Acetabular Cup Retention via Undercut Geometry and Thermal Assembly
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current hip prostheses face a high risk of luxation due to insufficient retention capacity of the spherical head in the articular insert, exacerbated by sterilization processes that degrade mechanical properties of polyethylene or equivalent materials, limiting the force required for secure engagement and retention.
Innovation Solution
The prosthetic acetabulum design includes a retaining means with a hemispherical articular surface extending beyond 190° and a continuous annular ring with a spherical crown, assembled before sterilization to enhance retention capacity, and differential thermal stress is applied to facilitate assembly, ensuring the spherical head is securely engaged and retained within the articular insert.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the spherical head is engaged with force in the articular cavity using a press-type tool, then the retention capacity is increased, but the outer surface of the head and inner surface of the articular insert are damaged, reducing prosthesis lifetime
Solution Approach 1:
The articular cavity is prepared in advance with an undercut geometry featuring a retention groove and retaining ledge. This preliminary structural preparation allows the spherical head to be retained through geometric interlocking rather than requiring high-force engagement that would damage surfaces. The retention groove (reference numeral 14) and retaining ledge (reference numeral 15) are formed during manufacturing, creating a built-in retention mechanism that eliminates the need for post-sterilization force engagement.
2Strength
If the admissible engagement force is limited during surgical implantation, then the risk of damaging articular surfaces is reduced, but the retention capacity of the head in the articular insert is insufficient
Solution Approach 1:
The invention changes the geometric parameters of the articular cavity by introducing an undercut configuration with specific angles. The cavity wall is inclined at an angle between 80° and 100° relative to the horizontal plane, creating an undercut that provides mechanical retention. This geometric parameter change allows retention forces to be generated through the shape of the cavity itself rather than through high engagement forces, thereby maintaining surface integrity while achieving sufficient retention capacity.
3Reliability
If sterilization is performed before assembly, then the components are sterile during assembly, but the mechanical properties of polyethylene materials are degraded, limiting retention capacity
Solution Approach 1:
The articular cavity with its retention features is prepared in advance during manufacturing, before sterilization. The undercut geometry, retention groove, and retaining ledge are all formed as preliminary structural features. This allows the polyethylene material to be sterilized while maintaining its mechanical properties, since the retention mechanism relies on pre-formed geometry rather than post-sterilization material modification or force engagement.
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
This design significantly increases the retention force beyond existing thresholds, reducing the risk of luxation and maintaining mechanical properties by performing sterilization after assembly, thereby enhancing the longevity and stability of the prosthetic joint.
Implementation Method 1
the retaining means is subjected to a differential thermal stress which temporarily modifies its dimensions in order to facilitate assembly, and then, after assembly, the retaining means is allowed to return to room temperature so as to oppose the withdrawal of the spherical head from the articular insert
Data Source
AI summary
An acetabular cup includes an articular insert (1) having a substantially semi-spherical articular cavity (1c), and a spherical head (2) engaged in the articular cavity (1c). A retaining device (10a) opposes the axial release (4) of the spherical head (2) from the articular cavity (1c) of the articular insert (1). For example, the retaining device can take the form of a back-tapered segment (10a) of the articular insert (1). The spherical head (2) is factory mounted in the articular insert (1), by temporarily heating the articular insert (1) and performing sterilization after assembly. In this way, the spherical head (2) retention capacity in the articular insert (1) is increased substantially in order to reduce the risk of luxation.