In Vivo Osseointegration Of A Randomized Trabecular Titanium Structure Obtained By Additive Manufacturing technique

Background Osteoarthritis of the hip is a very common disease in the population over the age of 50, with a prevalence of women. The replacement of the joint with surgical therapy makes use of prosthetic implants in titanium alloy, which allow a direct anchorage to the bone and a walking gait immediately after the intervention. Osseointegration, that is the direct contact between bone and prosthesis without interposition of connective tissue, is the key to the long-term success of these devices. Thanks to additive manufacturing techniques, it is able to realize three-dimensional titanium trabecular structures that mimic the trabecular structure of the bone. In order to test the bone response of the prosthetic devices with a randomized trabecular titanium structure produced by selective laser melting technique (SLM) an in vivo animal study was performed. Objectives An in vivo study in sheep was carried out with the aim of assessing the bone response and the speed of osteointegration of the trabecular structure by means of histological, histomorphometric analysis and biomechanical push-out test for the implant removal (Authorization of the Ministry of Health No. 496 / 2017- PR. 16/07/2017). Study Design & Methods In 6 sheep were implanted 48 specimens with a trabecular titanium structure according to the following scheme: - N 2 implants for right and left site at the distal epiphysis of the femur; - N 2 for right and left site at the level of the tibial plate; - N 3 implants for right and left site at the level of the tibial shaft. Three sheep were sacrificed after 6 weeks and 3 after 14 weeks. On the biopsy samples, 3 histological sections were obtained per site by means of a processing technique for hard tissues which involves inclusion in the resin and subsequent abrasion. Histomorphometric analysis was performed for the evaluation of Bone Implant Contact (BIC), e il Bone Ingrowth (BIN). Results In all the sections, no inflammatory infiltrate was found and the observed tissues were characterized by the presence of numerous blood vessels, a sign of good tissue trophism. The histomorphometric data obtained from BIC and BIN were used to calculate the mean and standard deviation of each group and showed a different regenerative behavior between compact bone, faster in the process, than the cancellous bone (BIC: 85% and 53,5%; BIN: 84% and 43,5% at last follow-up time). Osseointegration is already present at the first follow-up time, and is also correlated with a good value of BIN, which shows how the mineralized matrix at different stages of calcification, is present among the sample trabeculae in all the samples. The biomechanical push-out tests showed a rapid osseointegration of the specimens with trabecular structure, both in the spongiosa and in the cortical one (4,7kN and 1,5kN in compact and cancellous bone respectively at last follow-up time). Conclusions The three-dimensional metallic structure used for the realization of an acetabular cup for total hip arthroplasty is able to increase the bone response. All specimens were well fastly osseointegrated. The regenerated bone between the titanium trabeculae and in the peripheral area of the scaffold presents the peculiar characteristics of the new bone at various levels of mineralization.