Good morning, welcome, dear ladies and gentlemen. This is Jens Wermers. I am an engineer from the University Hospital in Münster, Germany. This is our lab, our KUKA robot, and in my presentation, I'd like to focus on the role of glenoid concavity in shoulder instability with anterior glenoid bone loss. This study was supported by a research grant from the Society for Arthroscopy and Joint Surgery in Switzerland. In addition, a human head implant was provided free of charge by Arthrex. When treating anterior shoulder instability with glenoid bone loss, surgeons are frequently faced with one key decision, soft tissue bunkered repair or bone block reconstruction. So far, the decision is usually based on a critical defect size of 20 to 25 percent related to the width or the length of the intact glenoid. However, in recent years, there has been an ongoing discussion regarding the critical threshold that provides the best decision making for all patients. The underlying biomechanical studies were usually based on the so-called stability ratio, a parameter to estimate the stability provided by concavity compression. The stability ratio is derived from the maximum dislocating force in relation to a given compression force. It is well proved that the stability ratio decreases with increasing defect size, but how important is the glenoid concavity to this loss of stability? Recent simulation-based studies revealed that the glenoid concavity has a significant effect on the loss of stability ratio. Evaluation of concavity could allow a more precise estimate of remaining stability than it has been previously attempted with a defect size measurement. However, the influence of concavity has not yet been investigated biomechanically. Moreover, the models of MAROTA et al. use only the bony structure and a mathematical approximation of the stability ratio. This parameter was then termed the bony shoulder stability ratio and is intended to provide an estimate of stability from radiological measurements of the glenoid. The relation between the measured stability ratio and the calculated bony shoulder stability ratio has also not yet been demonstrated. In this study, we therefore investigated the following research question. What is the biomechanical influence of concavity and bony defect size on stability? To gain insight, the three-dimensional surface of 17 human cadaveric glenoids was sampled with a 3D measuring arm at more than 100 points. This allowed an accurate assessment of concavity as well as the calculation of the bony shoulder stability ratio. Subsequently, anterior dislocations were induced in a robotic setup and anterior bony defects were created stepwise with a width of 2 mm. The generated defect lines were also measured in three dimensions. This allowed a precise evaluation of stability ratio, defect size, and concavity. The correlation between these three parameters was analyzed in linear mixed effects models. A significant effect of concavity on stability ratio was found, whereas the defect size had a minor explanatory power. A high correlation and a low error could be obtained with a model. However, when only the defect size was used to estimate the stability ratio, a substantially worsened correlation and an increased mean error were observed. Furthermore, the specimens were classified based on their initial concavity and the loss of stability ratio as a function of defect size was examined. This demonstrated that the loss of stability ratio for a certain defect size is significantly dependent on concavity. In addition, the correlation between the measured stability ratio and the calculated bony shoulder stability ratio was considered. Again, a linear relationship with high correlation was evident. The bony shoulder stability ratio thus appears to be a suitable parameter that could be obtained in clinical practice using radiological data. When interpreting the results, it must be kept in mind that only the stabilizing effect of bone and cartilage was investigated without considering capsulolabral and muscular influences. Nevertheless, the following findings can be deduced. The glenoid concavity is a crucial factor for the stability of the shoulder and has a significant influence on the loss of stability due to bony defects. It provides a more precise estimate of remaining stability ratio than the widely used measurement of bony defect size. The conclusion of concavity may allow for an improved and personalized clinical decision-making in the treatment of bony glenoid defects, for example, by determination of the bony shoulder stability ratio from radiological data. Future research priorities focus on the influence of concavity under consideration of muscle forces and capsulolabral tissues, as well as the correlation with radiological estimation of the bony shoulder stability ratio. Thank you for your attention. Thank you.

glenoid concavity

shoulder instability

anterior glenoid bone loss

bony shoulder stability ratio

personalized clinical decision-making