Published online Sep 07, 2023.
https://doi.org/10.4055/cios22253
Patella Cartilage Status Does Not Affect the Clinical Outcomes of Non-resurfaced Patella in Mobile-Bearing Total Knee Arthroplasty
Abstract
Background
During total knee arthroplasty (TKA), patellar retention is performed when the cartilage is fairly well preserved and the thickness of the patella is relatively thin. However, clinical outcomes of the non-resurfaced patella in TKA according to the cartilage status are lacking in the literature. The purpose of this study was to compare patient-reported outcome measures (PROMs) according to the grade and location of the patellar cartilage lesion in TKA patients.
Methods
The outcomes of 165 osteoarthritis patients (186 knees) who underwent cemented mobile-bearing TKA without patellar resurfacing were assessed and classified according to the grade and location of the patellar cartilage lesion. PROMs using the Western Ontario and MacMaster Universities Osteoarthritis index, the Knee Society Score (Knee Society Function Score and Knee Society Knee Score), and the Hospital for Special Surgery score were evaluated preoperatively and at postoperative 2, 4, 6, and 8 years. The correlations between PROMs and the grade and location of the cartilage lesion were assessed. Additionally, radiologic outcomes including the patellar tilt angle and patellar height were assessed and their correlation with the grade of cartilage lesion was analyzed. Analysis of variance was used to determine statistical significance.
Results
There was no significant difference between PROMs according to the grades and locations of cartilage lesions at any postoperative follow-up. Radiologic parameters also showed no significant differences according to the grades of patellar cartilage lesions.
Conclusions
The grade and location of the patellar cartilage lesion had no influence on clinical outcomes in mobile-bearing TKA with patellar retention at short- and long-term follow-up.
Total knee arthroplasty (TKA) is a widely established treatment option for knee osteoarthritis. Over the past several decades, surgical techniques of TKA have made significant progress. However, whether or not to resurface the patella still remains controversial in TKA.1, 2, 3)
Generally, patellofemoral pressure increases after TKA, which may subsequently lead to anterior knee pain. On the other hand, anterior knee pain might decrease after TKA owing to procedures such as patellar osteophyte removal and ligament balancing. Moreover, it is well accepted that denervation of the patella with electrocautery can reduce anterior knee pain after TKA even without patellar resurfacing.4)
Some authors advocate patellar resurfacing in that patients feel less pain and perform better in activities such as climbing stairs.5, 6) On the other hand, others argue that there are no advantages in pain or function after patellar resurfacing. Previous studies have reported that there was no difference in the revision rate between patellar resurfacing and non-resurfacing groups.7, 8) In addition, complications such as component wearing, patellar fracture, ligament rupture, patellofemoral malalignment, and anterior knee pain may possibly occur due to patellar resurfacing. Schiavone Panni et al.9) reported that the overall complication rate of patellar resurfacing was 7%. As described above, there are many different, conflicting opinions on patellar resurfacing in TKA.
According to various studies, patellar resurfacing may be decided based on several intraoperative factors.5, 10, 11, 12) Patellar retention is usually recommended when the cartilage status is not poor and the thickness of the patella is relatively thin. Keblish et al.13) suggested that there are some strong indications for patellar resurfacing: (1) large and thick patella, (2) deformed and non-conforming patella, (3) severe preoperative anterior knee pain, (4) multiple previous operations, and (5) poor patient compliance.
Poorer cartilage status may be closely related to anterior knee pain. However, little is known about the relationship between the cartilage status and the degree of anterior knee pain of the non-resurfaced patella in TKA. To the best of our knowledge, to date, no previous studies have focused on the relationship between the cartilage status of patella and the clinical outcomes of TKA.
The purpose of this study was to compare the patientreported outcome measures (PROMs) according to the grade and location of the patellar cartilage lesion. Radiological outcomes were also compared. The authors hypothesized that the grade and location of the patellar cartilage lesion may be associated with the clinical outcome of TKA.
METHODS
Study Participants
This prospective study was approved by the Institutional Review Board of Seoul National University Hospital (No. H-1104-065-358), and written informed consent was obtained from all participants. A total of 165 patients with degenerative knee osteoarthritis (186 knees) undergoing primary TKAs were enrolled from November 2008 to May 2011. All of the knees were operated using the same instrument: cemented Low Contact Stress (LCS; DePuy Orthopaedics, Warsaw, IN, USA) mobile-bearing system. The patella was preserved in all surgeries. Patients with systemic inflammatory disease such as rheumatoid arthritis and those with a history of knee joint infection were excluded (Fig. 1). Out of 165 patients, 12 patients were men and the average age and body mass index were 67.7 ± 7.7 years and 26.5 ± 3.4 kg/m2, respectively.
Fig. 1
Flowchart of patient selection in this study. TKA: total knee arthroplasty.
Surgical Technique
The TKAs were performed by a single, senior surgeon with more than 20 years of arthroplasty experience (MCL) using the same technique. After an anterior mid-line incision, a standard medial parapatellar arthrotomy was performed. Fat pad was minimally resected for joint exposure and guide insertion. An intramedullary guide was used for the femoral resection, while an extramedullary guide was used for the tibial resection. The posterior cruciate ligaments were retained, and mobile-bearing inserts were implanted in all patients. After an anteroposterior (AP) cut was completed using a femoral cutting block guide, the flexion gap was measured. If the flexion gap was larger than the extension gap, the femoral block was set 2 mm posterior to its initial position. The medial and lateral flexion gap differences were accepted if < 2 mm when measured using a laminar spreader. All prostheses were fixed with cement and the patella was managed by removal of osteophytes, peripheral electrocauterization for denervation, and additional contouring in cases with significant deformity. Before these procedures, patella thickness was measured using a surgical vernier caliper, and gross photographs of the patellar cartilage were taken intraoperatively to evaluate the severity and location of cartilage lesions. The same digital camera was used to take all the photographs by the same surgeon (MCL).
Patellar Cartilage Status Evaluation
The patellar cartilage was evaluated by the grade and location of the lesions. Cartilage lesion grade was determined using the International Cartilage Repair Society (ICRS) grading system. When there were more than 2 lesions, the grade of the more severe lesion was selected.
To describe the location of the patellar cartilage lesion, the authors quoted a previous paper14) published by our group. The classifications are as follows: type 1, no or minimal lesion; type 2, medial facet without central ridge; type 3, lateral facet without central ridge; type 4, central ridge only; type 5, medial facet with central ridge; type 6, lateral facet with central ridge; and type 7, global lesions (Fig. 2).
Fig. 2
Classification of the location of patellar cartilage lesions: type 1, no or minimal lesion; type 2, medial facet without central ridge; type 3, lateral facet without central ridge; type 4, central ridge only; type 5, medial facet with central ridge; type 6, lateral facet with central ridge; type 7, global lesions. L: lateral facet, C: central ridge, M: medial facet.
Clinical and Radiologic Evaluations
For clinical evaluation, PROMs including Hospital for Special Surgery score, Knee Society score (Knee Society score: Knee Society knee score and Knee Society function score), and Western Ontario and McMaster Universities (WOMAC) score were obtained. The clinical scores were measured by an independent observer blinded to the study (JYC). The following four elements that represent anterior knee pain and related-function in WOMAC questionnaire were separately analyzed: (1) pain when going up or down stairs, (2) difficulty ascending stairs, (3) difficulty descending stairs, and (4) difficulty rising from sitting. Additionally, the range of motion (ROM) of the knee was also assessed. All clinical evaluations were performed preoperatively and biannually thereafter. Correlations between the cartilage lesion grade and the clinical parameters were analyzed.
Furthermore, to figure out the relationship between the location of the patellar cartilage lesion and the clinical variables, two methods were used. First, medial, lateral, and global lesions were compared (types 2, 5 vs. types 3, 6 vs. type 7, respectively). Next, localized and diffuse lesions were compared (types 2, 3 vs. types 4, 5, 6, 7, respectively). Correlations between the cartilage lesion location and the clinical parameters were analyzed.
Radiologic evaluations were performed to figure out whether the patellar tilt or height was related to the grade of a patellar cartilage lesion. For radiologic evaluations, the patellar tilt angle and patellar height (Insall-Salvati ratio and Blackburne-Peel index) were measured at postoperative 2 years. The patellar tilt angle and patellar height were each measured on the axial and lateral plain radiographs. All radiologic variables were measured by two observers blind to the study (DHR and HSH). The intra-class correlation coefficient was 0.92. Radiologic measurements were compared according to the ICRS grade.
Statistical Analysis
Student t-test or Mann-Whitney test was used in comparing the 2 groups, while analysis of variance or Kruskal-Wallis test was used to compare three or more groups in analyzing the clinical and radiologic parameters. The statistical significance was set at p < 0.05. Post hoc test was performed using Bonferroni, Tukey, Duncan, and Dunnett’s T3 methods.
All statistical analyses were performed using IBM SPSS software ver. 25.0.0 (IBM Corp., Armonk, NY, USA).
RESULTS
The mean (standard deviation) patella thickness was 21.1 mm (2.0 mm). The grades and locations of the cartilage lesions of the studied patients are presented in Tables 1, 2, 3. There was no significant difference between the clinical scores according to the grade of cartilage lesion preoperatively and at any postoperative follow-up (Table 4). Likewise, there was no significant difference between postoperative radiologic parameters according to the ICRS grade of the patella (Table 5).
Table 1
The ICRS Grade of the Study Patients
Table 2
The Location of the Patellar Cartilage Lesion in the Study
Table 3
Two Different Classifications of Cartilage Lesion Location and the Number of Patients in the Study
Table 4
Clinical Variables According to the Grade of Patellar Cartilage Lesion in each Postoperative Time Period
Table 5
Average Patellar Tilt and Hieght According to the ICRS grade of Patellar Cartilage Lesion in the Study
Subgroup analyses were performed to evaluate the effect of the cartilage lesion location on PROMs. According to the above-mentioned two methods for classifying the cartilage lesion locations (Table 3), there was no significant difference between PROMs according to the location of the cartilage lesion at the short- and long-term follow-up (Tables 6 and 7).
Table 6
Clinical Variables According to the Location (Medial, Lateral and Global) of Patellar Cartilage Lesion in Each Postoperative Time Period
Table 7
Clinical Variables According to the Location (Localized and Diffuse) of Patellar Cartilage Lesion in Each Postoperative Time Period
DISCUSSION
This study is a long-term follow-up study of PROMs and radiological outcomes in patellar retention patients in TKA. The object of this study was to identify if there were any significant differences between the PROMs regarding the severity and location of the patellar cartilage lesions, and in short, no significant differences were observed.
As above-mentioned in the introduction, there have been many studies comparing the clinical outcomes of patellar resurfacing and retention in TKA, and conflicting results have been reported. According to certain previous studies,7, 8, 10) non-resurfacing of the patella in TKA can lead to good clinical results as in our study, whereas non-resurfacing of the patella may cause anterior knee pain and poorer functional outcome.5, 6) But to our knowledge, there has been no long-term study on the relationship between the characteristics of the patellar lesions and PROMs in patella-retained TKAs. We investigated not only the grade but also the location of patellar lesions and neither of them affected the PROMs. The results of our study suggest that maybe the patellar cartilage lesion itself is not the cause of anterior knee pain after TKA.
Meanwhile, the prosthesis design has been regarded as a core etiologic factor causing anterior knee pain after TKA.15) Although problems of the patellar clunk syndrome have been mostly resolved with the evolution of posterior-stabilized TKA designs, rotating platform (RP) designs are known to be susceptible to patellar clunk syndrome.16) Painful patellar clunk occurred in 9.7% of the patients with Press-Fit Condylar Sigma RP/rotating platform-flex knee system (PFC RP/RPF), while the incidence was low with the PS type of the same instrument. Similarly, high rates of patellar clunk syndrome have been also reported by other authors: 11 of 71 PFC RPF TKAs (16.7%) and 15 of 113 PFC RP TKAs (13.3%).17, 18) Several studies have claimed that prosthesis designs are associated with increased patellofemoral joint problems. For example, femoral box designs with a sharp transition into the intercondylar notch and proximally positioned or wide femoral box designs are associated with patellofemoral joint problems including patellar clunk syndrome and anterior knee pain.19, 20, 21, 22) Fukunaga et al.18) suggested that the larger intercondylar box ratio (ratio between the length of the intercondylar box and the AP dimension of the femoral component) might be one of the reasons for the higher incidence of patellar clunk syndrome. The design of LCS system we used in this study was relatively anatomical on the skyline view of the plain radiograph (Fig. 3). The intercondylar portion of the femoral component and the non-resurfaced patella were maintained with great congruency. Maybe this could have caused less patellofemoral contact stress and eventually led to prevention of anterior knee pain. There was no case of revision surgery due to patellofemoral joint problems including anterior knee pain in all 186 knees of this study.
Fig. 3
Skyline radiographs of a patient who underwent total knee arthroplasty using the Low Contact Stress system with patellar preservation. Note that the patella sits congruently on the femoral sulcus of the implant.
It is not to say that patellar resurfacing is unnecessary in all TKAs. Previously, many studies reported that resurfacing of the patella resulted in less anterior knee pain and better functional outcomes.5, 6, 10) But the authors carefully hypothesized that for certain instruments like LCS system that we used, patellar retention was not inferior to patellar resurfacing if the designs of patellofemoral components were similar to the native anatomy. Of course, tentative managements of the patella including osteophyte removal, peripheral electrocauterization for denervation, and contouring were needed in all cases.
There were several limitations of the study. First, in this study, there was a lack of a scoring system that specifically represents anterior knee pain, such as the Kujala anterior knee pain scale. Instead, the authors used 4 items of the WOMAC score questionnaire that may reflect the patellofemoral symptoms. Moreover, results cannot be directly applied to all TKA instruments because the study was performed using a single instrument system. In addition, there was no comparison between the patellar resurfacing group and the retention group. Nevertheless, long-term clinical outcomes of patellar retention in TKA could be obtained.
In conclusion, the grade and location of the cartilage lesions of the patella did not affect the clinical outcomes of the non-resurfaced patellae in mobile-bearing TKAs.
CONFLICT OF INTEREST:No potential conflict of interest relevant to this article was reported.
ACKNOWLEDGEMENTS
Ju Young Cho (JYC), who was a researcher at Seoul National University Hospital, conducted surveys to assess the clinical scores and was blinded to this study.
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