Patellar Implant Sizing Through Continuous Flexion Tracking
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Solution Overview
Problem
Existing methods for selecting patellar implants fail to ensure proper patellar kinematics over the entire flexion-extension path of a knee joint, often leading to complications such as patellar maltracking or altered kinematics due to improper sizing.
Innovation Solution
A surgical system with trackers and a tracking system to monitor the range of motion of the patella before and after resection, allowing for precise selection of a patellar implant by comparing the preoperative and postoperative paths to ensure a difference of less than 3 mm, thereby preventing patellar overstuffing or understuffing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If implant selection is based on a single or plurality of knee flexion-extension positions, then implant selection is simplified, but proper patellar kinematics over the entire flexion-extension path cannot be ensured
Solution Approach 1:
The patent transitions from evaluating implant fit at discrete points (single or plurality of positions) to evaluating the entire continuous path of patellar movement. The system captures and compares complete flexion-extension paths, adding the dimension of continuous motion analysis rather than static point assessment.
Solution Approach 2:
The system provides feedback by comparing the preoperative patellar path with the postoperative path predicted by each implant option. This allows the surgeon to select the implant that produces minimal deviation from the natural patellar trajectory, ensuring proper kinematics through iterative comparison and adjustment.
2Strength
If patellar implant is oversized (overstuffing), then implant provides structural support, but passive knee flexion and patellar kinematics are decreased
Solution Approach 1:
The system performs preliminary evaluation of multiple implant size options before final implantation. By predicting and comparing the flexion-extension paths for each potential implant size, the surgeon can pre-determine the optimal size that maintains both structural support and natural knee flexion mechanics.
Solution Approach 2:
The system varies the implant size parameter systematically to observe its effect on patellar kinematics. By changing the implant thickness and comparing resulting movement paths, the optimal parameter (implant size) is identified that maintains structural integrity without restricting natural flexion range.
3Ease of operation
If patellar implant is undersized (understuffing), then implant allows greater knee flexion, but moment arm is reduced and contact pressure increases
Solution Approach 1:
The system evaluates multiple implant size options before final selection, predicting the contact pressure and moment arm effects for each size. This preliminary assessment prevents undersizing by identifying the minimum implant thickness required to maintain adequate biomechanics while allowing sufficient flexion.
Solution Approach 2:
The patent replaces direct mechanical measurement of moment arm and contact pressure with a computational model that predicts these parameters based on implant size and observed patellar paths. This substitution allows comprehensive biomechanical evaluation without complex intraoperative measurements.
Data Source
AI summary
Disclosed herein are a surgical system for patella tracking and a method for selecting a properly-sized patellar implant utilizing the same. The surgical system may include first and second trackers and a patellar tracking system. The first tracker may be configured to contact an unresected or a resected patella, and the second tracker may be configured to contact a bone. The patellar tracking system may be configured to track the first and second trackers during patellar flexion and extension to generate patellar range of motion and patellar trial range of motion. A method for selecting a patellar implant may utilize the first and second trackers and the patellar tracking system.