Do optional implants improve the femoral fit during total knee arthroplasty in Asians? Comparison of the femoral fit between single- and dual-option implants

Abstract

Background

The purpose of this study was to evaluate the femoral fit in Asian patients during total knee arthroplasty by examining whether (1) the advanced single-option implant improves the fit of the femoral component in both the anterior flange and distal cutting surface and (2) the dual-option implants show better fit than the advanced single-option implant.

Methods

A total of 950 knees that underwent primary total knee arthroplasty were included. Two types of single-option implant systems (Optetrak Logic and Truliant) and three types of dual-option implant systems (Anthem, Attune, and Persona) were used. The difference between the resected surface of the femur and femoral component dimensions was analyzed in predefined six zones. Appropriateness of fit (good-fit, over-hang, under-hang) was also evaluated.

Results

The advanced single-option implant showed higher rates of good-fit and lower rates of over-hang and under-hang in almost all distinct zones than the old version single-option implant. The advanced single-option implant demonstrated similar good-fit, higher over-hang and lower under-hang rates than the dual-option implants. All single-option implants showed significantly higher over-hang rate (P < 0.05) and lower under-hang rate (P < 0.05) than all dual-option implant systems in the anterior flange transverse area. The narrow option was only selected in 12–20% of all cases.

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 when 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.

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.