# Quantifying the Biomechanical and Neural Factors Contributing to Shoulder Instability

> **NIH NIH F31** · NORTHWESTERN UNIVERSITY · 2021 · $10,540

## Abstract

PROJECT SUMMARY
Multidirectional instability (MDI) is a common shoulder pathology in younger individuals impacting those in the
military, employed in heavy lifting occupations, and participating in high demand activities. MDI is characterized
by multidirectional atraumatic shoulder laxity with concurrent pain that limits participation in activities of daily
living. Treatment for MDI begins with non-operative physiotherapy, but short-term and long-term outcomes are
often ineffective. Subsequent surgical treatment is unpredictable, especially when compared to similar surgical
treatment for unidirectional instability. In contrast to MDI, many individuals present clinically with
multidirectional atraumatic shoulder laxity but report no pain (asymptomatic) with shoulder function. It is
hypothesized that individuals with asymptomatic laxity, unlike patients with MDI, use neural activation of
shoulder musculature to compensate for any deficits in passive shoulder structures. However, research has yet
to investigate or quantify the inability to compensate with neural activation of shoulder musculature for passive
deficits in MDI. This proposal will focus on identifying and quantifying differences in active and passive
shoulder stability between individuals with MDI and asymptomatic laxity to isolate components of shoulder
mechanics unique to shoulders with MDI. Aim 1 will quantify translational impedance (resistance to joint
motion) of the shoulder in multiple directions and multiple arm postures during shoulder relaxation. Aim 2 will
quantify translational impedance of the shoulder during constant isometric torque production in three rotational
degrees-of-freedom. Passive and active translational impedance will be assessed in individuals with clinically-
diagnosed MDI, asymptomatic shoulder laxity, and asymptomatic shoulders negative for clinical laxity. A
custom-adapted linear motor will apply long slow (Aim 1) and small quick stochastic (Aim 1 and Aim 2)
translational perturbations to the shoulder. The stiffness component of impedance will be quantified with
computational analysis of shoulder displacement and forces following translational perturbations. The results of
this work will provide the first comparison of passive and active translational shoulder impedance in individuals
with MDI and asymptomatic laxity, informing future studies designed to predict individuals that progress from
asymptomatic laxity to MDI and develop personalized MDI treatments to target individual biomechanical
deficits.

## Key facts

- **NIH application ID:** 10083705
- **Project number:** 5F31AR074288-03
- **Recipient organization:** NORTHWESTERN UNIVERSITY
- **Principal Investigator:** Constantine Nicolozakes
- **Activity code:** F31 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $10,540
- **Award type:** 5
- **Project period:** 2019-02-01 → 2021-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10083705

## Citation

> US National Institutes of Health, RePORTER application 10083705, Quantifying the Biomechanical and Neural Factors Contributing to Shoulder Instability (5F31AR074288-03). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10083705. Licensed CC0.

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