# Humeral head deviation and velocity in multidirectional instability of the glenohumeral joint: a cine magnetic resonance imaging study

## TL;DR

This study uses MRI to objectively measure shoulder instability by analyzing humeral head movement during rotation.

## Contribution

The study introduces cine MRI as a tool to quantify dynamic shoulder instability, which was previously assessed subjectively.

## Key findings

- MDI shoulders showed significantly greater humeral head deviation compared to healthy controls.
- Deviation velocity in MDI shoulders was faster than in healthy shoulders.
- Deviation amplitude in MDI exceeded 35% of the glenoid width, surpassing clinical thresholds.

## Abstract

Manual clinical tests for shoulder instability rely heavily on subjective assessments of humeral head translation, making objective quantification challenging. This study hypothesized that patients with multidirectional glenohumeral instability (MDI) would demonstrate greater humeral head deviation and faster deviation velocity than healthy controls during active shoulder rotation, as assessed using cine magnetic resonance imaging (MRI).

Fourteen participants (eight shoulders with MDI and 20 healthy shoulders) underwent cine MRI while performing active shoulder rotation with the arm at the side. Humeral head deviation, deviation amplitude, and deviation velocity were calculated and compared between the groups using Welch's t-test.

The MDI group showed significantly greater humeral head deviation, wider amplitude of deviation, and faster deviation velocity than the control group (P = .008 for anterior deviation, P = .009 for posterior deviation). The deviation amplitude exceeded 35% of the glenoid width in MDI shoulders, surpassing established clinical thresholds.

Patients with MDI demonstrated quantifiable dynamic instability on cine MRI. This modality may provide objective support for clinical findings. However, validation in larger cohorts is warranted to confirm these findings, given the limited number of MDI shoulders (n = 8).