A Biomechanical Proof-of-Concept Study of Scaffold-Augmented Distraction Osteogenesis Using 3D-Printed Hyperelastic Bone™ in a Rabbit Tibial Lengthening Model.

Distraction osteogenesis (DO) for limb lengthening often requires prolonged fixation while the regenerate consolidates. Adjuncts that improve the regenerate quality could reduce morbidity and treatment time. Hyperelastic Bone™ (HEB) is a 3D-printed hydroxyapatite (HA)/polylactic-co-glycolic acid (PLGA) scaffold, but its efficacy as an osteotomy-site adjunct during DO is unclear. After IACUC approval, rabbits underwent left tibial lengthening with a mini-rail external fixator distracted at 0.75 mm/day to 20% tibial length and received no scaffold (control), traditional Hyperelastic Bone™ (10% PLGA/90% HA), or a biphasic formulation (10% PLGA/70% HA/20% β-tricalcium phosphate [β-TCP]) placed subperiosteally at the osteotomy site. The contralateral tibiae served as references. After 8 weeks of consolidation, radiographs, micro-CT (prespecified endpoint: regenerate BMD), and torsional testing (prespecified endpoint: stiffness) were performed. Fourteen rabbits underwent attempted lengthening. Intraoperative fractures (n = 2) and fixation loss (n = 3) reduced complete terminal datasets to nine, all of which completed micro-CT and torsion testing. Radiographs confirmed regenerate formation. Regenerate BMD remained below contralateral values with controls being intermediate to the traditional and biphasic HEB formulations (60.5%, 63.8%, and 54.7% of contralateral, respectively). Despite no mineral density improvement, scaffold-treated regenerate demonstrated higher torsional stiffness and strength metrics, greatest with the biphasic formulation, with lower failure displacement and higher polar moment of inertia. Statement of Clinical Significance: A scaffold that improves functional regenerate performance could enable earlier safer weight bearing and device removal and reduce nonunion/refracture risk in DO.