Automatic placement of reference grids and estimation of anatomical coordinate systems
Inventors
dos Santos Raposo, Carolina • de Almeida Barreto, João Pedro • ALMEIDA ANTUNES, Michel Gonçalves
Assignees
Smith and Nephew Orthopaedics AG • Smith and Nephew Asia Pacific Pte Ltd • Smith and Nephew Inc
Publication Number
US-12285221-B2
Publication Date
2025-04-29
Expiration Date
2043-06-22
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Abstract
Disclosed are systems and methods for a computerized framework that provides novel mechanisms for determining the automatic placement of a reference grid and an anatomical reference frame (ARF) of a bone. The disclosed framework is operational for the enablement of computerized mechanisms that, based on a three-dimensional (3D) model of a distal femur, can determine, provide and/or display the anatomically correct positions of femoral tunnels and/or other forms of surgical landmarks surgeons rely on for anterior cruciate ligament (ACL) procedures. The disclosed framework is also operational for the enablement of computerized mechanisms that, based on a three-dimensional (3D) model of a proximal tibia, can determine, provide and/or display the anatomically correct positions of tibial tunnels and/or other forms of surgical landmarks surgeons rely on for ACL procedures.
Core Innovation
The disclosed invention provides a computerized framework featuring systems and methods for the automatic placement of reference grids and estimation of anatomical reference frames (ARFs) of bones, specifically addressing the femur and tibia in the context of anterior cruciate ligament (ACL) procedures. This framework utilizes a three-dimensional (3D) model of the distal femur or proximal tibia to determine, provide, and display anatomically correct positions for surgical landmarks, including femoral and tibial tunnels, through novel, fully automated algorithms.
The invention solves the problem of observer variability and inaccuracy in manual placement of reference grids, such as the Bernard-Hertel (BH) grid for the femur and the tibial grid for the tibia, which are crucial for accurate tunnel positioning in ACL reconstruction. Current approaches suffer from unreliability due to dependence on anatomical landmarks that may not exist in some patients, as well as manual processes that are subject to intra- and inter-observer variability, thereby impacting the outcome of ACL surgeries.
By leveraging 3D models, the system automatically determines the sagittal, axial, and coronal directions necessary for ARF construction, places reference grids without prior anatomical knowledge or template alignment, and operates efficiently across different bone shapes and sizes. For the femur, the methodology includes aligning condyles to determine the sagittal direction, generating radiographic views, extracting intercondylar contours, and constructing the BH grid as a rectangle enclosing the condyles. For the tibia, it segments the tibial plateau, fits a plane to define the axial direction, generates a bi-tangent line for posterior contour alignment, and forms the tibial grid to guide tunnel placement, also detecting the tibial tuberosity. These methods claim to offer negligible error relative to manual techniques and are suitable for broad clinical application.
Claims Coverage
The patent includes multiple independent claims, particularly focusing on core methods, computer-readable media, and devices related to automatic placement of reference grids and anatomical reference frame estimation.
Automatic identification and analysis of 3D bone models for grid placement
The invention comprises a computer-implemented method that: - Identifies a three-dimensional (3D) model of the femur. - Analyzes the model to determine pairs of points with normal vectors orthogonal to a joining vector. - Determines the sagittal direction based on this analysis. - Further processes generate an intersection map with a curve value for the intercondylar region. - Determines the Blumensaat line from the intersection map. - Determines and places a Bernard-Hertel (BH) grid that encloses the condyles in lateral view, and overlays this digital grid on the 3D model.
Generation of anatomical reference frames (ARF) via geometric analysis
The method further: - Backprojects the BH grid and intersection map points onto the 3D model using a sectioning plane defined by sagittal direction and Blumensaat's line. - Obtains axial and coronal anatomical directions through circle fitting and cross-product calculations. - Establishes the complete anatomical reference frame (ARF) of the femur comprising sagittal, axial, and coronal directions.
Execution on computer-readable media and computing devices
The inventive features are embodied as computer-executable instructions stored on a non-transitory computer-readable medium, and on devices with one or more processors configured to: - Perform all steps of receiving, analyzing, and overlaying the BH grid on 3D bone models. - Compute the ARF as specified above and output or display these overlays for clinical/surgical use.
The claims cover automatic computational systems and methods for placing anatomical reference grids and establishing anatomical reference frames by analyzing 3D bone models, determining key geometric and anatomical features, and digitally displaying or overlaying these grids and reference frames, with embodiments as both software instructions and as system devices.
Stated Advantages
Reduces observer variability and enhances reliability by eliminating manual placement of reference grids through automation.
Provides negligible error in tunnel entry points compared to manual methods, with the disclosed method yielding errors much smaller than existing approaches.
Applicable to diverse bone shapes and sizes and does not require prior anatomical models, template alignment, or entire bone models, increasing versatility.
More computationally efficient and not susceptible to local minima issues affecting previous automatic or manual methods.
Not dependent on the curvature pattern of anatomical contours, making it suitable for different morphologies.
Applicable to a wider variety of input models and conditions as it does not require user intervention, shaft reconstruction, patient positioning, or models of adjacent anatomical structures.
Documented Applications
Preoperative and intraoperative planning and guidance for anterior cruciate ligament (ACL) reconstruction procedures, specifically for determining anatomically correct positions of femoral and tibial tunnels.
Assessment and planning of surgical landmarks on 3D models for bones such as the distal femur and proximal tibia, including use with CT scans and volume-rendered images.
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