Abstract
Objectives
The aim of this study was to explore the clinical outcomes and long-term survival of patellofemoral arthroplasty in treatment of isolated patellofemoral osteoarthritis.
Methods
We retrospectively studied a total of 46 type Y-L-Q PFAs that were designed at our institution in 38 patients. Implant survivorship was analyzed with a follow-up of 18.9–29.6 years. Knee Society Score (KSS), Oxford Knee Score (OKS), and University of California Los Angeles activity scale (UCLA) were used to assess functional outcomes.
Results
The implant survivorship was 83.6% at 15 years, 76.8% at 20 years, and 59.4% at 25 years 14 PFAs in 12 patients were revised into total knee arthroplasty at 16.0 ± 6.7 years; 13 for progression of tibiofemoral osteoarthritis and one for polyethylene wear. The mean Knee Society Score objective scores and functional scores were 73.0 ± 17.5 (range, 49–95) and 56.4 ± 28.9 (range, 5–90), respectively. The mean Oxford Knee Score was 25.8 ± 11.5 (range, 8–44).
Conclusion
Type Y-L-Q patellofemoral arthroplasty can be an effective method for treating isolated patellofemoral osteoarthritis with satisfactory survival.
Introduction
The prevalence of isolated patellofemoral joint osteoarthritis (OA) is around 19% in patients with knee-related symptoms. 1 Nonoperative treatment is often insufficient to relieve the pain caused by end-stage patellofemoral OA. Surgical options including osteotomy, patellofemoral arthroplasty (PFA), and total knee arthroplasty (TKA) become necessary at that time.
As a less invasive procedure that preserves bone stock and structural integrity of the knee, PFA has several advantages that include: (1) reproducing nearly natural knee kinematics;2,3 (2) requiring less operative time and blood transfusion; 4 (3) enabling faster recovery and better range of motion; 5 and (4) allowing simpler revision than a failed TKA, especially for young and active patients with long life span. Furthermore, revision from PFA to TKA does not compromise the results of TKA. 6
PFA was introduced more than 60 years ago, 7 but it is used far less frequently than TKA. A review of eight national registry data demonstrated that they accounted only for 0.45% of all knee replacements. 8 Dissatisfying results of PFA implant survivorship might be the main reason. A systematic review of studies has revealed higher revision (8.4% vs. 1.3%) 9 and reoperation rate (9.1% vs. 3.7%) 10 for PFA against TKA in treatment of isolated patellofemoral arthritis, which might be related to the design pitfalls and longer learning curve of the first-generation inlay PFA prostheses.
In the 1990s, a second-generation onlay-designed, the type Y-L-Q PFA prosthesis was designed at our institution and 46 PFA procedures were performed in 10 years, which accounted for 1/10 of knee replacement procedures of our institution during the same period. In 2002, Zhang et al. reported a mean of 45.4 months of follow-up results. Statistically significant improvements (p < 0.01) were observed for the Knee Society objective score (42.4 ± 6.5 vs 72.7 ± 13.5) and Knee Society functional score (26.7 ± 6.4 vs 73.9 ± 13.8). 11 Two decades have passed since, and the purpose of this study was to provide clinical results and survival in patients treated with this prosthesis for a minimum of 18.9 years (range, 18.9–29.6 years).
Methods
Ethics
Ethical approval was waived by our institutional ethics committee in view of the retrospective nature of the study and all the procedures being performed were part of the routine care. All data were collected for academic use only, and no identifiable information about the participants is included in the manuscript.
Study design
We retrospectively studied all 46 PFA procedures performed between 1991 and 2002 using prostheses (type Y-L-Q). PFA was indicated in patients with the following: (1) localized anterior knee pain provoked by activities that strain the patellofemoral joint; (2) pain interfering with daily work and activities and refractory to a half year of nonoperative treatment; (3) radiographic evidence of severe isolated patellofemoral joint osteoarthritis (joint space narrowing, subchondral sclerosis, and cyst formation) with/without patella subluxation. The contraindications included: (1) inflammatory arthritis; (2) symptomatic tibiofemoral arthropathy of the ipsilateral knee; (3) severe tibiofemoral malalignment or narrowness of tibiofemoral joint space width in standing anteroposterior radiography.
Demographic characteristics of the PFA recipients.
Prosthetic design
The type Y-L-Q prosthesis was designed in our institution and incorporates a femoral trochlear and a patellar component. The cemented femoral trochlear component is made of cobalt chromium molybdenum alloy with a fixed 30-mm sagittal radius of curvature and is available in three different sizes (36 mm × 48 mm, 40 mm × 52 mm, 43 mm × 54 mm) varying in height and width. The symmetric femoral trochlear component consists of two main pegs inserted into the medial and lateral condyles and two proximal pegs inserted into the anterior cortex. The all-polyethylene patellar component is a symmetric dome in shape with four different implant sizes available (diameters of 30 mm, 32 mm, 34 mm, and 38 mm).
Surgical procedure and postoperative rehabilitation
Patients underwent PFA using tourniquets under general or intraspinal anesthesia. A midline TKA incision was made, and then we exposed the femoral trochlea and patella articular facet through a medial parapatellar approach. A thorough inspection of the entire knee was performed to assess the state of the articular cartilage in three compartments, the meniscus, and the cruciate ligaments. We would start the patella preparation if a full-thickness cartilage defect was present only in the trochlea. Osteophytes were removed and a horizontal patellar osteotomy was performed with a saw to achieve 10–12 mm of remaining patella thickness. Then a hole was drilled for fixation of the patella component. Next, femoral anterior cortex osteotomy and two holes for fixation were done with the aid of a guide instrument. Afterward, we inserted the implants and fixed them with cement. If patellar maltracking existed, we would perform a lateral retinacular release with/without medial retinacular reefing. Wound closure was done after achieving a satisfactory range of motion and patellar tracking.
Active quadriceps femoris exercise and continuous passive motion were encouraged on the second-day post-operation and weightbearing mobilization was allowed on the third-day post-operation. Patients were discharged from hospital 2 weeks post-operation.
Clinical evaluation and survival analysis
At the final follow-up (range, 18.9–29.6 years), six patients (8 knees) were lost to follow-up, and 10 patients (10 knees) died with the prostheses in situ, none of whom had required a revision of their PFA. All patients without revisions were evaluated with the use of the Knee Society functional scale, University of California Los Angeles activity scale (UCLA), and Oxford Knee Score (OKS). 12 Conversion to TKA during the study period was considered a failure, and all causative factors for revision were documented.
Statistical analysis
Data were analyzed using SPSS software version 26.0 (IBMSPSS, New York, USA). Descriptive statistics are reported as mean values ±standard deviation and range. The survival rate was estimated by the non-parametric Kaplan-Meier method. Nonparametric Mann–Whitney U test was used to compare the mean of clinical outcome scores. The statistical significance was set at p-value <0.05. Survival curves with 95% confidence intervals were calculated using R (R Foundation for Statistical Computing, Vienna, Austria).
Results
All 38 patients underwent arthroplasty for primary patellofemoral OA. A patient was diagnosed with pigmented villonodular synovitis by postoperative pathology. Staged and simultaneous bilateral procedures were performed in six and two patients, respectively. Lateral retinacular release was performed in 23 knees, and 10 knees in combination with medial retinacular reefing. The mean surgical time for unilateral PFA was 77.0 ± 14.2 min (range, 55–115 min). The mean drainage volume was 128.0 ± 85.9 mL (range, 5–360 mL).
Perioperative complication
During the perioperative period, no major complications were recorded. One patient had superficial wound infection that did not require reoperation. In addition, one patient’s PFA was tight in flexion and the patient was readmitted to undergo continuous passive motion then achieving free flexion of 90°.
Implant survivorship
Ten living patients (14 prostheses) still had their PFA prostheses in situ and functioning for 24.1 ± 2.8 years (range, 18.9–29.6 years) (Figure 1). 12 patients (14 prostheses) underwent revision to TKA, with a mean time to conversion of 16.0 ± 6.7 years. There were 11 patients with persistent pain attributed to the progression of tibiofemoral OA. One patient received revision with TKA because of the recurrence of anterior knee discomfort caused by polyethylene wear. Radiographs of an 81-year-old female who received right PFA. (a) the AP view, (b) the lateral view, (c) the patellar axis view. The PFA have been functioning well (OKS of 44 points and UCLA of six points) for 26.8 years.
Kaplan-Meier analysis showed that the probability of survival of the prosthesis at 15, 20, and 25 years was 83.6%, 76.8%, and 59.4%, respectively, with revision for any reason as the endpoint (Figure 2). Kaplan–Meier curve denoting estimated proportion of patients unrevised with 95% confidence intervals (dashed line).
Functional outcomes
The mean Knee Society objective scores and functional scores were 73.0 ± 17.5 (range, 49–95) and 56.4 ± 28.9 (range, 5–90), respectively. As for patient-reported outcomes, the UCLA was 4.4 ± 1.7 (range, 2–7), and OKS was 25.8 ± 11.5 (range, 8–44).
Discussion
The most important finding of the present study is that patellofemoral arthroplasty can be durable in appropriate patients. We reported the type Y-L-Q PFA with cumulative survivals of 83.6% at 15 years, 76.8% at 20 years, and 59.4% at 25 years post-operation. Limited studies of long-term follow-up of PFAs reported over 15-years survivorships of 58%–79% and 20-years survivorships of 59–69%.13–16 The annual revision rate in our series was 1.65%, lower than the 2.18% reported in a systematic review including 9619 PFA from 1995 to 2010. 17 Prosthesis design and patient selection are the two major factors that influence PFA survivorship.
Prosthesis design features
Depending on the type of trochlear preparation — resurfacing or anterior cutting, the trochlear prostheses can be classified into inlay and onlay design. In the 1970s, the first-generation PFA prosthesis was introduced using an inlay design. 18 This kind of design only replaced the worn region without altering the trochlea’s shape, making it challenging to match the surrounding chondral surfaces. In addition, it failed to address the underlying trochlear dysplasia in the majority of patients with isolated patellofemoral OA. 19 Thus, the inlay designs are predisposed to surgical error, maltracking, and reoperation. 20 In order to avoid maltracking, the inlay design implants usually increased constraint with a relatively deep trochlear groove and small trochlear angle, which increased the incidence of postoperative catching, clunking and anterior knee pain. Therefore, though results were mixed, the inlay designs were associated with a high revision and reoperation rate. 21
In order to address these problems, second-generation onlay design implants were introduced in the 1990s using the same anterior femoral cut as TKA. This design made the implant positioning more easily and allowed to correct the underlying trochlear dysplasia. The type Y-L-Q prosthesis is an onlay design impant. However, the trochlear groove is relatively shallow (trochlear angle of 160°) compared with other designs, which enhanced patellar tracking and enabled the patella to be reduced easily if it was subluxated. Thus, patients seldom complained of post-operative discomfort and pain. Our trochlear component did not contain a portion to resurface the intercondylar region, which might be a pitfall. An intercondylar tail allows fluent transition from anterior flange to the weight-bearing surface of the femur and one of our patients had reported clunking going from flexion into extension.
Patient selection
The main cause of revision in our study was the progression of tibiofemoral OA, which is consistent with the findings of a recent systematic review 22 and registry data. 23 In addition, of the 14 unreplaced PFAs, 6 cases of radiographic tibiofemoral OA were found. The failure mode demonstrated not only implant durability but also the importance of patient selection.
Identifying patients at risk of progression of tibiofemoral OA is critical but difficult. Leadbetter recommended criteria should include varus deformity <5°, valgus deformity< 8°, free flexion of 120° and flexion contracture<10°. 24 As for radiographic assessment, we suggest at least incorporating plain radiographs including the weight-bearing anteroposterior view, lateral view, and patellar axial view as we used for pre-operative assessment. Considering the over-sensitivity of MRI in evaluating OA, pre-operative MRI results are not recommended for determining candidacy for unicompartmental knee arthroplasty. However, it is not exactly the same in PFA. Medial UKA can reduce the load and exert a protective effect on the lateral compartment to some extent; while PFA has nearly no influence on the tibiofemoral compartment. Therefore, progression of OA is the main reason for revision of PFA. Williams suggested routinely obtaining preoperative MRI to evaluate tibial-femoral compartment, 25 but its necessity requires further research. Recent research demonstrated that bone scan has better predictive value than MRI in patient selection. 26 However, surgeons should be cautious that these sensitive measures might result in abandonment of many appropriate PFA candidates.
Dejour et al. found a much higher revision rate in patients over 75 years because of early spread of arthritis. They suggested performing PFA in patients with end-stage patellofemoral OA secondary to moderate or severe trochlear dysplasia, who were unlikely to have early OA progression. 27 Walker defined the ideal candidate for PFA as quinquagenarians with isolated patellofemoral OA and without patellar malalignment. 28 There is no consensus about the influence of age on results. Although more than half of our patients underwent PFA in their fifties, no significant difference in implant survivorship was found between them and younger or older groups.
There are several limitations to this study. First, the study had only 38 patients; six patients were lost to follow-up, and 10 patients died of diseases unrelated to the surgery. Attrition is inherent in a long-term follow-up study of patients with relatively advanced age, and the implant survivorship in our study should be interpreted with caution. Second, we did not compare the most recent KSS scores with the preoperative scores. With a mean follow-up of more than 24 years, the 10 patients were aged around 80 on average and had median UCLA scores of 3.5 points. Many of them had limited activity levels, thus, comparing them with previous scores was of little moment. For comprehensively assessing their functional outcomes, we incorporate OKS in the final follow-up.
Conclusion
We demonstrated that PFA is an effective method of treatment in patients with isolated patellofemoral OA. Patient selection is critical to lengthen PFA survival, but the appropriate indications require further study.
Footnotes
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the grants from the institutional Foundation (No. ZC201904183) and the National Natural Science Foundation of China (No. 81972046).
