As the authors point out:
(1) Discussing the likely result of shoulder arthroplasty is an important part of the preoperative patient-surgeon conversation.
(2) Setting a realistic expectations is important for achieving patient satisfaction.
(3) Identifying risk factors for poorer outcomes may suggest approaches for addressing these factors before surgery.
They sought to develop a model to predict the 2-year American Shoulder and Elbow Surgeons (ASES) score in patients having shoulder arthroplasty using a set of preoperative patient factors and type of arthroplasty performed.
External validation was performed retrospectively by using 233 patients who had shoulder arthroplasty at a site that was not used to develop the model
Using their model, the mean difference between predicted and actual 2-year ASES score was 12.7 points. For 85% of patients the predicted ASES score was within published values for the minimal clinically important difference (MCID 13.5-21). Seven of the 26 variables included in this study—older age, higher preoperative ASES score, non-disability status, non-COPD status, alcohol use, anatomic rather than reverse total shoulder arthroplasty, and primary rather than revision shoulder arthroplasty—showed significant association with higher 2-year ASES scores.
These authors used the 2-year ASES score as the measure of success of shoulder arthroplasty.
A higher postoperative score was associated with a higher preoperative score – in other words the better a shoulder functioned before surgery, the better it functioned after arthroplasty. If the defining metric was the postoperative score, "better" outcomes could be achieved by selecting patients for arthroplasty that had higher preoperative ASES scores.
The value of a procedure to the patient is usually determined not by the postoperative score alone but rather by whether or not the preoperative score was improved by an amount equal to or exceeding the minimal clinically important difference (MCID).
In the hypothetical example below, a postoperative ASES score of 70 was achieved. However, because the preoperative ASES score was 60, the improvement did not exceed the MCID
In this cohort of patients it would be of great interest to know which factors were associated with improvement in the ASES score by the MCID for the ASES score (13.5-21)
The type of surgery might be considered a “modifiable” factor. This model suggests that aTSA is associated with better outcomes than RSA. However, diagnosis was not considered among the variables in the model. Patients having anatomic arthroplasty (aTSA) typically have a different distribution of diagnoses than those having a reverse arthroplasty (RSA); thus, the difference in final ASES score may be more related to diagnosis rather than procedure. As an example, for the patient with pseudoparalysis, an aTSA would not be expected to yield as good a result as an RSA.
The bottom line is that in assessing or predicting the benefit of a shoulder arthroplasty, it is important to understand the implications of different result metrics and to be sure that the most important patient and shoulder characteristics are included in the analysis.