In-house 3D printed porous implants: does strontium-coating enhance osseointegration? An in-vivo study in large animals

Introduction Early osseointegration is essential for the long-term success of uncemented custom-made prostheses, particularly in oncologic bone reconstruction where bone stock is compromised. Strontium (Sr) has demonstrated osteogenic potential, and Ti-Sr-O surface coatings may enhance local bone formation. Methods This study evaluated whether Ti-Sr-O coating improves early osseointegration of 3D-printed porous Ti6Al4 V implants in a large-animal 2 mm gap model. Twenty female Romney-Texel sheep were randomized to receive either uncoated (P1) or Ti-Sr-O–coated (Sr-P1) cylindrical porous implants in the proximal tibia ( n = 10/group). After four weeks, implant fixation was assessed using axial push-out testing, and blinded histomorphometric analysis quantified bone, fibrous tissue, and membrane fractions in defined regions of interest. Biomechanical outcomes included ultimate shear strength, apparent shear stiffness, and energy absorption. Data were analyzed using the Mann–Whitney U test ( α = 0.05). Results All animals completed follow-up without implant-related complications. No significant differences were observed between groups in shear strength ( p = 0.85), stiffness ( p = 0.91), or energy absorption ( p = 1.00). Histomorphometry demonstrated comparable bone volume fractions and bone–implant contact between groups ( p > 0.05), with both groups exhibiting early woven bone formation and no foreign body reaction. Discussion Within the limitations of this gap model and four-week observation period, Ti-Sr-O coating did not enhance early mechanical fixation or osseointegration, highlighting that, within the constraints of this gap model and observation period, the study may be insufficient to detect the localized effects of Sr release, and that alternative experimental designs should be considered.