Study finds positive short-term results from second-generation patellofemoral arthroplasty
For patients with isolated patellofemoral osteoarthritis, second-generation onlay patellofemoral arthroplasty showed safe and acceptable results at short-term and midterm follow-up, according to published results.
To study the efficacy of second-generation (2G) onlay patellofemoral arthroplasty (PFA) for patellofemoral osteoarthritis (PFOA), researchers performed a systematic review of 33 studies found in PubMed, Cohrane library, EMBASE and Google Scholar from 2005 to 2020.
Outcome measures included operative and nonoperative complications, required revision and/or conversion to total knee arthroplasty, and implant survivorship, according to the study.
Overall, researchers found 259 total studies on the topic. The mean age of patients was 59.7 years. Implant survivorship at a mean follow-up of 5.52 years was 87.72%; however, sub-analysis of studies with a minimum of 5 years follow-up revealed an implant survivorship of 94.24%.
Researchers also noted pain was the most common nonoperative complication and progression of PFOA was the most common operative complication. Additionally, revision was required for 1.37% of cases (n = 36), while conversion to TKA was required for 7.82% of cases (n = 205).
“This makes [PFA] an acceptable alternative to TKA or conservative measures in appropriately selected patients,” the researchers wrote in the study. “However, more extensive studies regarding functional outcomes need to be performed. In addition, future studies should be evaluated for long-term cost saving measures of performing a PFA [vs.] long-term conservative management in those patients who are too young to receive a TKA,” they concluded.
Perspective
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I was interested to read the article by Jordan C. Villa, MD, and colleagues evaluating the outcomes of onlay patellofemoral arthroplasty (PFA). The burden of osteoarthritis in our population continues to grow, and with 40% of all patellofemoral OA being isolated, the need for a solution is real. Success with first generation/inlay PFA has been moderate, with short-term to midterm revision rates between 15% and 20%, and 72% to 85% favorable results (Argenson and colleagues). Coupled with the reliable results of total knee arthroplasty for patellofemoral OA (Parvizi and colleagues), the relatively high midterm revision/conversion rates in PFA has tempered widespread utilization, but PFA volume is expanding as demand increases.
The potential benefits of second-generation design are intriguing. Patellar maltracking and instability are major causative factors for patellofemoral OA. Even in modern inlay PFA, abnormal baseline anatomy and maltracking (eg, elevated TT-TG) have been implicated as a contributing factor in failure (Feucht and colleagues), and concomitant realignment procedures have long been recommended for first-generation PFA to optimize results (Argenson and colleagues). Second-generation/onlay PFA allows surgeons to more directly alter extensor mechanism alignment, supplementing or potentially obviating additional realignment techniques. Logically, these changes could translate to more reliable results and longevity. In fact, a prior 2017 PFA systematic review, inclusive of inlay and onlay studies from 1995 to 2015, demonstrated a trend toward lower revision rates in more recent cohorts and registries (van der List and colleagues), suggesting second-generation designs may already be improving results.
Ultimately, when deciding how and when to utilize onlay PFA for our patients, it is important to understand whether these trends are real. Available results are mostly based on small cohorts, with limited randomized studies and high-level evidence. The strength of this systematic review is in its synthesis of a focused selection of studies, excluding first-generation implants and leveraging the increasing volume of PFA studies published after 2015 (49% of included knees, n=1,291/2,622). The results are promising, with 87.72% survivorship at a mean of 5.5 years overall, and 92.24% survivorship at 6.86 years in studies with at least 5-year follow-up. In this refined subgroup, 5-, 10-, 15- and 20-year onlay PFA survivorship are reported to be 94.3%, 88.9%, 83.8% and 79%, respectively, all of which are higher than prior reviews and registries including first-generation implants.
Despite the optimistic conclusions of this review, we should continue to closely monitor PFA results moving forward. While the combined conversion and revision rates in this systematic review were less than 10% in a large volume of cases (n=2,622), these numbers are still largely representative of low-quality studies. Among the 33 included articles, there was only a single, level 1 RCT among a large number of cohorts. Registries have shown significantly lower survivorship than published cohorts (71.4% vs. 83.3% at 10 years), and the current paper’s conclusions should be viewed against a similar backdrop (van der List and colleagues).
The article also fails to demonstrate any clear superiority of second-generation design. First, a single design (Avon) accounted for 70% of the implants in the current study, limiting generalizability to second-generation PFA as a whole. Second, despite trends toward better survivorship, the study’s mean follow-up for these second-generation PFAs is only 6.86 years, even after excluding studies with less than 5-year follow-up. Notably, several reports from specific inlay implants touted similar early findings before failure rates rose at longer follow-up. In fact, only two included studies with a limited number of cases (n=151 knees) reported data for survivorship at 10 year or greater, contributing to the high long-term survivorship reported in the review. It is unclear whether these findings will remain representative as more long-term data becomes available.
In summary, the systematic review by Villa and colleagues is an encouraging addition to the literature. Second-generation onlay PFA represents a real and reliable option for patients, with better overall short- to medium-term survivorship and results in comparison to the initial first-generation experience. It is unknown whether these trends will continue at long-term follow-up, or whether these improvements are in fact attributable to second-generation/onlay design or to improved surgical indications and techniques. Direct comparison studies with long-term follow-up are still needed.
Argenson JA, et al. Clin Orthop Relat Res. 2005;doi:10.1097/01.blo.0000187061.27573.70.
Feucht MJ, et al. Arch Orthop Trauma Surg. 2020;doi:10.1007/s00402-020-03651-9.
Parvizi J, et al. Clin Orthop Relat Res. 2001;doi:10.1097/00003086-200111000-00018.
van der List JP, et al. Knee Surg Sports Traumatol Arthrosc. 2017;doi:10.1007/s00167-015-3878-z.
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