Orthopaedic Coupling with Reverse Threads for Fracture Fixation
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Solution Overview
Problem
Current bone fixation devices, such as sliding hip screws and intramedullary nails, face high failure rates in treating unstable femoral fractures, particularly reverse oblique patterns, due to lack of lateral support, leading to complications like non-union, screw cut-out, and limb shortening.
Innovation Solution
A coupling system with an annular body featuring internal threaded sections of reverse orientation, integrated with an expandable orthopaedic device having a threaded shaft with opposing thread orientations, allowing for reversible engagement and mechanical pressure application to stabilize fractures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a sliding hip screw with side plate is used for stable fractures, then proximal fragment fixation is provided, but lateral support is insufficient for unstable reverse oblique fractures causing screw sliding
Solution Approach 1:
The threaded shaft is segmented into multiple sections with alternating thread orientations (first section with right-hand threads, second section with left-hand threads). This segmentation allows different portions of the shaft to engage with corresponding sections of the coupling in opposite rotational directions, providing balanced fixation strength and preventing unilateral screw sliding in unstable fracture patterns
Solution Approach 2:
The coupling employs asymmetric thread design with alternating right-hand and left-hand threaded sections. This asymmetry creates differential engagement forces that counteract the sliding tendency in reverse oblique fractures, where conventional symmetric threaded designs fail to provide adequate lateral support
2Reliability
If an intramedullary nail is used to provide lateral buttress support, then screw sliding is prevented, but device complexity and surgical invasiveness increase
Solution Approach 1:
The invention merges the functions of the threaded shaft and coupling into a single integrated expandable device. The coupling's internal threaded surface with alternating thread orientations is combined with the shaft's corresponding external threading, eliminating the need for separate intramedullary nails while maintaining sliding prevention capability through differential thread engagement
Solution Approach 2:
The expandable orthopaedic device serves multiple functions: it provides proximal fragment fixation through the threaded engagement, prevents screw sliding via the alternating thread orientations that create balanced counterforces, and offers expandable stability to adapt to different fracture patterns. This multi-functionality replaces the need for separate intramedullary nail support
3Reliability
If sliding of the hip screw is allowed for bone compression, then fracture healing is promoted, but limb shortening and abduction weakness occur
Solution Approach 1:
Instead of allowing uncontrolled screw sliding that causes limb shortening, the invention inverts the approach by using alternating thread orientations to create controlled differential movement. The first and second sections of the coupling engage with corresponding shaft sections to permit localized compression at the fracture site while the overall device structure prevents excessive sliding that would lead to limb shortening and abduction weakness
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 provides enhanced stability and fixation for unstable fractures by allowing controlled expansion and compression, reducing failure rates and complications, while being suitable for minimally invasive procedures.
Implementation Method 1
an annular body having an internal threaded surface comprising at least two sections, wherein the threads of a first section are in reverse orientation to the threads of a second or subsequent section
Data Source
AI summary
This invention relates to a coupling for an orthopaedic device. Also disclosed in an orthopaedic device comprising a coupling of the invention and method for the use of the orthopaedic device. The orthopaedic device finds utility as a bolt apparatus for fixation of bones such as fractures of the femur, although it may be used in any suitable bone.