Bone Screw with Expandable Sleeve for Medullary Pin Fixation
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Solution Overview
Problem
Existing bone fixation methods using bone screws and medullary pins often experience clearance issues, leading to instability in the fixation of bone fragments.
Innovation Solution
A bone screw design with a tapered shaft and a radially expandable sleeve, allowing secure fitting into a medullary pin's transverse borehole without clearance, utilizing a concentrically disposed sleeve with an internal thread and longitudinal slots for enhanced expansion and locking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bone screw with constant diameter is used in a medullary pin, then the screw can be easily manufactured, but clearance exists between the screw and the transverse borehole leading to instability
Solution Approach 1:
The bone screw incorporates a radially expandable sleeve that transitions from a compressed state during insertion to an expanded state within the transverse borehole. This dynamic transformation allows the screw to adapt its diameter to match the borehole, eliminating clearance and ensuring stable fixation without requiring a complex tapered geometry throughout the entire screw length.
Solution Approach 2:
The sleeve's radial dimension is changed from a smaller compressed diameter (allowing easy insertion) to a larger expanded diameter (providing stable fixation). This parameter change enables the screw to achieve both ease of insertion and fixation stability, resolving the contradiction between reliability and device complexity.
2Reliability
If a tapered shaft is used to eliminate clearance, then stable anchoring is achieved, but the manufacturing precision requirements increase
Solution Approach 1:
The bone screw is divided into distinct functional segments: a constant diameter shaft for easy manufacturing and insertion, and a separate radially expandable sleeve for achieving stable anchoring. This segmentation allows each component to be manufactured with standard tolerances, avoiding the need for high-precision tapered machining while still achieving the goal of clearance-free anchoring.
Solution Approach 2:
The expandable sleeve acts as an intermediary element between the constant diameter shaft and the transverse borehole. It provides the necessary dimensional adaptation to eliminate clearance, thereby achieving stable anchoring without requiring the shaft itself to have complex tapered geometry that would demand high manufacturing precision.
3Reliability
If a radially expandable sleeve is added to the bone screw, then clearance is eliminated and stable fixation is achieved, but the device complexity increases
Solution Approach 1:
The radially expandable sleeve is designed to expand automatically upon insertion into the transverse borehole, utilizing the insertion force itself to achieve the expansion. This self-service mechanism eliminates the need for additional actuators, motors, or complex control systems, thereby minimizing the increase in device complexity while still achieving stable fixation.
Solution Approach 2:
The sleeve transitions from a static compressed state during storage and insertion to a dynamic expanded state within the borehole. This dynamic behavior allows the sleeve to adapt to the borehole dimensions automatically, providing stable fixation with minimal structural complexity.
4Duration of action of stationary object
If the sleeve is made of non-absorbable material like PEEK, then durability and biocompatibility are improved, but the ability to be reabsorbed by bone tissue is reduced
Solution Approach 1:
The bone screw design accommodates multiple material options (non-absorbable PEEK, metals, and bio-absorbable plastics) for the expandable sleeve, allowing the same structural design to serve different clinical needs. This multi-functionality enables clinicians to select the appropriate material based on whether long-term durability or bio-absorbability is the priority, without requiring different structural designs.
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 bone screw achieves stable anchoring in the medullary pin, providing a secure fixation with reduced torque requirements and increased clamping force, suitable for various materials including PEEK and metals, ensuring biocompatibility and durability.
Implementation Method 1
a radially expandable sleeve, allowing secure fitting into a medullary pin's transverse borehole without clearance
Implementation Method 2
The external diameter d of the thread or the core diameter k of the shaft tapers in a middle region of the shaft from a larger dimension d2 or k2 respectively towards the distal end to a smaller dimension d1 or k1
Data Source
AI summary
The invention concerns a bone screw having a distal end and a proximal end, which has the distinguishing features a shaft with a core diameter “k” and having an external thread with an external diameter “d”. The external diameter “d” of the thread or the core diameter “k” of the shaft tapers in a middle region of the shaft from a larger dimension “d2” or “k2” respectively towards the proximal end to a smaller dimension “d1” or “k1”, respectively, where “d1” and “k1” do not equal zero. Further, the shaft is provided with a concentrically disposed, radially expandable sleeve, and the sleeve being positioned on the part of the shaft which has the smaller external diameter “d1”. The bone screw may be introduced into a transverse borehole of a medullary pin. The medullary pin is provided with a continuous cannulation, which extends coaxially with the longitudinal axis of the medullary pin and has an external diameter DN and a wall thickness WN. The transverse borehole may have a diameter DB, which is larger than d2 as well as larger than dB-L5. In one embodiment, diameter DB may be approximately 90% of the diameter dB-L3 of the sleeve. The sleeve may be inserted completely into the transverse borehole and, with the flange, is in contact with the wall of a facet of the transverse borehole.