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.
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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