No Clinically Important Differences Between Patellofemoral Arthroplasty and TKA in Range of Motion or Patient-reported Outcomes After 6 Years: A Randomized Trial
Authors: Odgaard Anders , Kappel Andreas , Madsen Frank , Kristensen Per Wagner , Stephensen Snorre , Attarzadeh Amir Pasha 
Published: March 2022

Background

In a previous study, we reported the 2-year outcomes of a parallel-group, equivalence, randomized controlled trial (RCT; blinded for the first year) comparing patellofemoral arthroplasty (PFA) and TKA for isolated patellofemoral osteoarthritis (PF-OA). We found advantages of PFA over TKA for ROM and various aspects of knee-related quality of life (QOL) as assessed by patient-reported outcomes (PROs). Register data show increases in PFA revision rates from 2 to 6 years after surgery at a time when annual TKA revision rates are decreasing, which suggests rapidly deteriorating knee function in patients who have undergone PFA. We intended to examine whether the early advantages of PFA over TKA have deteriorated in our RCT and whether revision rates differ between the implant types in our study after 6 years of follow-up.

Questions/purposes

(1) Does PRO improvement during the first 6 postoperative years differ between patients who have undergone PFA and TKA? (2) Does the PRO improvement at 3, 4, 5, and 6 years differ between patients who have undergone PFA and TKA? (3) Do patients who have undergone PFA have a better ROM after 5 years than patients who have had TKA? (4) Does PFA result in more revisions or reoperations than TKA during the first 6 postoperative years?

Methods

We considered patients who had debilitating symptoms and PF-OA as eligible for this randomized trial. Screening initially identified 204 patients as potentially eligible; 7% (15) were found not to have sufficient symptoms, 21% (43) did not have isolated PF-OA, 21% (43) declined participation, and 1% (3) were not included after the target number of 100 patients had been reached. The included 100 patients were randomized 1:1 to PFA or TKA between 2007 and 2014. Of these, 9% (9 of 100) were lost before the 6-year follow-up; there were 12% (6 of 50) and 0% (0 of 50) deaths (p = 0.02) in the PFA and TKA groups, respectively, but no deaths could be attributed to the knee condition. There were no differences in baseline parameters for patients who had PFA and TKA, such as the proportion of women in each group (78% [39 of 50] versus 76% [38 of 50]; p > 0.99), mean age (64 ± 9 years versus 65 ± 9 years; p = 0.81) or BMI (28.0 ± 4.7 kg/m2 versus 27.8 ± 4.1 kg/m2; p = 0.83). Patients were seen for five clinical follow-up visits (the latest at 5 years) and completed 10 sets of questionnaires during the first 6 postoperative years. The primary outcome was SF-36 bodily pain. Other outcomes were reoperations, revisions, ROM, and PROs (SF-36 [eight dimensions, range 0 to 100 best, minimum clinically important difference {MCID} 6 to 7], Oxford Knee Score [OKS; one dimension, range 0 to 48 best, MCID 5], and Knee Injury and Osteoarthritis Outcome Score [KOOS; five dimensions, range 0 to 100 best, MCID 8 to 10]). Average PRO improvements over the 6 years were determined by calculating the area under the curve and dividing by the observation time, thereby obtaining a time-weighted average over the entire postoperative period. PRO improvements at individual postoperative times were compared for the patients who had PFA and TKA using paired t-tests. Range of movement changes from baseline were compared using paired t-tests. Reoperation and revision rates were compared for the two randomization groups using competing risk analysis.

Results

In general, there were few differences in PRO scores beyond 2 years between patients treated with PFA and those treated with TKA, and there were no between-group differences in our primary outcome measure, SF-36 bodily pain score, when comparing PFA to TKA over the first 6 years (37 ± 21 versus 29 ± 17, mean difference 8 [95% CI -1 to 17]; p = 0.08) as well as at 6 years (40 ± 25 versus 30 ± 31, mean difference 9 [95% CI -3 to 22]; p = 0.15). Most of the secondary outcome metrics (a variety of PRO scores) demonstrated either no between-group differences or differences with effect sizes that were of questionable clinical importance. At the 6-year time point, only the SF-36 vitality score differed between the groups being in favor of PFA (17 ± 19 versus 8 ± 21; mean difference 9 [95% CI 0 to 18]; p = 0.04), whereas other PRO measures did not differ between the groups. At 5 years, ROM had decreased less from baseline for patients who underwent PFA than those who had TKA (-4° ± 14° versus -11° ± 13°; mean difference 7° [95% CI 1° to 13°]; p = 0.02), but the clinical importance of this is unknown. Revision rates did not differ between patients who had PFA and TKA at 6 years with competing risk estimates of 0.10 (95% CI 0.04 to 0.20) and 0.04 (95% CI 0.01 to 0.12; p = 0.24), respectively, and also reoperation rates were no different at 0.10 (95% CI 0.04 to 0.20) and 0.12 (95% CI 0.05 to 0.23; p = 0.71), respectively.

Conclusion

In general, 6-year follow-up on our randomized trial found that patients treated with PFA differed little from those treated with TKA in terms of patient-reported outcomes, range of motion, or reoperations and revisions. These findings show that most of the early advantages of PFA were no longer observed by 6 years, and longer-term studies are needed to ascertain whether one or the other group develops an advantage in terms of PRO results or late revision/reoperation risk. Our findings cannot explain the rapid deterioration of results implied by the high revision rates observed in implant registers, and it is necessary to question indications for the primary procedure and subsequent revision when PFA is in general use. The long-term balance of advantages will be determined by the long-term QOL, but based on the first 6 postoperative years and ROM, either implant type may be used for patients with severe isolated PF-OA. Because current PFA designs are much newer and a less used approach, we know less about its longer-term revision rate than we do in TKA, and this concern—the uncertainty associated with novelty, limited use, and the potential for an increased risk of revision over time—should be considered in shared decision-making conversations with patients.

Level of Evidence

Level I, therapeutic study.