Spinal Facet Screw with Variable Pitch Threads and Buttress Head
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Solution Overview
Problem
Current spinal facet fixation techniques rely on limited external screw-tightening forces, which are insufficient for effective bony fusion due to the fragile nature of the facet joint, and lack both internal and external compression mechanisms.
Innovation Solution
A spinal facet compression screw with variable pitch thread zones and a buttress head is designed, featuring proximal narrow-pitch threads, a non-threaded shaft, and distal wide-pitch threads, along with a screw head for external buttressing, to achieve both internal and external compression by rotating the screw, facilitating bone growth and stabilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If simple tightening of a lag screw is used to achieve external compression of the facet, then the procedure is simple, but the compression force is insufficient due to the limited ability of the fragile facet joint to withstand external screw-tightening forces
Solution Approach 1:
The screw thread is divided into two distinct zones: a proximal zone with a first pitch and a distal zone with a second pitch. This segmentation allows each zone to perform a different function - the proximal zone provides internal compression while the distal zone provides external compression, thereby achieving sufficient total compression force without exceeding the strength limits of the fragile facet joint
Solution Approach 2:
Different portions of the screw thread are given different local qualities through varying the pitch. The proximal narrow-pitch threads are optimized for internal compression within the facet joint, while the distal wide-pitch threads are optimized for external compression. This local differentiation allows the screw to apply compression forces appropriately matched to the structural capabilities of the facet joint
2Force
If variable pitch screws relying only on internal compression are used, then the screw design is simpler, but external buttressing is not provided to augment compression
Solution Approach 1:
The invention merges two compression mechanisms into a single screw device: internal compression through the variable pitch threads and external compression through the buttress head. By combining these functions in one integrated device, sufficient total compression force is achieved without significantly increasing device complexity
Solution Approach 2:
The screw is designed with multi-functionality, serving both as an internal compression device through its variable pitch threads and as an external buttressing device through its integrated buttress head. This universal design allows a single implant to provide both internal and external compression, eliminating the need for separate devices
3Reliability
If pedicle screw systems with separate rod or plate means are used, then fixation is achieved, but the procedure is more invasive and requires more screws per level
Solution Approach 1:
The facet compression screw serves multiple functions that would otherwise require separate components: it provides fixation, compression, and buttressing all in one device. This eliminates the need for separate rod or plate means, reducing the number of components while maintaining reliable fixation
Solution Approach 2:
The invention merges the functions of multiple separate fixation components (screws, rods, or plates) into a single integrated facet compression screw. By combining these functions, the procedure becomes less invasive and requires fewer components per level while achieving reliable fixation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The screw effectively compresses opposing facet joint surfaces, enhancing bony fusion by combining internal and external compression, thereby improving the stability and fusion of facet bones.
Implementation Method 1
Variable pitch screws have been used in orthopedic surgery, particularly trauma repair, in the past. This is exemplified by the Herbert screw, invented in 1976.
Implementation Method 2
a buttressing head associated with the first thread and being dimensioned to be larger than a diameter of the first threads to provide external buttressing as the first and second threads compress a first bone and a second bone together
Data Source
AI summary
A surgical implant comprising a screw element having a screw head, a first thread having a first thread pitch, a second thread having a second thread pitch and an intermediate portion coupling the first and second thread pitches with the first and second thread pitches being different. The implant has a buttressing head associated with the first thread, and it is dimensioned to be larger than a diameter of the first threads to provide external buttressing as the first and second threads compress a first bone and a second bone together.