Do optional implants improve the femoral fit during total knee arthroplasty in Asians? Comparison of the femoral fit between single- and dual-option implants
Introduction
Optimal fit of implants during total knee arthroplasty (TKA) is an important factor for successful outcome [1]. Inappropriate femoral fitting can affect the loads at the interface of the tibiofemoral and patellofemoral joints and lead to stiffness, instability, pain, and catastrophic early failure [2]. Increased tension and friction of the capsular and ligamentous structures due to oversized implants have an adverse effect on clinical outcome, while undersized implants have their own set of problems, theoretically allowing friction of soft tissue on the bony ridges of uncovered cancellous bone surfaces and causing pain [3], [4], [5].
Fitting of the femoral component may be more complicated than that of the tibial implant because femoral components need to be chosen considering both anterior–posterior (AP) and medial–lateral (ML) dimensions. In addition, they should also be properly fitted to the anterior flange area and distal cutting surface together. Therefore, various TKA systems have attempted to design and provide implants of different sizes and dimensions [5]. In addition, there have been trials to increase optimal fitting using two options, namely narrow and standard, for femoral components of the same AP size [6]. The narrow option of femoral components was developed by certain manufacturers to overcome peripheral component over-hang, especially common in Asian patients [6]. Prostheses manufacturers have increased the available size range such that the implants fit well and peripheral component over-hang can be prevented [7].
Even with the advancement and availability of various femoral implant sizes, selecting a femoral component for Asian patients to ensure a good-fit can be challenging. Most knee implants are based on studies involving North American and European patients. Although these continents have a variety of ethnic populations, the implant designs are mainly based on the average male Caucasian knee [8]. Asian knees are generally smaller than Caucasian knees and the ratio between the AP and ML dimensions is notably different [5], [9], [10], [11]. One Asian study performed a fitting study using dual-option implants (narrow and standard) [5]. They concluded that the availability of dual-option implants substantially improved the optimal fitting of femoral components in the Korean population. However, this study was limited to the old version of single-option implant and two types of dual-option implants. In addition, their analysis of the anterior flange that shows most prominent cases of over-hang was omitted because they did not evaluate the ML dimension of the anterior flange.
Therefore, the purpose of this study was to evaluate the fit in Asian patients by examining whether (1) the advanced single-option implant improves the fitting of the femoral component in both the anterior flange and distal cutting surface and (2) the dual-option implants show better fitting than the advanced single-option implant. The following hypotheses were proposed: (1) the advanced single-option implant will improve the fitting of the femoral component in both the anterior flange and distal cutting surface as compared with the old version and (2) the dual-option implants will show better fit in both the anterior flange and distal cutting surface than the advanced single-option implant.
Section snippets
Demographics
This study was performed as a retrospective case series consisting of 950 knees of Korean patients who underwent primary TKA performed by a single surgeon between February 2017 and July 2019 (mean follow up, 26.18 ± 6.42 months). The inclusion criteria were: (1) primary TKA for a diagnosis of primary varus osteoarthritic knee along with disabling pain in the knee joint, (2) posterior stabilized (PS) type prosthesis, and (3) femoral component size was decided with anterior referencing technique.
Demographics
Preoperative demographic characteristics are listed in Table 2. The distribution of implants was as follows. Among the 950 knees, 247, 189, 180, 178, and 156 knees were, respectively, implanted with the old version single-option implant system (Logic), advanced version single-option implant system (Truliant), Anthem, Attune, and Persona. Age, sex ratio, and body mass index (BMI) were not significantly different among the five types of implants.
Femoral cutting surface
Average length of femoral cutting surface generally
Discussion
The principal findings of this study were that (1) the advanced single-option implant system led to a better fit than the old version single-option implant system and (2) the fitting of the advanced single-option implant was comparable with that of the three dual-option implant systems. The advanced single-option implant showed higher good-fit rate than the old version single-option implant system in all anterior flange and distal femur cutting surface areas. In addition, the over-hang and
Conclusions
The advanced single-option implant system improved the fit of the femoral component when compared with the old version and showed similar good-fit rates compared with the dual-option implant systems. The narrow option of the dual-option implant systems was used less frequently than expected in Asian knees.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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