Anatomical considerations regarding the "bare spot" of the glenoid cavity.

Abstract

The "bare spot" of the glenoid cavity has recently been described as a constant reference point to quantify the amount of bone loss from the inferior portion of the glenoid cavity. In shoulder surgery this spot should help the surgeon to determine the width of the inferior portion of the glenoid cavity arthroscopically. The aim of this study was to determine the localization of the bare spot within the glenoid cavity and to prove its usefulness in shoulder surgery by means of a macroscopic study using embalmed glenohumeral joints ( n=20; 12 left, 8 right). Each glenoid cavity was photographed and transferred to a commercial AutoCAD software program. The bare spot was marked and the mean distances between the center of the bare spot and the inferior ( a), anterior ( b(1)) and posterior ( b(2)) inner margins of the glenoid labrum as well as its relationship ( c) to the mid-point of a virtual circle formed by the inferior portion of the glenoid cavity were measured (mean values : a=9.70, b(1)=10.88, b(2)=13.71, c=3.2 mm). In most cases, the bare spot showed a significantly excentric position within the inferior part of the glenoid cavity ( p<0.05). Due to the great variability in the shape of the glenoid cavity, an inferior circle according to previous descriptions could only be observed in half the specimens. From the results of our study the bare spot seems to be an unreliable landmark for the determination of the center of the inferior portion of the glenoid cavity, although it has a constant appearance and is probably expressed as the result of cartilaginous distribution due to dynamic shoulder activity.