Total knee arthroplasty (TKA) is one of the success stories of modern surgery, providing high patient satisfaction outcomes. Total knee prostheses are generally composed by a femoral component articulating on a polyethylene insert and a tibial tray.

Recently there has been particular attention on the component material; traditionally femoral components are made of cobalt alloys while tibial baseplates are made, in the great majority of cases, of metallic materials, but also polyethylene versions are available. There has been a degree of acceptance in some countries that metal related pathology may exist as demonstrated by the Australian Arthroplasty register where metal hypersensitivity was reported as the fifth most common cause for revision hip arthroplasty 2012 report, making up for 5.9% of all revisions. The wording was subsequently changed from "metal sensitivity" to "metal related pathology" in the 2014 report with 0.5% of all revision total hip arthroplasties (THA) associated with this term. The same change in terminology was used for TKA with metal sensitivity as a cause for revision in 1.3% of revisions in 2012 and in 2014, 1.8% of revision TKAs attributed to "metal related pathology" . The overall revision rate was 3.45% after 10 years in 396.472 TKAs, suggesting a revision rate of 0.06-0.32% secondary to metal or cement allergies. Up to today there is no question that metallic implants may generate wear debris that cause local reactions. This local reaction is not dose related nor predictable and therefore not purely due to the toxic effect of the debris but possibly due to an immunological host process. Hypersensitivity to metal undoubtedly exists but it cannot be stated at the moment to be an allergic reaction. To prevent issues arising due to metal related pathology, alternative solutions to conventional chrome cobalt material have been proposed, for example ceramic component or implant coating. In particular, TiNbN coating has been proposed by most companies thanks to its excellent biological properties. Preclinical studies have showed a high scratch resistance and low coefficient of friction, more resistance to fretting corrosion, reduction of wear, lower ion release rates and low fatigue cycle, as described in the review of Hove. Clinically, cohort of studies of TiN-coated implants showed an overall survival exceeding 90% with a follow-up of 15 to 77 months and good clinical outcomes. No reports of adverse effects related to TiN coating of CoCrMo knee implants have been showed. There are few studies that compared TiN-coated implants with the same uncoated version. Thienpont, comparing TiN-coated and uncoated CoCrMo implants, showed similar clinical and radiological outcomes at short-term follow up in both patients groups .

Overall we can conclude that in literature no adverse events have been reported concerning the TiNbN coating and in particular it has been showed that the coating doesn't not affect the performance of the device if compared with the same uncoated version.

The aim of this study is to evaluate the long term clinical and radiological performance of GMK Sphere total knee component, coated version.

Inclusion Criteria:

• Those older than 18 years old at the surgery time
• those suitable to undergo to a primary total knee arthroplasty for whom the GMK Sphere TiNb coated device will be implanted (according to the label indication/contraindications)
• Patients who are willing and able to provide written informed consent for participation in the study. Written informed consent must be obtained prior to patient's surgery

Exclusion Criteria:

• Those patients with metal implants containing Co, Cr and / or Ni
• Those patients who have had environmental or occupational exposure to toxic metals such as Co, Cr and / or Ni (solvents, industrial paints, welders)
• Those whose mental conditions may compromise their ability to provide informed consent to study participation, ability to complete questionnaires or complete 10-year follow-ups
• Those unable to give their consent to participate in the study or who do not want to participate
• Any condition not mentioned in inclusion criteria.

Sample size calculation has been performed according to one proportion test comparing expected survival at 10 year of 96.3%[5] with the bench mark value defined by ODEP Panel for a total knee arthroplasty at 10 yrs of 90%. With a significance level of 5% and a power of 80%, 141 patients are necessary to show a non-inferiority test. Considering a lost to follow-up rate of 10%, 155 patients will be recruited.

B. Bordini, C. Ancarani, and D. A. Fitch, "Long-term survivorship of a medial-pivot total knee system compared with other cemented designs in an arthroplasty registry," Journal of orthopaedic surgery and research, vol. 11, no. 1, p. 44, 2016