PCL Length Balancing in Knee Replacement
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Solution Overview
Problem
Current knee replacement surgical procedures face challenges in accurately managing soft tissue structures, particularly the posterior cruciate ligament (PCL), which affects the sizing, positioning, and orientation of prosthetic components, leading to potential laxity and tension issues during knee joint movement.
Innovation Solution
A data processing method that determines the femoral and tibial attachment positions of the PCL, calculates the required and maximum PCL lengths as a function of knee angle, and outputs a comparison to assist surgeons in planning implant positions, incorporating rollback adjustments to prevent excessive PCL length, using a computer-assisted surgery system with tracking and surgical robot integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional knee replacement surgical procedures are used to determine implant positions, then the surgical process is simple and quick, but the soft tissue balancing accuracy is poor leading to PCL laxity or tension issues
Solution Approach 1:
The patent replaces traditional mechanical measurement methods (physical probes and manual measurements) with a computer-assisted tracking system that uses optical or electromagnetic fields to detect and track the positions of surgical instruments and bone surfaces. This substitution enables precise 3D mapping of the PCL attachment points and real-time calculation of PCL length throughout the range of motion, significantly improving measurement accuracy while providing visual feedback to the surgeon.
Solution Approach 2:
The patent creates a virtual copy or digital model of the patient's knee joint geometry and soft tissue structures based on pre-operative imaging and intra-operative tracking data. This virtual model allows the surgeon to simulate different implant positions and assess their effect on PCL length and knee kinematics before making actual cuts, enabling precise soft tissue balancing without excessive surgical complexity.
2Force
If soft tissue release is performed to reduce tension, then the soft tissue tension is reduced, but the PCL may become excessively lax
Solution Approach 1:
The patent implements a feedback mechanism where the tracking system continuously monitors the calculated PCL length as the knee moves through its range of motion. The system provides real-time visual feedback to the surgeon showing whether the PCL is too tight or too lax for any given implant position. This allows the surgeon to make precise adjustments to implant positioning or perform targeted soft tissue releases only when and where needed, rather than performing blanket releases that could compromise PCL stability.
Solution Approach 2:
The patent enables preliminary assessment of soft tissue tension and PCL length before any soft tissue release is performed. By using the virtual model and tracking system to predict how different implant positions will affect PCL length, the surgeon can plan the minimal necessary soft tissue intervention in advance, performing only the specific releases needed to achieve balance without over-releasing and causing laxity.
3Manufacturing precision
If implant positions are adjusted to balance soft tissues, then the soft tissue balancing improves, but the surgical time and complexity increase
Solution Approach 1:
The patent allows preliminary planning of implant positions using pre-operative CT or MRI scans to create a patient-specific virtual model. The surgeon can simulate various implant configurations and predict their effect on soft tissue balancing before the actual surgery. During surgery, the tracking system provides real-time verification, allowing the surgeon to confidently proceed with the planned positions without extensive trial-and-error adjustments, thereby maintaining surgical efficiency while achieving precise positioning.
Solution Approach 2:
The patent replaces time-consuming manual trial-and-error adjustment methods with automated computer calculations that instantly determine the optimal implant positions based on the tracked anatomy and desired soft tissue balance. The system automatically computes the required implant positioning to achieve target PCL lengths throughout the range of motion, eliminating the need for multiple trial components and repeated measurements, thus reducing surgical time while improving positioning accuracy.
Data Source
AI summary
A data processing method, data processing apparatus and method for assessing the posterior cruciate ligament length for a knee replacement procedure are described. The loaded displacement and unloaded displacement between a tibia and a femur in the anterior-posterior direction are measured at a plurality of knee angles. An estimate of the maximum length of the posterior cruciate ligament for the plurality of knee angles is made using the loaded displacement. A planned knee joint separation between the tibia and the femur is determined from planned tibial and femoral implant positions and said unloaded displacement. An estimate of the required length of the posterior cruciate ligament for the plurality of knee angles is determined from the planned knee joint separation. A comparison of the estimate of the required length of the posterior cruciate ligament and an estimate of the maximum length of the posterior cruciate ligament is output as a function of knee angle.