Transacral Transdiscal Screws for High-Grade Lumbosacral Listhesis
For high-grade lumbosacral spondylolisthesis, posterior transdiscal (transacral) screw fixation from L5 to S1 represents a biomechanically superior and technically viable option that provides immediate three-column stabilization while being less technically demanding than circumferential fusion approaches. 1, 2
Biomechanical Superiority of Transdiscal Screws
The transdiscal screw technique demonstrates the most stable construct for high-grade L5-S1 spondylolisthesis when compared to alternative fixation methods:
Transdiscal screws provide the lowest range of motion in all loading modes (flexion, extension, lateral bending, and torsion) compared to the Bohlman technique (transdiscal fibular strut) and modified Bohlman technique (transdiscal titanium mesh cage). 1
Statistical superiority was specifically demonstrated in extension movements, which is critical given the high shear forces at the lumbosacral junction in high-grade slips. 1
The technique achieves immediate three-column stabilization of the lumbosacral junction, which is essential for managing the biomechanical instability inherent in high-grade spondylolisthesis. 3
Clinical Evidence and Outcomes
While guideline evidence addresses general spondylolisthesis management without specifying transdiscal techniques, the research literature provides compelling support:
A systematic review concluded that posterior transdiscal fixation is associated with better clinical outcomes when compared with standard pedicle screw fixation techniques for high-grade spondylolisthesis. 2
Clinical and radiological outcomes of transdiscal screws are similar to those achieved with transforaminal lumbar interbody fusion (TLIF), but the transdiscal technique is technically less challenging to perform. 2
The technique has demonstrated successful fusion in patients with established pseudarthrosis from prior failed fusion attempts, indicating its utility in revision scenarios. 3
Technical Considerations
The surgical approach involves:
Bilateral L5-S1 facetectomy and complete disc removal to address the high-grade slip (typically 50-60% displacement). 1
Posterior approach with L5-S1 transpedicular screw placement that traverses the disc space into the sacrum. 4
The screws can be combined with spinal decompression and bilateral L5 root foraminotomy as needed for neural element decompression. 4
Optional addition of a transvertebral interbody cage through the transsacral corridor to provide substrate for interbody arthrodesis and act as a biomechanical stabilizer preventing pedicle screw failure. 5
Guideline Context
Current guidelines emphasize that surgical decompression with fusion is recommended for symptomatic high-grade spondylolisthesis, but acknowledge insufficient evidence to recommend a standard fusion technique. 6
The decision-making process should factor in the patient's unique anatomical constraints and surgeon experience when determining the optimal strategy to maximize fusion potential while minimizing complications. 6
Pedicle screw stabilization is considered appropriate when instability is present, which is inherent in high-grade slips. 6, 7
Critical Advantages Over Alternative Techniques
Transdiscal screws offer specific benefits:
Less technically demanding than circumferential (360-degree) fusion approaches while achieving comparable outcomes. 2
Uses instrumentation common to spine surgery, making it accessible to surgeons familiar with standard pedicle screw techniques. 3
Provides more robust fixation than posterolateral fusion alone, which is particularly important given the high shear forces at L5-S1 in high-grade slips. 1
Common Pitfalls to Avoid
Proper screw insertion is more technically demanding than conventional pedicle screw fixation and requires careful trajectory planning to traverse the disc space and engage the sacrum adequately. 2
Inadequate screw length or improper trajectory may compromise the biomechanical advantage of the construct. 1
The technique requires complete disc removal and adequate visualization to ensure safe screw passage without neural injury. 1