What happens when glenoid version and inclination are "corrected"?

Posteriorly augmented glenoid components are increasingly being advocated for use in anatomic total shoulder arthroplasty. As pointed out in Augmented anatomic glenoid components - are they necessary? their value in terms of improving clinical patient outcomes is yet to be demonstrated. In addition to their increased cost, their use may be associated with increased loosening moments and difficulty in fitting the component to the glenoid bone.

  

Furthermore, the use of stepped, wedged, or half wedged glenoid components assumes that the two concavities in an eroded glenoid lie with one anterior and the other posterior. 

However it has become evident that the pathologic concavity need not be confined to the posterior direction and is not infrequently in the posterior superior aspect of the glenoid.

As a result, it may not be well fit by a posteriorly augmented glenoid component.

The authors of Three-dimensional analysis of biplanar glenoid deformities: What are they and can they be virtually reconstructed with anatomic total shoulder arthroplasty implants? discuss the three dimensional deformity in the arthritic glenoid and its implications for the use of augmented components. They defined "biplanar" glenoid deformities as those with a combined increase in both superior inclination and retroversion and suggest that these deformities are associated with difficulties in glenoid implantation and inferior clinical outcomes.

They analyzed 268 patients with glenohumeral osteoarthritis indicated for total shoulder arthroplasty.  Glenoids with superior inclination ≥10˚ and retroversion ≥20˚ were considered to have biplanar deformity. 49% of these shoulders had type B2 pathoanatomy. The direction of the deformity was directly posterior in 57% and posterior superior in 24%.

Their parameters for acceptable glenoid reconstruction included glenoid polyethylene implant position with ≥ 90% seating and less than 20% cancellous bone exposure, no central peg perforation, no more than a single peripheral peg perforation, and maintenance of prosthetic joint line lateral to pathologic joint line. 

Accepting less correction increased the rate of satisfactory reconstruction and decreased the planning system's suggested use of augmented glenoid components:

(1) The shoulders were first virtually planned for anatomic TSA attempting correction to neutral inclination and version.  Virtual aTSA planning indicated that 41% of the shoulders could not be reconstructed to neutral inclination and version using any implant. Of those that could, the system suggested that 94% have augmented implants. 

(2) The shoulders were then virtually planned for anatomic TSA accepting correction to 5˚ superior inclination and 10˚ retroversion. Virtual aTSA planning indicated that 10% could not be reconstructed with any implant.  Of those that could, the system suggested that 58% have augmented implants.

Final implant insertion commonly involved removal of substantial amounts of bone,  unseating in the posterosuperior quadrant, cancellous exposure in the anteroinferior quadrant, and vault perforation.

As the authors point out despite classical recommendations for 80% as the threshold for adequate glenoid implant seating, recent evidence suggests that even with 84% seating, the risk of glenoid loosening increases by up to 28% compared to full backside support. Seating values below 90% are associated with increases in bone stress and critical cement volumes. Furthermore, the importance of subchondral bone preservation is well-established, but specific thresholds for the amount of cancellous bone exposure are not defined. 

Comment: This is an important study. It makes us ask, is it more important to "correct" the glenoid pathoanatomy or to preserve glenoid bone stock and "accept" increased glenoid version and inclination? (see Glenoid version: acceptors and correctors). How should a surgeon optimize version, inclination, cancellous bone exposure, and component seating? Many of the publications attempting to address these questions are based on finite element analysis, simulation modeling, in vitro studies using Sawbones, theory, or studies using outdated components (e.g. those with keels or non-ingrowth pegs).  These studies can create a view of a "correct time zero implant position" or "acceptable resurfacing parameters" that may or may not relate to the outcome of the patients we treat. 

This study points out that correcting a biplane deformity to neutral version and inclination frequently frequently results in peg perforation, exposure of subchondral cancellous bone and inadequate backside support of the implant.

It may be that the most robust approach to glenoid component placement is to conservatively ream the glenoid face to a single concavity, accepting glenoid version and inclination, preserving maximal bone quality and quantity, and completely seating a standard round backed glenoid component that matches the reamed concavity. 

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Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).
Shoulder rehabilitation exercises (see this link).

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Shoulder arthroplasty with anterior glenoid bone deficiency - augmented glenoid or posteriorly eccentric humeral head?

Total shoulder arthroplasty with an augmented component for anterior glenoid bone deficiency.

These authors present 5 patients having total shoulder arthroplasty using an anteriorly augmented glenoid component. The preoperative diagnoses were anterior glenoid erosion in 2 patients, and 1 patient each with malunited glenoid fracture, nonunited glenoid fracture, and post-traumatic arthritis. The mean age at the time of surgery was 67.4 years (range, 53-75 years).

At an average of 33.2 months (range, 21.9-43.2 months) after surgery no patient had demonstrated radiographic or clinical signs of glenoid component loosening or instability. 

Comment: Anterior glenoid erosion predisposes the shoulder to anterior instability. As shown in this figure from the paper, it can usually be identified on a standardized axillary x-ray.

These authors have reported the use of an augmented glenoid component in the management of five such shoulders with durable results.

An alternative approach is to use a posteriorly eccentric humeral head component with a standard glenoid component accepting the glenoid anteversion as shown in the case below. This approach preserves the maximal amount of glenoid bone stock.

The posteriorly eccentric humeral head component has also improved useful in the management of failed arthroplasty with anterior glenoid bone deficiency, again accepting the anteversion of the glenoid.

The posteriorly eccentric humeral head can also manage post traumatic deformity in which the head is posteriorly malunited.

And one final case posted along with post surgical video showing the functional level achieved.

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Posteriorly augmented glenoid components - computing how much bone is lost on insertion

Augmented glenoid component designs for type B2 erosions: a computational comparison by volume of bone removal and quality of remaining bone

These authors used a computational modeling was to compare the volume of glenoid bone that would need to be removed in the implantation of three different designs of posteriorly augmented glenoid components in the management of B2 genoid erosion. They 'virtually implanted' a full-wedge, a posterior-wedge, and a posterior-step in 3-D reconstructions of 16 patients with B2 glenoids, correcting retroversion to 0° and 10°.

Importantly the amount of bone removed with these implants ranged from 1500 to 3000 cubic millimeters. When correcting to 0°, the posterior-wedge implant removed less bone than the posterior-step and the full-wedge. 

The residual glenoid bone density with the posterior-wedge was significantly greater than with the posterior-step.

Comment: This is an interesting study, suggesting that bone removal is necessary for fitting posteriorly augmented glenoids to the pathoanatomy encountered in glenohumeral arthritis. 

We have posted this concern previouslyl

Their implant fitting was virtual and not actual: implants could be manipulated to rotate (clockwise/ counterclockwise and superoinferior) and to translate (anteroposterior and superoinferior). The instrumentation for fitting the glenoid bone to the back of the glenoid component would seem to be quite complex. While the authors suggest that it would be best to use computerized

preoperative planning software making use of 3D CT-based models of the glenoid with properly sized implants, the problem of developing instrumentation to implement the plan remains.

While the authors conclude that " Augmented components can provide a bone-preserving option for B2 glenoid management." that statement is only correct if B2 glenoid management involves correction of retroversion. Our approach is manage the B2 glenoid by conservatively reaming only enough to convert the biconcavity to a single concavity without attempting to change version. See also this related article. this one, and this one as well.

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The variable biconcave glenoid, a challenge for fitting posteriorly augmented and step-cut components

Quantification of the position, orientation, and surface area of bone loss in type B2 glenoids

These authors evaluated 55 type B2 glenoids using computed tomography to create three-dimensional reconstructions.

They found the maximal erosion was usually posterior - inferior (8 o'clock in the right shoulder and 4 o'clock in the left shoulder), but there was a substantial degree of variability.  The line of erosion was curved in 35% of the cases. The pathological concavity accounted for an average of 44% ±  12% of the overall glenoid surface. The pathological concavity was flatter (radius 37mm ± 8) in comparison to the normal glenoid (radius 34mm ± 7). 

Comment: It would be of interest to know what percent of the total population of arthroplasty shoulders these 55 B2 glenoids represented.

The authors point out that the challenges in fitting the variable B2 pathology (such as that shown above) with posteriorly augmented or step-cut glenoid components.

Reaming and subsequent bone removal to accommodate posteriorly built-up glenoid components carries the risk of excess bone removal, reducing the quality and quantity of the remaining glenoid bone and leading to potentially compromised implant stability.

In our approach to prosthetic glenoid arthroplasty, we do not attempt to correct glenoid version, but rather we ream the glenoid bone as conservatively as possible to a single concavity, preserving glenoid bone stock.

As suggested in another recent related article "Glenoid component loosening in total shoulder arthroplasty may be prevented by component placement on a congruent and adequate bony surface."

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Glenoid component retroversion - what to do about it?

It is recognized that glenoid loosening is the leading cause of failure in total shoulder arthroplasty and that the risk of this complication is increased with increased glenoid deformity and glenoid bone loss.

Champions of special glenoid components state that "studies have shown that adequate correction of glenoid disease and accurate placement of prosthetic components are necessary to restore normal glenohumeral motion", yet the references in support of this statement (Effect of glenoid deformity on glenoid component placement in primary total shoulder arthroplasty and Glenoid implant orientation and cement failure in total shoulder arthroplasty: a finite element analysis) are based on computer simulations and finite element analyses rather than clinical data.

While has been said that ideal glenoid position is close to perpendicular to the plane of the scapula with the center peg of the component within bone and that the goal of glenoid implantation is to correct the glenoid version, this is but an hypothesis: it has not been demonstrated in clinical practice that correction of a retroverted glenoid to this position or that avoidance of peg penetration yield better results.

Postoperative humeral subluxation is associated with poor outcomes,  However a recent study found that there was no significant correlation between posterior humeral subluxation and postoperative glenoid version.

Thus the recent interest in augmented glenoid components needs to be tempered while we await a matched comparison between this approach and, for example, accepting a reasonable amount of retroversion and a reasonable amount of peg penetration while using asymmetric humeral heads and rotator interval plication to control the static posterior humeral head subluxation.

"Augmented glenoids are an important and innovative option; however, there is little evidence accessible to surgeons to guide in the selection and potential outcomes of these augmented implants."

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A computer model of a posteriorly augmented glenoid component

Correction of acquired glenoid bone loss in osteoarthritis with a standard versus an augmented glenoid component.

These authors modeled the reconstruction of shoulders with posterior bone deficiency and increased retroversion using a three-dimensional computer surgical simulation. They modeled both a standard glenoid component having a uniform thickness and a posteriorly augmented component.

Their model predicted 4.5 mm more medialization of the joint line with the standard component in comparison to the posteriorly augmented glenoid component. 

Comment: This is a report of a computer simulation. As the authors point out, " The importance of decreasing medialization while correcting excessive glenoid retroversion is not fully understood but may improve joint stability and strength of the shoulder by restoring better tension of the rotator cuff." However, in the actual practice of shoulder arthroplasty in vivo, the tension of the rotator cuff is optimized by the height of the humeral components, which can move the center of rotation to the position where mobility and stability are optimized. A tendency for posterior instability can also be managed by the use of asymmetric humeral head components and rotator interval plication.

At this point the clinical effectiveness and durability of augmented glenoid components have yet to be demonstrated. We will follow with interest.

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Glenoid component liftoff with posterior superior loading

Liftoff resistance of augmented glenoid components during cyclic fatigue loading in the posterior-superior direction

This study was funded by the company making the stepped glenoid design and all of the authors receive payments from the company.

The authors point out that most patients with glenohumeral osteoarthritis have posterior bone loss and that this posterior bone loss is associated with an increased risk of posterior instability and glenoid component failure. The authors and others have advocated the use of a posteriorly augmented glenoid component to lessen these risks, although the superiority of this approach over conventional means remains undocumented in clinical practice.

One of the concerns about posteriorly augmented glenoids is that they provide an increased lever arm for loosening with eccentric loading. The authors test the hypothesis is that a stepped augmented glenoid component will have less mechanical liftoff than augmented components of varying designs without a step. In a Saw Bones model, they compared four different prototypes in a model where a 170-lb compressive load and 4 mm of posterior-superior translation of the humeral head was applied for 100,000 cycles while anterior glenoid liftoff was measured. Each design changed the angle of the glenoid by 13 degrees. 

They found that the stepped glenoid component had significantly lower liftoff values than the other augmented designs. However, the stepped glenoid had approximately twice the liftoff of the non-augmented glenoid.

The concerns regarding the use of the stepped glenoid include (1) the risk of liftoff with eccentric loading, as investigated in this study, (2) the potentially increased risk of cold flow of the thickened posterior aspect of the component with years of eccentric loading and (3) the challenge of effecting an accurate match between the complex back side geometry of the stepped glenoid and the glenoid bone in the clinical setting.

Until long term clinical followup of this design becomes available, we continue to use a standard non-augmented glenoid component for total shoulders in the face of glenoid retroversion or a ream and run procedure. We do not attempt to correct glenoid retroversion with bone grafts or augmented components. Any tendency for posterior instability is managed with eccentric humeral heads and or rotator interval plication.

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You may be interested in some of our most visited web pages including:shoulder arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery.


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