The 2024 Australian Joint Replacement Registry reported a 12% 10yr cumulative revision rate for conventional total shoulders and a 4% 10yr cumulative revision rate for total shoulders using a stemless humeral component. Is it reasonable to expect that a change in the humeral implant could cut the revision rate to one third, or are other factors in action? What might account for this dramatic change in reported outcomes?
Let's first look at the stemless data which can be compared to those from my prior post on conventional total shoulders from the 2024 Australian Joint Replacement Registry
For the stemless arthroplasties, the distribution of diagnoses at the time of revision is shown in the figure below.
Female patients had a higher risk of revision (hazard ratio (HR) 1.4) predominantly due to an increased rate of instability.
Younger patients had a higher revision risk (HR 1.8).
Patients with a higher ASA score had an increased revision risk (HR 2)
BMI categories did not have a significant effect on revision rate. (HR 1).
Preoperative glenohumeral pathoanatomy had a significant effect on revision rate with type A2 having the highest overall revision rate (HR 1.8) and type A1 had the highest long-term revision rate in comparison to types B1 and B2. As for the conventional total shoulders, this is contrary to the common belief that type B pathoanatomy is a risk factor for adverse outcomes.
Hybrid fixation (glenoid component cemented, humeral component non-cemented) had the lowest revision rate, but cementing both components was associated with a higher revision rate.
A ceramic head on non crosslinked polyethlene appeared to have the highest long term revision rate.
Humeral head size did not have a strong effect on revision rate.
The use of expensive technologies (computer navigation, image derived instrumentation (IDI)) was not associated with a decrease in the risk of revision.
While there are some differences from the analogous data for conventional stems, these charts don't seem to be able to account for the drop in "10 year cumulative revision rate" from 12% (conventional) to 4% (stemless). What then might explain the data?
Some possibilities include
(1) Patient selection bias - might patients receiving stemless be better overall candidates for joint replacement (healthier, better socioeconomic determinants of health, less severe disease/deformity)?
(2) Surgeon selection bias - might more advantaged surgeons select stemless over conventional arthroplasty (high volume, fellowship trained, working in a major center, specializing in shoulder/elbow)?
(3) Different numbers of patients and different lengths of followup. One might think that because both series show "10 year cumulative failure rates" the series would be comparable. But we need to compare the two figures below.
Notice that the upper graph (conventional total shoulder) shows that reported revisions continue to occur at a steady rate after 6 years and out to 16 years after the index procedure. In comparison, the lower graph (stemless total shoulder) shows very few additional revisions after six years. The stemmed results show smooth curves indicating many events across a large denominator. The stemless data are flatter with sudden jumps: small number of events on a smaller base. This suggests that fewer stemless patients were available for followup.
From the two charts, we can make a guess about the number of patients available for followup (i.e. the numbers at risk) at different times after their indcx procedure.
As the chart below, the number of cases for stemless arthroplasty "evaporates" after 6 years
Comment: We cannot know the degree to which each of these three factors may confounded the difference in "10 year cumulative revision rates" between conventional and stemless total shoulder arthroplasty. Time will tell. Currently, admitting to surgeon and patient selection biases, I continue to use stemless humeral components when appropriate and follow my patients closely.
The stemless humeral component may be an elegant approach, but the proof will be in the long term outcomes.
Elegant trogan
Tucson, AZ
May, 2023
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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).
