A comparison of knee and function score of patients lost to follow-up withpatients reattending a prospective total knee arthroplasty study

Purpose: Survival analysis is correct when patients lost to follow-up are a s healthy as patients still being followed. Therefore, the results of patie nts who missed the follow-up visits were determined and compared with the r esults 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 1 989 and 1994 with yearly patient evaluation according to the Knee Society 5 3 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 te lephone. 56 patients with 61 implants lost to follow-up were examined by vi siting them at their homes (drop-outs) and compared to the 460 patients wit h 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 patie nts in the study. No revision surgery was performed in drop-out knees. Reas ons for not reattending the follow-up were mainly long travel and health. Conclusions: Patients reattending a study are healthier than drop-outs. Thi s censoring mechanism limits correct survival analysis. A complete follow-u p of patients and separate assessment of knee and functional status with re liable and valid instruments is required.