Six weeks ago, I had surgery to remove my arthritic shoulder joint and replace it with a shoulder replacement. When I was at my follow-up appointment, the surgeon mentioned doing some extra “reaming” to correct a tipped shoulder socket. Why would this be necessary? I kinda don’t get it but I didn’t say anything at the time. Now I’m wondering more about it.

Alignment of the glenoid (shoulder socket) in the scapula (shoulder blade — where the glenoid is located) is a key feature necessary for a smooth moving shoulder joint. The head of the humerus rotates inside the glenoid (socket) so a good match means full, normal motion in an arc of 360 degrees.

Poor alignment for any reason can put increased pressure or uneven pressure on the humeral head (round end of the humerus or upper arm bone that fits into the socket). The increased load can wear the bone down resulting in osteoarthritic degenerative changes. One of the pathologic changes that can be present in patients who develop these degenerative changes is known as retroversion. This term describes a tipped position of the socket as it sits inside the scapula. Normally, the relationship between the socket and scapula should be one where the socket is perpendicular to the scapula.

Studies show that 10 to 15 per cent of patients receiving a total shoulder replacement later develop loosening of the glenoid component (socket side of the implant). Loosening is observed on X-rays as osteolysis (bone loss as the body resorbs bone cells). It appears that retroversion (the tipped back position) of the socket may contribute to the osteoarthritic degenerative changes in the first place and may also be linked with osteolysis leading to loosening.

When there is too much retroversion, the surgeon tries to correct the problem. This correction can be done by shaving or cutting away excess bone along the front of the glenoid. The goal is to create a glenoid (socket) that is as close to perpendicular to the scapula as possible.

In some cases, the surgeon is unable to obtain a perfect fit with complete correction. To get complete correction of glenoid retroversion would require taking off too much bone. It is better to remove as much bone as possible to re-align the glenoid but without taking so much that it was no longer possible to insert the glenoid component.

Experts suggest that whenever possible, glenoid retroversion should be corrected to within 15 degrees before placing the implant into the shoulder. Surgeons are advised to use advanced imaging studies to look for pathology (i.e., problems with alignment, presence of bone deficiency) preoperatively. It sounds like your surgeon made every effort to do this for you but you may want to revisit this conversation at your next appointment and ask for more details.