The authors of Prospective Observational Study of Anatomic and Reverse Total Shoulder Arthroplasty Utilizing a Single Implant System With Long-Term Follow-Up used a multicenter data registry to identify patients undergoing primary anatomic (aTSA) or reverse (rTSA) total shoulder arthroplasties that had a minimum of 8-year follow-up.

A total of 364 aTSA patients and 278 rTSA patients were included. The two groups had different preoperative characteristics.

At latest follow-up, aTSA had greater active abduction, forward elevation, external rotation, and Simple Shoulder Test scores.

Complications in aTSA patients included 15 aseptic glenoid loosening, 10 rotator cuff tears, 3 infections, and 1 periprosthetic humeral fracture.

Complications in rTSA patients included 9 periprosthetic humeral fractures, 5 aseptic glenoid loosening, 3 dislocations, 3 scapular fractures, and 1 acromial fracture.

While aTSA patients had a greater revision rate (5.8%) than rTSA patients (1.8%) it is noteworthy that older patients (as in the rTSA group) are less likely to agree to a revision and that some of the rTSA complications (e.g. scapular and acromial fractures) may not be amenable to surgical revision.

Comment: Long-term followup in shoulder arthroplasty is critically important, but it is difficult. While the title of this paper indicates that this is a prospective study, it does not assess the number of potentially eligible patients that were lost to followup. The importance of this assessment is discussed here: Losing patients to followup can artificially inflate outcomes and shown in the chart below showing that the percent of good results increases with the percentage of patients lost to followup: the biasing effect of the missing patients.

The longer the followup, the higher the percentage of patients lost to followup (because of death, moving to another city, unwillingness to return for followup, dissatisfaction, complications treated by a different surgeon, etc). Without knowing the percentage of patients lost to followup, we cannot estimate the rates of complications, revisions or good outcomes or the fragility of the data (see How fragile is our knowledge about shoulder arthroplasty?). See also Patients Lost to Follow-up in Shoulder Arthroplasty: Descriptive Characteristics and Reasons, which will be the object of a subsequent post.

In a prospective study it is vitally important to record the numbers of patients enrolled at the outset and to reveal the number of these patients that were included in the final analysis. This information is typically included in the classic "Figure 1". See this example from What Factors are Predictive of Patient-reported Outcomes? A Prospective Study of 337 Shoulder Arthroplasties.

Thus it would be valuable to know what percent of the initial operated cohort is represented by the reported 364 aTSA patients and 278 rTSA patients.

This points to the importance of facilitating the capture of the largest percentage of enrolled patients for the longest time. Using outcome scores that require the patient to return to the office for followup (e.g. to obtain range of motion measurements) or that require the use of a computer interface can introduce barriers to followup that bias the assessment of outcome. For that reason, among others, we use the Simple Shoulder Test that requires neither return for followup or a computer (see The value of shoulder outcome scores - what does the patient care about?).

Finally, this paper compares aTSA and rTSA outcomes for different patients with different diagnoses. The information we would really like to have is a comparison of these two procedures in similar patients (age, sex, comorbidities, prior surgery) stratified by diagnosis (osteoarthritis with an intact cuff, cuff tear arthropathy, etc). That knowledge would help inform our discussion of implant type with our patients.

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