Low protein intake is associated with impaired titanium implant osseointegration

Introduction: Low protein intake is highly prevalent among elderly patients in orthopaedic wards and could retard fracture healing. It was previously shown that reduced protein intake decreases bone strength. Whether dietary protein intake could influence titanium implant osseointegration is unknown. We studied the effects of an isocaloric low protein diet on the resistance to pull-out of titanium rods implanted into rats proximal tibia. Materials and Methods: Forty-eight 11-month-old female rats were fed isocaloric diets containing 2.5% (low protein) or 15% (normal protein) casein from 2 weeks before the implantation of a 1-mm-diameter cylindrical titanium rod in the proximal metaphysis of each tibia. Four, 6, and 8 weeks after implantation, the tibias were removed for mu CT histomorphometry to quantify bone-to-implant contact and bone trabecular microarchitecture around the implant. Resistance to implant pull-out was tested by recording the maximal force necessary to completely loosen the implant. Results: Pull-out strength was significantly lower in rats fed an isocaloric low protein diet by 6 and 8 weeks after implantation (-43%, p < 0.001 and -42%, p < 0.001, respectively) compared with rats fed a normal protein diet. Bone-to-implant contact was significantly lower in the low protein group 8 weeks after implantation (p < 0.05). Bone-to-implant contact and pull-out strength were correlated (r(2) = 0.57, p < 0.0001). BV/TV around the implant was 19.9 +/- 2.2% (SE) versus 31.8 +/- 3.3% (p < 0.05) at 6 weeks and 20.1 +/- 1.9% versus 29.8 +/- 3.2% (p < 0.05) at 8 weeks after implantation in the low protein and normal protein intake groups, respectively. Trabecular thickness was 96.2 +/- 3.7 versus 113.0 +/- 3.6 mu m (p < 0.01) at 6 weeks and 101.4 +/- 2.7 versus 116.2 +/- 3.3 mu m (p < 0.01) at 8 weeks in the corresponding groups. In a structure model index analysis, there was a significant shift to a more rod-like pattern in the low protein diet groups. All these changes were associated with lower plasma IGF-I levels. Conclusions: Isocaloric low protein intake impairs titanium implant osseointegration, with decreased strength needed to completely loosen the implant and altered bone microarchitecture in the vicinity of the implant.