These authors sought to evaluate glenoid component position and radiolucency following anatomic total shoulder arthroplasty (TSA) using sequential 3-dimensional computed tomography (3D CT) analysis in a series of 152 patients (42 Walch A1, 16 A2, 7 B1, 49 B2, 29 B3, 3 C1, 3 C2, and 3 D glenoids) undergoing anatomic TSA with a polyethylene glenoid component.
Sequential 3D CT analysis was performed preoperatively (CT1), early postoperatively (CT2), and at a minimum 2-year follow-up (CT3).
The preoperative CT was used to characterize the "premorbid" anatomy of the shoulder, that is what it was likely to have looked like before the onset of arthritis.
Glenoid component shift was defined as a change in component version or inclination of ≥ 3 degrees from CT2 to CT3.
Glenoid component central anchor peg osteolysis (CPO) was assessed at CT3.
Glenoid component shift occurred from CT2 to CT3 in 78 (51%) of the 152 patients.
CPO was seen at CT3 in 19 (13%) of the 152 patients, including 15 (19%) of the 78 with component shift; increased inclination was the most common direction
Most (81%) of the patients with glenoid component shift did not develop CPO.
Walch B2 glenoids with a standard component and glenoids with higher preoperative retroversion were associated with a higher rate of shift, but not of CPO.
B3 glenoids with an augmented component and glenoids with greater preoperative joint-line medialization were associated with CPO, but not with shift.
More glenoid component joint-line medialization from CT2 to CT3 was associated with higher rates of shift and CPO.
A greater absolute change in glenoid component inclination from CT2 to CT3 and a combined absolute glenoid component version and inclination change from CT2 to CT3 were associated with CPO.
Neither glenoid component shift nor CPO was associated with worse clinical outcomes.
Most of the components shifting occurred without deformation of the implant; however, a subset of 14 components demonstrated bending of the central anchor peg between CT2 and CT3 without CPO.
CPO was associated with a higher rate of shift with larger absolute changes in glenoid component version and inclination and a greater odds of component medialization from CT2 to CT3 compared with cases without CPO, findings suggestive of early implant loosening and subsidence that raise concern about eventual implant failure.
Comment: This is a very thorough and interesting study. It seems that patient reported shoulder comfort and function is relatively insensitive to component shift or central peg osteolysis at a minimum of two years after arthroplasty. It also appears that in the great majority of cases using a fluted central peg, there is bone ingrowth into the central peg that persists at two years. It is interesting that the central peg can bend with component shift without loosening. Preoperative retroversion and version correction appear to be associated with an increased rate of component shifting.
We will continue to learn from these authors which surgeon-controlled variables will optimize the long term success of shoulder arthroplasty for our patients: what is the best way to manage preoperative retroversion? what is the best way to manage preoperative joint line medialization? To answer these questions carefully controlled studies will be required to determine how much version correction is needed and, if version correction is important, how can it be best accomplished.
