Lobed Pilot Aperture for Bone Screw Retention
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Solution Overview
Problem
Current methods for installing orthopedic screws into bones face challenges such as high variability in force required, creation of machining residue, and inability to incorporate bone growth materials, leading to insecure screw attachment and limited bone growth promotion.
Innovation Solution
A method of forming pilot apertures with multiple lobes that provide three-point contact for screw shanks, allowing for reliable positioning and retention, and incorporating slots for bone growth materials to enhance screw stability and induce bone growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pilot hole is formed using a Jamshidi needle or drill bit, then the screw can be inserted along a predetermined path, but high and variable force is required for penetration and high torque is needed for screw insertion
Solution Approach 1:
The pilot hole is segmented into multiple lobes (typically three lobes spaced 120 degrees apart) rather than a continuous circular hole. This segmentation reduces the contact area between the screw shank and bone, thereby reducing the force and torque required for screw insertion while maintaining reliable positioning through the three-point contact geometry
Solution Approach 2:
The pilot hole structure is changed from a uniform circular shape to a lobed shape with specific geometric characteristics. The lobes create localized contact points that provide sufficient guidance and positioning while reducing overall material removal and insertion resistance, addressing the local quality of bone-screw interaction
2Manufacturing precision
If a machined pilot hole is formed with a drill bit, then the screw path is precisely controlled, but machining residue is created that interferes with screw insertion
Solution Approach 1:
The continuous machined hole is segmented into discrete lobes, which changes the material removal pattern. This segmentation reduces the total volume of bone material removed and minimizes the generation of machining residue compared to traditional circular drilling, while still providing precise path control through the guided lobe structure
Solution Approach 2:
The harmful machining residue is extracted or minimized by changing from a continuous drilling process to a lobed hole formation process. The lobed structure allows for more efficient material ejection and reduces the accumulation of bone debris that would otherwise interfere with screw insertion
3Ease of manufacture
If traditional pilot hole formation is used, then screw insertion is straightforward, but there is no space for bone growth material and the screw/bone bond strength is limited
Solution Approach 1:
The pilot hole structure is transformed from a two-dimensional circular cross-section to a three-dimensional lobed structure with radial slots. This dimensional change creates additional space within the hole structure that can accommodate bone growth material, while the overall lobed geometry maintains compatibility with standard screw insertion procedures
Solution Approach 2:
The pilot hole is designed with an inherently porous or slotted structure that can accommodate and retain bone growth materials such as bone cement, demineralized bone matrix, or morselized bone. These slots create a porous-like environment that allows material placement and integration, enhancing the screw/bone bond strength
4Strength
If the pilot hole diameter is made smaller than the screw root diameter to ensure good attachment strength, then thread formation strength is improved, but high compressive load is applied to the bone during thread formation
Solution Approach 1:
The continuous thread formation process is modified by the lobed hole structure, which segments the contact between screw and bone. This segmentation reduces the cumulative compressive load on the bone during thread formation while maintaining adequate attachment strength through the distributed three-point contact geometry of the lobes
Solution Approach 2:
The pilot hole is designed with asymmetric lobed geometry rather than a symmetric circular shape. This asymmetry allows for optimized stress distribution during screw insertion, reducing peak compressive loads on the bone while maintaining sufficient thread engagement strength through the strategically positioned lobe contact points
Data Source
AI summary
The present invention provides a method of forming pilot apertures for surgical screws. The method provides at least three points of contact to the screw shank to provide reliable positioning and retention of the bone screw. The method also provides slots or areas for insertion and retention of bone growth promoting materials which further secure the bone screw over time. The method is useful for patients of all ages, and may be particularly useful for patients that have osteoporosis or patients that are very active by providing additional securement of the bone screw to the underlying bone.