The efficacy of poly-d,l-lactic acid- and hyaluronic acid-coated bone substitutes on implant fixation in sheep

BACKGROUND/OBJECTIVE: The present study investigated the efficacy of poly-d,l-lactic acid (PDLLA) and hyaluronic acid (HyA) on implant fixation when coated onto hydroxyapatite/beta-tri-calcium phosphate (HA/βTCP) granules. METHODS: The effect was assessed in a clinically relevant in vivo gap model in sheep. Thus, four titanium implants combined with either allograft (control), pure HA/βTCP, HyA infiltrated HA/βTCP, or PDLLA reinforced HA/βTCP granules were bilaterally inserted into the trabecular bone of the distal femurs in eight sheep. The insertion created a 2-mm peri-implant gap. After 12 weeks, histomorphometry and push-out test was used for quantification of newly formed bone in the gap, bone-implant contact, and implant fixation. RESULTS: The histomorphometric analysis revealed the presence of newly formed bone in all groups, though substitute groups showed fragments of nonabsorbed substitute material. A significant larger bone volume was found in the allograft group versus the HA/βTCP-PDLLA group (Zone 1), and in Zone 2 a statistically significantly larger bone volume was found in the allograft compared with the HA/βTCP group. The mechanical properties and the bone-implant contact revealed no statistically significant differences between the groups. CONCLUSION: This study demonstrates that HA/βTCP granules coated with PDLLA and HyA have similar bone ingrowth and implant fixation as those with allograft, and with mechanical properties resembling those of allograft in advance, they may be considered as alternative substitute materials for bone formation in sheep.