Low protein intake is associated with impaired titanium implant osseointegration.
Low protein intake is highly prevalent among orthopaedic elderly patients. We studied the effects of an isocaloric low protein diet on the resistance to pull-out of titanium rods implanted into rats proximal tibia. Isocaloric low protein intake impairs titanium implant osseointegration, with a decreased strength needed to completely loose the implant and altered bone microarchitecture in its vicinity.


BACKGROUND
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.


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 microCT 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 (r2= 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 microm (p < 0.01) at 6 weeks and 101.4 +/- 2.7 versus 116.2 +/- 3.3 microm (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.
Dayer
Romain
R
Service of Bone Diseases (WHO Collaborating Center for Osteoporosis Prevention), Department of Rehabilitation and Geriatrics, University Hospital of Geneva, Geneva, Switzerland.
Rizzoli
René
R
Kaelin
André
A
Ammann
Patrick
P
D000818:Animals; D001835:Body Weight; D031204:Caloric Restriction / Q000009:adverse effects*; D018753:Diet, Protein-Restricted / Q000009:adverse effects*; D005260:Female; D020007:Implants, Experimental; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000378:metabolism; D016348:Osseointegration; D051381:Rats; D013977:Tibia / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D014025:Titanium / Q000378:metabolism; D014057:Tomography, X-Ray Computed
D007334:Insulin-Like Growth Factor I; D014025:Titanium