Locking Screw with Wedge Passage for Intramedullary Nail
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Solution Overview
Problem
Intramedullary nail locking screws often have clearance issues due to targeting inaccuracies, which can hinder successful bone healing by allowing bone fragments to move relative to the nail, and existing solutions like internal threads do not fully address this problem.
Innovation Solution
A locking screw design with a screw shaft featuring an external thread and a screw head with a passage for a longitudinal wedging element, allowing for the elimination of clearance between the screw and the intramedullary nail, while maintaining the ability to rotate and be easily inserted or removed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the external diameter of the locking screw is underdimensioned relative to the diameter of the transverse borehole to accommodate targeting errors, then the locking screw can be passed through the transverse borehole in spite of targeting error, but there is clearance between the locking screw and the transverse borehole that allows bone fragments to move
Solution Approach 1:
The locking screw is segmented into functional zones: a reduced-diameter shank portion that fits within the transverse borehole and a larger head portion that engages the bone fragment. This segmentation allows the shank to accommodate targeting errors while the head provides stable fixation.
Solution Approach 2:
A longitudinal wedge element is introduced as an intermediary component between the locking screw and the transverse borehole. This wedge element fills the clearance and transmits forces effectively, eliminating the harmful gap while maintaining the underdimensioned shank design.
2Reliability
If the clearance between locking screw and intramedullary nail is eliminated by wedging, then fixation stability is improved, but the ability to rotate the locking screw may be blocked
Solution Approach 1:
The locking screw shank is segmented with a reduced-diameter portion that rotates within the transverse borehole while the wedge element fills the radial clearance. This segmentation allows rotational movement along the longitudinal axis while maintaining radial stability through the wedge.
Solution Approach 2:
The wedge element is designed to be insertable and removable, allowing the clearance elimination to be a dynamic process. During insertion, the wedge is introduced to eliminate clearance; during rotation, the wedge accommodates the longitudinal movement while maintaining radial contact.
3Stability of the object's composition
If internal thread is used in the locking hole to prevent axial movement, then axial freedom is restricted, but clearance still exists and does not fully solve the problem
Solution Approach 1:
The longitudinal wedge element serves as an intermediary that addresses both axial and radial stability simultaneously. Unlike the internal thread that only prevents axial movement, the wedge element fills the radial clearance and prevents both axial and radial movements of the bone fragment.
Solution Approach 2:
The solution changes the approach from restricting only axial movement (internal thread) to restricting both axial and radial movements (wedge element). This parameter change in the type of constraint provided eliminates the clearance issue while maintaining axial stability.
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 solution eliminates clearance between the nail and screw, ensuring stable fixation without blocking rotation, allowing for secure screwing and easy extraction, thus enhancing bone healing outcomes.
Implementation Method 1
A passage is formed through the screw head configured and dimensioned to receive a longitudinal wedging element
Data Source
AI summary
A locking screw for an intramedullary nail having at least one transverse hole. The locking screw has a central longitudinal axis and includes a screw shank, which is at least partially provided with an external thread, and a screw head. The diameter of the screw head is greater than the outer diameter of the external thread, and the screw head includes a passage extending generally parallel to the longitudinal axis of the screw and the external thread. The passage is configured to receive a longitudinal wedge element. As a result, any gap between the locking screw and the intramedullary nail is eliminated and the screw is wedged in position in the transverse hole of the intramedullary nail.