Glenoid Bone Loss After Unidirectional Versus Combined Shoulder Instability: Response

Authors’ Response

The authors thank Christopher Femino for his insightful letter regarding our recent article, “Comparison of Glenoid Bone Loss After Unidirectional Versus Combined Shoulder Instability in a Military Population,” which raises an important question regarding the utility of the “perfect circle” technique. ¹⁵

Combined-type shoulder instability among the active-duty servicemember population remains an underexplored topic, and there is substantially less understanding of the dissimilarities among glenoid bone loss with combined-type instability as compared with the well-studied anterior-type instability. We firmly believe this area of research is an important one, especially to surgeons such as ourselves who routinely treat military servicemembers in their practice.

As specified in our Limitations section, the perfect circle technique is flawed. Our research group has sought to further investigate this concern, finding poor to moderate inter- and intraobserver reliability for measurements of both the perfect circle diameter and the amount of bone loss using magnetic resonance imaging (MRI), which are substantially lower than what other groups have reported.^9,10 And while 3-dimensional computed tomography, as originally described by Sugaya et al,^12,13 continues to be the gold standard for quantifying glenoid bone loss, multiple studies have validated the use of the perfect circle technique and the use of MRI in obtaining these measurements.^4-7,11,14

The two-thirds glenoid height technique, as published by Makovicka et al ⁸ in 2024, certainly represents an exciting and seemingly readily reproducible technique by which to measure glenoid bone loss, and we are optimistic about its use in the future. However, we acknowledge that this work is a preliminary study based on an intact glenoid and has not been validated with anterior instability, let alone the rarer posterior and combined-type instability often found among active-duty servicemembers.^1-3 At the time of our data collection in early 2023, the two-thirds glenoid height technique was extremely new. We remained hesitant to incorporate a new methodology immediately after its publication and instead opted to use a well-published technique frequently applied in the clinical setting. Of course, we sought to maintain careful collection and reporting of our data, with measurements performed by 2 shoulder and elbow fellowship–trained surgeons and a third resolving any discrepancies. Regardless, we are excited about the two-thirds glenoid height technique and the simplification of the measuring process that it appears to offer.

Thank you for your interest in our work; we similarly hope that the two-thirds glenoid height technique will become widely adopted and, if so, would consider repeating this study with the most current method for measuring glenoid bone loss. We also strongly encourage other research groups to conduct similar studies with a variety of measurement and imaging methodologies and patients to ensure that our findings are generalizable. We look forward to continuing the exploration of this important topic in the future.

Alexis B. Sandler, MD Annette H. Yoon, MD John P. Scanaliato, MDEl Paso TX, USA Nata Parnes, MDCarthage, NY, USA