Total knee arthroplasty (TKA) is the most effective surgical treatment for end-stage osteoarthritic knee disease when all non-operative methods have failed. TKA has shown good clinical outcomes since the introduction of cemented TKA in the 1960s, but aseptic loosening remains an unsolved problem [1
]. Although the cause of loosening in cemented TKA is multifactorial, delayed instability of the prosthesis-cement interface is the leading cause of loosening [2
The influence of prosthesis surface texture on the stability of the prosthesis-cement interface have been studied, and several mechanical studies have demonstrated that bonding strength between prosthesis and cement increase with increasing surface roughness of the prosthesis [5
]. However, it is debatable whether roughened prostheses are clinically desirable [8
]. In hip arthroplasty, rough surfaced femoral stems produced more wear debris caused by tension between cement and bone, resulting in more stem loosening through osteolysis than polished femoral stem [8
]. But to our knowledge, no study has compared the clinical results of total knee prostheses with different undersurface roughness.
We examined the use of the prosthesis with an identical design and material but different undersurface roughness in primary TKA. The senior author has been using Buechel and Pappas (B-P) knee prostheses (L-F Knee System, Cellumed Co., Ltd., Seoul, Korea) for primary TKA since May 2009. The manufacturer increased the surface roughness of this prosthesis by changing the surface finish treatment in October 2013.
The purpose of the present study was to compare the clinical and radiological outcomes and prosthesis survivals in patients who underwent TKA using prosthesis with identical designs of different surface roughness. We hypothesized that increasing the surface roughness of total knee prosthesis would improve clinical and radiological outcomes and prosthesis survivals, and reduce aseptic loosening rates.
The present study was undertaken to investigate the effects of the undersurface roughness of total knee prosthesis on clinical outcomes, and the results showed that rough surfaced prostheses produced significantly better functional results and enhanced prosthesis survival.
The success of joint arthroplasty is directly related to prosthesis lifetime, aseptic loosening between cement and prosthesis and/or bone is one of the persistent problems of cemented arthroplasty [1
]. Despite widespread awareness of the problems, the specific mechanisms of failure initiation and progression in prosthetic loosening have not been completely understood. Harris et al. [3
] suggested that the early separation between prosthesis-cement resulted in an acceleration of the loosening process. This suggestion was based on experimental studies which showed that loose components were easily removed from cement and there were few fibrous membranes between cement and bone in revision arthroplasty [8
]. Even in revision TKA for aseptic loosening, debonding between prosthesis-cement in surgical findings was reported by retrieval studies [24
]. We also experienced the dissociation of prosthesis-cement in all cases of revision TKA for aseptic loosening. These results and observations suggested that increasing prosthesis-cement bond strength might effectively prevent early aseptic loosening.
Various surface treatments in orthopaedic prosthesis have been employed to enhance the ability of prostheses to bond with cement; polishing, porous coatings, and roughening of textures by sand-blasting [9
]. Pittman et al. [5
] reported a mechanical study about surface roughness of total knee prosthesis and demonstrated that prosthesis-cement bonding strength increased with increasing surface roughness. However, no study had been performed to determine whether increasing prosthesis surface roughness is clinically desirable or whether it affects rates of aseptic loosening after TKA. Kutzner et al. [26
] reported, by a case-control study with retrieval analyses, that the comparatively low surface roughness made tibial baseplate more susceptible to mechanical loosening. However, they compared two different prosthesis designs, that is, Low-Contact Stress, Ra
= 3.7 μm (DePuy Synthes, Warsaw, IN, USA) and Profix, Ra
= 9.1 μm (Smith and Nephew, Memphis, TN, USA). In our present study, we compared prosthesis with identical designs but with different surface roughnesses (Ra
, 5.0 μm vs. 11.6 μm) and observed that the rougher prosthesis (Ra
= 11.6 μm) had a lower revision rate due to aseptic loosening and lower tibial osteolysis and/or radiolucent line development rates. Our results provide clinical support for the results of the mechanical study by Pittman et al. [5
] that showed prosthesis-cement bonding strength increased as the surface roughness increased and suggests that using the roughened total knee prosthesis is useful for preventing aseptic loosening.
Our results for TKA were quite different from those previously reported for hip arthroplasty. In hip arthroplasty, earlier studies reported that rough surfaced femoral stems were shown to be clinically inferior to polished femoral stems because rough stems produced more wear debris caused by stresses between cement and bone than polished femoral stems, resulting in more stem loosening through osteolysis [6
]. However, in the present study, roughened surfaced total knee prosthesis had less incidence of loosening and radiologic tibial osteolysis by wear debris. Kutzner et al. [26
], similar to our results, reported that the low surface roughness makes the prosthesis more susceptible to loosening. We believe that these differences between hip and knee arthroplasties were probably due to differences in bone quality where cemented prosthesis is attached. In order to reduce loosening, the bond strength ratios at both interfaces (prosthesis-cement and cement-bone) should be considered [27
]. Increasing the bond strength at prosthesis-cement would cause high stresses at the cement-bone interface [28
]. Interfaces between cement and bone can be classified as cement to cancellous bone or cement to cortical bone interfaces, and cement-cancellous bone bond strengths are much higher than those of cement-cortical bone strengths [27
]. In hip arthroplasty, the femoral stems are typically in contact with femoral cortical bone, whereas in knee arthroplasty, tibial components contact cancellous bone. We believe that this difference explains why smooth undersurfaces are advantageous for hip arthroplasty, whereas roughened undersurfaces are a better option for knee arthroplasty.
In the present study, a roughened surface was associated with osteolysis at the tibial baseplate, but not with osteolysis of the femoral component. We think that this difference was because the femur with a femoral component had a higher portion of cortical bone than tibia with tibial baseplate [9
]. Therefore, our results indicate that strengthening bonding at the prosthesis-cement interface by increasing surface roughness is a better clinical option when a prosthesis is fixed in cancellous bone.
However, the surface roughness of prosthesis with exceeding a certain Ra
value can lead to cement damage [9
]. It is questionable whether prosthesis with Ra
over 11.6 μm can produce better clinical results because we only compared prosthesis with two different surface roughnesses. In addition, optimal surface roughness depends on many factors such as prosthesis shape and geometry, loading modes, and the physical properties of bone and cement [9
]. For these reasons, it is difficult to formulate quantitative specifications for prostheses surface roughness. Further research on this topic should be performed by comparing prosthesis with various surface roughnesses.
The present study contains several limitations. First, follow-up periods differed in the two groups. To account for this, we compared clinical and radiological outcomes and prosthesis survival rates in the two groups at the same time points. Second, the cementing technique, which could affect prosthesis-cement bonding strength, was not considered as a risk factor of aseptic loosening, and differences between cement compositions, timings, and curing temperatures may have affected the results. However, we tried to reduce these differences by using the same cementing technique (modern cementing technique) [14
] and the same bone cement in all patients. Despite these limitations, our findings are meaningful as they provide evidence of the clinical effects on using prosthesis with identical designed but different surface roughness, and provide a rationale for how to treat undersurface of the total knee prosthesis to prevent aseptic loosening.