RECENT INPUT OF US SPINE SOCIETIES ON SPIKES, FLANGES, AND SCREWS IN POSTERIOR CERVICAL INTERFACET AND SACROILIAC (SI) JOINT TRANSFIXION SUFFERS FROM BIOMECHANICAL FLAWS

Challenging Biomechanical Misconceptions:

The Case for Integrated Spinal and SI Joint Fixation Devices

1. Integrated Device Design and Functionality:

• Modern intersegmental fusion devices are designed to incorporate spikes, flanges, or screws as integral parts of a cohesive system. This integration is essential for providing stability and ensuring successful fusion. The perspective that these components are independent instrumentation overlooks the fact that the biomechanical effectiveness of the fusion process relies on the combined action of the fusion device and its integrated components. These elements function synergistically to provide stability and effectively distribute mechanical loads.

1. Misconception of Biomechanical Independence:

• The belief that instrumentation must be biomechanically independent to be effective is not always practical. The stability offered by fusion devices often results from the synergy between the fusion device and its integrated instrumentation. Dismissing these integrated components fails to recognize their critical role in achieving spinal stability and promoting successful fusion.

1. Comprehensive Fixation Beyond Joint Space:

• In SI joint fixation, devices frequently extend beyond the intra-articular space to engage more bone in the sacrum and ilium. This approach captures the lateral sacral and medial iliac cortices, providing greater anchorage and stability. The fixation strategy relies on securing a robust bone-device interface on both sides of the joint, which enhances overall stability and load distribution.

1. Stress Distribution and Multiplanar Stability:

• Intersegmental spinal fusion devices and SI joint fixation devices that engage more bone outside the immediate joint area distribute mechanical stresses over a broader area. This reduces localized stress concentrations that can lead to device failure or bone damage. Extending beyond the joint space offers stability in multiple planes, which is crucial for managing the complex loading patterns experienced by the spine and SI joint during various activities.

1. Enhanced Fusion Potential:

• Devices that engage more bone outside the immediate joint or intersegmental space provide a larger contact area for bone growth and fusion. This increased contact area promotes better biological fixation and fusion, essential for the long-term stability of the fusion site. Ignoring the benefits of a more extensive bone-device interface undermines the potential for successful arthrodesis.

1. Clinical Evidence:
   

• Clinical evidence supports the effectiveness of devices that extend beyond the intra-articular space or intersegmental area. These devices have shown improved pain and functional outcomes in patients, demonstrating their practical benefits in clinical settings. Focusing narrowly on the need for biomechanical independence or solely transfixing the joint fails to consider this evidence.
  

• Furthermore, measures taken to safeguard Relative Value Units (RVUs) for older CPT codes often disregard the impact on patient-centered outcomes. Prioritizing the preservation of RVU values for outdated procedures over their clinical effectiveness and patient benefits is misguided. Increasing the RVU value for newer, biomechanically advanced devices and techniques might better align incentives with the goal of improving patient care and ensuring the adoption of superior technologies.

1. Summary:
   

• The recent input from US Spine Societies on the biomechanics of modern intersegmental fusion devices incorporating spikes, flanges, or screws as integral parts of a cohesive system is conceptually flawed because it does not recognize the advantages of integrated device designs and comprehensive fixation strategies. Effective stabilization and fusion require a holistic approach that considers the synergistic action of all components, the distribution of mechanical stresses, and the engagement of more bone area beyond the immediate joint space. Ignoring these factors undermines the potential for successful arthrodesis and does not reflect the reality of how these devices achieve spinal and SI joint stability.

Author:

Morgan Lorio