Establishment of a clinically relevant large animal model to assess the healing of metaphyseal bone

Abstract

Despite the high incidence of metaphyseal bone fractures in patients, the mechanisms underlying the healing processes are poorly understood due to the lack of suitable experimental animal models. Hence, the present study was conducted to establish and characterise a clinically relevant large-animal model for metaphyseal bone healing.Six female adult Merino sheep underwent full wedge-shaped osteotomy at the distal left femur metaphysis. The osteotomy was stabilised internally with a customised anatomical locking titanium plate that allowed immediate post-operative full-weight bearing. Bone healing was evaluated at 12 weeks post-fracture relative to the untouched right femur.Histological and quantitative micro-computed tomography results revealed an increased mineralised bone mass with a rich bone microarchitecture. New trabeculae healed by direct intramembranous ossification, without callus and cartilaginous tissue formation. Stiffness at the cortical and trabecular regions was comparable in both groups. Functional morphological analysis of the osteocyte lacunae revealed regularly arranged spherically shaped lacunae along with the canalicular network. Bone surface biochemical analysis using time-of-flight secondary-ion mass spectrometry showed high and homogeneously distributed levels of calcium and collagenous components. Ultrastructure imaging of the new trabeculae revealed a characteristic parallel arrangement of the collagen fibrils, evenly mineralised by the dense mineral substance. The specialised bone cells were also characterised by their unique structural features. Bone remodelling in the fractured femur was evident in the higher expression levels of prominent bone formation and resorption genes. In conclusion, the novel metaphyseal fracture model is beneficial for studying healing and treatment options for the enhancement of metaphyseal bone defects.

Why Animal Experiments Are Still Indispensable in Bone Research: A Statement by the European Calcified Tissue Society

“…(25,166,167) Furthermore, osteoporotic fractures in metaphyseal regions can be modeled in this species, which is difficult in small animals. (130,168,169) Other sheep models to study centrally induced bone loss have been developed. (152,158,(170)(171)(172)(173) One example is the study from Bindl and colleagues, which analyzed metaphyseal fracture healing after surgical disconnection of the hypothalamus and pituitary gland, resulting in delayed bone formation, as it is often observed in osteoporotic patients.…”

Animal models for studying metaphyseal bone fracture healing

“…The other available studies used metaphyseal fracture models at the distal femur (Alagboso et al, 2019;Bindl et al, 2013;Claes et al, 2011a;Claes et al, 2009). In one study, a full wedge-shaped osteotomy was created at the lateral femoral condyle, which was rigidly stabilised by a custom-made locking plate (Alagboso et al, 2019). All animals tolerated the surgery well and returned to full weight-bearing within the first 3 postoperative days.…”