Glenoid component failure remains the most important indication for revision surgery of total shoulder arthroplasty [
17‐
19]. Biomechanical studies have shown that placement of a glenoid component in more than 10° of retroversion causes eccentric loading of the prosthesis, and this can lead to instability, rocking horse phenomenon, and early loosening [
7,
20‐
24]. Correction of the version helps to restore the glenohumeral relationship and rebalances the force couple of the rotator cuff. Downreaming of the anterior glenoid is an accepted method to correct the retroversion, but limited by the volume of the glenoid vault. Excessive reaming can result in loss of glenoid bone stock and medialization of the joint line jeopardizing solid fixation and with the risk of peg perforation [
25‐
27]. If the retroversion is less than 15° to 20°, downreaming of the anterior glenoid is advised. However, there are no explicit guidelines regarding the amount of version that can be safely corrected by eccentric reaming without compromising the glenoid bone stock [
28]. We do know that there are limits and clinical experience proved reverse shoulder arthroplasty to be a viable surgical option to solve both the problem of severe glenoid erosion in patients with a biconcave glenoid without rotator cuff insufficiency [
29].
The amount of bone resected by the different types of reamers (nipple or K-wire guided, flat and convex) is unknown. To our knowledge, this is the first study investigating the effect of reaming with different reamers on bone volume and surface area in two different-shaped glenoids. This study shows that convex reamers cause more bone loss than flat reamers in uniconcave type A glenoids. This is partly due to the deeper reaming range as a result of the convexity. Corrective reaming of biconcave type B2 glenoids with convex reamers tends to cause slightly more bone loss than with flat reamers, but the difference is not significant. In A glenoids, the reaming angle is as close to neutral as possible, so this does not interfere with bone loss. The depth of reaming does have a significant effect on bone loss, and every millimeter of additional reaming depth accounts for an extra 215 mm
3 of bone loss. In B2 glenoids, the angle of correction along the
X-axis (representing the version angle correction) is an important factor in determining the bone loss; every additional degree of correction along the
X-axis results in an extra 56 mm
3 of bone loss. Similarly, the depth of reaming has an important effect on bone loss; every millimeter of additional reaming depth accounts for an extra 235 mm
3 of bone loss. Obviously, it is the degree of retroversion and biconcavity, and the intended correction, which dictates the loss of bone volume after reaming in biconcave glenoids. If a surgeon decides to correct more by reaming, this has a direct effect on the amount of bone loss. There is a significant difference between surgeons in the correction of version in the B2 glenoids in this study. This is probably due to the surgeons’ intention and experience to correct as close as possible to the native version [
15]. In recent publications, Iannotti et al. [
30] and Karelse et al. [
14] came to a similar conclusion that in biconcave glenoids, correction of version by reaming is not reproducible. Until now, corrective reaming is performed by “carpenters eye,” helped by the experience and the natural 3D orientation of the surgeon. Several studies show that the accuracy of the position of the glenoid prosthesis in the transverse plane can be improved by intraoperative navigation and patient-specific instrumentation; this is particularly so in severely retroverted glenoids [
31‐
35]. Convex reamers create a larger surface area than flat reamers in both A and B2 glenoids, and this is not affected by the correction angle. This finding differs from the results from Youngpravat et al. [
15], where smaller version corrections increase the surface area. A larger surface area obviously increases the contact area for a glenoid component. In biconcave glenoids, the convex reamers are at slight disadvantage to flat reamers concerning bone loss, but they win back in a larger surface area of the glenoid after reaming. For uniconcave type A glenoids, which are considered non-pathological glenoids, reaming with convex reamers causes more bone loss than with flat reamers. The difference in surface area between the reamers is small given the fact that reaming depth must be minimal in these non-eroded glenoids. If however glenoids are centrally eroded to type A1 and A2 glenoids according to Walch, and excessive medialization of the joint line should be avoided, minimal reaming with a more conforming reamer is the objective. A convex reamer with a radius of curvature mimicking the radius of the native articular surface can maximally preserve the surface area and existing bone stock in centrally eroded glenoids [
36], whereas flat reamers would reduce both surface area and bone stock. Another explanation for the reduced bone loss after flat reaming can be that the radius of flat reamers is chosen accordingly to the largest radius of the glenoid, thereby reaming mainly the circumferential bone and not reaching the centrally eroded part.
The surface area of B2 glenoids is larger after reaming over K-wires than nipple guided using flat reamers. The difference may partly be explained by the difference in diameter of the K-wire and the nipple, 2 and 6 mm, respectively.