CT-based methods for the assessment of glenoid bone loss

Recurrent anterior shoulder dislocation often causes progressive damage and bone loss of the anteroinferior glenoid rim, which is a key factor in persistent shoulder instability. Correct measurement of bone loss is essential before surgery, as it helps decide whether a soft tissue repair is sufficient or if a bone graft procedure, such as the Latarjet, is required. In the past, arthroscopy was considered the standard method for evaluating glenoid bone loss, using the so-called "bare spot" as a reference point. However, this landmark is not always visible and has shown poor reliability, which has reduced its clinical value. For this reason, imaging methods with CT and MRI are now preferred. One of the best-known imaging techniques is the PICO CT method, which calculates bone loss by inscribing the glenoid in a circle. Although widely used, this method has significant limitations because the glenoid surface is not truly circular. As a result, variability between observers is high, and clinical accuracy is reduced. To improve precision, the PARMA method was developed. This technique uses curved multiplanar CT reconstructions (cMPRs) to follow the real concavity of the glenoid surface. Cadaveric studies have shown that PARMA is more accurate and reproducible than traditional CT methods, with good agreement compared to high-precision laser scanning. In addition, Hill-Sachs lesions must also be evaluated. The on-track/off-track concept combines humeral and glenoid bone loss to predict the risk of recurrent dislocation. Off-track lesions have a higher chance of surgical failure if treated with soft tissue repair alone and usually require bone procedures. Overall, modern CT-based techniques and combined lesion assessment improve accuracy and allow more tailored treatment of shoulder instability. The aim of this review is to provide an overview of the CT methods most employed to quantify glenoid bone loss in traumatic shoulder instability, emphasizing their strengths and limitations.