Available online 17 November 2022

The purpose of the present study was to investigate the characteristics of unrecognized glenoid fracture in opposite shoulders with symptomatic anterior instability.

Participants were 38 patients, who had complaints of instability on only one side (symptomatic shoulder) and had no complaints despite of a glenoid fracture on the other shoulder (asymptomatic shoulder) from 2011 to 2020. Factors that could influence the onset of symptoms including glenoid rim morphology were retrospectively investigated.

Among the asymptomatic shoulders, 16 had a single traumatic event and 22 had no history of trauma. The glenoid morphology was normal in 6, erosion in 12 and bony Bankart in 20 on the symptomatic side, whereas the respective shoulders were 0, 16 and 22 on the asymptomatic side. Bone union of bony Bankart was complete in 9, partial in 3 and non-union in 8 on the symptomatic side, whereas the respective shoulders were 18, 3 and 1 on the asymptomatic side. The mean glenoid defect size was 10.4% and 7.8%, and the mean bone fragment size was 5.0% and 4.5%, respectively. The mean medial displacement of bone fragments was 2.6 mm and 1.0 mm, respectively (p < 0.001). A larger glenoid defect (≥10%) was recognized in 19 symptomatic shoulders and 10 asymptomatic shoulders. Among them, erosion was solely recognized in 5 symptomatic shoulders. In shoulders with bony Bankart, all 10 asymptomatic shoulders had a completely or partially united fragment with less than 2 mm displacement. On the other hand, among 14 symptomatic shoulders, united fragment was solely recognized in 8 shoulders, in which medial displacement was less than 2 mm in 3 shoulders.

Even if a glenoid fracture occurred, symptom such as instability or pain was not always recognized by all patients. Regardless of glenoid defect size, shoulders with a completely or partially united bone fragment and with less than 2 mm displacement were found to be asymptomatic.

Sugaya et al. reported that in patients with recurrent anterior instability, abnormal glenoid morphology could be detected in up to 90% of patients [1]. Therefore, we should recognize that dislocation of the shoulder is not just a dislocation, but a dislocation fracture accompanying a glenoid fracture. As even at recurrent instability young athletes sometimes feel only pain but continue to play without recognizing instability, Boileau et al. termed such condition as unstable painful shoulder (UPS) [2].

On the other hand, when a patient complains of instability even in one shoulder, we usually perform CT examination on bilateral shoulders at the same time. At that time, unrecognized glenoid fracture is sometimes observed in the other shoulder without any complaint of instability or pain (Fig. 1). While some patients have a single traumatic event, others do not have a history of trauma. The purpose of the present study was to investigate the characteristics of unrecognized glenoid fracture in opposite shoulders with symptomatic anterior instability. We hypothesized that such patients had glenoid fractures, but bone fragments were completely united with minimal displacement.

This was a retrospective study of prospectively collected clinical data. The study was approved by the local institutional review board, and participants gave written informed consent to participate. From April 2011 to December 2020, we have performed CT examinations on both shoulders at the same time for all patients with traumatic anterior instability. Among patients who had complaints of unilateral instability, patients, who had a glenoid fracture on the opposite shoulder without any

From April 2011 to December 2020 CT examinations on both shoulders were performed in 813 patients, who complained of unilateral or bilateral traumatic anterior shoulder instability (unilateral: 644, bilateral: 159). Among 644 patients who had complaints of unilateral instability, 38 patients had a glenoid fracture on the opposite shoulder without any complaints of instability or pain prior to CT examination. In the interview after CT, 22 had no history of trauma. While 16 had a single traumatic

The most important finding of the present study was that even if a glenoid fracture occurred, symptom such as instability or pain was not always recognized by all patients. Even in patients with a glenoid defect of 10% or larger, shoulders with a completely or partially united bone fragment and with less than 2 mm displacement could be asymptomatic.

Maquieira et al. reported that nonoperative treatment of larger displaced glenoid rim fragments has led to excellent results in 14 consecutive

Even if a glenoid fracture occurred, symptom such as instability or pain was not always recognized by all patients. Regardless of glenoid defect size, shoulders with a completely or partially united bone fragment and with less than 2 mm displacement were found to be asymptomatic.

The study was approved by the local institutional review board, and participants gave written informed consent to participate.

Shigeto Nakagawa, Takehito Hirose, Hiroto Hanai, Toshitaka Tsunematsu, Tomoki Ohori, Hiroyuki Yokoi, and Ryohei Uchida: These authors, their immediate families, and any research foundation with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.

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© 2022 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.