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 

Patients who underwent PFA had a larger improvement in the SF-36 bodily pain score during the first 6 years than those who underwent TKA (35 ± 19 vs. 23 ± 17; mean difference 12 [95% CI 4 to 20]; p = 0.004), and the same was true for SF-36 physical functioning (mean difference 11 [95% CI 3 to 18]; p = 0.008), KOOS Symptoms (mean difference 12 [95% CI 5 to 20]; p = 0.002), KOOS Sport/recreation (mean difference 8 [95% CI 0 to 17]; p = 0.048), and OKS (mean difference 5 [95% CI 2 to 8]; p = 0.002). No PRO dimension had an improvement in favor of TKA. 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 

Our RCT results show that the 2-year outcomes did not deteriorate during the subsequent 4 years. Patients who underwent PFA had a better QOL throughout the postoperative years based on several of the knee-specific outcome instruments. When evaluated by the 6-year observations alone and without considering earlier observations, we found no consistent difference for any outcome instruments, although SF-36 vitality was better for patients who underwent PFA. These combined findings show that the early advantages of PFA determined the results by 6 years. 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. Our data do not suggest that there is an inherent problem with the PFA implant type as otherwise suggested by registries. The long-term balance of advantages will be determined by the long-term QOL, but based on the first 6 postoperative years and ROM, PFA is still the preferable option for severe isolated PF-OA. A possible high revision rate in the PFA group beyond 6 years may outweigh the early advantage of PFA, but only detailed analyses of long-term studies can confirm this.

Level of Evidence 

Level I, therapeutic study.

中文翻译：

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6 年后，髌股关节置换术比 TKA 带来更好的时间加权患者报告结果：一项随机对照试验

背景 

在之前的一项研究中，我们报告了一项平行组、等效性随机对照试验（RCT；第一年盲法）的 2 年结果，该试验比较了髌股关节置换术 (PFA) 和 TKA 治疗孤立性髌股骨关节炎 (PF-OA) 的效果。我们发现，根据患者报告结果 (PRO) 评估，PFA 相对于 TKA 在 ROM 和膝关节相关生活质量 (QOL) 的各个方面具有优势。登记数据显示，在每年 TKA 翻修率下降的同时，PFA 翻修率从术后 2 至 6 年增加，这表明接受 PFA 的患者膝关节功能迅速恶化。我们打算在我们的随机对照试验中检查 PFA 相对于 TKA 的早期优势是否已经恶化，以及经过 6 年随访后，我们的研究中种植体类型之间的翻修率是否存在差异。

问题/目的 

(1) 接受 PFA 和 TKA 的患者术后前 6 年的 PRO 改善是否不同？(2) 接受 PFA 和 TKA 的患者在 3、4、5 和 6 年时的 PRO 改善是否不同？(3) 接受 PFA 的患者 5 年后的 ROM 是否比接受 TKA 的患者更好？(4) 在术后前 6 年中，PFA 是否会比 TKA 导致更多的翻修或再次手术？

方法 

我们认为有衰弱症状和 PF-OA 的患者有资格参加这项随机试验。筛查初步确定 204 名患者可能符合资格；7% (15) 人被发现没有足够的症状，21% (43) 人没有孤立的 PF-OA，21% (43) 人拒绝参与，1% (3) 人在达到 100 名患者的目标数量后未纳入其中已经达到了。纳入的 100 名患者在 2007 年至 2014 年间按照 1:1 的比例随机接受 PFA 或 TKA。其中，9%（100 人中的 9 人）在 6 年随访前失访；PFA 组和 TKA 组分别有 12%（50 人中的 6 人）和 0%（50 人中的 0 人）死亡（p = 0.02），但没有死亡可归因于膝关节疾病。接受 PFA 和 TKA 的患者的基线参数没有差异，例如每组中女性的比例（78% [50 人中的 39 人] 对比 76% [50 人中的 38 人]；p > 0.99）、平均年龄（64 ± 9 岁与 65 ± 9 岁；p = 0.81）或 BMI（28.0 ± 4.7 kg/m ²与 27.8 ± 4.1 kg/m ²；p = 0.83）。患者接受了五次临床随访（最近一次为 5 年），并在术后前 6 年完成了 10 套问卷。主要结局是 SF-36 身体疼痛。其他结果包括再次手术、翻修、ROM 和 PRO（SF-36 [八个维度，范围 0 到 100 最佳，最小临床重要差异 {MCID} 6 到 7]、牛津膝关节评分 [OKS；一维，范围 ​​0 到 48]最佳，MCID 5]，以及膝关节损伤和骨关节炎结果评分 [KOOS；五个维度，范围 0 到 100 最佳，MCID 8 到 10]）。6 年期间的平均 PRO 改善是通过计算曲线下面积并除以观察时间来确定的，从而获得整个术后期间的时间加权平均值。使用配对 t 检验比较接受 PFA 和 TKA 的患者在各个术后时间的 PRO 改善情况。使用配对 t 检验比较相对于基线的运动变化范围。使用竞争风险分析比较两个随机分组的再手术和翻修率。

结果 

接受 PFA 的患者在前 6 年中 SF-36 身体疼痛评分比接受 TKA 的患者有更大的改善（35 ± 19 比 23 ± 17；平均差 12 [95% CI 4 至 20]；p = 0.004），SF-36 身体功能也是如此（平均差 11 [95% CI 3 至 18]；p = 0.008），KOOS 症状（平均差 12 [95% CI 5 至 20]；p = 0.002 ）、KOOS 运动/娱乐（平均差 8 [95% CI 0 至 17]；p = 0.048）和 OKS（平均差 5 [95% CI 2 至 8]；p = 0.002）。没有 PRO 维度有利于 TKA 的改进。在 6 年时间点，只有 SF-36 活力评分在支持 PFA 的组之间存在差异（17 ± 19 与 8 ± 21；平均差 9 [95% CI 0 至 18]；p = 0.04），而其他 PRO 指标在各组之间没有差异。5 年时，接受 PFA 的患者的 ROM 较基线下降幅度小于接受 TKA 的患者（-4° ± 14° 对比 -11° ± 13°；平均差 7° [95% CI 1° 至 13°]； p = 0.02），但其临床重要性尚不清楚。6 年时接受 PFA 和 TKA 的患者的翻修率没有差异，竞争风险估计值分别为 0.10（95% CI 0.04 至 0.20）和 0.04（95% CI 0.01 至 0.12；p = 0.24），再手术率也没有差异。分别为 0.10（95% CI 0.04 至 0.20）和 0.12（95% CI 0.05 至 0.23；p = 0.71），无差异。

结论 

我们的随机对照试验结果表明，2 年结果在接下来的 4 年中并未恶化。根据多种针对膝关节的结果仪器，接受 PFA 的患者在术后几年的生活质量更好。当仅通过 6 年观察进行评估且不考虑早期观察时，我们发现任何结果工具都没有一致的差异，尽管 SF-36 活力对于接受 PFA 的患者更好。这些综合研究结果表明，PFA 的早期优势决定了 6 年后的结果。我们的研究结果无法解释种植登记中观察到的高翻修率所暗示的结果迅速恶化，并且有必要对普遍使用 PFA 时初次手术和后续翻修的适应症提出质疑。我们的数据并不表明 PFA 种植体类型存在与注册机构其他建议不同的固有问题。长期的优势平衡将由长期 QOL 决定，但基于术后前 6 年和 ROM，PFA 仍然是严重孤立性 PF-OA 的首选选择。PFA 组 6 年以上可能的高翻修率可能超过 PFA 的早期优势，但只有长期研究的详细分析才能证实这一点。

证据水平 

I 级，治疗研究。