# Three-dimensional changes of scapulothoracic orientation in patients with acromioclavicular joint dislocations

## TL;DR

This study is the first to show 3D changes in scapula position in patients with shoulder joint dislocations, revealing altered rotation and tilt.

## Contribution

The study introduces the first in vivo 3D analysis of scapulothoracic orientation changes following acromioclavicular joint dislocations.

## Key findings

- The injured scapula showed more internal rotation compared to the healthy side.
- The injured scapula exhibited increased tilt and decreased upward rotation.
- No significant differences were found in scapular translation or protraction.

## Abstract

Acromioclavicular joint (ACJ) dislocations have been linked to altered scapulothoracic orientation and scapula dyskinesis, but research on three-dimensional (3D) changes in scapulothoracic orientation after such injury in vivo has not been described before. The aim of our pilot study was to analyze scapulothoracic orientation changes in patients with ACJ dislocations using three-dimensional computed tomographic (CT) image reconstruction.

Patients with ACJ dislocations who underwent CT imaging were included retrospectively and consecutively. Minors and cases with spine, neurologic or systemic diseases, and shoulder girdle fractures were excluded. Each CT was performed in supine position with elbows rested on the scanning table and had to depict the complete shoulder girdle. After 3D image reconstruction, tilt, upward rotation, internal rotation, translation, and protraction of the scapula were measured based on three osseous landmarks: the glenoid (the deepest point of its concavity), the medial root of the scapular spine, and the inferior scapular angle. The healthy contralateral side was used as a paired control. ACJ dislocations were graded according to Rockwood (RW) on strict frontal CT image reconstruction, including the contralateral shoulder, where measurements were also performed to enable comparison. Cases were labeled as acute or chronic with a 3-week injury-to-diagnosis interval cut-off.

The mean age of the 14 patients (11 males and 3 females) was 38.6 ± 15.6 years (range, 18-71). Ten cases were defined as acute (RW types II: 1; III: 3; V: 6) and four as chronic (II: 1; III: 2; V: 1). On the injured side, the scapula showed more internal rotation (46.2° ± 5.3° vs. 42.1° ± 4.4°; P = .003), more scapular tilt (20.2° ± 4.6° vs. 17.9° ± 3.5°; P = .022), and less upward rotation (10.1° ± 3.6° vs. 12.0° ± 4.8°; P = .043). No difference between sides was found for scapular translation (P = .342) and scapular protraction (P = .385). There was a trend toward more internal rotation for RW type V injuries (P = .097).

In this first 3D in vivo study, patients with ACJ dislocations displayed changes in scapulothoracic orientation in all planes. The scapula of the injured side was more internally rotated, forwardly tilted, and less upwardly rotated than on the healthy contralateral side.