Force-Indicating Retractor for Standardized Joint Tension Measurement

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Solution Overview

Problem

Existing orthopedic implants, particularly for joints like knees and hips, face challenges in achieving a proper fit due to inconsistent measurement of soft tissue tension and laxity, leading to variable sizing and potential misalignment during surgical procedures.

Innovation Solution

A force-indicating retractor device with strain gauges and pressure sensors is used to measure distraction forces between joint surfaces, providing standardized data for robotic surgical systems to ensure accurate implant sizing and alignment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If manual or z-retractor methods are used to apply varus/valgus stress, then the procedure is simple to perform, but the force applied is not standardized leading to inconsistent measurement of ligament laxity

Engineering Contradiction:

Improvemeasurement of ligament laxityVSAvoidforce application mechanism

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces manual mechanical force application with a robotic system that uses sensors and actuators to apply standardized varus/valgus stress. The robotic system measures forces through strain gauges and pressure sensors, converting mechanical input into precise quantitative data for ligament laxity assessment.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The system incorporates force indicators that provide real-time feedback on the magnitude of varus/valgus forces applied to the knee. This feedback mechanism allows the robotic system to maintain standardized force levels throughout the range of motion, ensuring consistent measurement of soft tissue tension and ligament laxity.

Inventive Principle:

Principle #23Feedback

2Manufacturing precision

If hand measurements and visual estimates are used to determine implant size, then the process is quick and simple, but the sizing is inconsistent and may be too loose or too tight

Engineering Contradiction:

Improveimplant sizing accuracyVSAvoidtime for implant planning

Core Design Contradiction:

Manufacturing precisionVSLoss of time

Solution Approach 1:

The patent replaces subjective hand measurements and visual estimates with an automated robotic system that objectively measures soft tissue tension and ligament laxity. The system uses sensors to collect precise biomechanical data during range of motion assessment, eliminating human variability in implant sizing decisions.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The robotic system acts as an intermediary between the surgeon's implant planning and the actual implant selection. It processes biomechanical measurements and provides objective data that guides implant sizing, serving as a bridge between subjective surgical judgment and precise quantitative measurement.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Manufacturing precision

If robotic assistance is used for total knee arthroplasty, then implant placement accuracy is improved, but the system requires objective soft tissue data that is currently lacking

Engineering Contradiction:

Improveimplant placement accuracyVSAvoidsoft tissue tension data

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent replaces subjective assessment of soft tissue tension with objective robotic measurement. The system uses strain gauges and pressure sensors to quantitatively measure forces in the soft tissues during knee movement, providing reliable data that complements robotic implant placement accuracy.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The system transforms unquantifiable soft tissue properties into measurable parameters by monitoring forces during varus/valgus stress application. This parameter transformation converts subjective soft tissue assessment into objective numerical data that can be reliably used for implant planning.

Inventive Principle:

Principle #35Parameter changes

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 of soft tissue tension, enhancing the accuracy of implant fitting and reducing inconsistencies in surgical outcomes by standardizing the application of forces during joint procedures.

Implementation Method 1

The retractor device includes one or more strain gauges configured to measure the force applied to the retractor device

Methodology Applied

Scientific EffectStrain gauge: Piezoresistive Effect

Implementation Method 2

A force-indicating retractor device with strain gauges and pressure sensors is used to measure distraction forces between joint surfaces

Methodology Applied

Scientific EffectPressure sensing: Piezoelectric Effect

Data Source

PatentUS12569237B2Force-indicating retractor device and methods of use

Publication Date: 2026.03.10 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.