Knee Joint Balancing With Isolated Collateral Ligament Tension Sensing

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Solution Overview

Problem

Existing methods for identifying ligament tension in knee joint balancing during total knee arthroplasty are inaccurate due to the inability to individually isolate and measure the tension of the medial and lateral collateral ligaments, leading to improper soft tissue tensioning and instability.

Innovation Solution

A system and method using a sensor assembly with sensors and an inertial measurement unit to measure load and deflection angles, allowing for the determination of stress-strain curves of the medial and lateral collateral ligaments, enabling precise identification of target ligament tension.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If joint distraction device with force sensors is used to measure soft tissue tension, then measurement capability is provided, but the ability to individually isolate and measure MCL or LCL tension is lost

Engineering Contradiction:

Improvesoft tissue tension measurementVSAvoidindividual ligament isolation capability

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The sensor assembly is divided into separate medial and lateral sensor components that can independently measure forces on each side of the joint. This segmentation allows individual isolation and measurement of MCL and LCL tension separately, resolving the contradiction by providing both measurement capability and individual ligament isolation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The sensor assembly acts as an intermediary device placed within the joint space that indirectly measures ligament tension through force sensors detecting the forces applied to the joint during rotation. This intermediary approach enables precise measurement while maintaining the ability to isolate individual ligaments through controlled rotational movements.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If manual force application and subjective observation is used to evaluate ligament stress-strain properties, then patient-specific properties can be identified, but accuracy is dependent on surgeon skill

Engineering Contradiction:

Improvepatient-specific property identificationVSAvoidsoft tissue tension assessment accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The manual mechanical assessment method is replaced with an instrumented sensor assembly that uses force sensors and inertial measurement units to objectively measure ligament tension and joint kinematics. This substitution eliminates surgeon skill dependency while maintaining the ability to identify patient-specific ligament properties through quantitative stress-strain curve generation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The system provides real-time feedback through quantitative measurements of force and angular position, allowing objective determination of ligament stress-strain properties. The feedback mechanism replaces subjective observation with precise sensor data, enabling accurate patient-specific property identification independent of surgeon expertise.

Inventive Principle:

Principle #23Feedback

3Measurement precision

If distracting medial or lateral side of the joint is performed, then joint distraction and soft tissue tension measurement is enabled, but tension in the opposite ligament is inevitably caused

Engineering Contradiction:

Improvesoft tissue tension measurementVSAvoidunintended ligament tension

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The system uses dynamic rotational movements of the tibia in the coronal plane to selectively load individual ligaments. By controlling the rotation direction and speed, the system dynamically isolates each ligament for measurement while the sensor assembly compensates for opposite ligament tension through differential force measurement, eliminating the harmful effect of unintended ligament tension.

Inventive Principle:

Principle #15Dynamics

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 accurate, patient-specific ligament tensioning by isolating and measuring the medial and lateral collateral ligaments, improving joint balance and reducing implant instability.

Implementation Method 1

The sensors may include an inertial measurement unit to measure the first deflection angles

Methodology Applied

Scientific EffectInertial measurement: Accelerometer

Implementation Method 2

measuring first load values at a first condyle using a first sensor during the rotation step

Methodology Applied

Scientific EffectForce measurement: Force

Data Source

PatentUS20260060817A1Joint Balancing

Publication Date: 2026.03.05 HOWMEDICA OSTEONICS CORP

AI summary

Disclosed herein are a system for determining ligament tension and a method for utilizing the same in a knee balancing procedure. The system according may include a first sensor to measure a first load at a first condyle of a femur, a second sensor to measure a second load at a second condyle of the femur, an inertial measurement unit to measure angular change of a tibial mechanical axis of a tibia during a rotation of the tibia in a coronal plane, and a display in communication with the first sensor, the second sensor and the inertial measurement unit for displaying a ligament stress-strain curve. The method may include the steps of rotating a tibia toward a first condyle, measuring first load values and first deflection angles of the tibia, and determining a stress-strain curve of a first ligament from the first load values and first deflection angles.