Unicondylar Balancer for Precise Knee Distraction Measurement
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Solution Overview
Problem
Existing methods for assessing distraction force and spacing in knee surgery, such as using sprung platforms or torque handles, do not allow for precise balancing of distraction height with force, and existing devices lack the ability to measure distances and forces accurately during knee arthroplasty procedures.
Innovation Solution
A unicondylar balancer with a first and second jaw for contacting the femoral condyle and tibial plateau, respectively, featuring a threaded collar and rod adjustment mechanism, biasing element, and manually operable locking mechanism to control distraction force and measure distances accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a torque handle design is used to apply distraction force, then force application is simplified, but the ability to balance distraction height with force is lost
Solution Approach 1:
The device transitions from a static torque handle to a dynamic system with a movable first body portion that can be adjusted relative to the second body portion. The threaded rod and collar mechanism allows continuous adjustment of distraction height while the spring provides continuous force, enabling the user to balance height and force dynamically during the procedure.
Solution Approach 2:
The device is divided into separate functional components: a second body portion with fixed jaw, a movable first body portion with adjustable jaw, a threaded adjustment mechanism, and a spring force mechanism. This segmentation allows independent optimization of each function while maintaining overall system capability to balance height and force.
2Measurement precision
If markings are added to measure distance, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The device uses visual markings (color-coded or numbered indicators) on the body portions to indicate distance measurements. These markings provide precise measurement feedback without adding mechanical complexity, as they are simply printed or etched indicators that align during adjustment.
3Reliability
If a locking mechanism is added to prevent inadvertent movement, then reliability is improved, but device complexity increases
Solution Approach 1:
The locking function is extracted as a separate, simple mechanism distinct from the adjustment mechanism. This allows the locking feature to be added without complicating the threaded rod and collar adjustment system, maintaining clarity and ease of use while providing reliable measurement stabilization.
4Measurement precision
If a sprung platform is used to assess distraction force, then force assessment is enabled, but the ability to gradually apply compression while noting force is limited
Solution Approach 1:
The spring mechanism serves dual functions: it automatically provides the distraction force needed to separate the jaws while simultaneously acting as a measurement tool. As the user gradually compresses the spring by adjusting the threaded rod, the spring force increases proportionally, providing real-time force feedback that corresponds to the distraction applied.
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
Enables precise measurement of distance and distraction force between the femoral condyle and tibial plateau, allowing for accurate determination of resection planes for prosthetic implant placement, with the locking mechanism preventing inadvertent movement during measurement.
Implementation Method 1
the first body portion is coupled to the threaded rod via a biasing element, wherein the biasing element biases the first jaw away from the second jaw
Implementation Method 2
the adjustment mechanism comprises: a threaded collar captured in a slot in the second body portion; and a threaded rod received through the threaded collar
Data Source
Figure 1
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AI summary
A unicondylar balancer (10) for knee surgery and a method of knee surgery. The balancer includes a first body portion (6) including a first jaw (2). The balancer also includes a second body portion (8) slideably attached to the first body portion, the second body portion comprising second jaw (4). The balancer further includes an adjustment mechanism selectively to distance the first jaw from the second jaw. The adjustment mechanism includes a threaded collar (20) captured in a slot (26) in the second body portion, and a threaded rod (30). The first body portion is coupled to the threaded rod via a biasing element (50), which biases the first jaw away from the second jaw. The balancer further includes a manually operable locking mechanism (140), to lock the first body portion with respect to the second body portion.