Effects of substitute coated with hyaluronic acid or poly-lactic acid on implant fixation: Experimental study in ovariectomized and glucocorticoid-treated sheep.

Investigated in healthy animal models, hyaluronic acid (HyA) and poly-D,L -lactic acid (PDLLA) demonstrate osteoconductive properties when coated onto hydroxyapatite (HA) and β-tricalcium phosphate (βTCP) scaffolds. In this study, we examined the efficacy of HA/βTCP granules coated with HyA or PDLLA on implant fixation when applied as graft materials in 2-mm size defects created in the femur condyles of ovariectomized (OVX) glucocorticoid-treated (GC) sheep. Titanium alloys were inserted into the femur condyles of OVX and GC-treated sheep, and the concentric gaps were filled with either allograft obtained from a healthy donor sheep (control), pure HA/βTCP, HA/βTCP-HyA or HA/βTCP-PDLLA. After 12 weeks, the bone formation adjacent to the implant surface was evaluated by histology and histomorphometry, while the implant fixation was measured by a push-out test. The investigation showed a bone formation in the HA/βTCP-HyA and HA/βTCP-PDLLA groups not significantly different from allograft (p  >  0.05), whereas the HA/βTCP group revealed a significantly reduced formation of bone compared with allograft (p  <  0.05). Bone-implant contact (BIC) and mechanical properties were similar comparing HA/βTCP-HyA and HA/βTCP-PDLLA with allograft (p  >  0.05). This study demonstrated that bone substitutes infiltrated with PDLLA and HyA possess osteoconductive properties comparable to allograft when tested in sheep with an OVX and GC-induced bone loss. With no significant difference in implant fixation and bone formation, HyA and PDDLA are indeed considered valuable as new coating materials for composite ceramics when tested in a sheep model - even in bones of a compromised quality.