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

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 (SRCT) by 2 surgeons independently. Biomechanical testing was then performed on patient-specific 3-dimensional (3D)–printed glenoid models to calculate the SR (SR3Dprint), which was used to (1) analyze the reliability of SRCT and (2) examine if the BDA could predict SR3Dprint. To validate whether the 3D-printed glenoid could reflect the actual biomechanical properties of the shoulder, the SR from 5 cadaveric glenoid specimens (SRcadaver) was also calculated and compared with that from the 3D-printed glenoid (SR3Dprint) under 6 osteotomy conditions. Linear regression and intraclass correlation coefficients (ICCs) were used for statistical analysis. Results: The interrater reliability of SRCT measurements was high (ICC = 0.95). SRCT was highly correlated with SR3Dprint ( 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 SR3Dprint ( R 2 = 0.31; ICC = -0.46). The cadaveric validation experiment indicated that SRcadaver was highly correlated with SR3Dprint ( 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.

Association of the Stability Ratio With Postoperative Clinical Function and Recurrence of Instability in Patients With Anterior Shoulder Instability: A Retrospective Cohort Study

“…Fifth, calculating the SR using the biomechanical test is complex and inconvenient for clinical application. However, our previous study 6 demonstrated a strong correlation ( r = 0.97) between the SR calculated using the biomechanical method and that obtained using the more straightforward CT-based method. Sixth, there were no data on pre- and postoperative sporting activities among the study patients.…”

“…The SR was calculated via a biomechanical test of the 3D glenoid model of corresponding patients on the customized inclination platform based on our previous study. 6 In brief, patient-specific 3D glenoid models were designed and produced. A customized biomechanical testing platform was constructed in which the inclination angle of the platform could be manually altered.…”

“…Based on a study by Moroder et al, 17 , 18 we conducted a previous study 6 in which we proposed and verified a new computed tomography (CT)-based method to estimate the SR that overcame the shortcomings of traditional SR calculation methods. This study aimed to evaluate whether the SR is associated with postoperative clinical function and recurrence of instability after arthroscopic Bankart repair in patients with ASI.…”