Successful cementless acetabular designs require sufficient initial stability between implant and bone (with interfacial motions <150 μm) and close opposition between the porous coating and the reamed bony surface of the acetabulum to obtaining bone ingrowth and secondary stability. While prior generations of cementless components showed good clinical results for long term fixation, modern designs continue to trend toward increased porosity and improved frictional characteristics to further enhance cup stability. We intend to experimentally assess the differences in initial stability between a hemispherical acetabular component with a highly porous trabecular tantalum fixation surface (Continuum® Acetabular System, Zimmer Inc, Warsaw, IN)(Fig 1) and a hemispherical component with the new highly porous Trabecular Titanium® surface (Delta TT, Lima Corporate, Italy)(Fig 2) manufactured by electron beam melting.Introduction
Objectives
The optimal management of severe tibial and/or femoral bone loss in a revision total knee arthroplasty (TKA) has not been established. Reconstructive methods include structural or bulk allografts, impaction bone-grafting with or without mesh augmentation, custum prosthetic components, modular metal augmentations of prosthesis and tumor prosthesis. Recently metaphyseal fixation using porous tantalum cones (Zimmer, Warsaw, IN) has been proposed as alternative strategy for severe bone loss. The purposes of this study were to determine the clinical and radiographic outcomes in patients who underwent revision knee arthroplasty with tantalum cones with a minimum of 5-year follow-up.Introduction
Objectives
Tapered cementless femoral components have been used in total hip arthroplasty (THA) constructs for more than 20 years. The Synergy femoral component was introduced in 1996 as a second generation titanium proximally porous-coated tapered stem with dual offsets to better restore femoral offset at THA (Figure 1). The purpose of this study was to evaluate the outcome of the authors' experience using the Synergy stem at minimum 15 years of follow-up. We retrospectively reviewed a consecutive series of 102 patients (112 hips) who underwent surgery between November 1996 and October 1998 for primary THA using cementless Synergy stem with a minimum 15-years follow-up. The mean age at the time of surgery was 61 years, and the mean duration of follow-up was 16.3 years. Seventeen patients were lost at FU (8 died before the 15 years mark, 8 changed residency, 1 not willing to be seen) with no problems related to the replaced hip. Ninety-four hips in 85 patients were available for clinical and radiologic analysis. Clinical results of the 94 THAs with more than 15 years of follow-up were assessed preoperatively and postoperatively at 5, 10 and 15 years by means of standard evaluation tools: SF12, WOMAC and Harris Hip Score. Thigh pain frequency and intensity were also recorded. Radiographic analysis (Figure 2) was focused on stem alignment, bone ingrowth, radiolucent lines presence, width and progression, stress-shielding and heterotopic ossification (HTO). Student paired test and Kaplan-Meier survival analysis were used for statistical analysis.Background
Material and methods
Pure tantalum has been proposed in orthopaedic surgery. Its chemical and physical properties have been widely studied in the past. From pure tantalum is obtained a spongy structure (Trabecular Metal Technology: TMT) that shows a full thickness porosity which is 2–3 times higher compared to other surfaces available for bone ingrowth with a three-dimensional porous arrangement in rough trabeculae. Pores (average diameter of 650 mm) are fully interconnected and represent 75–80% of the whole volume. TMT acetabular components have an elliptical shape and have an irregular external surface which both allow an optimal mechanical fit. We retrospectively reviewed 212 cases of monoblock porous tantalum acetabular cup (Hedrocel, Stratec) implanted between 1999 and 2003 in a single centre with a minimum follow-up of 9–10 years; There were 98 men and 114 women, with an average age of 65 years. They all underwent primary or revision total hip arthroplasty or to acetabular component revision alone. In all patients a monoblock porous tantalum acetabular component with polyethylene directly compression molded into cup, with or without peripheral holes for screws, was implanted. In all primary procedures the same femoral stem (Synergy, Smith and Nephew) was implanted. All patients were evaluated with a clinical examination (Harris Hip Score: HHS) and with standard radiographs of the pelvis preoperatively and 1, 3, 6 months and yearly postoperatively. The stability of the acetabular cup was determined by modified Engh's criteria. The HHS score improved from 42 preoperatively to 94 after one year; at 13 years follow-up it was 95. The subjective outcome was widely satisfying, with the majority of patients experimenting good functional recovery and return to daily activities. Osteointegration of the acetabular component was present in all X-rays controls at one year after surgery. All post-operative evidence of residual bone loss (geodes, bone defects in revisions and in displasia) were no more radiographically evident after 1 year postoperatively as the host bone quickly filled these gaps. We did not observe osteolysis nor progressive radiolucent lines at the latest follow-up. None of the cups was revised, except 3 cases, revised for infection. Both clinical and radiographic results are the same or even superior to those of coated implants. Our experience confirms that trabecular metal tantalum cups can avoid the formation of bone-implant interface membrane and consequently can avoid implant loosening. The most important advantages of TMT monoblock cups are: no potential for polyethylene backside wear, prevention of loosening and osteolysis, increased early fixation via friction, improved late biological stability, maximum bone-implant contact. High biocompatibility of porous tantalum and its elastic modulus very close to bone influence positively earlier and wider osteointegration of the implant. Larger series are needed to confirm the positive our preliminary results.
