Adjustable Implant Load Sensing for Smaller Bone Lengthening

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Solution Overview

Problem

Conventional intramedullary adjustable implants are bulky, impractical for smaller bones, difficult to precisely determine load, and suffer from communication-based issues such as signal interference.

Innovation Solution

An adjustable implant with a housing, an adjustable member, and an actuation assembly that includes a gear assembly, a sleeve with a load cell, and a transducer for precise load measurement, allowing non-invasive adjustment and load monitoring without direct bone anchor measurement.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If conventional intramedullary adjustable implants are used, then bone lengthening or compression can be achieved, but the implant becomes bulky and impractical for smaller bones

Engineering Contradiction:

Improveimplant sizeVSAvoidapplicability to smaller bones

Core Design Contradiction:

Volume of moving objectVSAdaptability or versatility

Solution Approach 1:

The patent implements nesting by placing the actuation assembly inside the adjustable member, and the sleeve inside the actuation assembly. This nested configuration allows multiple functional components to occupy overlapping spatial volumes, significantly reducing the overall implant footprint while maintaining all necessary functions for bone lengthening or compression.

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The patent utilizes the radial dimension by positioning the load cell in the radial direction between the actuation assembly and adjustable member. This radial arrangement allows load measurement functionality to be added without increasing the axial length of the implant, effectively using unused dimensional space to reduce overall size.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Measurement precision

If conventional intramedullary adjustable implants are used, then adjustment functionality is provided, but precise load determination becomes difficult

Engineering Contradiction:

Improveload measurement accuracyVSAvoidmeasurement system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent introduces a sleeve as an intermediary component between the actuation assembly and adjustable member. This sleeve provides a dedicated structural element for mounting the load cell, serving as a mediator that translates mechanical load into measurable signal without requiring complex integration of sensing elements into existing components.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces indirect mechanical load measurement methods with a direct electrical measurement system using a load cell. This substitution eliminates the need for complex mechanical linkages or indirect calculations, providing precise load determination through electrical signals while simplifying the overall measurement system architecture.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If conventional intramedullary adjustable implants are used, then distraction and compression functions are achieved, but signal interference from implant components occurs

Engineering Contradiction:

Improvecommunication reliabilityVSAvoidsignal interference

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent extracts the transducer from the interior of the implant components and positions it externally or in a location isolated from metallic structures. This extraction removes the source of signal interference caused by metallic components blocking or distorting wireless signals, thereby improving communication reliability between the implant and external devices.

Inventive Principle:

Principle #2Taking out (Extraction)

4Reliability

If external fixation frames are used, then bone lengthening can be achieved, but pin placement sites become sites for infection and remain painful

Engineering Contradiction:

Improveinfection risk reductionVSAvoidpatient comfort

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent replaces the external mechanical fixation frame system with an intramedullary implant that operates entirely inside the bone marrow cavity. This substitution eliminates the need for skin-penetrating pins and external hardware, thereby removing infection pathways through the skin and eliminating pain associated with pin tract wounds, while maintaining bone lengthening functionality.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 precise load measurement and non-invasive adjustment of smaller bones, reducing bulkiness and mitigating signal interference, providing controlled bone lengthening or compression.

Implementation Method 1

the sleeve including a load cell coupled with the transducer

Methodology Applied

Scientific EffectStrain gauge measurement:

Implementation Method 2

the adjustable member including a transducer adjacent an outer wall thereof

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Data Source

PatentUS12533164B2Adjustable implant

Publication Date: 2026.01.27 NUVASIVE SPECIALIZED ORTHOPEDICS INC

AI summary

One aspect of the disclosure relates to an aspect of the disclosure relates to an adjustable implant including: a housing; a first adjustable member at least partially positioned within the housing and moveable relative to the housing; and a first actuation assembly positioned within the first adjustable member and configured to move the first adjustable member relative to the housing.