Reliability of a two-thirds glenoid height technique for CT-based measurement of glenoid bone loss : a comparison with the circle of best fit method.

Abstract

Aims Glenoid bone loss is a major contributor to recurrent shoulder instability. This bone loss significantly increases failure rates of soft-tissue stabilization procedures. There are multiple ways of assessing bone loss radiologically, all of which have their flaws. A recent study by Makovicka et al described a simple technique using two-thirds of the glenoid height to determine the diameter of the circle of best fit (COBF) for estimating bone loss. The aim of our study was to assess the accuracy and reliability of the described technique when it is applied to CT scans of glenoids with known bone loss. We hypothesized that the two-thirds technique would demonstrate accuracy within ± 1 mm of true glenoid width and reliability (ICC ≥ 0.75), comparable to standard COBF methods. Methods We performed CT scans and 3D reconstructions of three anatomically accurate scapular models, each with a known anterior bone defect. Four orthopaedic surgeons and three radiologists, blinded to the actual bone loss, measured the long axis of the glenoid. We did three separate analyses: 1) assessing the maximum superior-inferior diameter of the glenoid on 3D reconstructions; 2) comparing the value obtained by calculating two-thirds of the long axis of the glenoid to the known measurement of the glenoid width; and 3) comparing percentage bone loss determined using the diameter of COBF obtained from the two-thirds technique with percentage bone loss determined using ipsilateral COBF linear techniques. Results The true long axis measured 37.5 mm, whereas the mean CT measurement was 36.3 mm (27.6 to 37.8; SD 1.2), indicating a mean underestimation of 1.2 mm by CT. The two-thirds method resulted in a mean underestimation of bone loss of 9.4 percentage points. The two-thirds method was less accurate, but showed improved intraclass correlation coefficient compared to an ipsilateral COBF method. Conclusion The two-thirds technique may be a simpler and more consistent method for estimating bone loss, but it significantly underestimates the defect in clinically relevant models. Relying on this technique may lead to mismanagement of patients.