Parathyroid hormone 1-34 enhances titanium implant anchorage in low-density trabecular bone:: A correlative micro-computed tomographic and biomechanical analysis

The use of endosscous titanium implants is the standard of care in dentistry and orthopaedic surgery. Nevertheless, implantation in low-density bone has a poor prognosis and experimental studies show delayed implant anchorage following gonadectomy-induced bone loss. Intermittently administered human parathyroid hormone 1-34 [iahPTH(1-34)] is the leading bone anabolic therapy. Hence, this study assessed whether iahPTH (1-34) enhances titanium implant integration in low-density bone. Threaded titanium implants, 0.9 mm in diameter, were inserted horizontally into the proximal tibial metaphysis of 5-month-old rats, 7 weeks postorchiectomy (ORX). Subcutaneous administration of iahPTH(1-34), at 5, 25 and 75 mu g/kg/day commenced immediately thereafter and lasted for 8 weeks. Quantitative micro-computed tomography (ACT) at the implantation site was carried out at 15 mu m resolution using high energy and long integration time to minimize artifacts resulting from the high implant radiopacity. Osseointegration (OI) was calculated as percent implant surface in contact with bone (%OI) quantified as the ratio of "bone"-to-total voxels in contact with the implant. Additionally, the trabecular bone volume density (BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N) and connectivity density (Conn.D) were measured in the peri-implant bone. All mu CT parameters were stimulated by iahPTH(1-34) dose-dependently; the percent maximal enhancement was %OI = 143, BV/TV = 257, Tb.Th = 150, Tb.N = 140 and Conn.D = 193. The maximal values of %OI, BV/TV and Tb.Th in iahPTH(1-34)-treated ORX rats exceeded significantly those measured in the implantation site of untreated sham-ORX controls. The same specimens were then subjected to pullout biomechanical testing. The biomechanical parameters were also enhanced by iahPTH(1-34) dose-dependently, exceeding the values recorded in the sham-ORX controls. The percent iahPTH(1-34)-induced maximal enhancement was: ultimate force = 315, stiffness = 270 and toughness = 395. Except for the BV/TV and Tb.Th, there was no significant difference between the effect of the 25 and 75 mu g/kg/day doses. There was a highly significant correlation between the morphometric and biomechanical parameters suggesting the use of quantitative CT as predictive of the implant mechanical properties. These findings demonstrate that iahPTH(1-34) effectively stimulates implant anchorage in low-density trabecular bone and thus the feasibility of administering iahPTH(1-34) to improve the clinical prognosis in low-density trabecular bone sites. (c) 2006 Elsevier Inc. All rights reserved.