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What is creeping sustitution?

Asked by Kesavan 

Creeping substitution is a term commonly used in bone healing, graft incorporation and avascular necrosis of bone.

When a bone graft is placed, avascular nature of graft causes resorption by osteoclasts, while new bone is laid down by osteogenic cells originating from the recipient bed rather than the graft (osteoblasts creep from recipient site to the graft). This phenomenon is called the creeping substitution. Due to creeping substitution, bone graft is weakest at 6 months.

Reference: Spine Surgery: Techniques, Complication Avoidance, and Management, Volume 1
edited by Edward C. Benzel

In cases of avascular necrosis (AVN), deposition of granulation tissue occurs at the border of the lesion that allows vascular proliferation to form a bridge between the dead and the living bone tissue. On this bridge, mesenchymal bone marrow stem cells can reach the necrotic area and differentiate into osteogenic cells rehabitating the dead trabeculae and building new bone on them. This phenomenon is also the creeping substitution. Core decompression and autologous bone grafting allows the sclerotic perilesional barrier to be opened and creeping substitution "conduced" by autologous bone fragments.

Reference: Avascular Necrosis of the Femoral Head: Current Trends: Current Trends
edited by F.S. Santori, N. Santori, A. Piccinato