Orthopedic Rod Locking Aperture Multi-Lead Thread Design
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Solution Overview
Problem
Locking apertures in orthopedic rods are difficult to use due to axial misregistration issues between internal and external threads, leading to increased bone damage, installation difficulties, and undesirable sounds during fastener advancement.
Innovation Solution
The orthopedic rod features locking apertures with a multi-threaded internal structure, including two or more thread leads adjacent the same end, interspersed internal threads, or shallow thread depth, which facilitates improved threadability and engagement with fasteners, reducing bone damage and installation effort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a locking aperture with a single internal thread is used, then the aperture provides secure locking engagement, but the threaded fastener may arrive at the aperture at an unsuitable rotational disposition causing difficulty in threading
Solution Approach 1:
The internal thread structure is segmented into multiple thread leads (e.g., two or three leads) instead of a single continuous thread. This segmentation creates multiple potential engagement points around the aperture circumference, increasing the probability that at least one thread lead will be properly aligned with the approaching fastener, thereby resolving the rotational disposition mismatch problem while maintaining secure locking engagement.
2Strength
If the internal thread depth is increased to improve locking security, then the locking strength is enhanced, but the bone damage and thread stripping risk increase
Solution Approach 1:
The internal thread depth is designed to be partial rather than excessive - specifically, the internal thread extends only a limited distance into the aperture from the surface, rather than spanning the entire aperture depth. This partial threading provides sufficient locking strength for secure engagement while reducing the risk of bone damage and thread stripping by limiting the engagement depth to what is necessary for functional security.
3Strength
If a threaded fastener with deep external thread is used for cancellous bone engagement, then the bone anchorage is improved, but the misregistration problem with the internal thread is compounded
Solution Approach 1:
Different portions of the fastener-aperture system have different thread characteristics optimized for their specific functions: the external thread on the fastener has deep engagement for strong bone anchorage, while the internal thread in the aperture has multiple shallow leads for easy alignment and engagement. This local differentiation of thread qualities allows each component to excel at its primary function while compensating for the other's limitations.
Data Source
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AI summary
System, including methods and apparatus, for treating orthopedic conditions using a rod member structured for placement in a medullary canal of a bone and including at least one locking aperture with an internal thread structure. In some embodiments, the internal thread structure may include two or more thread leads disposed adjacent the same end of the locking aperture, two or more interspersed internal threads, and/or a thread depth substantially less than that of a corresponding threaded fastener for the locking aperture.