Showing posts with label backside cement. Show all posts

Tuesday, October 11, 2022

The glenoid component in total shoulder arthroplasty: getting it done right.

Glenoid component loosening has been and remains an important cause of failure of anatomic total shoulder arthroplasty (data below from AOANJRR)

However, the survivorship of a pegged, cemented, cross linked, all-polyethylene glenoid component is excellent, with a 13 year cumulative percent revision rate of less than 5%. No metal backed or hybrid glenoid component has matched this outcome.

This type of glenoid arthroplasty serves shoulders across the range of glenoid types, with the lowest revision rates being for the B1 and B2 glenoids.

So, how might surgeons make the good results with the cemented, pegged all-polyethylene component even better? Here are some important concepts that can be put into action.

Careful preparation of the glenoid bone.

From the authors of Edge displacement and deformation of glenoid components in response to eccentric loading. The effect of preparation of the glenoid bone we learn that the wobble and warp of the polyethylene component is minimized by spherically reaming the bone to precisely match the back of the component.

Glenoid bone stock is preserved by reaming only enough to create a single concavity, rather than trying to "correct" glenoid version.

The adequacy of glenoid reaming can be evaluated by using a pegless trial with the same backside curvature as the actual component and assuring that there is no rocking with eccentric loading. The goal is complete congruency.

Assuring optimal seating and cementing of the component.

From the authors of The radiographic evaluation of keeled and pegged glenoid component insertion we learn that poor seating and poor cement technique contribute to poor fixation as evidenced by radiolucent lines on the immediate postoperative x-rays.

Poor seating is evidenced by the presence of cement between the glenoid bone and the backside of the component.

Good seating is indicated by the absence of cement between the component and bone (below top), rather than using cement as putty in an attempt to compensate for inadequate reaming.

A thin layer of cement between the bone and component is brittle and subject to cracking, displacement and loss of support for the glenoid implant.

Optimal cementing is reflected by the absence of radiolucent lines on postoperative radiographs.

We have learned that this can be achieved by drying each fixation hole with a CO2 spray

Immediately before pressurizing the cement into the hole

Comment: The survivorship of cemented, pegged, all-polyethylene glenoid components has yet to be surpassed by other types of glenoid implants (see Total shoulder replacement stems in osteoarthritis-short, long, or reverse? An analysis of the impact of crosslinked polyethylene). Attention to the details of bone-preserving bone preparation, complete seating of the component and modern cement technique may further improve the clinical outcomes of anatomic total shoulder arthroplasty. Our technique for this procedure is shown in this link.

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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).

Monday, September 25, 2017

Total shoulder, cement and bone density

Cement stress predictions after anatomic total shoulder arthroplasty are correlated with preoperative glenoid bone quality

These authors developed an objective automated method to quantify preoperative glenoid bone quality in different volumes of interest (VOIs): cortical bone, subchondral cortical plate, subchondral bone after reaming, subchondral trabecular bone, and successive layers of trabecular bone.

Average computed tomography (CT) numbers (in Hounsfield units [HU]) were measured in each VOI from preoperative CT scans. In parallel, they built patient-specific finite element models of simulated anatomic TSAs to predict cement stress, bone-cement interfacial stress, and bone strain around the glenoid implant. Is is of note that a 0.5-mm-thick uniform cement layer was assumed around the backside and keel.

CT measurements and finite element predictions were obtained for 20 patients undergoing aTSA for primary glenohumeral osteoarthritis.

Average CT numbers gradually decreased from cortical (717 HU) to subchondral and trabecular (362 HU) bone. Peak cement stress (4-10 MPa) was located within the keel hole, above the keel, or behind the glenoid implant backside. Cement stress, bone-cement interfacial stress, and bone strain were strongly negatively correlated with preoperative glenoid bone quality, particularly in VOIs behind the implant backside (subchondral trabecular bone) but also in deeper trabecular VOIs.

Comment: Two important points can be made here:

(1) Backside cement (cement between the backside of the component and the bone) is avoided in our practice because we recognize that a thin layer of cement is brittle and prone to failure leaving the glenoid component unsupported (as shown below).

Instead, we strive for precise preparation of the glenoid bone surface so that the polyethylene rests securely on properly contoured bone - under these conditions, backside cement is not needed or desirable.

(2) Glenoid bone stock needs to be preserved, so that the component rests on dense supportive bone. Thus we keep reaming to the minimum amount needed to achieve the good fit described in #1.

For a shoulder with preoperative x-rays like this:

our goal is post operative films that look like this (maximal bone preservation, minimal cement):

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The reader may also be interested in these posts:

Healing through joint replacement

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Monday, September 4, 2017

Rocking horse loosening in a superiorly unstable total shoulder

Recently we found this interesting Grashey view that nicely demonstrates superior rocking horse glenoid component loosening associated with superior instability after a total shoulder.
While no clinical information was available, the image is interesting in that it demonstrates the possible consequence when the humeral head is not centered in the prosthetic glenoid. This film also shows a substantial amount of backside cement, which we've found to predispose to glenoid component loosening.