Wednesday, June 14, 2017

Total shoulder: pegged or keeled glenoid?

Comparison of Pegged and Keeled Glenoid Components for Total Shoulder Arthroplasty A Systematic Review

These authors conducted a systematic review of level I, II, and III studies comparing the development of radiolucent lines and glenoid failure after total shoulder arthroplasty with pegged or keeled glenoid components was conducted. Four articles were included in the final analysis with a total of 203 total shoulder arthroplasties comprising 107 pegged and 96 keeled glenoid components.

They found that the development of radiolucent lines was less likely with pegged glenoid components with a risk difference of −0.32 (95% CI −0.62, −0.03) favoring the pegged design. There was no statistically significant difference in the rate of radiographically at-risk glenoids, clinical glenoid failure, or the composite endpoint.

Comment: There are many factors that influence the survivorship of a glenoid component. First and foremost are (1) the quality of preparation of the glenoid bone that supports the component and (2) the soft tissue balancing that assures centering of the humeral component on the glenoid. With respect to pegs vs. keels,

it is important to recognize that all pegged designs are not alike. Some offer out of plane anterior and posterior pegs with a fluted central peg for bone ingrowth

while others offer only smooth pegs all in the same plane.

Such differences can confound the comparisons published in the literature. 

While it is technically more demanding, we prefer a pegged glenoid with a central fluted peg because it offers ingrowth fixation without a metal back and because it preserves the glenoid bone stock that is lost when a slot is created for a keeled component.

Our approach to glenoid arthroplasty briefly described here.
The goals for total shoulder arthroplasty include establishing maximal stability and maximal contact area for distribution of the humeral load to the glenoid. In addition, the procedure needs to achieve support of the prosthetic glenoid by precisely contouring the bone supporting it as well as secure and durable fixation of the component to the underlying bone. In that glenoid bone stock is a most precious commodity when performing shoulder arthroplasty and in that excessive reaming has been associated with increasing rates of glenoid component failure, preservation of glenoid bone is a high priority. Both bone preservation and the quality of fixation are enhanced by the precise drilling of the holes for peg fixation of a glenoid component rather than the less precise preparation for a keeled component. This precision has the additional benefit of minimizing the amount of cement used, reducing the risk of thermal damage.

The glenoid is exposed by excising the labrum from the bony glenoid, removing any tissue that may interfere with complete glenoid component seating. If the preoperative axillary view shows posterior humeral head decentering, the inferior glenohumeral capsule is left intact.

The size of the glenoid component is determined using round back glenoid trials. The center of the glenoid face is marked and a burr hole is made at this point to guide the drill for the reamer. The angle of glenoid reaming is adjusted to preserve as much glenoid subchondral bone as possible. Glenoid bone is preserved by orienting the reaming and the component along the glenoid axis rather than the scapular axis. Reaming is always started by hand; power is used very sparingly except in hard bone. Appropriate positioning of retractors facilitates this reaming. In that the goal of reaming is to conservatively establish a single glenoid concavity, it is important to check the progress of reaming frequently so that the reamer does not inadvertently remove more bone than necessary. The adequacy of the glenoid bone preparation is checked by inserting the round back glenoid trial component and ensuring that it does not rock even when eccentric loads are applied to the rim.

After the hole for the central peg is drilled, the peripheral drill guide is inserted into the central peg hole and set firmly on the reamed glenoid surface to precisely guide the drilling of the additional holes for the peripheral pegs. The drill guide needs to be oriented to take maximal advantage of the available glenoid bone; care must be taken to assure that the drill guide sits flush on the reamed glenoid surface so that the hole position will match the position of the component pegs. After each peripheral hole is drilled, a derotation peg is placed in it to maintain alignment of the guide while the subsequent holes are completed and to make sure that the hole is of the proper depth. Each hole is checked to determine whether it penetrates the scapula.

After irrigation with antibiotic containing saline solution, the holes are cleaned and dried with a spray of sterile CO2 gas removing all tissue and fluid from the holes so that the injected cement will directly contact bone without interposed fluid or the blood clot that results from the use of thrombin. It is apparent that neither fluid nor clot will turn into bone or cement, so the presence of either will compromise the quality of fixation.

Unpenetrated holes are pressurized with a syringe. Penetrating holes are cemented, but the cement is not pressurized. The use of a carbon dioxide gas spray and cement pressurization has essentially eliminated the problem of postoperative radiolucent lines


No cement is placed on the bony face of the glenoid; if the back of the glenoid component matches the prepared bony face, there is no advantage to an interposed layer of cement, which could fail and become displaced and consequently leave the glenoid component relatively unsupported as shown below.

While some surgeons have been concerned about avoiding penetration of the holes for glenoid fixation, glenoid perforation does not appear to affect the clinical outcome of total shoulder arthroplasty. It is evident, however, that penetration is more likely in severely pathological glenoids that have substantial medial or posterior bone erosion and for this reason, rather than the penetration itself, shoulder arthroplasty may be less successful in cases of particularly severe arthritic deformity.

Reamed bone retrieved during the glenoid preparation (reaming and drilling) is used to create a bone paste that is interposed between the flutes of the central anchor peg to help facilitate bone tissue integration. The glenoid component is firmly impacted into position, assuring that its posterior aspect is completely seated on bone by sliding a finger over the back of the component to feel the bone that should lie immediately beneath. The joint space is checked to assure that no bits of cement or bone remain. From the time the glenoid component is in place, it is important to prevent the humerus from dislodging it by the ‘bottle cap’ mechanism; we use a broad flat retractor to safely deliver the proximal humerus into the wound after the glenoid has been implanted.

Here is a related post: Rates of Radiolucency and Loosening After Total Shoulder Arthroplasty with Pegged or Keeled Glenoid Components

There is no question that survivorship of the glenoid component is the key to survivorship of a total shoulder arthroplasty. We have presented our approach to glenoid arthroplasty here.

This is an important study in that it seeks literature evidence on the cost-effectivenss of pegged vs. keeled glenoid components with particular emphasis on the risk of revision surgery. After a thorough analysis of the published data, they found that pooled risk ratio for revision was 0.27 (95% CI, 0.08 to 0.88) in favor of pegged components (p = 0.028). Their value analysis indicated that pegged glenoid designs were more cost-effective than keeled glenoid designs.

One of the key differences between a pegged and keeled component is that with a pegged component the geometry of the fit is more precisely controlled by the fact that concentric reaming takes place around the same axis as is used to fix the component.

Thus the risk of poor bony support for the component (shown below) is reduced. 

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