Porous Orthopedic Screws for Bone Ingrowth Fixation
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Solution Overview
Problem
Existing bone screws and pegs often fail to provide adequate fixation and are susceptible to backing out due to variations in bone quality and properties, leading to poor stability in orthopedic surgical contexts.
Innovation Solution
The development of porous screws and pegs with a biocompatible material core and a porous layer that replicates natural cancellous bone, formed using additive manufacturing techniques, which enhances bone integration and fixation by embedding porosity within the threading and interstitial spaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional non-porous bone screws are used, then manufacturing is simple and device structure is straightforward, but bone fixation is poor and screws are susceptible to backing out
Solution Approach 1:
The patent applies porous materials by coating the screw threads with porous tantalum or other porous biocompatible materials. This porous coating provides interconnected pores that allow bone ingrowth into the screw structure, creating a biological anchor that prevents backing out while maintaining structural integrity. The porous layer transforms the dense non-porous traditional screw into a bio-integrated fixation device.
Solution Approach 2:
The patent uses composite materials by combining a metal core (such as titanium or stainless steel) with a porous outer layer (such as porous tantalum or porous polymer). This composite structure provides both the mechanical strength of the metal core and the bone-ingrowth capability of the porous outer layer, resolving the contradiction between structural simplicity and fixation reliability.
2Reliability
If porous material is added to enhance bone integration, then bone fixation improves, but manufacturing complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-forming porous tantalum beads or particles before the coating process. These pre-formed porous structures are then applied to the screw threads through various deposition techniques. This preliminary preparation simplifies the overall manufacturing process compared to creating porosity directly on the screw threads during the coating stage.
Solution Approach 2:
The patent utilizes porous materials with controlled pore sizes and distributions that have been pre-characterized and validated for bone ingrowth. By selecting from a library of pre-tested porous materials with known properties, the manufacturing process becomes more standardized and less complex, as the porosity characteristics are predetermined rather than requiring real-time control during manufacturing.
3Reliability
If porous coating is applied to thread faces, then bone ingrowth is facilitated, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies local quality by selectively coating only specific regions of the screw, particularly the thread faces that contact bone. The porous material is applied preferentially to the distal thread faces and less to the proximal faces, creating a gradient of porosity that matches the biological requirements for bone ingrowth while maintaining precision requirements at manageable levels. This localized approach reduces the total surface area requiring precise coating control.
4Reliability
If porosity is increased in the screw structure, then bone fixation improves, but mechanical strength may be compromised
Solution Approach 1:
The patent applies segmentation by dividing the screw into distinct functional zones: a dense strong core for structural integrity and load-bearing, and a porous outer layer for bone ingrowth and fixation. This segmentation allows each zone to be optimized for its specific function without compromising the other, as the dense core provides the mechanical strength while the porous coating provides the biological fixation.
Solution Approach 2:
The patent uses composite materials to resolve the strength-porosity contradiction by combining materials with complementary properties. The metal core (titanium or stainless steel) provides high mechanical strength and stiffness, while the porous coating (porous tantalum or polymer) provides bone-ingrowth capability. The composite structure allows the strong core to bear mechanical loads while the porous outer layer facilitates biological fixation, eliminating the trade-off between strength and porosity.
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 porous screws and pegs improve bone integration and stability by facilitating bone ingrowth, reducing the likelihood of backing out and enhancing fixation in various orthopedic applications, including joint replacements and trauma surgeries.
Implementation Method 1
The porous material can include a porosity of 70%-90% and an interconnected pore structure that replicates the architecture of human cancellous bone.
Data Source
AI summary
Various different porous screws and pegs are disclosed herein, as are methods of manufacturing such porous pegs or screws. The porous screws and pegs, in certain examples, are formed through additive manufacturing and have improved porosity for bone ingrowth. In certain cases, additive manufacturing or another manufacturing technique can be used to cover only part or all of the threads of the screws or pegs disclosed herein with a porous material. Such screws or pegs can have porosity but also threads that are capable of effectively digging into bone.