Teriparatide therapy enhances devitalized femoral allograft osseointegration and biomechanics in a murine model

Abstract

Despite the remarkable healing potential of long bone fractures, traumatic injuries that result in critical defects require challenging reconstructive limb sparing surgery. While devitalized allografts are the gold standard for these procedures, they are prone to failure due to their limited osseointegration with the host. Thus, the quest for adjuvants to enhance allograft healing remains a priority for this unmet clinical need. To address this, we investigated the effects of daily systemic injections of 40 µg/kg teriparatide (recombinant human parathyroid hormone) on the healing of devitalized allografts used to reconstruct critical femoral defects (4 mm) in C57Bl/6 mice. The femurs were evaluated at 4 and 6 weeks using micro CT, histology, and torsion testing. Our findings demonstrated that teriparatide induced prolonged cartilage formation at the graft-host junction at 4 weeks, which led to enhanced trabeculated bone callus formation and remarkable graft-host integration at 6-weeks. Moreover, we observed a significant 2-fold increase in normalized callus volume (1.04 ± 0.3 vs. 0.54 ± 0.14 mm 3 /mm; p<0.005), and Union Ratio (0.28 ± 0.07 vs. 0.13 ± 0.09; p<0.005), compared to saline treated controls at 6-weeks. Teriparatide treatment significantly increased the torsional rigidity (585±408 versus 1175±311 N.mm 2 ) and yield torque (6.8±5.5 versus 10.5±4.2 N.mm) compared to controls. Interestingly, the Union Ratio correlated significantly with the yield torque and torsional rigidity (R 2 =0.59 and R 2 =0.77, p<0.001, respectively). These results illustrate the remarkable potential of teriparatide as an adjuvant therapy for allograft repair in a mouse model of massive femoral defect reconstruction, and warrant further investigation in a larger animal model at longer time intervals to justify future clinical trials for PTH therapy in limb sparing reconstructive procedures.

Quantifying Massive Allograft Healing of the Canine Femur In Vivo and Ex Vivo: A Pilot Study

“…As a result, investigators have developed preclinical adjuvant therapies [6,11,12,15,19,24,26,[30][31][32][33]. As yet, their clinical application has been unrealized, largely because a large-animal model has not been established, nor have clinically relevant diagnostic tools that can noninvasively quantify graft healing.…”

“…These limitations, in addition to graft type (intercalary/osteochondral), preservation technique, and internal fixation approach, are associated with a 25% to 35% failure rate due to nonunion and fracture [2,14] and a 10-year survival rate of less than 50% due to the accumulation of unremodeled microfractures, which compromise their mechanical properties [29]. To address these shortcomings, investigators have developed biologic adjuvant therapies (ie, BMP-2 [6,15,32], teriparatide [19,24]), stem cell [26,30,33], and gene [11,12,31]), which stimulate integration of cortical allografts. While these technologies have accelerated healing in small-animal models, their application in humans has been unrealized.…”

Intermittent Parathyroid Hormone Enhances Cancellous Osseointegration of a Novel Murine Tibial Implant

“…Ninety ten-week-old female C57BL/6 mice (Jackson Laboratory, Bar Harbor, Maine) were injected subcutaneously with either 40 mg/kg of PTH 25,26 (Amgen, Thousand Oaks, California) or a vehicle (0.9% saline solution) (n = 45 per treatment group) five days per week throughout the duration of the experiment (Fig. 1).…”

Skeletal Healing

“…therapy for fracture healing in patients with nonunion has been proposed. In addition to several case reports, recent studies in humans [97] and animals [98][99][100][101][102] show compelling evidence of positive actions of PTH on bone healing. While the mechanism underlying the ability of PTH to enhance healing remains to be determined, recent fi ndings suggest that PTH increases mesenchymal cell proliferation and accelerates chondrogenesis via enhanced upregulation of SOX-9 in rat femur fractures [103] .…”