Monday, August 10, 2015

Shoulder arthritis and the glenoid pathoanatomy, 50 shades of "B".

Outcomes of anatomic shoulder arthroplasty in primary osteoarthritis in type B glenoids

These authors analyzed 112 anatomic total shoulder arthroplasties (104 patients) with B glenoids. Based on preoperative computed tomography they classified 64 B1glenoids and 48 B2 glenoids.
They found a significant difference between B1 and B2 glenoids in average retroversion (11 vs.16; P <.001) and average posterior humeral subluxation (65% vs. 75%; P <.001). 

All patients underwent anatomic total shoulder using one of the following: the PROMOS shoulder system (Smith & Nephew) with either a cemented all-polyethylene pegged or keeled glenoid component; the Aequalis shoulder system with either a cemented all polyethylene pegged or keeled glenoid component; and the Aequalis Ascend shoulder system with a cemented all polyethylene anchor pegged glenoid component. 

To address either severe retroversion or a biconcave glenoid, the anterior glenoid was asymmetrically reamed to try and achieve retroversion between 0 and 10 with the limitation of removing less than 5 mm of bone. No glenoids in this cohort had structural posterior bone grafting procedures or an augmented glenoid component.

At average follow-up of 60 months (range, 23-120 months), for 50 B1s and 37 B2s there were glenoid component radiolucencies in 51.6% of the B1s and 47.9% in the B2.

Clinical outcomes were not significantly different between the 2 groups. Four revisions (4.6%) were documented for acute postoperative infection (2.3%), subscapularis failure (1.1%), and glenoid loosening (1.1%).

The authors were unable to find significant differences in clinical or radiographic outcomes for the two types of glenoids.

Comment: We now recognize that there is a continuum in "B" glenoids - between those that have minimal biconcavity to those that have severe biconcavity as shown in the diagram below. In fact as our recent posts show, there are many types and many shades of glenoid pathoanatomy.

In our experience, every shoulder with posterior humeral subluxation has some degree of biconcavity, so maybe there is no such thing as a pure B1.

This study has the problem of having used 5 different glenoid implants, making it difficult to discern the factors associated with their quite high glenoid lucent rate (50%). Without a multivariate analysis that considered not only preoperative glenoid type but also preoperative version and the type of glenoid implant, it will be difficult to discern what may be causing their glenoid lucencies. 

In our practice we treat all glenoids the same: any biconcavity is conservatively reamed to a single concavity without attempting to change glenoid version so that the glenoid component is supported with minimal bone removal. Any tendency for posterior instability is managed with anteriorly eccentric humeral heads and / or rotator interval plication.


Check out the new Shoulder Arthritis Book - click here.

Use the "Search" box to the right to find other topics of interest to you.

You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and runreverse total shoulderCTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'