Do Metaphyseal Cones and Stems Provide Any Biomechanical Advantage for Moderate Contained Tibial Defects in Revision TKA? A Finite-Element Analysis Based on a Cadaver Model

Abstract

Background Satisfactory management of bone defects is important to achieve an adequate reconstruction in revision TKA. Metaphyseal cones to address such defects in the proximal tibia are increasingly being used; however, the biomechanical superiority of cones over traditional techniques like fully cementing the implant into the defect has not yet been demonstrated. Moreover, although long stems are often used to bypass the defects, the biomechanical efficacy of long stems compared with short, cemented stems when combined with metaphyseal cones remains unclear. Questions/purposes We developed and validated finite-element models of nine cadaveric specimens to determine: (1) whether using cones for addressing moderate metaphyseal tibial defects in revision TKA reduces the risk of implant-cement debonding compared with cementing the implant alone, and (2) when using metaphyseal cones, whether long, uncemented stems (or diaphyseal-engaging stems) reduce the risk of implant-cement debonding and the cone-bone micromotions compared with short, cemented stems. Methods We divided nine cadaveric specimens (six male, three female, aged 57 to 73 years, BMI 24 to 47 kg/m2) with standardized tibial metaphyseal defects into three study groups: no cone with short (50-mm) cemented stem, in which the defect was filled with cement; cone with short (50-mm) cemented stem, in which a metaphyseal cone was implanted before cementing the implant; and cone with long, diaphyseal-engaging stem, which received a metaphyseal cone and the largest 150-mm stem that could fit the diaphyseal canal. The specimens were implanted and mechanically tested. Then, we developed and validated finite-element models to investigate the interaction between the implant and the bone during the demanding activity of stair ascent. We quantified the risk of implant debonding from the cement mantle by comparing the axial and shear stress at the cement-implant interface against an experimentally derived interface failure index criterion that has been previously used to quantify the risk of cement debonding. We considered the risk of debonding to be minimal when the failure index was below 10% of the strength of the interface (or failure index < 0.1). We also quantified the micromotion between the cone and the bone, as a guide to the likelihood of fixation by bone ingrowth. To this end, we assumed bone ingrowth for micromotion values below the most restrictive reported threshold for bone ingrowth, 20 µm. Results When using a short, 50-mm cemented stem and cement alone to fill the defect, 77% to 86% of the cement-implant interface had minimal risk of debonding (failure index < 0.1). When using a short, 50-mm cemented stem with a cone, 87% to 93% of the cement-implant interface had minimal debonding risk. When combining a cone with a long (150-mm) uncemented stem, 92% to 94% of the cement-implant interface had minimal debonding risk. The differences in cone-bone micromotion between short, cemented stems and long, uncemented stems were minimal and, for both configurations, most cones had micromotions below the most restrictive 20-µm threshold for ingrowth. However, the maximum micromotion between the cone and the bone was in general smaller when using a long, uncemented stem (13-23 µm) than when using a short, cemented stem (11-31 µm). Conclusion Although the risk of debonding was low in all cases, metaphyseal cones help reduce the biomechanical burden on the implant-cement interface of short-stemmed implants in high-demand activities such as stair ascent. When using cones in revision TKA, long, diaphyseal-engaging stems did not provide a clear biomechanical advantage over short stems. Future studies should explore additional loading conditions, quantify the interspecimen variability, consider more critical defects, and evaluate the behavior of the reconstructive techniques under repetitive loads. Clinical Relevance Cones and stems are routinely used to address tibial defects in revision TKA. Despite our finding that metaphyseal cones may help reduce the risk of implant-cement debonding and allow using shorter stems with comparable biomechanical behavior to longer stems, either cones or cement alone can provide comparable results in contained metaphyseal defects. However, longer term clinical studies are needed to compare these techniques over time.

Cemented Versus Hybrid Technique of Fixation of the Stemmed Revision Total Knee Arthroplasty: A Literature Review

“…A recent experimental study evaluating the use of cones with stems fixed by either hybrid or fully cemented modes in moderate metaphyseal defects showed that the cones provided stability to the whole construct with both modes of stem fixation performing equally well. 36 Clinical studies have shown excellent results at a short-term to medium-term follow-up with low aseptic loosening rates when porous metal cones are used with stems in patients with high-grade (AORI 2B/3) defects.…”

“…A recent experimental study evaluating the use of cones with stems fixed by either hybrid or fully cemented modes in moderate metaphyseal defects showed that the cones provided stability to the whole construct with both modes of stem fixation performing equally well. 36…”

Model Properties and Clinical Application in the Finite Element Analysis of Knee Joint: A Review

“…87 Bone defects in total knee arthroplasty (TKA) revisions might be treated with a prosthesis with conical mesh, which could reduce the stress load between the prosthesis and the bone cement. 88 Using finite element analysis, Zhao et al evaluated the biomechanical differences in high tibial osteotomy (HTO) using reverse screws and bone grafting. 89 Both reduced the stress on the tibia, but there was a risk of plate fracture with reverse screws.…”

“…compared the results of metal blocks and cement screws for tibial defects and found that cement screws were more compatible and suitable for minor bone defects; metal blocks were stronger and ideal for large bone defects, 86 with better results for personalized and customized metal blocks 87 . Bone defects in total knee arthroplasty (TKA) revisions might be treated with a prosthesis with conical mesh, which could reduce the stress load between the prosthesis and the bone cement 88 . Using finite element analysis, Zhao et al .…”

Management of Bone Loss in Revision Total Knee Arthroplasty: An International Consensus Symposium

“…A recent experimental cadaveric and computational study compared long hybrid and short fully cemented stems in the presence of cones to address moderate contained metaphyseal defects (Fig. 4) [168], and reported that long uncemented stems provide little biomechanical advantage over short stems for tibial fixation. The biomechanical behavior of short cemented tibial stems was similar whether cones or cement alone were used to address the defect.…”