Posterior glenoid bone loss and total shoulder arthroplasty

Two years ago a middle age patient presented with pain, stiffness and a sensation of posterior instability of the right shoulder. There was no history of seizures or prior injury to either shoulder. The exam showed stiffness, pain and posterior translation as the arm was elevated. X-rays showed posterior superior displacement of the humeral head on an eroded glenoid.

The patient wished to avoid a reverse total shoulder arthroplasty and asked to have an anatomic total shoulder. Two years after a total shoulder with a standard glenoid component,  the patient has a comfortable, stable and functional shoulder. Current x-rays show centering of the humeral head in the prosthetic glenoid without evidence of instabilty or loosening.

Interestingly the left shoulder is becoming similarly symptomatic and has the radiographic appearance shown below.

The patient desires a similar procedure on the left.

Comment: This pathology is unusual in our experience. For this active patient, we elected the most bone-conserving method of reconstruction. Should this fail down the line, there would be sufficient bone stock for a reverse total shoulder.

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Total shoulder outcomes and value for arthritis with concentrically and eccentrically eroded glenoids

The effects of glenoid wear patterns on patients with osteoarthritis in total shoulder arthroplasty: an assessment of outcomes and value

These authors conducted a comparative cohort study of 309 patients with a total of 344 TSA procedures for primary glenohumeral osteoarthritis. 196 had concentric wear by CT scan and 148 had eccentric wear.

Notably in performing the arthroplasty, these authors did not try to make a major change in glenoid version, rather they only reamed until a concentric surface was obtained. In concentric cases, increased native retroversion of the glenoid was left uncorrected. In reaming the eccentric glenoids, a compromise in version was made between the pathological and the normal version. Anterior highside reaming was minimized in an attempt to preserve as much subchondral bone as possible. Bone graft was not used in cases of eccentric biconcavity.

At an average of over 4 years of followup, there was no significant difference in American Shoulder and Elbow Surgeons (ASES) score in the concentric group (80.8 ± 20.8) compared with the eccentric group (77.6 ± 21.2). Range of motion and final visual analog scale for pain score were similar between the 2 groups. 

However, radiographic evidence of gross glenoid loosening was significantly lower in the concentric group [11 of 195 (5.6%)] compared with the eccentric group [18 of 147 (12.2%)] 

The average total hospital costs for a primary total shoulder (with either a concentric or eccentric glenoid) was $15,900.

A value assessment also showed no significant difference between the concentric and eccentric groups [concentric 26.1 vs. eccentric 25.5 (ΔASES score/$10,000 hospital cost) . The cost included preoperative, intraoperative, and postoperative hospital costs associated with the admission, but apparently not the surgeon's fee.

Revision rates were similar between the concentric group [4 of 195 (2.0%)] and the eccentric group [3 of 147 (2.0%)]. The average total hospital costs for a revision were $37,449.

Comment: This is an interesting study that points to the difficulties in managing the posteriorly eroded glenoid.

While the discussion includes the statement that for eccentric glenoids, "... greater economic value could be gained by investing in advanced surgical instrumentation (i.e., patient specific) and new implant options (i.e., augmented glenoids, reverse shoulder arthroplasty)." - it remains to be seen if any of these options yield superior outcomes for the eccentrically eroded glenoid.

Finally, the terms 'concentric' and 'eccentric' do not fully describe the pathoanatomy. For example,  the authors state that "concentric glenoid wear demonstrates a symmetric distribution of bone sclerosis, cyst formation, and bone erosion. It is considered uniconcave only and is independent of glenoid version and glenohumeral subluxation measurements, as shoulders with increased native retroversion or subluxation are still considered concentric as long as there are no signs of asymmetric wear." Thus it would appear that the highly abnormal glenoid shown on the image below would reconsidered 'concentric'.

                                   

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Technique for the reverse total shoulder for the BAT (bad arthritic triad)

Technique for Reverse Total Shoulder Arthroplasty for Primary Glenohumeral Osteoarthritis with a Biconcave Glenoid

This technique paper is authored by some true experts in reverse total shoulder arthroplasty and merits a close read. It deals with the use of the reverse total shoulder to manage the BAT (bad arthritic triad): glenoid retroversion+glenoid biconcavity+posterior subluxation of the humeral head on the glenoid. They point out that multiple authors have found unsatisfactory results with conventional total shoulder replacement in the presence of the BAT. Specifically, the authors recently published "Results of anatomic nonconstrained prosthesis in primary osteoarthritis with biconcave glenoid" in which they retrospectively evaluated 92 anatomic TSAs performed in 75 patients with primary osteoarthritis and a biconcave glenoid. At an average follow up of 77 months 15 revisions had been performed for glenoid loosening, posterior instability, or soft tissue problems. Only 66.3% of patients were very satisfied or satisfied. Glenoid loosening was observed in 20.6% and was significantly associated with the depth of posterior bone erosion and posterior humeral head subluxation.

We have provided a previous post on the results of this surgical technique.

We have found that some BAT shoulders can be managed with a ream and run procedure, however it older individuals with substantial glenoid bone loss the reverse total shoulder with a humeral head bone graft is a consideration as explained here.

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Ream and run for the posteriorly eroded type B2 glenoid with posterior humeral displacement

At a time when some surgeons are considering special plastic glenoid components or even reverse total shoulders for arthritic shoulders with major posterior glenoid erosion and posterior displacement of the humeral head on the glenoid, we continue to apply the ream and run technique to selected patients with this all-too-common pathology.

Here is a case from our OR yesterday in a very active gentleman in his forties. Note that the standardized x-ray revealed his glenoid pathology without a CT scan.

Using an eccentric humeral head and a rotator interval plication, his shoulder was stabilized. Note in the films below, his glenoid retroversion was not changed, yet his humeral head is now centered in the new glenoid concavity.

 In spite of having a very stiff shoulder before surgery, he was able to elevate his arm passively to 150 degrees on the evening of surgery.

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Pattern of erosion in type B glenoids - is there such thing as a B1?

Three-dimensional computed tomography scan evaluation of the pattern of erosion in type B glenoids

The humeral head is often posterior displaced and the posterior glenoid is often eroded in glenohumeral osteoarthritis and in capsulorrhaphy arthropathy. Posterior head displacement without glenoid erosion is referred to as a Walch B1 type and posterior head displacement with posterior glenoid erosion is refferred to as a Walch B2 type glenoid, although intermediate forms are common.

The authors performed 3D reconstruction of 24 type B1 glenoids and 48 type B2 glenoids. Posterior erosion averaged 4.2 mm (range 1.7 to 9.6 mm).  The erosion was typically in the posteroinferior direction (119°; SD, 26.8).

While the authors stated that 3-D scans are necessary to evaluate the glenoid, we have found that a standardized axillary view provides the information necessary for surgical reconstruction. However, this article is important in that it demonstrates that all type B glenoids (i.e. those with posterior displacement of the humeral head)  have at least some degree of posterior erosion. Thus, all type B glenoids may be type B2s with a degree of biconcavity.

Posterior inferior glenoid erosion is important because it favors posterior instability of the elevated arm.

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The Walch B2 glenoid in a young active person - a recurrent theme.

This morning I received these images from an active 40+ individual who reports the inability to lift the left shoulder much more than parallel to the ground for nearly 4 years.  In the beginning pain was the primary issue and now the problem is lack of use. The individual desires to continue sports and weight training.

We share this case with you for a couple of reasons. First, the AP view (first image below) makes this look like a straightforward case of osteoarthritis, but the axillary view (second image) shows that in fact it is a type B2 glenoid with biconcavity and severe posterior displacement of the humeral head on the glenoid. No need for a CT scan to show the pathology!

The second reason for showing this case is that it is now recognized that this pathology has been associated with a high rate of glenoid component loosening, instability and wear if a total shoulder arthroplasty is performed. Currently some surgeons are recommending a reverse total shoulder for this pathoanatomy, however that would seem suboptimal for a person in middle age desiring to be physically active.

These situations are not rare: osteoarthritis and capsulorrhaphy arthropathy not uncommonly produce this pathoanatomy. Our practice is to offer such shoulders a ream and run procedure, recognizing that the surgery is technically difficult and the rehabilitation tougher than with a 'cake walk' type A glenoid. See such a case here.

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Measuring glenoid version and the position of the humeral head on the glenoid.

Here is the method we use for characterizing glenoid retroversion and the position of the humeral head relative to the glenoid on the axillary view plain film.

See below: the glenoid version is represented as the angle between a line connecting the anterior and posterior edges of the glenoid (green line) on one hand and a line drawn down the center of the scapular body on the other (red line).

See figure below: the anteroposterior position of the humeral head on the glenoid is represented as the ratio of the length of the line segment drawn from the anterior lip of the glenoid to the center of the glenohumeral area of contact (red line) to the length of the line segment drawn between the front and back lips of the glenoid (green line).

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Primary glenohumeral osteoarthritis: clinical and radiographic classification. The Aequalis Group.

Primary glenohumeral osteoarthritis: clinical and radiographic classification. The Aequalis Group.

This often-quoted article forms the basis for what has become known as the Walch classification of pathoanatomy of the arthritic shoulder.

The authors obtained CT scans on 151 shoulders with primary osteoarthritis. They found that the average glenoid was retroverted and that posterior subluxation was present in almost half of the cases. They divided the radiographic appearance into type A without posterior erosion or displacement and type B with posterior erosion and/or displacement. They noted that posterior subluxation did not correlate with glenoid retroversion.  Importantly, they make an observation overlooked by many surgeons: posterior instability is not necessarily resolved by normalizing glenoid version. They suggest that persistent posterior subluxation after total shoulder arthroplasty may give rise to what we have described as 'rocking horse' loosening of the glenoid component.

The categories of glenoid anatomy are shown in their diagram below.

This is very useful in showing some of the ends of the spectrum. It is apparent, however, there are many shades of grade between A1 and A2, between A1 and B1, between B1 and B2, between A2 and B2, and between B2 and C.

We've found that it is quite straightforward to see the glenoid on a properly done axillary view.

So, to show the 'shades of grade' issue, here are a few examples of what seem to be A1 glenoids.

First, minimal joint space narrowning

Next central thinning

Next anterior thinning

And next posterior thinning

Moving on to A2's, some appear on the borderline

While others are more obvious

Some A2's seem to border on B1's

 And others show an anterior wear pattern, not part of the Walch classification.

Here are few B1's.

But some B1's border on B2's

Then there are the somewhat more obvious B2's

We reserve the "C" classification for glenoid dysplasia

All of this is to make two points: (1) CT scans are not necessary to determine glenoid pathology and (2) the categories as described in this article represent classic examples, but many shades exist between them. It is the classic issue of using categories to represent parametric variables, such as the degree of erosion or the posterior displacement of the head on the glenoid.

A final point. The authors propose a somewhat complex method for measuring the degree of subluxation:

 where x-x' is a line parallel to the glenoid surface, y-y' is the perpendicular bisector of the articular segment of x-x' and z-z' is a line parallel to x-x' passing through the medial third of the humeral head. This method has the problem that slight alterations in the angle at which x-x' is drawn can have a substantial effect on the apparent anterior-posterior position of the head relative to the glenoid.

We are more interested in the degree to which the glenohumeral contact is centered on the glenoid.  A subsequent post will describe a simple method for quantitating the head position relative to the glenoid.
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Glenoid morphology rather than version predicts humeral subluxation: a different perspective on the glenoid in total shoulder arthroplasty JSES

Glenoid morphology rather than version predicts humeral subluxation: a different perspective on the glenoid in total shoulder arthroplasty JSES.

This is a very important article. It indicates that glenoid shape, rather than glenoid version is the key factor in determining whether or not the humeral head is centered in the glenoid. 

There has been a lot of press recently directed at 'correcting' increased glenoid retroversion to increase stability, but these authors point out that shoulders with retroversion and a single glenoid concavity usually have the humeral head centered in the glenoid fossa. Thus, reaming the glenoid to 'normalize' the version or the use of 'steptech' glenoid components may not be necessary and may even lead to instability if the humeral head does not follow the change in version.

The reason that retroversion is not necessarily associated with subluxation lies in the concavity compression mechanism of glenohumeral stability. As long as the ball is pressed into a suitable concavity, the shoulder is stable.

With the biconcave glenoid, however, the humeral head is pressed into the posterior concavity and remains there unless the biconcavity is corrected. The correction of posterior humeral subluxation and biconcavity with a ream and run is shown in this post.

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The ream and run in the face of severe posterior glenoid erosion

One of the biggest challenges we face in shoulder arthroplasty is the posteriorly eroded glenoid.
Here's a recent example. Note that the anteroposterior view doesn't look all that remarkable.

However a well done axillary shows the problem.

We know that in this circumstance, a plastic glenoid has an increased chance of failure because of rocking horse loosening.

On the other hand, doing a hemiarthroplasty alone does not address the glenoid biconcave deformity.

Our approach starts with a conservative capsular release, preserving the inferior glenohumeral ligament complex.

Next, we convert the glenoid biconcavity into a single concavity, without trying to change the glenoid version.

We then insert the humeral trial component to see if there is unwanted posterior translation - a positive 'drop back' sign when the arm is lifted forward,

If this occurs, in spite of using a large sized humeral head prosthesis, we use an eccentric humeral head with the eccentricity anterior to re-center the head in the glenoid.

If a positive drop back remains, we perform a rotator interval plication.

Here are some postoperative films showing the effectiveness of these methods in centering the head in the early postoperative period, using the case above as an example.

Additional support against posterior instability can be gained by external rotation strengthening exercises.

Managing this complex situation is difficult and requires careful attention to surgical technique and postoperative care.

See this post for an example of the effectiveness of this approach.

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