Force-Indicating Retractor for Standardized Knee Joint Tension

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Solution Overview

Problem

Existing orthopedic implant procedures, particularly in robotically assisted total knee arthroplasty (TKA), face challenges in standardizing the collection of soft tissue tension and laxity information due to the lack of objective methods for applying varus/valgus force, leading to inconsistent results.

Innovation Solution

A device comprising a tissue retractor with force indicators, such as strain gauges and pressure sensors, is used to measure and standardize the application of forces between articular surfaces, communicating with a robotic surgical system to provide standardized soft tissue tension data.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If manual or z-retractor application of varus/valgus force is used, then the procedure is simple to perform, but the force applied is not standardized leading to inconsistent soft tissue tension measurements

Engineering Contradiction:

Improvesoft tissue tension measurementVSAvoidforce application device

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces manual mechanical force application with an instrumented retractor that uses sensors (strain gauges, pressure sensors) to objectively measure and standardize the force applied to the knee joint. This substitution transforms subjective manual force into quantifiable, standardized mechanical data.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The instrumented retractor provides real-time feedback through force indicators that display the magnitude of varus/valgus force being applied. This feedback mechanism allows the surgeon to standardize force application by monitoring and adjusting based on the displayed measurements, ensuring consistent soft tissue tension assessments.

Inventive Principle:

Principle #23Feedback

2Reliability

If visual estimates and hand measurements are used to determine implant size, then the process is quick and simple, but the results vary and lack objectivity

Engineering Contradiction:

Improveimplant sizing accuracyVSAvoidtime for implant sizing

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent replaces subjective visual estimation and hand measurements with objective instrumented measurement systems. The force indicators and sensors provide quantifiable data on soft tissue tension and gap measurements, eliminating variability associated with manual assessment methods.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The instrumented retractor acts as an intermediary device between the surgeon and the knee joint, providing standardized force application and objective measurement. This intermediary tool bridges the gap between manual surgical technique and precise quantitative assessment.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Stability of the object's composition

If standardized force application is implemented, then soft tissue tension data consistency improves, but the device and procedure complexity increases

Engineering Contradiction:

Improvesoft tissue tension data consistencyVSAvoidforce indication system

Core Design Contradiction:

Stability of the object's compositionVSDevice complexity

Solution Approach 1:

The force indicators provide real-time visual feedback on the force being applied, enabling the surgeon to maintain standardized force levels throughout the procedure. This continuous feedback ensures consistent soft tissue tension measurements while keeping the surgeon in control of the process.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The instrumented retractor is designed to be manually operated by the surgeon, who applies force through the handle while the device automatically measures and displays the force magnitude. This self-service design allows the surgeon to maintain control while benefiting from automated measurement and standardization.

Inventive Principle:

Principle #25Self-service

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

The device enables precise measurement and standardization of soft tissue tension, enhancing the accuracy of implant fitting by providing real-time feedback and improving the consistency of surgical outcomes.

Implementation Method 1

The one or more force indicators include one or more strain gauges located in the base end of the tissue retractor

Methodology Applied

Scientific EffectStrain gauge: Piezoresistive Effect

Implementation Method 2

The one or more force indicators include one or more pressure sensors located in the insertion end of the tissue retractor

Methodology Applied

Scientific EffectPressure sensor: Piezoelectric Effect

Data Source

PatentUS20260000391A1Force-indicating retractor device and methods of use

Publication Date: 2026.01.01 SMITH & NEPHEW INC

AI summary

Devices, systems, and methods for measuring a force applied to a joint during a surgical procedure are disclosed. The device includes an insertion tool, a handle, and one or more force indicators. The insertion tool includes an insertion end and a base end. The one or more force indicators may be attached to the insertion tool and the handle. The insertion end of the device may be inserted into a joint during a surgical procedure and used to apply a force to the joint and/or measure the force using the one or more force indicators when the force is applied.