Rotary Mill Guide Projection Prevents Tibial Damage
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Solution Overview
Problem
In partial knee replacement surgeries, the impingement of the polyethylene bearing component on femoral condylar bone tissue during knee articulation can lead to post-operative pain, damage, and eventual failure due to insufficient bone removal from the femoral condyle, and existing rotary mills risk damaging the tibia during milling.
Innovation Solution
A rotary mill with a guide portion and inter-engageable guide formations, including a central bore and guide peg, that allows precise bone removal while preventing tibial impingement by ensuring the leg is sufficiently flexed and guiding the milling surface to avoid contact with the tibia, using nodules as depth stops to control bone removal and a guard projection to protect the tibia.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the leg is insufficiently flexed or the anatomy of the patient is such that the tibia projects more than is normal, then the rotary mill may contact the tibia during milling, but using a standard rotary mill without protective features makes it difficult to prevent tibial contact while maintaining milling effectiveness
Solution Approach 1:
The rotary mill is divided into distinct functional segments: a body portion with milling surface, a guide portion with guide body, and a projection element. This segmentation allows each component to perform its specific function - the guide portion and projection work together to prevent tibial contact while the body portion performs milling, resolving the contradiction between protection and milling effectiveness.
Solution Approach 2:
The projection acts as an intermediary protective element between the rotary mill's milling surface and the tibia. It serves as a physical barrier that prevents direct contact between the milling surface and tibial bone, thereby protecting the tibia from damage while allowing the milling operation to proceed effectively on the femoral condyle.
2Object-affected harmful factors
If insufficient bone is removed from the femoral condyle, then the bearing component can impinge on femoral condylar bone tissue during knee articulation, but removing excessive bone can compromise the structural integrity of the femur
Solution Approach 1:
The guide body is configured to establish the correct milling depth and orientation before the actual bone removal begins. By pre-positioning the guide body against the femoral condyle and using it to guide the milling surface, the system ensures that the precise amount of bone is removed - enough to prevent bearing impingement but not so much as to compromise femoral strength.
Solution Approach 2:
The invention replaces reliance on surgeon judgment and manual depth control with a mechanical guiding system. The guide body and milling surface form a mechanical guide that automatically controls the depth and angle of bone removal, eliminating the need for the surgeon to estimate the appropriate resection depth and thereby preventing both insufficient and excessive bone removal.
3Manufacturing precision
If the guide body does not provide adequate guidance, then the milling surface may not be precisely positioned, but adding complex guidance mechanisms increases device complexity
Solution Approach 1:
The guide body and milling surface are merged into an integrated assembly where the guide body is positioned relative to the milling surface at precise predetermined angles and distances. This merging eliminates the need for separate, complex adjustment mechanisms while maintaining high precision in bone resection. The integrated design achieves manufacturing precision without proportionally increasing device complexity.
Solution Approach 2:
The guide body serves multiple functions simultaneously: it provides angular guidance for the milling surface, establishes the correct depth of resection, and ensures proper positioning on the femoral condyle. By consolidating these multiple guidance functions into a single component, the invention achieves high manufacturing precision without the need for multiple separate complex guidance mechanisms.
Data Source
Figure 1~4
Figure 2
Figure 3~6
AI summary
A rotary mill (2) comprising a body portion (4) having a milling surface (10) for milling a first bone, a guide portion (6) having a guide body (22), and inter-engageable guide formations (20, 24) formed on the body portion (4) and guide portion (6), the guide body (22) having a projection (7) which is adapted to hold a second bone (11) away from the rotary mill during the milling operation.