TKA is a highly effective procedure that provides reliable relief from pain, improves physical function in patients with advanced knee arthropathy. Long-term follow-up study has been reported for Western Caucasian in literature with more than 90% of survivor rate after 10 postoperative years.11 It was also reported a 92.7% survival rate at 10 years follow-up with improved clinical outcome and pain relief for TKA in Chinese people.12 But as for whether or not the patella should be routinely resurfaced during primary TKA and the criteria for resurfacing, the decision still remains controversial.
We found the clinical outcome evaluation with HSS knee score, anterior knee pain, patellar complication were not statistically different after more than 10 years follow-up between the patellar resurfacing and nonresurfacing group. The nonresurfacing group had higher rate of lateral subluxation according to radiographic evaluation. The nonresurfacing group also had higher rate of AKP. Our opinion was supported by the study by Li et al.16 as well as other studies of outcome of patellar resurfacing after TKA.3,5,8,17 Li et al conducted a systematic review of patellar resurfacing in TKA, in which the indication of operation included both OA and RA, and demonstrated the average incidence of AKP of nonresurfacing group and resurfacing group was 24.1% and 12.9% respectively, patellar resurfacing in TKA can reduce the risk of reoperation with no benefit to postoperative knee function or patient satisfaction than in TKA without patellar resurfacing.16 The authors of other studies also concluded that although the nonresurfacing group had more cases of revision due to patellar cause, there was no difference of clinical outcome between different patellar strategy both for OA and RA patients.3,5,8,17 Furthermore, according to 700 cases study of Arnold et al,18 the patella remodeled over the years and matched the condylar design of the femoral prosthesis after primary TKA without patellar resurfacing. The author concluded even TKA without patellar resurfacing gave excellent long term results. In this study, patellar scoring system was adopted to evaluate the outcome of patellar resurfacing. The result also demonstrated no statistical difference between the two groups, with 27.8 point for nonresurfacing group and 28.33 for resurfacing group. Our result was consistent with the study of Fellar et al's.10 Our study also indicated that the long term survivorship was not statistically different between the two groups. The unique to this study was the using patellar related complication as the extra definition of failure for survivorship analysis. So we could study more accurately the impact of patellar strategy to long term survivorship after primary TKA. To consider the studies in literature up to now, more knee surgeon concluded it was not necessary to regularly resurface the patella during primary TKA.5,8,10,19
In this study, no difference was present for relationship of patella with the joint line between two groups. Although patellar non-resurfaced group had higher incidence of lateral subluxation from radiological results, there was no difference of anterior knee pain and HSS knee score between patients with patellar resurfacing and those without. In literature, many studies have focused on the impacting factor to clinical outcome and patellofemoral complication after TKA, but the results were controversial. It was reported the postoperative patellofemoral complication was mainly correlated with the patellar malalignment and with the impaired mechanical axis of the lower extremity.19,20 So, the patellofemoral congruency was essential to overcome the patellar related complication in TKA procedures.20 Nevertheless, other study reported there was no significant difference between the knees with no patellar incongruence and the knees with incongruence,21 and patellar strategy was not associated with the patellar congruence angle and clinical outcome.22 In future, with more high level evidence be available, it will help to answer the question.
Because thinner patellar is at higher risk of fracture given the high mechanical pressures subjected. For successful patellar resurfacing, a residual bone thickness of 15 mm was suggested after patellar osteotomy according to literature in Caucasian.23 The average thickness of patella was 20.6 mm for female and 23 mm for male in our series. The thickness was less than that of Western population, which was 22.5 mm for female and 25.3 mm for male.24 Our result was supported by the study by Li et al.8 We preferred the residual bone thickness of 12 mm for patellar resurfacing in Chinese in our practice. This opinion was also supported by the study of Kim et al.9 Furthermore, in our practice, we found the anterior femoral condyle was relatively thinner.8 With the morphological features of the knee joint in Chinese, we predicted the pressure in the patellofemoral joint in Chinese was lower than in Western patients and the incidence of patellofemoral complication was also lower.8 This may be the reason of lower AKP rate in our study than in other studies,3,13,25 with 7.3% AKP rate in patellar nonresurfacing group and 3.6% in resurfacing group, and this is what we hypothesized in the introduction of this study. Furthermore, in order to reduce the patellar related complication, the lower extremity mechanical axis should be adjusted within the physiological limits following the total knee arthroplasty.26 Jeffery et al26 reported that when the mechanical axis passed through the middle 1/3 of the prosthesis, the subsequent loosening was 3% in all of the cases; and when the mechanical axis passed through other parts of the prosthesis, the incidence of loosening was increased to 24%.26 In our practice, the lateralization of femoral component was preferred to adjust the mechanical axis within the physiological limits. Because the postoperative patellofemoral complication was mainly correlated with the patellar malalignment,20 patellofemoral tracking should be assessed after implantation of implants by ‘no thumb test’, and patellar congruence should be acquired before wound closure. Furthermore, internal rotation of the femoral or tibial component, failure to balance the soft tissue, proximally elevating of joint line and extreme valgus position of the knee should be avoided in TKA procedure with or without patellar resurfacing.14,19
For the impacting factor to the patellar complication, which included the preoperative diagnosis and the PCL strategy, the diagnosis of RA was more significant in this study according to the ‘Cox's Hazard Model’. The patellar related complication was higher in RA patients than in OA patients in our series. Patellar resurfacing during TKA was considered to have the effect to eliminate the reaction between patellar cartilage and inflamed synovium and to reduce the postopearative patellar related complication.14,15,27 So RA knee was considered an indication for patellar resurfacing in some studies. It was reported that RA patients with TKA and patellar resurfacing were more satisfied with the clinical outcome and had lower rate of AKP than the opposite side.13,27 On the contrary, some other studies reported there were no difference in terms of pain relief and patellar related complication between the two groups for RA patients.28,29 Furthermore, Fern et al29 reported even the postoperative moderate to severe AKP for RA patients who underwent TKA with patellar nonresurfacing was about 13.5%, none had secondary resurfacing. One more factor when considering the patellar resurfacing for RA patients was that the patients were reported to have high incidence of osteopenia and small patellar, according to Shoji et al's study,28 which increased the risk and difficulty for patellar resurfacing. The author concluded when RA patients had little or no deformity of patellar, it was not advisable for patellar resurfacing.28 According to our study, we more preferred that RA can be an indication of patellar resurfacing during TKA with lower postoperative complication, when the patellar bone was competent for resurfacing procedure. The knee surgeon should refer the patellar thickness, bone quality, patellar deformity after intraoperative inspection as the selection criteria of patellar resurfacing. Selective patellar resurfacing can be a reasonable strategy during TKA for RA patients.
The main limitations of the present study were that the data were collected retrospectively and the relatively higher rate of lost to follow-up. Our results were similar to the other long-term studies which had high patient attrition by 10 years.5,17 Nevertheless, in our study, the lost to follow-up had an average ROM of 95.9° at their latest follow-up which was comparable to patients completing follow-up. Furthermore, referred to the Joshi et al's study which reported a lower rate of failure for revision surgery and higher satisfactory results even in “lost to follow-up” compared with patients completing follow-up.30 Furthermore, this study represented a mixture sample of TKA with various prostheses, and the patella-friendly design and non-patella-friendly designs were not easily separated in this study. We conclude further long-term follow-up of modern prostheses in randomized studies is needed in future. However, as for the result in this study, we thought it reflected a common set-up in which many patients were treated, thus providing a typical representative of early TKAs in China. Furthermore, the power of this study was the limited long-term follow-up study in the mainland of China. We concluded, at the least, our study could provide the information about the long term follow-up outcome of patellar resurfacing and nonresurfacing in Chinese.
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