research is needed to confirm these findings with CT imaging and evaluate the technical feasibility of screw placement.

Specifying the Starting Point for S1 Iliosacral Screw Placement in the Dysmorphic Sacrum

BACKGROUND

Sacral dysmorphism is not uncommon and complicates S1 iliosacral screw placement partially because of the difficulty of determining the starting point accurately on the sacral lateral view. We propose a method of specifying the starting point.

METHODS

The starting point for the S1 iliosacral screw into the dysmorphic sacrum was specifically set at a point where the ossification of the S1/S2 intervertebral disc (OSID) intersected the posterior vertebral cortical line (PVCL) on the sacral lateral view, followed by guidewire manipulation and screw placement on the pelvic outlet and inlet views. Computer-simulated virtual surgical procedures based on pelvic computed tomography (CT) data on 95 dysmorphic sacra were performed to determine whether the starting point was below the iliac cortical density (ICD) and in the S1 oblique osseous corridor and to evaluate the accuracy of screw placement (with 1 screw being used, in the left hemipelvis). Surgical procedures on 17 patients were performed to verify the visibility of the OSID and PVCL, to check the location of the starting point relative to the ICD, and to validate the screw placement safety as demonstrated with postoperative CT scans.

RESULTS

In the virtual surgical procedures, the starting point was consistently below the ICD and in the oblique osseous corridor in all patients and all screws were Grade 1. In the clinical surgical procedures, the OSID and PVCL were consistently visible and the starting point was always below the ICD in all patients; overall, 21 S1 iliosacral screws were placed in these 17 patients without malpositioning or iatrogenic injury.

CONCLUSIONS

On the lateral view of the dysmorphic sacrum, the OSID and PVCL are visible and intersect at a point that is consistently below the ICD and in the oblique osseous corridor, and thus they can be used to identify the starting point.

LEVEL OF EVIDENCE

Therapeutic Level III . See Instructions for Authors for a complete description of levels of evidence.

The ideal site of cement application in cement augmented sacroiliac screw fixation: the biomechanical perspective

Purpose

To compare construct stability of cement augmented sacroiliac screws using two different cementation sites in a biomechanical fragility fracture model of the pelvis.

Methods

A fracture model with an incomplete fracture of the sacral ala and complete fracture of the anterior pelvic ring mimicking a FFP IIB fragility fracture of the pelvis was established in five fresh frozen human cadaveric pelvises. Sacral fracture stabilization was achieved with bilateral 7.3 mm fully threaded sacroiliac screws. Cement augmentation was performed at the tip of the screw (body of S1; Group A) on one side, and at the midshaft of the screw (sacral ala; Group B) on the contralateral side. Biomechanical testing was conducted separately on both sides comprising cyclic loading of axial forces transferred through the tested hemipelvis from L5 to the ipsilateral acetabulum. Combined angular displacement in flexion and internal rotation (“gap angle”), angular displacement of the ilium in relation to the screw (“screw tilt ilium”), and screw tip cutout were evaluated.

Results

Relative interfragmentary movements were associated with significantly higher values in group A versus group B for “gap angle” (2.4° vs. 1.4°; p < 0.001), and for “screw tilt ilium” (3.3° vs. 1.4°; p < 0.001), respectively. No significant difference was indicated for screw tip cutout between the two groups (0.6 mm [Group A] vs. 0.8 mm [Group B]; p = 0.376).

Conclusion

The present study demonstrated less fragment and screw displacements in a FFP IIB fracture model under physiologic cyclic loading by cement augmentation of sacroiliac screws at the level of the lateral mass compared to the center of vertebral body of S1.

Analysis of trans-sacral corridors in stabilization of fractures of the pelvic ring

Percutaneous screw fixation combined with pelvic reduction is a surgical technique used to stabilize fractures of the posterior pelvic ring. This is the standard surgical treatment of unstable posterior pelvic ring injuries. The primary goal of this treatment is an anatomic reduction and stable fixation. This has been shown to reduce pain and improve the patients' long-term well-being. The aim of this analysis was to determine the possible screw lengths and the positioning of the screws in the S1 and S2 sacral segments. A population of 697 pelvises from the Stryker Orthopaedic Modeling and Analytics database were analyzed. The dimensions of the S1 and S2 screw corridors were determined and after assessing for sacral dysmorphism, the correct screw placement was chosen to determine the necessary screw length for surgical treatment. The measurements of the screw lengths show a Gaussian distribution for the analyzed population. The percentage of dysmorphic pelvises for the S1 screw corridor was 31.3% and for the S2 corridor 8%. Average screw length for S1 was 163.8 ± 16.2 mm and for the S2 137.3 ± 9.5 mm. The results show that the S1/S2 axis cannot be used for a trans-sacral screw placement in every patient. The study shows that intraosseous screw corridors are present in 68.7% of the patients in the S1 position and in 92% at the S2 level where an intended implant can be placed fully intraosseous.

Assessment of osseous corridor for transiliac-transsacral screws and clinical applications: Computational simulation study

BACKGROUND

Transiliac-transsacral (TITS) screw fixation might be necessary in some cases involving the vertical shearing injuries with transforaminal fracture and bilateral posterior ring injuries. However, the possibility of S₁ TITS screw should be preoperatively assessed because the pelvic ring injuries with sacral dysmorphism had the insufficient osseous corridors.

HYPOTHESIS

AxW_S2 may predict the possibility of TITS screw fixation and be used as the new indicator to discriminate the sacral dysmorphism.

MATERIALS & METHODS

The conventional CT images of eighty-two cadaveric pelvis imported into Mimics® software to reconstruct three-dimensional (3D) models. A 7.0 mm-sized screw was processed into a 3D model using a 3D-sensor at actual size and virtually implanted as S₁ and S₂ TITS screw using Mimics® software. The cortical violation around screw path was evaluated using 3D biplanar and conventional CT images. The osseous corridor widths around TITS screws were measured in the axial plane images and defined as AxW_S1 and AxW_S2, respectively.

RESULTS

Despite no cortical violation in S₂ of all models, cortical violation of S₁ TITS screw was found in 20 models. Of them, 14 models (impossible models) were identified in the 3D biplanar images, and all 20 models (CT-violation models) were identified only in CT axial plane images. AxWS₁ was<7mm in the impossible models and<9.0mm in the CT-violation models. AxW_S2 negatively correlated with AxW_S1 (R -0.450, p<0.01). By receiver operating characteristic curve analysis to identify the CT-violation model using AxW_S2, the cut-off value of AxW_S2 was 13.32mm (sensitivity 0.70, specificity 0.70).

DISCUSSION

By using AxW_S2, the possibility of S₁ TITS screw fixation could be predicted and safely placed without cortical violation, if AxW_S2 was less than 13mm. Considering the negative relationship with AxW_S1, AxW_S2 should be used as a new indicator to predict safe S₁ TITS screw fixation.

LEVEL OF EVIDENCE

III, controlled laboratory study.

Anatomical conditions and patient-specific locked navigation templates for transverse sacroiliac screw placement: a retrospective study

Objective

To analyse the anatomical conditions of transverse sacroiliac screw (TSS) about the S1 and S2 segments in order to develop and validate a locked navigational template for TSS placement.

Methods

A total of 22 patients with sacral fractures were involved in this study from May 2018 to February 2019. Patients were divided into two groups according to the surgery procedure: locked template group and conventional group. The CT data of 90 normal sacra were analysed. The long axis, short axis and lengths of TSS, cancellous corridors were measured through 3D modelling. A patient-specific locked navigation template based on simulated screws was designed and 3D printed and then used to assist in TSS placement. The operative time and radiation times were recorded. The Matta criteria and grading score were evaluated. The entry point deviation of the actual screw placement relative to the simulated screw placement was measured, and whether the whole screw was in the cancellous corridor was ob`served.

Results

S1 screws with a diameter of 7.3 mm could be inserted into 69 pelvises, and S2 screws could be inserted in all pelvises. The S1 cancellous corridor had a long axis of 25.44 ± 3.32 mm in males and 22.91 ± 2.46 mm in females, a short axis of 14.21 ± 2.19 mm in males and 12.15 ± 3.22 mm in females, a corridor length of 153.07 ± 11.99 mm in males and 151.11 ± 8.73 mm in females, and a proportional position of the optimal entry point in the long axis of the cancellous corridor of 35.96 ± 10.31% in males and 33.28 ± 7.2% in females. There were significant differences in the corridor long axis and corridor short axis between sexes (p < 0.05), and there were no significant differences in corridor length and proportional position of the optimal entry point in the long axis of the cancellous corridor between sexes (p > 0.05). The S2 cancellous corridor had a long axis of 17.58 ± 2.36 mm in males and 16 ± 2.64 mm in females, a short axis of 14.21 ± 2.19 mm in males and 13.14 ± 2.2 mm in females, a corridor length of 129.95 ± 0.89 mm in males and 136.5 ± 7.96 mm in females, and a proportional position of the optimal entry point in the long axis of the cancellous corridor of 46.77 ± 9.02% in males and 42.25 ± 11.95% in females. There were significant differences in the long axis, short axis and corridor length (p < 0.05). There was no significant difference in the proportional position of the optimal entry point in the long axis of the cancellous corridor (p > 0.05). A total of 20 transversal sacroiliac screws were successfully implanted into 10 patients with the assistance of locked navigation templates, and a total of 24 transversal sacroiliac screws were successfully implanted into 12 patients under C-arm fluoroscopy. There was a significant difference in surgical time (88 ± 14.76 min vs 102.5 ± 17.12 min, p = 0.048), radiation times (11.5 ± 1.78 vs 54.83 ± 6.59, p < 0.05) and screw grading between two groups (nineteen screws in grade 0, one screw in grade 1 and 0 screws in grade 2 vs fourteen screws in grade 0, 8 screws in grade 1 and 2 screws in grade 2, p = 0.005). All screw entry point deviations were shorter than the short axis of the cancellous corridor, and all screws were located completely within the cancellous corridor.

Conclusion

Approximately 76% of males and females can accommodate screws with diameters of 7.3 mm in S1, and all persons can accommodate the same screw in S2. From the standard lateral perspective of the sacrum, the optimal entry point of the transverse screw is in the first 1/3 of the cancellous corridor for S1 and the centre of the cancellous corridor for S2. The patient-specific locked navigation template assisted in TSS placement with less operative time, less intraoperative fluoroscopy and higher safety of screw placement compared with traditional surgery.

The effect of robot-navigation-assisted core decompression on early stage osteonecrosis of the femoral head

BACKGROUND

The aim of the current paper is to evaluate the effects of robot-navigation-assisted core decompression compared with conventional core decompression surgery for early-stage osteonecrosis of the femoral head.

METHODS

Twenty patients with a total of 36 hips who were diagnosed with Association Research Circulation Osseous stage 2 avascular necrosis of the femoral head and who received core decompression with or without robotic assistance were reviewed. The Harris hip score and visual analog scale score were used to assess clinical function. Intraoperative radiation exposure and operation time were used to evaluate the effectiveness of the robot-assisted system.

RESULTS

At a mean follow-up of 26.4 months (24-36 months), the Harris hip score, visual analog scale score, and survival rate of the patients were similar between the conventional and robot-assisted groups. The guidewire insertion time, number of guidewire attempts, and radiation exposure during guidewire insertion were all significantly lower in the robot-assisted group than in the conventional group.

CONCLUSIONS

Robot-assisted core decompression of the femoral head is as safe and effective as a conventional core decompression surgery. It can reduce operation time and decrease intraoperative radiation exposure.

Space available for trans-sacral implants to treat fractures of the pelvis assessed by virtual implant positioning

INTRODUCTION

The use of trans-sacral implants to treat fractures of the sacrum is limited by the variable pelvic anatomy. We were interested in how many trans-sacral implants can be placed per pelvis? If a trans-sacral implant cannot be placed in S1, where is the cortex perforated, and is the use of sacroiliac screws safe in these pelves?

MATERIALS AND METHODS

3D pelvic models were created from CT scans of 156 individuals without fractures (92 European and 64 Japanese, 79 male and 77 female, mean age 66.7 ± 13.7 years). Trans-sacral implants with a diameter of 7.3 mm were positioned virtually with and without a surrounding safe zone of 12 mm diameter.

RESULTS

Fifty-one percent of pelves accommodated trans-sacral implants in S1 with a safe zone. Twenty-two percent did not offer enough space in S1 for an implant even when ignoring the safe zone. Every pelvis had sufficient space for a trans-sacral implant in S2, in 78% including a safe zone as well. In S1, implant perforation was observed in the sacral ala and iliac fossa in 69%, isolated iliac fossa perforation in 23% and perforation of the sacral ala in 8%. Bilateral sacroiliac screw placement was always possible in S1.

CONCLUSIONS

The use of trans-sacral implants in S1 requires meticulous preoperative planning to avoid injury of neurovascular structures. S2 more consistently offers space for trans-sacral implants.

[Precise sacroiliac joint screw insertion without computed tomography, digital volume tomography or navigation systems]

OBJECTIVE

Improvement of sacroiliac positioning of screws by detailed preoperative planning with a DICOM (Digital Imaging and Communications in Medicine-the international standard to store and process medical imaging information) workstation in the absence of advanced technical facilities like intraoperative computer tomography (CT), digital volume tomography (DVT) or a navigation system.

INDICATIONS

Mono- or bilateral non- or minor displaced, longitudinal sacral fractures type Denis I and II and pelvic ring fractures (Orthopedic Trauma Association) OTA type B possibly in combination with a ventral procedure.

CONTRAINDICATIONS

Displaced sacral fractures type Denis II and III, fractures with central comminution and circulatory unstable patients to be stabilized in the context of emergency care.

SURGICAL TECHNIQUE

Preoperative calculation of virtual conventional standard view X‑rays with the CT dataset using common DICOM software (e.g., Siemens via® or Sectra®). Typical landmarks such as screw entry point and end point are projected into the virtual X‑rays. Intraoperative navigation is performed by comparing the virtual standard views with fluoroscopic images of the C‑arm, thereby, simplifying the operative procedure.

POSTOPERATIVE MANAGEMENT

Postoperative CT scan, pain adapted partial weight bearing and X‑rays of the pelvic ring after 6 and 12 weeks.

RESULTS

Over a 13 month period, an orthopedic surgeon inserted 26 sacroiliac screws in 19 patients utilizing the described method. Postoperative CT scans revealed that all except three screws were precisely positioned without any bone perforation. Of these three screws one had a grade one perforation and two had a grade two perforation according to Smith. No revision was necessary and no neurological deficits were detected. The operating time was on average 33 min and duration of radiation 3.8 min.

Percutaneous Sacroiliac Screw Placement: A Prospective Randomized Comparison of Robot-assisted Navigation Procedures with a Conventional Technique

Background:

Sacroiliac (SI) screw fixation is a demanding technique, with a high rate of screw malposition due to the complex pelvic anatomy. TiRobot™ is an orthopedic surgery robot which can be used for SI screw fixation. This study aimed to evaluate the accuracy of robot-assisted placement of SI screws compared with a freehand technique.

Methods:

Thirty patients requiring posterior pelvic ring stabilization were randomized to receive freehand or robot-assisted SI screw fixation, between January 2016 and June 2016 at Beijing Jishuitan Hospital. Forty-five screws were placed at levels S1 and S2. In both methods, the primary end point screw position was assessed and classified using postoperative computed tomography. Fisher's exact probability test was used to analyze the screws’ positions. Secondary end points, such as duration of trajectory planning, surgical time after reduction of the pelvis, insertion time for guide wire, number of guide wire attempts, and radiation exposure without pelvic reduction, were also assessed.

Results:

Twenty-three screws were placed in the robot-assisted group and 22 screws in the freehand group; no postoperative complications or revisions were reported. The excellent and good rate of screw placement was 100% in the robot-assisted group and 95% in the freehand group. The P value (0.009) showed the same superiority in screw distribution. The fluoroscopy time after pelvic reduction in the robot-assisted group was significantly shorter than that in the freehand group (median [Q₁, Q₃]: 6.0 [6.0, 9.0] s vs. median [Q₁, Q₃]: 36.0 [21.5, 48.0] s; χ² = 13.590, respectively, P < 0.001); no difference in operation time after reduction of the pelvis was noted (χ² = 1.990, P = 0.158). Time for guide wire insertion was significantly shorter for the robot-assisted group than that for the freehand group (median [Q₁, Q₃]: 2.0 [2.0, 2.7] min vs. median [Q₁, Q₃]: 19.0 [15.5, 45.0] min; χ² = 20.952, respectively, P < 0.001). The number of guide wire attempts in the robot-assisted group was significantly less than that in the freehand group (median [Q₁, Q₃]: 1.0 [1.0,1.0] time vs. median [Q₁, Q₃]: 7.0 [1.0, 9.0] times; χ² = 15.771, respectively, P < 0.001). The instrumented SI levels did not differ between both groups (from S1 to S2, χ² = 4.760, P = 0.093).

Conclusions:

Accuracy of the robot-assisted technique was superior to that of the freehand technique. Robot-assisted navigation is safe for unstable posterior pelvic ring stabilization, especially in S1, but also in S2. SI screw insertion with robot-assisted navigation is clinically feasible.

Percutaneous screw fixation of the iliosacral joint: A case-based preoperative planning approach reduces operating time and radiation exposure

INTRODUCTION

A preoperative planning approach for percutaneous screw fixation of the iliosacral joint provides specific entry points (EPs) and aiming points (APs) of intraosseous screw pathways (as defined by CT scans) for lateral fluoroscopic projections used intraoperatively. The potential to achieve the recommended EPs and APs, to obtain an ideal screw position (perpendicular to the iliosacral joint), to avoid occurrence of extraosseous screw misplacement, to reduce the operating time and the radiation exposure by utilizing this planning approach have not been described yet.

METHODS

On preoperative CT scans of eight human cadaveric specimen individual EPs and APs were identified and transferred to the lateral fluoroscopic projection using a coordinate system with the zero-point in the center of the posterior cortex of the S1 vertebral body (x-axis parallel to upper S1 endplate). Distances were expressed in relation to the anteroposterior distance of the S1 upper endplate (in%). In each specimen on one side a screw was placed with provided EP and AP (New Technique) whereas at the contralateral side a screw was placed without given EP and AP (Conventional Technique). Both techniques were compared using postoperative CT scans to assess distances between predefined EPs and APs and the actually obtained EPs and APs, screw angulations in relation to the iliosacral joint in coronal and axial planes and the occurrence of any extraosseous screw misplacement. The "operating time (OT)" and the "time under fluoroscopy (TUF)" were recorded. Statistical analysis was performed by the Wilcoxon signed-rank test.

RESULTS

EPs were realized significantly more accurate using the new technique in vertical direction. The screw positions in relation to the iliosacral joint showed no significant difference between both techniques. Both techniques had one aberrantly placed screw outside the safe corridor. The (mean±SD) "OT" and the (mean±SD) "TUF" were significantly decreased using the new technique compared to the conventional technique (OT: 7.6±2min versus 13.1±5.8min, p=0.012; TUF: 1.5±0.8min versus 2.2±1.1min).

CONCLUSION

The presented preoperative planning approach increases the accuracy in percutaneous screw fixation of the iliosacral joint, reduces operating time and minimizes radiation exposure to patient and staff.

[Percutaneous internal fixation of pelvic fractures. German version]

BACKGROUND

Percutaneous internal fixation of pelvic fractures is increasing in popularity with multiple new techniques reported.

OBJECTIVES

The purpose of this article is to outline the imaging, indication, planning, equipment, surgical technique and complications of these methods.

METHODS

A review of the literature is provided and the techniques for anterior and posterior pelvic stabilization are discussed.

RESULTS

High-quality preoperative CT scans are essential in planning for this technique. The anterior internal fixator ("InFix") is an effective method for stabilizing the anterior ring and should be usually used in conjunction with posterior fixation. Good technique avoids neurovascular injury, which can be a devastating complication. The retrograde anterior column screw (RACS) is a technique that can be used in most patients, although in smaller patients smaller screw diameters may be needed. The entry point for the screw is more lateral in women than men. Iliosacral screws (ISS) are an effective method of posterior stabilization and can be placed using 2D or 3D fluoroscopy, computer navigation or CT navigation.

CONCLUSION

Percutaneous fixation of pelvic fractures requires high-quality imaging and can be aided by computer navigation. Safe techniques are reproducible; however, not all patients and fracture patterns can be treated using these techniques.

A Useful Preoperative Planning Technique for Transiliac-Transsacral Screws

Stabilization of posterior pelvic ring injuries is increasingly performed using percutaneously placed iliosacral and transiliac-transsacral screws. Understanding the unique and specific anatomical variations present in each patient is paramount. Multiple methods of evaluating potential osseous fixation pathways for screw placement exist, but many require specific imaging protocols, specialized software, or modification of data. Not all surgeons and institutions have access to these options for a variety of reasons. A simple technique to preoperatively plan for safe transiliac-transsacral screws is proposed.