Drilling and Microfracture Lead to Different Bone Structure and Necrosis during Bone-Marrow Stimulation for Cartilage Repair

Bone marrow stimulation is performed using several surgical techniques that have not been systematically compared or optimized for a desired cartilage repair outcome. In this study, we investigated acute osteochondral characteristics following microfracture and comparing to drilling in a mature rabbit model of cartilage repair. Microfracture holes were made to a depth of 2 mm and drill holes to either 2 mm or 6 rum under cooled irrigation. Animals were sacrificed 1 day postoperatively and subchondral bone assessed by histology and micro-CT. We confirmed one hypothesis that microfracture produces fractured and compacted bone around holes, essentially sealing them off from viable bone marrow and potentially impeding repair. In contrast, drilling cleanly removed bone from the holes to provide access channels to marrow stroma. Our second hypothesis that drilling would cause greater osteocyte death than microfracture due to heat necrosis was not substantiated, because more empty osteocyte lacunae were associated with microfracture than drilling, probably due to shearing and crushing of adjacent bone. Drilling deeper to 6 mm versus 2 mm penetrated the epiphyseal scar in this model and led to greater subchondral hematoma. Our study revealed distinct differences between microfracture and drilling for acute subchondral bone structure and osteocyte necrosis. Additional ongoing studies suggest these differences significantly affect long-term cartilage repair outcome. (C) 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:1432-1438, 2009