The glenoid - the key to shoulder arthroplasty

The restoration of the humeral (ball) side of the arthritic shoulder is relatively straightforward. The real challenge in surgical reconstruction exists on the socket side of the joint.

The normal shoulder socket is shallow so that the range of motion of the joint is optimized. The shape of the socket has two important functions.

First it distributes forces from the arm to the shoulder blade.

A comfortable force transmission requires that the load be distributed evenly across the joint surface.

When the joint surface is not congruent with the ball, we have load concentration (recall the princess and the pea) and a painful joint.

The second function of the socket is to provide a geometry that centers the ball within it.

 The primary mechanism for this centering is concavity compression - the same mechanism by which a golf ball is centered on the tee. The tee is concave and gravity provides the compressive force. Without these factors, the ball rolls out of the tee. In the shoulder, the stability of the joint is provided by the concave shape of the socket and the muscles pressing the ball into this concavity.

This is nicely demonstrated by this video prepared by my colleague John Sides. In subsequent posts, we'll discuss some of the ways that load distribution and stability can be provided when the arthritic shoulder is surgically reconstructed.

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Failed, Unsatisfactory Shoulder Joint Arthroplasty - glenoid component loosening

As we saw in the June 27 post 59% of patients coming to us for consultation because they were dissatisfied with their total shoulder joint replacement arthroplasty had loose or worn glenoid components.

The concern about glenoid component failure comes from careful followup of patients having shoulder replacements in the past using a variety of older component designs and older techniques. 

Our shoulder fellow Lazarus published a nice paper pointing to the challenges of achieving a perfect glenoid component insertion and the effect of surgeon experience.

Ideal contouring of the bone beneath the glenoid component (as shown below) is essential as pointed out by shoulder fellow Collins.

When the bone is not properly prepared, there is a tendency to pack in a bit of cement to fill in the defect ('putty carpentry'). This is commonly seen in the posterior (back) half of the glenoid as shown below left. However, this wedge of cement is brittle and not fixed to either the component or bone so it can slip out leaving the component unsupported and at risk for loosening (below right).

The earliest sign of loosening is a dark line (radiolucency) seen on the x-ray as shown below at the "L".

From a very well done study of 333 total shoulders, here is a graph showing a 50% radiographic survivorship of glenoid components put in 10 years ago.

Loosening seems to be particularly common when the glenoid design consists of a keel that is fixed into the bone of the shoulder blade using a wad of cement as shown below left and in the color photograph of a retrieved glenoid component

Cement cures with an exothermic reaction - this heats the bone to an amount determined by the amount of cement used. Excessive cement can result in thermal death of the bone with loss of fixation as shown by the thermal camera images below.

Removing a loose glenoid component leaves a big hole in the glenoid bone, making subsequent reconstruction difficult.

We have vigorously investigated the causes of failure and ways in which the security of the component can be optimized. We continue to use a modern glenoid component in the majority of our shoulder joint replacements, because it provides predictable recovery of shoulder comfort and function

Time will tell whether the newer design and our modern techniques will improve the long term durability of the glenoid component.

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Failed, Unsatisfactory Shoulder Joint Arthroplasty - stiffness

As noted in the previous post, stiffness is a common feature among unsatisfactory shoulder joint replacements. By stiffness we mean that the shoulder is not capable, even with the help of the other arm, to move through a normal range of motion (see March 29 post). Arthritic shoulders are usually stiff (see April 5 post), so it is not surprising that stiffness may remain a problem even after joint replacement. This is why we are so interested in early post-surgical rehabilitation to maintain the range of motion achieved at surgery (see April 18 and 19 posts). In a technically well-done arthroplasty, range of motion is usually restored and maintained by these rehabilitation exercises.

However there are several surgical principles that are important to re-establishing motion to a stiff, arthritic shoulder. First is that the tight capsule around the joint must be released by sharp dissection as shown in the figure below.

Second is that the bone spurs (osteophytes) be removed to make sure they do not block motion. We refer to the inferior aspect of the joint as Pooh Corner (below left), so that we don't forget to check it and remove any possibility of unwanted contact between the inferior humerus and the glenoid.

We also check for unwanted contact in the posterior aspect of the shoulder that blocks external rotation as shown below.

This can be noted at surgery as the 'open book' phenomenon when the arm is externally rotated - the humeral head is levered away from the glenoid as shown below.

And finally, the surgeon must avoid 'overstuffing' the joint, by inserting such a large humeral head that the soft issues are put under excessive tension (bottom of the figure below) rather than one that puts the soft tissues under normal tension (top of figure below).

Overstuffing can also arise from the insertion of a thick glenoid component - this is one of several issues with metal backed components as shown below right

Finally, overstuffing can arise from varus malposition of the humeral component (the prosthesis is angled toward the socket, rather than being inserted straight) in which case the humerus along with its rotator cuff attachments is pushed away from the glenoid (W), tightening the tissues around the joint.

At surgery, we optimize the shoulder range of motion by assuring that the joint is capable of 40 degrees of external rotation

50% posterior translation

and 60 degrees of internal rotation with the arm out to the side

We refer to these as the 40, 50, 60 rules for achieving ideal soft tissue balance and avoiding an unsatisfactory arthroplasty because of intraoperative causes of stiffness. A good rehabilitation program is still essential to a good result.

If a shoulder stays or becomes stiff after a shoulder arthroplasty and if it does not respond to a good rehabilitation program, revision surgery may be considered to re-release the soft tissue, check to make sure no blocking osteophytes are present, and assure that the humeral head is of the proper size.

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Shoulder arthritis at the 2011 ASES meeting - glenoid loosening

Three papers presented at the most recent open meeting of the American Shoulder and Elbow Surgeons (February 19, 2011, San Diego) relate to the issue of glenoid component failure, even with modern components and techniques in expert surgical hands.


Out of 518 total shoulders from 10 European surgical centers using a third generation anatomic prosthesis, radiographic loosening was found in 32% at an average of 8.6 years after surgery (Walch G, Young AA, Boileau P, et al.: Patterns of loosening of a cemented polyethylene keeled glenoid component in primary osteoarthritis - Results of a multicenter study).


The Mayo Clinic group reported essentially identical results with a different prosthesis:  in 157 total shoulder arthroplasties using a cemented Cofield II keeled all-polyethylene glenoid component, 32% of the glenoids showed radiographic failure at 10 years ( Fox TJ, Foruria A, Klika B, et al.: Radiographic survival in total shoulder arthroplasty).


A multicenter French report using a modern uncemented metal-back glenoid component found that at 12-year follow-up, approximately half of the glenoid prostheses had been revised for wear or loosening (Moineau G, Morin-Salvo N, Walch G, et al.: Long-term results of anatomical total shoulder arthroplasty with metal-backed glenoid components implanted for primary glenohumeral joint osteoarthritis).


These studies indicate the need for long term followup to determine the survivorship of the glenoid component in total shoulder arthroplasty.

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Shoulder arthritis articles from the June JBJS - glenoid preparation, rocking horse loosening

The June issue of the JBJS provides a "specialty update" on 'What's New in Shoulder and Elbow Surgery'.
The authors state that 'asymmetric reaming to correct glenoid retroversion is commonly performed, but is thought to decrease the glenoid bone available for component implantation'. This is a critical point, since preservation of glenoid bone is a key element of glenohumeral arthroplasty - overzealous reaming sacrifices this precious commodity as shown below.

 It turns out that soft tissue balance, and not glenoid version, is the key element of shoulder arthroplasty stability. Thus our approach is to accept a substantial amount of retroversion, if necessary, to preserve the glenoid bone stock, as shown below, and achieve stability by soft tissue balancing.

The authors of this review suggest that it is preferable to insert a smaller sized glenoid component in less retroversion. Our experience is the opposite: shoulders are more stable with a larger glenoid component - inserted in retroversion if necessary - coupled with soft tissue balancing.

The authors of this review go on to comment on the amount of retroversion that can be 'corrected' before a pegged glenoid component would penetrate the vault. Actually, penetration of the glenoid vault by fixation pegs is not a critical consideration, in that the support of the component comes primarily from the accuracy of the contouring of the surface on which the component is placed as demonstrated by our fellow David Collins in his study on eccentric loading 

This review also comments on the use of computer-assisted technology to 'improve the accuracy of glenoid implantation'. While computer assistance yielded 'correct' glenoid version more consistently, there is no evidence presented that 'correcting' glenoid version improved stability or the clinical result. It did signficantly lengthen operative time, however.

Finally, the authors point to a randomized comparison of pegged versus keeled glenoid components. After 26 months, the keeled components had a 46% glenoid lucency rate as compared to a 15% lucency rate for the pegged components. This replicated the results of our fellow Mark Lazarus published in 2002. The superiority of peg fixation may be in part due to the unique positioning of component on the glenoid surface reamed around the central radial peg as shown below. Such precise positioning is more difficult to accomplish with a keeled component.

The superiority of pegs over keels may also be due to the ability of pegs that are not all in line to resist the 'lift off' seen with rocking horse loosening of the glenoid component.

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Ream and Run for Shoulder Arthritis - shaping the arthritic socket - research foundation 1

As the idea of the ream and run procedure progressed towards clinical application, shoulder fellows Weldon and Boorman carried out some important laboratory research on Optimizing the Glenoid Contribution to the Stability of a Humeral Hemiarthroplasty. In this study on cadaver shoulders they found that the glenoid contribution to shoulder stability (as measured by the balance stability angle) was decreased by the removal of cartilage and labrum and was restored by spherical reaming to a level similar to resurfacing the glenoid with a polyethylene component. They studied the stability of four different glenoid states:

Interestingly, they found that removal of the cartilage from the glenoid surface dramatically diminished the stability provided by the glenoid socket - especially in the posterior inferior direction (compare 'native' to 'denuded' on the figure below - the 225 degree direction is posterior inferior). This helps understand why the humeral head often starts to slip posteriorly in arthritis as shown in previous posts.

When the face of the glenoid is spherically reamed, as we do in performing a ream and run, the stability is restored - even beyond that of the normal glenoid (see 'reamed 22.5' and 'reamed 25.0' on the figure above. As the table below shows, the stability of the reamed glenoid is comparable to that of a polyethylene glenoid component.

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Total shoulder replacement: x-ray evidence of loosening

In yesterday's post, we discussed radiolucent lines (RLL's) and the possible role of heat generated in the preparation of the glenoid in their creation. Here are two x-rays showing RLL's from our artilce on
failure of the polyethylene glenoid component.

In the first, an axillary view, one can see the metal humeral component at upper left. The small metal oval in the center of the picture is a marker in the plastic glenoid component. The plastic glenoid component itself cannot be seen on x-ray. Below this oval is the keel of the component and surrounding cement shown in white, surrounded by a darker area indicated by the small arrows. This darker zone is the radiolucent line. The larger arrow points to a radiolucent line underneath the face of the plastic glenoid component.

In the second x-ray, an anteroposterior view of the shoulder, the arrows point to a radiolucent line between cement on beneath the glenoid component  (the thin white curved line) and the bone that normally would support the glenoid component. The darker area between the cement and the humeral prosthesis is the location of the face of the glenoid component.

These radiolucent lines seen on x-ray represent areas where there is no bone, cement, or glenoid prosthesis. Instead the area is filled with fibrous tissue that does not securely fix the component to the bone. As pointed out in previous posts, these lines are often progressive and lead to symptoms of glenoid component loosening.

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Total shoulder replacement: avoiding heat damage

One of the concerns about fixation of the glenoid component in total shoulder replacement is the observation that 'radiolucent lines (RLL's)' may develop between the bone on one hand and the component and cement on the other. These RLL's suggest that the connection of the component to bone is not as strong as it should be. Of greater concern is that these RLLs are often progressive, that is, the fixation of the component becomes less secure with time. This is well shown in the article by Walch et al in the SUNDAY, MAY 1, 2011 post. 

There has been little study of the factors that may contribute to the development and progression of RLL's, especially in cases where no lucent lines are seen immediately after surgery.

One factor that we have studied is the possibility of heat damage to the bone of the glenoid causing local death and resorption of the bone over time with progressive mechanical loosening.  In a study with shoulder fellows Churchill, Boorman and Fehringer, Glenoid cementing may generate sufficient heat to endanger the surrounding bone, we found that the amount of heat generated was related to the volume of cement used in fixing the glenoid component. This is because cement cures with an exothermic, or heat generating reaction. With larger amounts of cement, the temperature of bone can rise to a level that can kill the bone.

This observation led us to explore methods of glenoid fixation that used only minimal amounts of cement: precise 'carpentry' with the removal of a minimal amount of bone.

In second study by shoulder fellows Clinton and Lynch along with resident Olson, we found that reaming of the bone could cause thermal damage: Thermal effects of glenoid reaming during shoulder arthroplasty in vivo. The figure below was taken during surgery using a thermal camera. 

We found that irrigating the wound with cool saline solution at the time of reaming kept the temperature of the bone within safe limits.

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Total shoulder: the glenoid component, Part III

We have spent a substantial amount of effort in identifying causes of failed total shoulder arthroplasty; examples are the investigations of our shoulder fellows Hasan and Franta. One of the most common causes of total shoulder failure is failure of the glenoid component. In our research on this issue we have identified a number of factors, very important among which is the technique of insertion of the glenoid component. Our shoulder fellow Lazarus conducted a multicenter study in which radiographic evaluation of glenoid components demonstrated that many components inserted around the country were not well seated and or not well fixed. This may be due in part to the observation by our shoulder fellow Hasan that many surgeons doing shoulder joint replacement have less experience than those doing hip or knee surgery.

When the glenoid bone surface is not properly contoured to fit the back of the glenoid component, bone cement can be used to fill in the gaps as shown in the left hand diagram below. However, loading of the glenoid component can lead to fracture and loosening of this thin layer of cement, leading to its displacement and loss of support for the glenoid component as shown on the right hand diagram below.

In the investigation by Lazarus, glenoid component designs with pegs outperformed glenoid component designs with keels. This article also pointed out the importance of the experience of the surgeon: 80% of the glenoid components inserted by the most experienced surgeon had better cementing in comparison to 50% for the remaining surgeons. There are some other important articles relating to the effect of surgeon experience to the outcome of shoulder arthroplasty. An article by Hasan shows that 75% of shoulder arthroplasties are done by surgeons performing only one or two per year. Articles by Hammon and Jain show that surgeons performing higher numbers of shoulder arthroplasties have a lower rate of complications.

At present, the optimal approach to glenoid fixation combines (a) reaming the glenoid bone to precisely fit the back of the glenoid component

(b) drying the bone with a carbon dioxide jet to remove blood, fluid and debris before cement is inserted (as the divers among you will recognize, we use CO2 because of its solubility in water and blood, so that nitrogen bubbles (the bends) are avoided).

(c) pressurizing the cement in to the holes

(d) removing the excess cement so that none remains on the surface of the bone

(e) inserting the component so that the precise geometry of the pegs and back surface of the component meet the precise geometry of the holes and reamed surface of the glenoid bone

and (f) vigorously impacting the component into the prepared bone

This technique minimizes the amount of cement used, so that excessive heat is not generated by the curing of the methylmethacrylate, a risk pointed out by our shoulder fellow Churchill.
A detailed view of the postoperative film shown in yesterday's post reveals excellent seating of the glenoid component on the prepared bone surface with penetration of the pressurized cement into the bone (arrow) - note the absence of radiolucent lines.

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Total shoulder: the glenoid component, Part II

As per the last post, the glenoid component looks like this.

The use of a prosthetic glenoid component as a part of a total shoulder arthroplasty enables the restoration of the shape of the glenoid socket in a shoulder with arthritis where the joint space as been destroyed as shown on the preoperative x-rays below.

While the glenoid component cannot be seen directly on the postoperative x-ray, the space between the metal ball and the bone of the glenoid occupied by the glenoid compnent is evident on the post operative films from a patient we treated last week. The staples used to closed the skin are shown at left. The careful observer will also note that the humerus has been moved away from the scapula, re-tensioning the muscles around the shoulder. Also, faintly visible within the bone of the scapula to the right, one can see a thin white line representing a metal marker within the plastic socket component.

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