Wednesday, September 9, 2020

Total shoulder arthroplasty - what materials should we be using?

 The Biomaterials of Total Shoulder Arthroplasty Their Features, Function, and Effect on Outcomes

These authors review the materials used in total shoulder arthroplasty (TSA). They point out that the 2 main metal alloys used in TSA implants are Ti-6Al-4V (titaniumaluminum-vanadium) and CoCrMo (cobalt-chromium-molybdenum). Ti alloys are softer than CoCr alloys, making them less wear-resistant and more susceptible to damage, but they have improved osseointegration and osteoconduction properties. While some surgeons are interested in "osseointegration" of the humeral component, bone ingrowth is not necessary for secure durable fixation; furthermore, revision of an ingrowth stem carries with it a much higher complication risk than the revision of an impaction grafted smooth stem (see this link).

While metal allergy may be a concern in some patients having problems after TSA, the diagnosis of this metal allergy is difficult. This concern is not sufficiently compelling to merit the routine use of "hypoallergenic" prostheses. Prosthesis without nickel or chromium seem to be mechanically inferior, so avoiding the risk of "metal allergy" may give rise to other problems. For example, while ceramic and pyrolytic carbon humeral heads may have theoretical advantages, they also pose an increased risk of fracture - a complication unknown with cobalt chrome heads. 

On the glenoid side, cross linked polyethylene glenoids have an excellent record of survivorship as shown by the data from the Australian Orthopaedic Association. 

Comment: With the current state the art, total shoulder arthroplasty using standard implants has an established track record of excellent clinical outcomes. Efforts to improve on this track record may result in more costly implants and in unexpected outcomes (see this link).

Our time tested approach to total shoulder arthroplasty is shown in this link.

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