Tapered Knee Implant Stem Wedging Bone Canal Fixation
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Solution Overview
Problem
Conventional cylindrical stems used in knee replacement revision surgeries often fail to provide sufficient mechanical fixation due to mismatch with the tapered shape of bone canals, leading to instability and increased bone loss, and existing solutions require large inventories of components to match specific patient geometries.
Innovation Solution
A tapered stem with a continuously tapered outer surface that wedges into the bone canal, optionally featuring projections and surface textures like hydroxyapatite coatings, to enhance rotational stability and eliminate the need for bone cement, allowing for a more secure and versatile fixation without the need for extensive component inventory.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a cylindrical stem is used to fit into a tapered bone canal, then the stem can be manufactured with simple geometry, but voids form between the stem and bone canal walls causing instability and movement
Solution Approach 1:
The stem geometry is changed from cylindrical to continuously tapered, matching the natural taper of the bone canal. This parameter change eliminates voids between the stem and bone canal walls, preventing movement and providing stable mechanical fixation without requiring bone cement.
2Reliability
If bone cement is used to fill voids between the cylindrical stem and bone canal walls, then fixation stability is improved, but bone loss increases and future revision becomes more difficult
Solution Approach 1:
The invention extracts and eliminates the need for bone cement by using a tapered stem design that naturally fits the tapered bone canal. This removes the harmful element (bone cement) that causes bone loss and complicates future revisions, while maintaining fixation stability through the tapered geometric match.
3Reliability
If the stem length is increased to project further into the bone canal for more support, then mechanical fixation is improved, but patient pain increases
Solution Approach 1:
Instead of increasing stem length, the invention changes the stem's geometric parameter (taper) to match the bone canal. This provides adequate mechanical fixation support through the tapered fit without requiring excessive length that would project deeper into the bone canal and cause patient pain.
4Manufacturing precision
If multiple stem and cone components are used to match specific patient geometries, then fixation precision is improved, but inventory complexity and surgical time increase
Solution Approach 1:
The continuously tapered stem design provides a universal solution that can accommodate various patient anatomies through the continuous variation of the taper angle, eliminating the need for multiple discrete stem and cone components. This reduces inventory complexity while maintaining the ability to match specific patient geometries.
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 tapered stem design provides superior mechanical fixation, increases the longevity of knee implants, simplifies surgery, reduces bone loss, and minimizes the need for bone cement, while reducing inventory requirements and facilitating easier removal of the implant.
Implementation Method 1
The continuously tapered outer surface of the stem at the distal end may be configured to mechanically fix the knee replacement to the patient's bone by being wedged within the bone canal
Implementation Method 2
surface textures like hydroxyapatite coatings
Data Source
AI summary
A fixation device for a knee replacement. The fixation device includes a stem configured to be fixedly attached to one of a tibial component of the knee replacement and a femoral component of the knee replacement. The stem has a continuously tapered outer surface and has a distal end that is distal to said one of the tibial component and the femoral component. A tapered projection is positioned on the continuously tapered outer surface and is tapered in the same direction as the continuously tapered outer surface. The stem and the tapered projection are configured so that the continuously tapered outer surface and the tapered projection engage a patient's bone when the stem is inserted into a bone canal within the patient's bone. In addition, the continuously tapered outer surface of the stem at the distal end of the stem and the tapered projection are configured to mechanically fix the knee replacement to the patient's bone by being wedged within the bone canal.