Abstract
Background
Patellofemoral arthroplasty (PFA) can be considered in patients with patellofemoral disease. However, the use of partial arthroplasty often causes concern among clinicians and patients that revision to total knee arthroplasty (TKA) will be needed and, if so, whether this revision will be straightforward or more complicated.
Questions/purposes
We set out to determine if conversion of a PFA to a TKA was more similar to a primary or to a revision TKA in terms of surgical characteristics, knee scores, range of motion, and complications.
Methods
Between 2001 and 2008, we revised 21 PFAs to TKAs, all of which were available for followup at a minimum of 5 years (median, 6 years; range, 5–12 years). These patients were matched one-to-one by age, sex, body mass index, length of followup, and preoperative Knee Society Scores (KSS) to 21 primary and 21 revision TKAs. We analyzed operative time and amount of blood loss. Clinical outcomes assessed were range of motion and KSS.
Results
Blood loss (405 mL versus 460 mL versus 900 mL; odds/hazard ratio, 1.33, 95% confidence interval [CI], 0.3–5.85; p = 0.14 for primary TKA versus revision PFA and odds/hazard ratio, 0.13, 95% CI, 0.03–0.52; p < 0.01 for revision PFA versus revision TKA) and operative time (52 minutes versus 72 minutes versus 115 minutes; odds/hazard ratio, 5.45, 95% CI, 1.23–27.4; p = 0.02 for primary TKA versus revision PFA and odds/hazard ratio, 0.5, 95% CI, 0.01–0.44; p < 0.001 for revision PFA versus revision TKA) were not different between the primary TKA and revision PFA groups but higher in the revision TKA group. KSS (knee and function) were higher in the primary TKA group (92 [range, 60–100] and 91 [range, 65–100]) than they were in the revision PFA (85 [range, 40–100] and 85 [range, 30–100]) and revision TKA groups (75 [range, 30–100] and 68 [range, 25–100]; p < 0.001). Flexion was better in the primary TKA (125 [range, 105–130]) and revised PFA (120 [range, 100–130]) groups than the revision TKA group (105 [range, 80–115]; p = 0.0013). There were more complications in the revision PFA group (two of 21) compared with the primary TKA group (zero of 21, p = 0.005) but not compared with the revision TKA group (three of 21; p = 0.85).
Conclusions
With the numbers available, we found that revising a PFA is comparable to a primary TKA in regard to surgical characteristics and postoperative clinical outcomes (including knee scores and range of motion), and both are superior to revision TKA, although the frequency of complications was higher in the revision PFA group than it was in the primary TKA group. The majority of patients undergoing revision of a PFA to a TKA can be treated with a standard implant.
Level of Evidence
Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.
Introduction
Isolated symptomatic patellofemoral (PF) osteoarthritis can occur in approximately as many as 10% of men and 25% of women older than 55 years of age [10, 20]. It can cause anterior knee pain that may limit daily activities such as standing up from a chair or climbing stairs. Several medical and surgical treatments have been proposed [11, 25]. In cases of failed conservative management, isolated replacement of the PF joint can be considered as an alternative to a TKA. McKeever was the first to publish results of patellar resurfacing in 1955 [21]. The first generation of patellofemoral arthroplasties (PFAs), developed during the 1970s, was a pure resurfacing technique without any anterior femoral cut (“inlay” technique). Since then, studies have reported a survival rate between 58% and 86% with a followup between 10 and 17 years [3, 4, 6, 7, 9, 14, 19]. Better survival rates (approximately 90% at 10 years) have been reported with a second generation (“onlay technique”) of PFAs, which have a different design requiring an anterior femoral cut [1, 9, 16, 17, 22], whereas other studies showed lower survival rates [9, 12].
Progression of the disease in the medial compartment and loosening of the components are the two major causes of failure, which may be related to poor indications, problems with implant design, and/or poor surgical technique [5, 15, 27]. If revision is required, most PFAs are converted to a TKA [5, 27]. Whereas a few studies have investigated the outcomes of TKA after PFA [12, 18, 28], there are limited clinical outcomes data and high complication rates reported in the literature [12].
As such, the goals of our study were to compare (1) surgical characteristics and complexity; (2) clinical outcomes, including knee scores and ROM; and (3) complications of revised PFAs to both primary and revision TKAs in a one-to-one matched cohort.
Patients and Methods
Between 2001 and 2008, we revised 21 PFAs to TKAs, 100% of whom were available at a minimum of 5 years (median, 6 years; range, 5–12 years). One patient died 6 years after the revision and was therefore not available for the last review. For this patient, the systematic 5-years followup examination was used. In this comparative retrospective study, all the patients included were operated on at a single institution by one of two senior surgeons (J-NAA, SP). These patients were then matched one to one based on age, sex, body mass index (BMI), preoperative Knee Society Score, and date of the index surgery (± 6 months) to 21 patients who underwent primary TKA and 21 patients who underwent revision TKA. All patients had a minimum followup of 5 years (median, 6 years; range, 5–12 years). During the study period, revision PFA represented 0.5% and revision TKA 10% of all knee arthroplasties performed in our department.
Patients were included in the revision PFA group if they had an “inlay” or “onlay” PFA, aseptic loosening, or progression of disease in additional compartments and chose to undergo revision. Patients undergoing primary TKA were included if they had severe clinical and functional limitations and radiological evidence of end-stage arthritis according to the Ahlback grading system [2]. Patients in the revision TKA group were revised for aseptic loosening (13 patients), instability (two patients), malrotation (four patients), or pain related to an oversized component (two patients) based on the correlations between the CT scan and the physical examination. Revision TKAs were performed with a posterior-stabilized (PS) implant, and all patients had a minimum followup of 5 years. The exclusion criteria included the following: history of infection of the knee, septic loosening, or revision performed with a hinged TKA. Thus, 21 patients were included in each of the three groups. Patients were stratified according to the Charnley classification [8]. Demographics including age, sex, and BMI were comparable in the three groups with a median age of 77 years (range, 42–88 years), the majority of patients being women (75%) with a median BMI of 26 kg/m2 (range, 21–47 kg/m2) (Table 1).
Table 1.
Demographics of the three groups
| Demographic* | Revision PFA (N = 21) | Revision TKA (N = 21) | Primary TKA (N = 21) |
|---|---|---|---|
| Age (years)† | 77 (42–88) | 75 (45–87) | 76 (43–90) |
| Male sex† | 5 | 5 | 5 |
| BMI (kg/m2)† | 26 (21–47) | 27 (21–45) | 26 (20–44) |
| Median number of previous knee procedures | 2 (1–3) | 2 (1–4) | 1 (0–2) |
| Followup (years)† | 6 (5–12) | 6 (6–12) | 6 (5–11) |
| Charnley classification [8] | |||
| A | 10 | 5 | 15 |
| B | 8 | 13 | 5 |
| C | 3 | 3 | 1 |
* Data presented as number, except where indicated as median and range; †no statistical difference between any groups; PFA = patellofemoral arthroplasty; BMI = body mass index.
Reason for revision was mainly progression of arthritis (80%) in the revision PFA group and aseptic loosening (62%) in the revision TKA group (Table 2). In all three groups, implant choice was based on a standardized preoperative radiographic evaluation including AP, lateral, and Merchant views of the knee in addition to a full-length standing hip-to-ankle radiographs. From a surgical standpoint, all patients had a standard medial parapatellar approach and all femoral and tibial components were cemented. In keeping with our standard practice, a high-flexion PS TKA system was used for all primary TKAs and revision PFA, whereas a revision PS system was chosen for the revision TKAs. In the revision PFA group, defects left by the trochlear prostheses were generally removed by the standard successive cuts of the femur. No differences in terms of trochlear bone defects were observed between the removal of “inlay” or “onlay” prostheses. Four patients had additional procedures at the time of PFA, including three who underwent anterior tibial tuberosity transfer and one who underwent high tibial osteotomy. Any hardware from these procedures that interfered with prosthesis fit at the time of revision was removed. Stems and augments were used in 100% and 71% of cases, respectively, in the revision TKA group, whereas none were required in the revision PFA group (Fig. 1). In the two groups of revisions (ie, revision PFA and revision TKA), the patellar implant was only revised if loosening, malposition, wear, or maltracking was noted. This occurred in 38% of cases in the revision PFA group and 48% of cases in the revision TKA group. In keeping with our standard practice, the patella was replaced in all primary TKAs. The same drainage protocol was used for all the patients with the drain removed on postoperative day 2. All patients were weightbearing as tolerated postoperatively and all patients received routine prophylaxis with low-molecular-weight heparin postoperatively for 31 days.
Table 2.
Surgical characteristics of the three groups
| Revision PFA group (N = 21) | Primary TKA group (N = 21) | Revision TKA group (N = 21) | ||||
|---|---|---|---|---|---|---|
| Time from index operation to revision (years), median (range) | 9 (1–21) | NA | 10 (1–17) | |||
| Reasons for revision | Progression of disease | 17 | NA | Aseptic loosening | 13 | |
| Aseptic loosening | 3 | Malrotation | 4 | |||
| Wear | 1 | Instability | 2 | |||
| Oversized component | 2 | |||||
| Implant removed | Inlay | 18 | NA | CR cementless | 8 | |
| CR cemented | 8 | |||||
| Onlay | 3 | |||||
| PS cemented | 5 | |||||
| Amount of revision constraint | Posterior-stabilized | 21 | Posterior-stabilized | 21 | CCK | 21 |
| Stem used | 0 | 0 | 21 | |||
| Augments used | 0 | 0 | 15 | |||
| Patellar prosthesis exchanged | 8 | NA | 10 | |||
| Mean polyethylene thickness (mm), median (range) | 11 (10–14) | 11 (10–14) | 13 (10–17) | |||
PFA = patellofemoral arthroplasty; NA = not applicable; CR = cruciate-retaining; PS = posterior-stabilized; CCK = condylar constrained knee.
Fig. 1A–D.
Preoperative (A) AP and (B) lateral radiographs showing a failed PFA for progression of arthritis 17 years after implantation. The revision PFA (C) AP and (D) lateral radiographs at 6 years postoperatively reveal that the components are well-fixed and well-aligned.
Operative time was assessed using the time from incision to the end of the closure. Blood loss was analyzed using the Mercuriali method [23].
At last followup, patients were analyzed clinically and radiologically by an independent observer (AL, MO) using the Knee Society rating system [13]. ROM was assessed by using a two-arm goniometer.
Complications were reported as a reoperation when no implant exchange was performed and as a revision if the prosthesis was removed and replaced.
Statistical Analysis
Patient demographics, results of ROM, and Knee Society knee and function scores were described using medians (ranges) for continuous variables or numbers (percent) for categorical variables. The Wilcoxon test for pair comparison was used to analyze results of the objective clinical improvement as described by the mean Knee Society knee and function scores and the ROM. Odds ratios were reported with 95% confidence intervals (CIs) and considered significant if excluding the value of 1. Endpoints for odds ratio calculation were defined as 750 mL for blood loss, which is the cutoff value between Grade I and Grade II of the acute blood loss categories defined by the American College of Surgeons. The endpoint for surgical time was defined as 60 minutes, which is our mean surgical time for a primary TKA in the department. Analysis was performed using SPSS software (Version 20; SPSS Inc, Chicago, IL, USA). All statistical tests were two-sided, and p values of < 0.05 were considered statistically significant.
Results
Surgical Characteristics
Median blood loss was 405 mL (range, 380–1000 mL) for the primary TKA group, 460 mL (range, 250–1000 mL) in the revision PFA group, and 900 mL (range, 600–1500 mL) in the revision TKA group. For an estimated 750-mL blood loss, the odds/hazard ratio was 1.33 (95% CI, 0.3–5.85; p = 0.14) for primary versus revision PFA, and the odds/hazard ratio was 0.13 (95% CI, 0.03–0.52; p < 0.01) for revision PFA versus revision TKA. Median operative time was 52 minutes (range, 45–92 minutes) for the primary TKA group, 72 minutes (range, 55–102 minutes) for the revision PFA group, and 115 minutes (range, 60–140 minutes) in the revision TKA group. For an estimated operative time of 60 minutes, the odds/hazard ratio was 5.45 (95% CI, 1.23–27.4; p = 0.02) for primary versus revision PFA, and the odds/hazard ratio was 0.5 (95% CI, 0.01–0.44; p < 0.001) for revision PFA versus revision TKA. Surgical characteristics of revision PFA were more like a primary TKA than a revision TKA (Table 3).
Table 3.
Comparison of surgical characteristics, clinical outcomes, and complications among the three groups
| Parameters analysed in the different groups | Primary TKA, mean (N = 21) |
p value | Revision PFA, mean (N = 21) |
p value | Revision TKA, mean (N = 21) |
|||
|---|---|---|---|---|---|---|---|---|
| Blood loss (mL) | 405 (380–1000) | 0.15 | 460 (250–1000) | < 0.001 | 900 (600–1500) | |||
| Operative time (minutes) | 52 (45–92) | 0.005 | 72 (55–102) | < 0.001 | 115 (60–140) | |||
| Preoperative | Postoperative | Preoperative | Postoperative | Preoperative | Postoperative | |||
| ROM (°) | 110 (90–130) | 125 (105–130) | 0.55* | 95 (90–125) | 120 (100–130) | 0.0013* | 90 (65–110) | 105 (80–115) |
| KSS | Preoperative | Postoperative | Preoperative | Postoperative | Preoperative | Postoperative | ||
| Knee | 60 (25–84) | 92 (60–100) | < 0.001* | 60 (35–87) | 85 (40–100) | < 0.001* | 58 (25–85) | 75 (30–100) |
| Function | 45 (22–85) | 91 (65–100) | < 0.001* | 43 (16–83) | 85 (30–100) | 0.003* | 42 (15–83) | 68 (25–100) |
| Complications | ||||||||
| Reoperation | 0 | 0.005 | 2 | 0.85 | 2 | |||
| (Re-)revision | 0 | 0 | 1 | |||||
Ranges are shown in parentheses; *statistical comparison for the postoperative results; PFA = patellofemoral arthroplasty; KSS = Knee Society Score.
Clinical Outcomes
Median flexion at 125° (range, 105°–130°) in the primary TKA group was not different compared with 120° (range, 100°–130°) in the revision PFA groups (p = 0.55). The flexion in the revision TKA group was lower than both other groups at 105° (range, 80°–115°) (p = 0.0013). No stiffness (defined as flexion less than 100°) was observed in the primary TKA or revision PFA groups. However, two patients in the revision TKA group had flexion < 90° and were treated with passive and active flexion physiotherapy.
At most recent followup, patients undergoing primary TKA had higher Knee Society knee and function scores than did either of the revision groups. The postoperative Knee Society knee score was different at 85 (range, 40–100) in the revision PFA group compared with 92 (range, 60–100) in the primary TKA group (p < 0.001) and 75 (range, 30–100) in the revision TKA group (p < 0.001). The postoperative Knee Society function score was different at 85 (range, 30–100) in the revision PFA group compared with 91 (range, 65–100) in the primary TKA group (p < 0.001) and compared with 68 (range, 25–100) in the revision TKA group (p = 0.003). Improvements were observed for the Knee Society knee and function scores in all three groups but with higher improvement in the primary TKA group compared with the two revision groups.
Complications
There were more postoperative complications in the revision PFA group (two of 21) compared with the primary TKA group (zero of 21, p = 0.005), but with the numbers available, the number of complications was not different between the revision PFA group and the revision TKA group (three of 21; p = 0.85). No reoperation or revision was required in the primary TKA group, and no rerevision was required in the revision PFA group. However, one repeat revision was required in the revision TKA group as a result of a deep periprosthetic infection resulting in septic loosening. This patient was treated with a two-stage exchange; at last followup, there was no sign of infection with satisfactory clinical results. Two patients in the revision PFA group had acute hematomas on the fourth postoperative day. Both patients required a reoperation consisting of open irrigation and débridement. Prostheses were intact in both cases and no infection was identified after 14 days of cultures. One patient in the primary TKA group had a postoperative hematoma at 10 days postoperatively. However, this was treated nonoperatively.
No intraoperative complications occurred.
Discussion
Patellofemoral arthroplasty is an option for younger patients with isolated PF disease with mixed results reported for revision to TKA. Although two papers have reported satisfactory results [18, 28], a third highlighted the high rate of complication related to the extensor mechanism [12]. We sought to determine whether the results of revision PFA were more comparable to results observed after primary TKA than those after revision TKA. Specifically, the goals of this study were to compare (1) surgical characteristics; (2) clinical outcomes, including knee scores and ROM; and (3) complications of revised PFAs to both primary and revision TKAs. We found that the operative time and blood loss of revising a PFA to TKA were not different with the numbers available to a primary TKA but less than a traditional revision TKA. Moreover, Knee Society knee and function scores improved in all three groups but were better for the primary TKA and revision PFA groups compared with the revision TKA group. However, the frequency of complications was higher in the revision PFA group than it was in the primary TKA group. With the numbers available, in this regard the revision PFA group could not be distinguished from the revision TKA group.
Our study has limitations. Foremost, this is a retrospective study and thus does not necessarily capture all aspects of each patient’s clinical presentation. Although we attempted to address this by matching our patients with respect to demographic attributes and KSS, patients presented for surgery with different preoperative levels of ROM. Patients also presented with different associated procedures. As such, an exact match for each patient was not possible and this may represent a selection bias. To limit the selection bias, the matching was including as many factors as possible including patient demographics, timing of surgery, and patient preoperative performance. The small number of patients was also a limitation in our study and limits the comparison between “inlay” and “onlay” PFA revisions as well as whether the patellar button is exchanged. Thus, we cannot comment on the possible differences between these surgical options. The number of patients included however is one of the largest reported in the literature and the comparison of the results is original in the literature.
We sought to determine whether the operative time and blood loss in revision PFA would be similar to that of primary TKA. There was minimal femoral bone loss associated with the PFA; therefore, the use of a standard primary device was possible without the need for supplemental stems, augments, or bone grafting and could explain the surgical ease with which these patients were revised. This is similar to the findings of two previously published series [18, 28], in which a standard prosthesis was used for the revision. However, in the studies of Huten [12], a stem was required on the femoral implant in two cases and autologous bone grafting was required in nine cases as a result of severe bone loss in the trochlear. Thus, as advocated by Lonner et al. [18], a stem was used if there was a notch in the anterior cortex of the femur that extended more proximal than the proximal portion of the anterior flange of the femoral component. In regard to operative time and blood loss of revising a PFA, both appeared more similar to a primary TKA rather than to a revision TKA, likely for the reasons noted.
Functional results improved in all three groups but were better for the primary TKA group. In addition, ROM was lower in the revision TKA group when compared with the two other groups. Our results are similar to other studies [12, 18, 28] (Table 4). However, unlike other studies, we did not perform any manipulations under anesthesia. This may be attributable to the fact that our patients were older (mean age, 75 years; median age, 77 years) compared with the other series. Younger age has been shown to be a risk factor for stiffness by Parvizi et al. [24]. In the other series of revision PFAs to TKAs, the mean ages at revision were 50 years [18], 67 years [28], and 65 years [12]. However, patients undergoing primary TKA fared better in regard to both the Knee Society pain and function scores. It is important to note that the two groups of revision PFA and revision TKA had a higher proportion of Charnley B (eight of 21 in revision PFA and 13 of 21 in revision TKA) and C patients (three of 21 in revision PFA and three of 21 in revision TKA) when compared with the primary TKA group (six of 21). Our results are in accordance with a recent paper [26], in which patient limitations of daily living (walking, climbing stairs, and rising from a chair) after primary or revision TKA improved, but to a lesser degree after a revision TKA.
Table 4.
Functional scores after TKA for revision of patellofemoral arthroplasty in the different series of the literature
| Series | Number of knees | Number of centers | Mean followup (years) | KSS pain | KSS function | ROM |
|---|---|---|---|---|---|---|
| Huten [12], 2012 | 52 | 12 | 4.5 | 79 | 52 | 108° |
| Lonner et al. [18], 2006 | 12 | 1 | 3.1 | 96 | 91 | 122° |
| Van Jonbergen et al. [21], 2009 | 14 | 1 | 5.7 | 76 | 82 | 117° |
| Current series, 2014 | 21 | 1 | 7.2 | 80 | 79 | 120° |
KSS = Knee Society Score.
The frequency of complications was higher in the revision PFA group than it was in the primary TKA group, and with the numbers available, in this regard the revision PFA group could not be distinguished from the revision TKA group. The most common complications after revision PFA are related either to stiffness or extensor mechanism problems such as loosening or fracture of the patellar button, extensor mechanism rupture, or patellar instability [12]. In our series, the patellar button was exchanged in 38% of cases secondary to loosening or wear. However, we did not appreciate any complications with the extensor mechanism. This is likely related to the fact that minimal bone loss had occurred and all patellar buttons removed had a small central peg. However, it may also be because extensor mechanism complications such as fracture, rupture, and gross patellar instability are relatively uncommon, and our series was small with only 21 revisions. Van Jonbergen et al. [28] revised the patellar component in all cases because the prosthesis had a long midline central ridge, which could lead to maltracking and/or increased wear. In the series by Lonner et al. [18], the design of the femoral prosthesis used was accommodating to the retained patellar prosthesis, and in each knee, the original all-polyethylene dome-shaped patellar prosthesis was left in place. In both studies [18, 28], no complications were reported related to the extensor mechanism. It is important to highlight that a polyethylene dome-shaped patellar button compatible with conventional TKA designs should be considered for primary PFAs to facilitate future revisions [4].
In conclusion, PFA represents a valuable treatment option for isolated end-stage osteoarthritis of the PF joint. However, even with appropriate indications, meticulous surgical technique, and the use of reliable implants, revisions of PFAs remain common. In our experience, revising a PFA is more similar to a primary TKA than to a revision TKA in terms, operative time, blood loss, and clinical outcomes (such as ROM and knee scores). However, postoperative complications are more common in revision PFA than in primary TKA, and patients need to be counseled accordingly.
Acknowledgments
We thank Vanessa Pauly PhD, in Health Economic and Statistics for her help with the statistical analysis.
Footnotes
The institution of one or more of the authors (MPA) has received funding from Biomet (Warsaw, IN, USA), DePuy (Warsaw, IN, USA), Stryker (Mahwah, NJ, USA), and Zimmer (Warsaw, IN, USA). One author certifies that he (J-NA), or a member of his immediate family has received between USD 100,000 and USD 1,000,000 from Zimmer Inc (royalties and consultant). One author certifies that he (SP), or a member of his immediate family, has received between USD 10,000 and USD 100,000 from Zimmer Inc (development of educational programs).
All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research ® editors and board members are on file with the publication and can be viewed on request.
Each author certifies that his or her institution approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained.
This work was performed at Aix-Marseille University, Marseille, France.
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