The avascular talus: revascularization in an animal model

Avascular necrosis of bone such as the talus can lead to collapse and loss of function. To avoid this, early revascularization has been proposed as an important event. Revascularization can occur either by vessel growth directly through the bony surface, or by vessel growth into the periosteum or ligaments with secondary reconnection to the bone. The ability to attract new vessels (angiogenesis) of the bony surface and the connective tissue was compared in an animal model. A talus isograft (all cortical surface, periosteum, and ligaments remaining; n = 11) or a sector of a femoral head isograft (cancellous surface, no connective tissue; n = 12) of adult mice was implanted into dorsal skinfold chambers of mice of the same strain. The implants were observed by intravital microscopy every 12 hours. First indicators of angiogenesis were hemorrhages around the implants (tali: 11 of 11, 72 +/- 12 hours; femoral heads: 6 of 12, 84 +/- 24 hours). Next, a sudden redness of the transplant indicated marrow hemorrhage (tali: 9 of 11 after 84 +/- 36 hours; femoral heads: 10 of 12 after 96 +/- 36 hours). Histology showed clear growth of capillaries into the cancellous surface of the femoral heads and possible growth of capillaries into the ligament stumps (tali). However, there was widespread necrosis of the marrow cells indicating failure of recirculation. A cancellous bony surface as well as the soft tissues attached to the bone provided a stimulus to rapid revascularization of the grafts. This model was able to evaluate differing rates of early partial revascularization for various bone surfaces, which may have implications for studying treatment options for certain fracture dislocations (e.g., in the talus).