Our aim was to test the validity of arthroscopic method with reference to the bare spot for quantifying glenoid bone loss in patients with shoulder instability. 3D-CT scans of both shoulders were obtained from 19 patients with anterior instability (13 males, 6 females: mean age 23.9 years old) and 27 patients without instability (18 males, 9 females: mean age 59.2 years old) prior to arthroscopy. For the patients without instability, the glenoid width was measured on CT images in both shoulders, and the distances from bare spot to anterior and posterior glenoid rim were measured arthroscopically according to Burkhart. For the patients with instability, the rate of glenoid bone loss was calculated with CT and arthroscopic measurement. Among the patients without instability, two patients showed more than 5% difference of glenoid width measured on 3D-CT between the two shoulders, and were excluded in this study. In the 25 patients with normal glenoid, we could not identify the bare spot in 3 shoulders. The bare spot was identified at the center in only 8 shoulders, and it was found more than 2mm anterior from the center in 4 shoulders. Among 19 patients with instability, we could not identify the bare spot in 2 shoulders. Pearson's correlation coefficient showed significant (p<0.001) correlation (r=0.84). However, more than 5% difference of glenoid bone loss rate between 3D-CT and arhtorsocpy was found in 6 shoulders. The results showed that bare spot is not consistently located at the center of the inferior glenoid, and the arthroscopic measurement of the glenoid bone loss using the bare spot as a landmark may not be accurate for some patients. Bare spot method combined with preoperative 3D-CT evaluation would be preferable for evaluating the glenoid bone defect precisely.
