Zirconia has considered a good material for manufacturing of ball heads in total hip replacement due to high mechanical properties of this ceramic material. However in the literature the problem of heads biocompatibility is still debated. The Authors reported their experience in ten years of research on the biological properties of this material. In vitro tests were performed onto materials in form of powders, analyzing the inhibitory effects on human lymphocyte mitogenesis, and in form of plates measuring adhesion and spreading of 3T3 fibroblasts. A mutagenic test was also performed. In vivo tests were performed by injection of powders in mice and evaluating the survival of animals according to ASTM F – 750. We also inserted ceramic in form of cylinders into proximal tibial metaphysis of NZW rabbits and analysed local and systemic reaction due to material diffusion. We also developed a system of production of Zirconia particles by inserting ceramics under patellar tendon of NZW rabbits.

In vitro tests showed that Zirconia powders and plates induced a similar effect of Alumina ones; no mutagenic effect were observed using our samples, demonstrating that Zirconia has no carginogenic effects. In any case the diffusion of particles didn’t show modifications into internal organs (lung, kidney, liver, spleen) of mice and rabbits. In time (one year after operation) the connective tissue present at bone ceramic interface is transformed into lamellar bone.

Our experience demonstrates that Zirconia may be considered a good material for prosthetic implants.

To evaluate the osseointegration enhancement, a consecutive randomized series of 50 on a total of 483 cementless titanium prostheses were prospectically studied. The features of the stem were the following: tapered, straight, low-profile neck, metaphyseal and hystmic fit, proximal 1/3 hydroxyapatite coated (HA) and titanium porous coated (PC). The acetabular component was hemispherical, titanium porous coated. A zircornia or Co/Cr head (28mm) was used. Female were 53% and average age 65. The general diagnosis was ostheoarthritis, congenital hip dysplasia, fracture, aseptic loosening, osteonecrosis, previous femoral osteotomy, previous pelvic osteotomy. Clinical objective assessment was based on the HHS. A patient oriented evaluation (Womac and SF12) was obtained. Radiological assessment was based on the Engh’s method. The general and prospectical group results have been evaluated.

In all the groups the HHS, Womac and SF12 questionnaires showed a statistically significant improvement in quality of life. Consistent evidence of proximal bone ingrowth were present in 100 % (HA) and 96 % (PC), stable proximal fibrous ingrowth in 4 % (PC). Cortical hypertrophy (50 % zone 3–5), stress shielding (56 % zone 1) and pedestal ( one case) were assessed. Nor osteolysis neither subsidence were identified. No significant general complications such as infections or periprosthetic fractures were observed. The use of HA seems to improve the mechanism of osseointegration and earlier clinical outcomes, even if this difference is not significant. Patient oriented evaluation and radiographic assessments confirmed the reliability of this cementless prosthesis. Less osteolysis could be predicted in the future, according to the reported results of other authors in the HA coated stems.

Bone Loss is the main problem in failed total hip arthroplasties. Revision surgery must be conformed to the degree of the bone loss. Since 1986, 330 cases of failed THA underwent to revision surgery. Different solutions were adopted according to Paprosky femoral defects classification. In type I, a primary cementless stem was implanted (23%). In type II and IIIa, were proximal fixation is still possible to achieve, Mid PCA-Howmedica (5%) and modular S-ROM-J& J revision stems (18%) were implanted. In all the other degree of bone loss (IIIb–IV) cementless distal fixation stems, Long PCA-Howmedica (17 %), Wagner-Sulzer (18 %) and modular (MP-Link, Profemur-Wright) (19 %), were used. Patients were clinically and radiographically evaluated by HHS and according to Engh’s criteria. Best results were observed in Type I group (HHS=90). Long and mid PCA stems presented poor clinical (HHS=60) and radiographical results and required re-revision in 15% of cases. Intermediate results were observed in Wagner prostheses. Modular revision stems showed best results although earlier F-U. (HHS=80). Of these, re-revision surgery was performed in two cases, one of which because of infection and the other one due to severe thigh pain.

Cementless modular stems seem to be the most suitable technique. Distal fixation associated with proximal fill permit to manage the majority of femoral bone defects minimizing bone grafts. The modular stems, allow to conform the design of the components to the bone defects permitting to achieve primary stability (press-fit), restoring the centre of rotation and muscles tension, reducing pain and restoring hip function.

The problem of early mechanical stability and late biological osseointegration of the tibial component is still a debated issue in total knee arthroplasty. We are among those authors that stress the necessity of cementing the tibial component to avoid the risk of failure due to the high torque stresses at this interface. In fact while on the femoral edge a good stability can be achieved even in uncemented implants, the stability of traditional tibial components is harder to obtain even in cemented implants.

To solve this problem it has been proposed to use additional devices such as screws, pegs or keels to better fix the tibial plateau. Tantalum monobloc tibial tray is a new answer to this problem. It consists in a cement-less tibial tray made of porous tantalum with monobloc polyethylene. Chemical, physical and biological properties of the raw tantalum are very similar to those of titanium. Porosity of the processed material is 80% (2–3 times compared to plasma spray, beads and fiber mesh coatings) and pores, which diameter is 650 mm, are fully interconnected in the whole bulk of the implant. This trabecular spongy structure, that is not a coating, allows the bone at the interface to deeply grow into the pores, and to achieve optimal stability. In addiction, the fusion of polyethylene into the tantalum mesh completely abolish the back side wear problem. With this technology is yet in use an acetabular component, with which we have a 5 years experience in 150 implants, and now is available a new tibial plateau; the first implant in Europe was performed in our department.

Despite our short series and follow up (6 implants in 2 months) the properties of porous tantalum, already tested in acetabular implants, represent an alternative to the traditional ways of tibial tray fixation.

Aseptic loosening is one of the most frequent cause of total knee arthroplasty (TKA) failure; it is related to a fatigue-type wear which can rapidly break up a tibial polyethylene (PE) inlay. PE debris production is the result of this wear and depend on contact stress between the components. This crucial parameter is more related to conformity than to load tranfer. That is why mobile bearing TKA seems to represent a valid solution to the PE debris production. In fact this implant offers great tibio-femoral conformity without an increased risk of loosening due to increased axial torque. Mobile bearing TKA also eneables the surgeon to self correct tibial component malrotation. On the other hand this implant could lead to new problems such as bearing dislocation or breakage and a possible new wear pattern at the PE-tibial metal tray interface.

We performed 100 consecutive cemented posterior stabilised TKA using randomly in 50 cases a mobile bearing and in 50 cases the same implant with a fixed bearing. The mean follow up was 15 months. The results in mobile bearing group are the following. Hospital for Special Surgery (HSS) score improved from 38 to 91 after the surgery. Preoperative Range of Movement (ROM) was 71 while the post op value was 107. No lucencies > 1 mm were observed. There were no statistically significant differences among the mobile bearing group and the fixed bearing one. Despite our short follow up, this implant offers the same good clinical results if compared to other devices, and allows the surgeons to correct errors in positioning the implant.

In future we have to consider that this possibility will lead to an abnormal load stresses distribution and to a higher risk of late loosening.