Limb Positioning Apparatus Shoulder Rotation Alignment

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Solution Overview

Problem

Current limb positioning devices for shoulder surgery often result in inconsistent arm positioning due to manual handling, leading to assistant fatigue and limited abduction angles, as they are typically mounted to the operating table foot and have mismatched centers of rotation for the shoulder and hinge system.

Innovation Solution

A limb positioning apparatus with a vertical post and boom member connected by a hinge, utilizing a lockable gas spring to adjust the angle between them, and an internal cable/traction system that replicates the natural range of motion of the shoulder joint, allowing closer alignment of the centers of rotation and enhanced control over arm positioning.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If a physician's assistant manually rotates and holds the arm in a fixed position, then the surgeon can access different areas of the joint, but the assistant experiences fatigue leading to inconsistent positioning

Engineering Contradiction:

Improvearm positioning consistencyVSAvoidpositioning reliability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The positioning device automatically maintains arm position without requiring continuous manual intervention. The gas spring mechanism provides self-sustaining positioning capability, eliminating assistant fatigue and ensuring consistent arm positioning throughout the surgical procedure

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The manual mechanical system of assistant-held positioning is replaced with an automated mechanical system incorporating gas springs and hinges. This substitution transforms the positioning function from human-dependent to device-dependent, improving reliability while maintaining ease of operation

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Stability of the object's composition

If limb positioning devices are mounted to the foot of the operating table, then the devices are stable, but the center of rotation for the shoulder and system hinge are at different geometric locations limiting abduction angle

Engineering Contradiction:

Improvedevice stabilityVSAvoidabduction angle range

Core Design Contradiction:

Stability of the object's compositionVSAdaptability or versatility

Solution Approach 1:

The device employs asymmetric mounting configuration where the hinge center is deliberately positioned to align with the shoulder's center of rotation rather than using a symmetric foot-mounted arrangement. This asymmetric design enables the boom to achieve the full natural range of motion including greater abduction angles while maintaining stability through proper structural support

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The mounting position is transitioned from the foot of the table (distal dimension) to near the shoulder (proximal dimension). This dimensional change in mounting location allows the hinge center to coincide with the shoulder's center of rotation, enabling unrestricted abduction motion while the vertical post provides stability in the vertical dimension

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Device complexity

If the center of rotation for the shoulder and system hinge are at different geometric locations, then the device structure is simplified, but the obtainable abduction angle of the shoulder is limited

Engineering Contradiction:

Improvestructural complexityVSAvoidrange of motion

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The device merges the shoulder's center of rotation with the hinge center into a single geometric location. This merging of two previously separate centers enables the boom to follow the natural arc of shoulder motion, achieving full abduction and adduction ranges without requiring complex multi-axis mechanisms, thus maintaining structural simplicity while maximizing range of motion

Inventive Principle:

Principle #5Merging (Combining)

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

This design improves intraoperative control and increases the range of motion for arm positioning, reducing user fatigue and providing more stable and ergonomic support during shoulder surgery by aligning the centers of rotation and allowing greater flexibility in positioning.

Implementation Method 1

a lockable gas spring attached to the hinge. The vertical post and the boom member house the internal cables for transferring the primary traction load to the operative limb

Methodology Applied

Scientific EffectGas spring: Spring

Data Source

PatentUS10918552B2Limb positioning apparatus and methods of use thereof

Publication Date: 2021.02.16 SMITH & NEPHEW ASIA PACIFIC PTE LTD

AI summary

A limb positioning apparatus comprises a vertical post connected to the operating table near the shoulder of the patient and a boom member connected to the vertical post through a hinge. The hinge allows the angle between the vertical post and the boom member to be adjusted with assistance from a lockable gas spring attached to the hinge. The vertical post and the boom member house the internal cables for transferring the primary traction load to the operative limb.