In this retrospective cross-sectional survey-based study, we randomly selected 360 patients who had received a primary unilateral TKA at our institution (Copenhagen University Hospital, Hvidovre, Denmark) between January 2010 and January 2013. They had not undergone previous open knee surgery and did not have revision surgery after primary TKA. The patients who were invited to participate in the study were treated either with a cemented previous-generation fixed-bearing, cruciate retaining TKA (AGC; Biomet, Warsaw, IN), a cemented newer-generation fixed-bearing, cruciate retaining TKA (Vanguard CR; Biomet) or an uncemented, mobile-bearing, cruciate retaining TKA (Vanguard ROCC; Biomet). All 3 prosthetic designs have shown good clinical results (Emerson et al. 2000 (link), Worland et al. 2002 (link), Ritter 2009 (link), Stormont and Chillag 2009 (link), Bercovy et al. 2012 (link), Thomsen et al. 2013 (link), Atrey et al. 2014 (link), Kievit et al. 2014 (link), Schroer et al. 2014 (link)).
The study was conducted according to the COSMIN guidelines (Mokkink et al. 2010 (link)) and consisted of 2 parts, a validity study and a reliability study. In January 2014, all 360 patients were invited to participate in the study, giving a follow-up period of 1–4 years. All participants received a set of questionnaires consisting of a Danish version of the FJS and OKS questionnaires. If participants had not returned the questionnaires within 2 weeks, a new set of questionnaires was sent. After 4 weeks, 315 participants had completed the questionnaires sufficiently well. The 315 participants who completed the first survey were included in the validity study.
The first 200 participants who returned the first set of questionnaires were then invited to participate in the reliability study. These participants were asked to complete a second FJS questionnaire 4 weeks after the first set of questionnaires had been delivered to the patients. Patients were excluded from the reliability study if they reported a change in knee pain or function in the period between the first questionnaire and the second one. 150 participants completed the second questionnaire sufficiently well and were included in the reliability study (Figure 1 and Table 2 ).
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Table 1 . For each question, the participant can choose between 6 response options: never, almost never, seldom, sometimes, mostly, or not relevant for me.
The OKS is a previously validated PROM based on a 12-item questionnaire. It has been widely used to evaluate outcome after TKA. Participants can have a total score of 0 to 48, where 48 indicates the best possible outcome. In the case of missing responses, the mean value representing all of their other responses is used. If more than 2 responses are missing, the total score should be discarded (Dawson et al. 1998 (link)).
The study was conducted according to the COSMIN guidelines (Mokkink et al. 2010 (link)) and consisted of 2 parts, a validity study and a reliability study. In January 2014, all 360 patients were invited to participate in the study, giving a follow-up period of 1–4 years. All participants received a set of questionnaires consisting of a Danish version of the FJS and OKS questionnaires. If participants had not returned the questionnaires within 2 weeks, a new set of questionnaires was sent. After 4 weeks, 315 participants had completed the questionnaires sufficiently well. The 315 participants who completed the first survey were included in the validity study.
The first 200 participants who returned the first set of questionnaires were then invited to participate in the reliability study. These participants were asked to complete a second FJS questionnaire 4 weeks after the first set of questionnaires had been delivered to the patients. Patients were excluded from the reliability study if they reported a change in knee pain or function in the period between the first questionnaire and the second one. 150 participants completed the second questionnaire sufficiently well and were included in the reliability study (
Flow diagram presenting participants who were invited to participate in the study and included in the analysis.
Demographics of patients included in the validity and reliability studies. The numbers in parentheses are standard deviations (SDs) where the data were normally distributed, or percentages of the total
| Validity study n = 315 | Reliability study n = 200 | |
|---|---|---|
| Female | 187 (59%) | 82 (55%) |
| Age (range) | 65 (36–91) | 66 (44–91) |
| Prosthesis | ||
| Van-CR | 35 (11%) | 19 (12%) |
| Van-ROCC | 68 (22%) | 40 (27%) |
| AGC | 212 (67%) | 91 (61%) |
| Year of surgery | ||
| 2010 | 28 (9%) | 17 (11%) |
| 2011 | 111 (35%) | 56 (37%) |
| 2012 | 164 (52%) | 72 (48%) |
| 2013 | 12 (4%) | 5 (3%) |
| FJS | 53 (SD 29) | 56 (SD 31) |
| OKS | 35 (SD 10) |
Questions included in the FJS questionnaire
| Are you aware of your artificial knee … | |
|---|---|
| 1 | … in bed at night? |
| 2 | … when sitting on a chair for more than one hour? |
| 3 | … when you are walking for more than 15 minutes? |
| 4 | … when taking a bath/shower? |
| 5 | … when traveling in a car? |
| 6 | … when climbing stairs? |
| 7 | … when walking on uneven ground? |
| 8 | … when standing up from a low-sitting position? |
| 9 | … when standing for long periods of time? |
| 10 | … when doing housework or gardening? |
| 11 | … when taking a walk or hiking? |
| 12 | … when doing your favorite sport? |
The OKS is a previously validated PROM based on a 12-item questionnaire. It has been widely used to evaluate outcome after TKA. Participants can have a total score of 0 to 48, where 48 indicates the best possible outcome. In the case of missing responses, the mean value representing all of their other responses is used. If more than 2 responses are missing, the total score should be discarded (Dawson et al. 1998 (link)).
