These authors studied the use of a stepped augmented glenoid component for management of Walch B2 (n=29) and B3 (n=21) glenoids and compared the radiographic and clinical outcomes at short-term follow-up with those achieved with a non-augmented component of the same design in Walch A1 glenoids (n=42).
Sequential 3-dimensional (3D) computed tomography (CT) imaging was performed preoperatively, within 3 months postoperatively with metal artifact reduction (MAR) to define implant position, and at a minimum of 2 years postoperatively with MAR.
Preoperatively, these images showed that the alignment of the humeral head to the glenoid (HGA - represented by the circles in the graph below) was independent of glenoid version. Type B3 (yellow symbols) showed centering of the humeral head on the glenoid that was comparable to type A1 (blue symbols). On the other hand, the alignment of the humeral head to the scapular body (HSA - represented by the triangles) was strongly related to glenoid version.
Similarly at two years after surgery the humeroscapular alignment (but not the humeroglenoid alignment) was closely related to glenoid version.
The desired implant placement was achieved in all (100%) of the 42 A1 glenoids, 27 (93%) of the 29 B2 glenoids, and 15 (71%) of the 21 B3 glenoids.
Radiographic followup at two years showed:
A1 glenoids: Central peg osteolysis (CPO) was present in 5% of the A1 glenoids. 40% had glenoid component shift.
B2 glenoids: There was only a small difference in the frequency of CPO between B2 glenoids with the augmented component (10%) and A1 glenoids (5%) with the standard component. The short-term clinical and radiographic results were equivalent to those for patients without glenoid bone loss (Walch A1) treated with a non-augmented component. 55% had glenoid component shift.
B3 glenoids: Central peg osteolysis (CPO) with or without implant shift occurred in a higher percentage of B3 glenoids treated with the augmented glenoid component (29%) than A1 glenoids treated with a standard component (5%) B3 glenoids were associated with more component medialization relative to the premorbid joint line compared with A1 and B2 glenoids. 62% had glenoid component shift.
The two year clinical outcome scores were not different for the three glenoid types.
Comment: This authors have continued their careful and thoughtful analysis of arthritic glenohumeral anatomy. Their observations on glenoid component shift and central peg osteolysis obtained with metal subtraction imaging provide knowledge that informs our understanding and management of shoulder arthritis.
They point out both the severity and the shape of glenoid bone loss are important when considering the type of glenoid component to use and its location in aTSA. Use of the stepped augmented glenoid component requires more anterior glenoid reaming to correct pathologic glenoid retroversion in moderate-to-severe B3 glenoids, resulting in implant medialization. These B3 glenoids had a higher rate of central peg osteolysis and persistent postoperative joint-line medialization relative to the premorbid joint line. They do not recommend use of the stepped augmented glenoid component for correction of severe B3 glenoid retroversion that requires excessive anterior glenoid reaming.
Recognizing that high degrees of retroversion, bone loss and humeral head decentering on the glenoid are indicators of worse pathoanatomy and that each of these - separately or in combination - can negatively affect the durability of the arthroplasty, several questions arise:
(1) How important is it to re-establish the premorbid joint line; how much medialization of the the joint line be compensated for by modification of the prosthetic head curvature and thickness?
(2) How important is it to re-establish the premorbid version in the B2 glenoid at the expense of removing sclerotic glenoid bone; how much abnormal glenoid retroversion be compensated for by using soft tissue balancing and anteriorly eccentric humeral components to center the humeral head?
(3) How important is it to re-establish the premorbid version in the B3 glenoid at the expense of removing sclerotic glenoid bone; since the humeral head is centered in the glenoid is it necessary to change the version?
(4) How important is it to avoid peg perforation; might perforation of the glenoid neck by the central peg actually enhance fixation as it appears to do with many designs of reverse total shoulder?
In sum, what is the best way to balance bone preservation vs "correction" of the pathoanatomy?
