Measurement of the Balance Stability Angle to Predict the Stability Ratio in Patients With Recurrent Anterior Shoulder Dislocation: A Novel Computed Tomography-Based Protocol

Qingxiang Hu; Guangcheng Zhang; Di Wu; Haoyu Zhang; Hai Hu; Shi Zhan; Yaohua He

doi:10.1177/23259671221140908

Measurement of the Balance Stability Angle to Predict the Stability Ratio in Patients With Recurrent Anterior Shoulder Dislocation: A Novel Computed Tomography-Based Protocol

Orthop J Sports Med. 2022 Dec 12;10(12):23259671221140908. doi: 10.1177/23259671221140908. eCollection 2022 Dec.

Authors

Qingxiang Hu¹, Guangcheng Zhang¹, Di Wu¹, Haoyu Zhang², Hai Hu^{1

3}, Shi Zhan³, Yaohua He⁴

Affiliations

¹ Department of Orthopaedics, Shanghai Sixth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
² Department of Biostatistics, Harvard T.H. Chan School of Public Health, Harvard University, Boston, Massachusetts, USA.
³ Orthopaedic Biomechanical Laboratory, Department of Orthopaedics, Shanghai Sixth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
⁴ Department of Orthopaedics, Jinshan District Central Hospital, Shanghai University of Medicine & Health Sciences, Shanghai, China.

Abstract

Background: The stability ratio (SR) is an important biomechanical parameter for evaluating glenoid stability in patients with recurrent anterior shoulder dislocation (RASD), and it cannot be practically and conveniently measured in clinical scenarios.

Purpose: To investigate a novel computed tomography (CT)-based protocol to estimate the SR efficiently.

Study design: Descriptive laboratory study.

Methods: A total of 102 patients with RASD were included. Demographic information, CT scans, and bone defect area (BDA) were collected. The new protocol, based on balance stability angle (BSA) measurements on CT, was conducted to estimate the SR (SR_CT) by 2 surgeons independently. Biomechanical testing was then performed on patient-specific 3-dimensional (3D)-printed glenoid models to calculate the SR (SR_3Dprint), which was used to (1) analyze the reliability of SR_CT and (2) examine if the BDA could predict SR_3Dprint. To validate whether the 3D-printed glenoid could reflect the actual biomechanical properties of the shoulder, the SR from 5 cadaveric glenoid specimens (SR_cadaver) was also calculated and compared with that from the 3D-printed glenoid (SR_3Dprint) under 6 osteotomy conditions. Linear regression and intraclass correlation coefficients (ICCs) were used for statistical analysis.

Results: The interrater reliability of SR_CT measurements was high (ICC = 0.95). SR_CT was highly correlated with SR_3Dprint (R ² = 0.86; ICC = 0.92). The mean BDA was 11.44% ± 6.72% by the linear ratio method, with a weak correlation with SR_3Dprint (R ² = 0.31; ICC = -0.46). The cadaveric validation experiment indicated that SR_cadaver was highly correlated with SR_3Dprint (R ² = 0.86; ICC = 0.77).

Conclusion: Results indicated that (1) the proposed CT-based protocol of obtaining BSA measurements is promising for the SR estimation in patients with RASD, (2) the BDA was not an effective parameter to predict the biomechanical SR, and (3) the 3D-printed glenoid could reflect the biomechanical properties of cadaveric shoulders regarding the SR estimation.

Clinical relevance: Traditional BDA measurements cannot accurately reflect the biomechanical stability of the glenoid. The newly proposed CT-based protocol is practical for surgeons to estimate the SR.

Keywords: balance stability angle; bone defect area; recurrent anterior shoulder dislocation; stability ratio.