[Comparison of knee and functional outcomes of patients lost to follow-up with patients remaining in a prospective total knee arthroplasty study].
OBJECTIVE
Survival analysis is correct when patients lost to follow-up are as healthy as patients still being followed. Therefore, the results of patients who missed the follow-up visits were determined and compared with the results of the patients still in the study. Revision surgery and the reasons for failing to reattend the follow-up visits were recorded.


METHODS
Of 680 unconstrained total knee arthroplasties implanted between 1989 and 1994 with yearly patient evaluation according to the Knee Society 53 patients with 60 implants died, 17 patients with 19 implants could not be used for the study and 21 patients with 24 implants were interviewed by telephone. 56 patients with 61 implants lost to follow-up were examined by visiting them at their homes (drop-outs) and compared to the 460 patients with 516 implants still in the study.


RESULTS
The drop-outs were older at surgery and had more medical infirmity than the remaining patients. Drop-outs had a lower mean function score and a tendency to a lower mean knee score at follow-up compared with the patients in the study. No revision surgery was performed in drop-out knees. Reasons for not reattending the follow-up were mainly long travel and health.


CONCLUSIONS
Patients reattending a study are healthier than drop-outs. This censoring mechanism limits correct survival analysis. A complete follow-up of patients and separate assessment of knee and functional status with reliable and valid instruments is required.
D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D010352:Patient Dropouts; D011446:Prospective Studies; D020127:Recovery of Function / Q000502:physiology*