A recent post pointed out that it is difficult to accurately assess long term outcomes from shoulder arthroplasty (see Comparing anatomic and reverse total shoulder arthroplasty outcomes - long term followup is difficult): the longer the period of followup, the fewer of the original group of patients that are available for study and the "better" the average outcomes are for the available patients. In other words, the process of long term followup selects for patients who have good results while tending to omit those with poor outcomes, those having revisions, those in poor health, and those who are deceased. Sort of a Darwinian "survival of the fittest", resulting in the paradox that long term outcomes appear to be better than short term outcomes.

This topic was addressed by the authors of Patients Lost to Follow-up in Shoulder Arthroplasty: Descriptive Characteristics and Reasons. Paraphrasing their introduction, incomplete follow-up represents one of the major sources of bias. Patients lost to follow-up may differ from those that do not drop out and the rate of patients lost may differ between study groups. Patients lost are not random; they may have poorer outcomes than respondent patients, thereby making for an overestimation of the outcomes when only respondents are included. The characteristics of the patients lost to follow-up may differ with respect to the type of pathology, age, sex, socioeconomic status, distance of their home from the provider, education, language, ethnicity, co-morbidities and adverse outcomes. The longer the follow-up, the greater the number of patients lost to follow-up and the less representative the patients with long term followup are in comparison to the original cohort.

These authors sought to determine the number of patients in their practice lost to follow-up by year after shoulder arthroplasty and to investigate the characteristics of the patients lost to follow-up in comparison to those not lost to follow-up. They reviewed 251 shoulder arthroplasties performed from January 2008 to December 2014.

At 8 years after surgery, 86 patients (34.3%) were lost to followup. The cumulative percent of patients lost to followup by year after surgery is shown below.

The patients lost to followup were more likely to be severely obese, to be elderly, to have higher ASA scores, to have arthroplasties performed for fracture-related diagnoses. Patients with complications had a lower risk of being lost.

In 81 of the 86 patients lost to follow-up, several telephone contacts were tried at the end of the present study. Fourteen patients did not respond to the calls. Sixteen patients died during the time of data collection and analysis. Ten of the 47 patients that responded to the

call (21.2%) agreed to have another visit if they could, 36 did not agree (76.6%), and 4 (8.5%) declined to respond. Among the reasons that the patients or their relatives gave for not going to their appointments, 8 patients were too old to make the trip, 15 were in a bad state, 18 thought there was no reason to come back for the visit, 6 did not return due to administrative problems, and 5 had other reasons.

Comment: Several conclusions can be drawn:

(1) In the study of shoulder arthroplasty, followup beyond 5 years is essential, because that is when the failures start to occur, yet such studies are at risk for sampling error.

(2) Clinical investigators need to implement followup strategies that optimize the percentage of patients who continue to participate for longer than five years. Such strategies include using a followup instrument that is user-friendly for older patients, for those in poor health, for those for whom English is the second language, for those who live remotely, and for those with limited education and financial resources. These patients tend to be systematically excluded by followup systems that require patients to return to the office for followup, that require range of motion and strength measurements, that require the use of a computer interface, or that require complex/long forms to complete. Followup for these patients can be most easily achieved by a patient friendly tool, such as the Simple Shoulder Test, that can be completed by the patient using only a pencil in less than a minute while assessing individual shoulder functions that are important to the patient.

(3) Reports of clinical outcomes need to include

(a) the number of patients that received the procedure being studied and the number and reasons for patients that were lost to followup as well as

(b) a comparison of the important characteristics of patients lost to followup in comparison to those not lost to followup: type of pathology, age, sex, and co-morbidities. Ideally, socioeconomic status, education, and ethnicity would also be included to determine the extent to which the subset with followup was representative of the entire cohort of patients receiving the procedure.

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