Transient Retention of Endochondral Cartilaginous Matrix With Bisphosphonate Treatment in a Long-Term Rabbit Model of Distraction Osteogenesis

Abstract

Bisphosphonates induce major increases in strength of callus in distraction osteogenesis in the short term. Poor understanding of the underlying mechanism, however, raises concerns about long-term consequences. In this long-term study in 32 rabbits, zoledronic acid transiently increased trabeculae by delayed temporal progression of endochondral bone remodeling but did not prevent radiographic completion of bone repair. Introduction:We hypothesized that bisphosphonate inhibition of osteoclast-mediated resorption would retain bone during repair, producing a larger callus in the short term. However, if remodeling was not restored, completion of the bone repair process in the long term could be jeopardized. Materials and Methods: Juvenile rabbits underwent right tibial osteotomy and 2 weeks of distraction, followed by a period of consolidation. Animals received saline (controls) or zoledronic acid (ZA; 0.1 mg/kg at surgery and again 2 weeks later), and distracted tibias were examined by radiograph, DXA, histology, and histomorphometry at 2, 4, 6, 18, and 44 weeks after surgery. Results: Regenerated bone in ZA-treated animals was denser than controls on radiographs at 6 weeks and had more distinct radiodense trabeculae and retention of original cortices at 18 weeks. By 44 weeks, controls and ZA-treated animals were radiographically healed and indistinguishable. Regenerate BMD and BMC increased between 2 and 4 weeks in all animals, with a greater effect in ZA. At 6 weeks, BMD and BMC in ZA-treated animals were 1.6-and 2-fold greater, respectively, than controls (p Ͻ 0.01). From 6 to 44 weeks, the control values gradually increased and approached the ZA-treated values. Regenerate bone volume and trabecular number by histomorphometry were from 1.6-to 2-fold greater in ZA-treated animals at 6 and 18 weeks (p Ͻ 0.05). Endochondral cartilaginous matrix volume was up to 2.4-fold greater in ZA-treated animals at 2 and 4 weeks (p Ͻ 0.05). TRACP ϩ cells in ZA-treated animals were larger with more nuclei. Mineral apposition rate and osteoblast number and surface were lower in ZA-treated animals at 6 weeks (p Ͻ 0.01) but not at later times. Conclusions: Disruption of TRACPϩ cell function by ZA during bone regeneration seems to lead to an accretion of cancellous bone built on a larger endochondral cartilaginous matrix and increased bone mass, consistent with reported increases in short-term callus strength. This increase in bone mass, caused by a delay in remodeling, provided a transient advantage without preventing radiographic completion of the bone repair process in the long term. Noncontinuous treatment with nitrogen-containing bisphosphonates thus can have short-term beneficial effects without preventing long-term bone repair.

Surface-bound bisphosphonates enhance screw fixation in rats—increasing effect up to 8 weeks after insertion

“…The gradual migration of bisphosphonates away from the implant surface, which seems to be the only explanation for the increasing effect on strength, requires that some bisphosphonatecontaining bone is in fact resorbed. Thus, it seems unlikely that the bone will remain totally unresorbed and eventually becomes fatigued (Rodan et al 2004, Smith et al 2004.…”

Biological basis of distraction osteogenesis – A review

“…Abbaspour et al in their animal studies have recognized the positive effect of bisphosphonates in distraction process [64]. In another study conducted on rabbits Smith et al [65] showed that during bone regeneration Zoledronic acid disrupts the TRACP + cell function which leads to an accumulation of cancellous bone on a larger endochondral cartilaginous matrix and increased bone mass, with reported increases in short-term callus strength. This increase in bone mass, which is caused by a delay in remodeling, provides a momentary advantage without interrupting radiographic completion of the bone repair process in the long term.…”

Tribological Study on New Therapeutic Bionic Lubricants

“…As another component of the therapeutic lubricants, the BPs, have been shown to be preventing particleinduced osteolysis and implant loosening in a canine model [29], in a rat model [30], and to prevent implant-induced peri-implant bone loss in total hip arthroplasty in human [31]. Several studies have adopted Nitrogen-containing BPs to distract osteogenesis and increase bone volume around the regenerated bone [32,33]. Therefore, the BPs in the therapeutic bionic lubricant may play a key role in treatment of the particle-induced osteolysis.…”