Transiliac Transsacral Screw: Indications and Clinical Insights

Stabilizing pelvic fractures and sacral injuries is challenging due to the region’s complex anatomy and high biomechanical demands. The transiliac transsacral screw provides rigid fixation while preserving soft tissues, making it a valuable option in select cases.

Its success depends on proper patient selection, precise anatomical knowledge, and advanced imaging guidance to optimize outcomes and minimize complications.

Surgical Indications

The transiliac transsacral screw is primarily used for unstable pelvic ring injuries, particularly those involving the sacrum and posterior pelvis. High-energy trauma, such as motor vehicle collisions or falls from significant heights, often causes these injuries, leading to sacral disruptions and instability. This screw offers rigid fixation, especially when traditional iliosacral screws fail to provide sufficient purchase due to sacral dysmorphism or comminuted fractures.

Common indications include sacral fractures classified under the Denis and AO/OTA systems, particularly Zone II and Zone III fractures that affect the sacral foramina or central canal. In these cases, maintaining neurological integrity while ensuring mechanical stability is crucial. Studies indicate that transsacral fixation reduces the risk of nonunion and malalignment compared to unilateral fixation, especially in vertically unstable sacral fractures. A retrospective analysis in The Journal of Orthopaedic Trauma found lower postoperative displacement rates and improved functional outcomes with transsacral fixation compared to unilateral iliosacral screws.

Pelvic ring disruptions involving sacroiliac joint instability also benefit from this technique. In cases of sacroiliac dislocation or ligamentous insufficiency, unilateral iliosacral screws may not provide adequate rotational control. The transsacral approach enables bilateral stabilization with a single implant, reducing micromotion and improving load distribution. This is particularly useful in osteoporotic patients, where screw loosening is a concern. A Clinical Biomechanics study demonstrated that transsacral screws provide superior resistance to shear and torsional forces compared to unilateral fixation methods.

Beyond acute trauma, this technique is also used for sacral insufficiency fractures, particularly in elderly osteoporotic patients. These fractures, often resulting from minimal trauma, can lead to severe pain and progressive deformity. While conservative management is preferred, persistent pain or displacement may necessitate percutaneous transsacral fixation. A study in The Journal of Bone and Joint Surgery reported significant pain relief and improved mobility in osteoporotic patients treated with transsacral screws, underscoring their role in fragility fracture management.

Anatomical Pathway

Placing a transiliac transsacral screw requires precise knowledge of the osseous corridor spanning the ilium and sacrum, as well as the spatial relationships between critical neurovascular structures. The screw traverses the sacral ala and sacral body, emerging contralaterally in the opposite ilium. Proper trajectory planning is essential to avoid breaching the sacral foramina or compromising lumbosacral nerve roots.

Sacral dysmorphism, which alters sacral body shape and upper sacral segment orientation, can complicate screw placement. Individuals with a high-riding iliac crest or small upper sacral segments may have a narrowed osseous corridor, increasing the risk of cortical breach. A Spine Journal cadaveric study found that 41% of specimens exhibited dysmorphic features that could limit safe screw placement, necessitating preoperative imaging to assess bone stock and ensure adequate containment.

The screw typically passes between the S1 and S2 foramina, making precise trajectory crucial to avoid foraminal breach and nerve injury. A Journal of Orthopaedic Trauma study reported foraminal violations in 12% of cases when relying solely on standard fluoroscopic guidance, emphasizing the need for meticulous preoperative planning and intraoperative verification.

Vascular structures also present concerns. The lateral sacral arteries, branching from the internal iliac artery, course along the posterior sacrum. While the screw pathway is primarily intraosseous, cortical penetration can put these vessels at risk. Cases of postoperative hemorrhage due to vascular injury have been documented, particularly in revision surgeries. A case series in Injury highlighted instances of excessive bleeding following misplaced transsacral screws, reinforcing the need for precise placement.

Imaging Guidance

Accurate imaging is critical to safely placing transiliac transsacral screws due to the sacrum’s complex anatomy. Preoperative and intraoperative imaging helps define the osseous corridor, assess sacral morphology, and ensure proper screw trajectory. Fluoroscopy, computed tomography (CT), and three-dimensional (3D) reconstructions provide essential guidance.

Fluoroscopic Views

Fluoroscopy is the most commonly used intraoperative imaging modality, offering real-time visualization. Proper C-arm positioning is necessary to confirm a safe screw trajectory. The inlet view assesses anterior-posterior alignment, ensuring the screw remains within the sacral body. The outlet view helps prevent foraminal violation, while a true lateral sacral view confirms the screw remains within the osseous corridor.

However, fluoroscopy has limitations, particularly in sacral dysmorphism cases where standard views may not adequately define the safe zone. Studies indicate that fluoroscopy alone can lead to misplacement in up to 15% of cases. Some surgeons use oblique fluoroscopic angles tailored to patient morphology to improve accuracy.

CT Reference

Preoperative CT imaging is invaluable for assessing sacral morphology and planning the optimal screw trajectory. High-resolution CT scans with thin-slice reconstructions allow for detailed evaluation, particularly in dysmorphic sacra where fluoroscopic landmarks may be unreliable. CT-based measurements help determine the maximum allowable screw diameter and length, reducing cortical breach risk.

Intraoperative CT navigation enhances accuracy by providing real-time, multiplanar imaging. A Journal of Bone and Joint Surgery study found that CT-guided screw placement reduced foraminal breaches from 12% to under 2%, significantly improving safety. However, increased operative time and equipment requirements may limit its routine use.

3D Reconstructions

Three-dimensional CT reconstructions provide advanced visualization of sacral anatomy, allowing for precise preoperative planning. These reconstructions help assess the transsacral corridor and simulate screw placement, particularly in complex fractures or anatomical variations.

Recent advancements in intraoperative 3D imaging, such as cone-beam CT and robotic-assisted navigation, have further improved accuracy. A Clinical Orthopaedics and Related Research study found that 3D navigation-assisted screw placement achieved a 98% accuracy rate, compared to 85% with conventional fluoroscopy. While 3D imaging offers superior precision, its availability and cost may limit widespread adoption.

Implant Materials

The choice of implant materials for transiliac transsacral screws influences biomechanical stability, biocompatibility, and long-term durability. Common materials include titanium alloys, stainless steel, and composite variants, each with distinct properties suited to specific patient needs.

Titanium Alloy

Titanium alloy is favored for its high strength-to-weight ratio, biocompatibility, and corrosion resistance. Its lower modulus of elasticity compared to stainless steel reduces stress shielding, promoting better load distribution and minimizing implant-related bone resorption. Additionally, titanium’s osseointegration properties enhance bone-implant bonding, particularly beneficial in osteoporotic patients.

Stainless Steel

Stainless steel offers greater rigidity, making it ideal for high-impact injuries requiring robust mechanical support. It is also more cost-effective. However, its higher modulus of elasticity can contribute to stress shielding and potential bone resorption. While modern stainless steel alloys improve corrosion resistance, studies suggest titanium implants have superior long-term longevity.

Composite Variants

Composite materials, including carbon fiber-reinforced polymers and bioresorbable composites, provide emerging alternatives. Carbon fiber-reinforced screws improve postoperative imaging clarity, as they do not produce the artifacts seen with metal implants. Bioresorbable composites, designed to degrade over time, eliminate the need for implant removal in select cases. While early studies show promise, further research is needed to determine their role in high-stress pelvic fixation scenarios.

Surgical Steps

Proper transiliac transsacral screw placement requires meticulous technique. The patient is positioned supine or prone on a radiolucent table. Fluoroscopy identifies sacral landmarks, and a percutaneous or minimally invasive approach minimizes soft tissue disruption.

A small incision is made over the iliac crest, and a guidewire is inserted under fluoroscopic control. The inlet, outlet, and lateral views confirm the trajectory. A cannulated drill prepares the bone, and the transsacral screw—typically 6.5 to 8.5 mm in diameter—is placed with bicortical purchase for stability. Final fluoroscopic confirmation ensures proper positioning before wound closure.

Biomechanical Considerations

Transiliac transsacral screws provide superior resistance to vertical shear and rotational forces by engaging both iliac cortices. This bilateral engagement enhances load distribution, reducing stress concentration. Finite element modeling studies show that transsacral screws reduce micromotion, accelerating healing and lowering nonunion risk.

Bone density affects fixation strength, particularly in osteoporotic patients. Augmentation techniques, such as cementation or fenestrated screws, improve grip. Longer screws spanning the entire sacral body offer enhanced stability compared to shorter constructs. In severe instability cases, supplemental fixation methods may be necessary to reinforce the construct.