Erratum to: Patellofemoral Arthroplasty Results in Better Time-weighted Patient-reported Outcomes After 6 Years than TKA: A Randomized Controlled Trial

In the study, “Patellofemoral Arthroplasty Results in Better Time-weighted Patient-reported Outcomes After 6 Years than TKA: A Randomized Controlled Trial,” the authors uncovered an error in the algorithm calculating areas under the curve of the patient-reported outcomes. This error is limited to calculations beyond two years and has resulted in differences between the two treatment groups (PFA and TKA) being incorrectly claimed for the endpoints of SF-36 bodily pain, SF-36 physical functioning, KOOS Symptoms, KOOS Sport/Recreation, and OKS. After consultation with an independent statistician, the following changes to the text must be made. The online version of the article has been updated to reflect these changes.

The title of the article should now read, “No Clinically Important Differences Between Patellofemoral Arthroplasty and TKA in Range of Motion or Patient-reported Outcomes After 6 Years: A Randomized Trial” to reflect the changes in the main findings.

In the Abstract, the first two sentences of the Results section should read, “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.”

In the Abstract, the Conclusion should now read, “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.”

In the Results section on page 1712, the section labeled “Average PRO Improvement During the First 6 Postoperative Years” should read: “There were no differences in the time-weighted 6-year change of the primary outcome measure, SF-36 bodily pain, between PFA and TKA patients (37 ± 21 versus 29 ± 17, respectively, mean difference 8 [95% CI -1 to 17]; p = 0.08) (Table 2). The large majority of secondary outcomes endpoints did not differ between the groups, and those that did were of questionable clinical importance in terms of effect sizes (Table 2).”

Table 2.

Mean change during the first 6 years from baseline of the 14 PRO dimensions studied

Patient-reported outcome	PFA time-adjusted changea	TKA time-adjusted changea	Mean difference (95% CI)	p value
SF-36 Bodily pain	37 ± 21	29 ± 17	8 (-1 to 17)	0.08
SF-36 Physical role	27 ± 32	32 ± 42	-5 (-22 to 12)	0.55
SF-36 Physical functioning	27 ± 22	18 ±19	10 (0 to 19)	0.047
SF-36 Emotional role	27 ± 32	32 ± 42	-5 (-22 to 12)	0.55
SF-36 Vitality	15 ± 18	9 ± 17	6 (-2 to 13)	0.16
SF-36 Social role	10 ± 19	6 ± 21	4 (-5 to 13)	0.37
SF-36 Mental health	8 ± 14	5 ± 13	3 (-3 to 9)	0.33
SF-36 General health	2 ± 17	4 ± 17	-1 (-9 to 6)	0.70
KOOS Pain	32 ± 14	30 ± 19	3 (-5 to 10)	0.48
KOOS Symptoms	25 ± 17	17 ± 18	9 (1 to 16)	0.032
KOOS ADL	27 ± 13	28 ± 17	-1 (-8 to 5)	0.66
KOOS Sport/Recreation	25 ± 21	19 ± 22	6 (-4 to 16)	0.22
KOOS QoL	37 ± 18	34 ± 21	3 (-6 to 11)	0.57
OKS	15 ± 7	12 ± 7	2 (-1 to 5)	0.12

^aData are presented as mean ± SD; SF-36 range is 0-100 (best), MCID is 6-7 for physical dimensions; KOOS range is 0-100 (best), MCID is 8-10; OKS range is 0-48 (best), MCID is 5.

Additionally, Table 2 on page 1712 has been replaced with the version shown below.

The first paragraph of the Discussion section on page 1714 should read, “Our main aim for this RCT was to compare the outcomes of PFA and TKA to guide surgeons to the better treatment. We wanted to collect knee-specific and generic QOL measures using PROs, and we intended to collect these measures frequently enough to allow calculations of average improvements over the entire postoperative study period rather than focus on any particular follow-up time. In a previous publication from this RCT [28], PFA demonstrated advantages over TKA in the first 2 years. However, since registers have shown increased revision rates from 2 to 6 years [16], the present study had the dual purpose of analyzing results up to 6 years and determining whether patients who underwent PFA still had an advantage over those who had a TKA or whether their results had deteriorated, as implied by register publications [16, 24, 27]. There are two main findings of our analyses. First, we found no compelling advantages to PFA over TKA at 6 years, since most of our outcomes metrics did not differ between the groups, and the few differences between the groups were small, with the effect sizes being barely clinically important (as defined by the MCIDs [2, 4, 10, 31]). Given the lack of important between-group differences in PRO scores, reoperations, or revisions by the 6-year time point, our findings seem to support either surgical approach. But because current PFA designs are much newer, the longer-term revision risk is an unanswered question, and this should be disclosed during shared decision-making conversations with patients, given the lack of obvious advantages to that approach here.”

In the Limitations subsection of the Discussion, the word “and” was omitted from a sentence within the first paragraph on page 1716. The sentence should read, “The goal was to minimize variation, so that indications, surgical technique, and the perioperative pathway would cause minimal confounding, and the outcome should mainly reflect differences in the inherent qualities of the two implant types for treating PF-OA.”

Additionally, in the Discussion section, the subsections “Average PRO Improvement During the First 6 Postoperative Years” and “PRO Improvement at 3, 4, 5, and 6 Years” on pages 1716 and 1717 should be combined, and now read:

 

“Mean PRO Improvements During the First 6 Postoperative Years

The comparison of time-weighted improvements from baseline for the two patient groups demonstrated that neither group had a clear advantage over the other group. This was specifically the case for the main outcome, SF-36 bodily pain, where no difference was found. Most secondary PRO scores did not differ between the groups; the few slight advantages favoring PFA were of questionable clinical importance (Table 2). Limiting studies to fixed timepoints (such as 5 or 10 years) as prior studies have done has the potential to miss differences that matter in the years leading up to those time points, and so we felt it important to examine patients more closely over the span of time. However, here, even using this approach, we found no compelling advantage to PFA over TKA, and this must be considered against the absence of long-term follow-up for PFA.

We observed no consistent change in any of the PRO dimensions from 1 year onward for patients who underwent either PFA or TKA. This agrees with a previous cohort study that found no deterioration from 1-year observations to final follow-up at an average of 10 years [6].”

Finally, in the Discussion section, the subsections “ROM,” “Revisions and Reoperations,” as well as “Conclusion” on page 1717 should now read:

“ROM

At 5 years, patients undergoing PFA demonstrated marginally better ROM than patients undergoing TKA (patients were seen for clinical follow-up at 4 months and 1, 2, and 5 years; a 10-year follow-up is planned). Our data demonstrate that patients who underwent PFA had regained their preoperative ROM at 12 months, whereas patients who had a TKA did not reach the baseline ROM, even at 5 years. We are not aware of a study that estimates an MCID for knee ROM after arthroplasty. A study of patients who have had a stroke has shown the MCID to be 7° to 8° [12], and we assume that similar differences in ROM can be important for patients with PF-OA. Studies have demonstrated a positive correlation between ROM and knee-related PRO [18, 29] as well as a positive effect on functional ability and satisfaction [8].

Revisions and Reoperations

At 6 years, there was no difference in the risk of revision or any other reoperation between the patient groups. The cumulative revision rates at 6 years were 10% and 4% for PFA and TKA, respectively. This suggests the possibility that there may be more revisions in the PFA group, but our study was underpowered to demonstrate this. A sample size calculation aimed at demonstrating a difference between the mentioned frequencies would require a much larger sample size. We found varying indications for reoperations, and there may be a pattern of more manipulations under anesthesia in the TKA group and more procedures for patellofemoral instability in the PFA group. We expect that long-term analyses of our data will show more revisions in the PFA group. There are three arguments for this. First, there could be disease progression in the tibiofemoral compartments [25]. Second, surgeons may be reluctant to perform TKA revisions, and they may be more willing to perform revisions of PFAs. Third, general perceptions about the success of a certain type of implant will affect clinical practice, and registry reports uniformly show poor survival of PFA compared with TKA; this may affect surgeons’ expectations, which inform their practices, and perhaps, may influence revision rates. In this setting, adjusting clinical practice based solely on registry data without considering why revisions occur could result in a bias against an appropriate treatment. Only randomized studies with long-term follow-up will be able to determine what the preferable treatment of isolated patellofemoral osteoarthritis ought to be.

Conclusion

In general, we 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 by 6 years after surgery. These RCT findings show that the early advantages of PFA were no longer present by 6 years. Given the absence of convincing quality-of-life differences or differences in reoperations or revisions by the 6-year time point, the results of this RCT seem to support either surgical approach. However, we note that current PFA designs represent a much newer approach, and for now at least, we know less about its longer-term revision rate than we do in TKA. This concern—the uncertainty associated with novelty and the potential for an increased risk of revision over time—should be considered in shared decision-making conversations with patients. Longer-term studies are needed to ascertain whether one or the other group develops an advantage in terms of quality of life or of late revision or reoperation risk.”

The authors apologize for these errors.