• Mona Eldracher, Patrick Orth, Magali Cucchiarini, Dietrich Pape, and Henning Madry.
• Center of Experimental Orthopaedics, Saarland University, Homburg, Germany.
• Am J Sports Med. 2014 Nov 1; 42 (11): 2741-50.

BackgroundSubchondral drilling is an established marrow stimulation technique.HypothesisOsteochondral repair is improved when the subchondral bone is perforated with small drill holes, reflecting the physiological subchondral trabecular distance.Study DesignControlled laboratory study.MethodsA rectangular full-thickness chondral defect was created in the trochlea of adult sheep (n = 13) and treated with 6 subchondral drillings of either 1.0 mm (reflective of the trabecular distance) or 1.8 mm in diameter. Osteochondral repair was assessed after 6 months in vivo by macroscopic, histological, and immunohistochemical analyses and by micro-computed tomography.ResultsThe application of 1.0-mm subchondral drill holes led to significantly improved histological matrix staining, cellular morphological characteristics, subchondral bone reconstitution, and average total histological score as well as significantly higher immunoreactivity to type II collagen and reduced immunoreactivity to type I collagen in the repair tissue compared with 1.8-mm drill holes. Analysis of osteoarthritic changes in the cartilage adjacent to the defects revealed no significant differences between treatment groups. Restoration of the microstructure of the subchondral bone plate below the chondral defects was significantly improved after 1.0-mm compared to 1.8-mm drilling, as shown by higher bone volume and reduced thickening of the subchondral bone plate. Likewise, the microarchitecture of the drilled subarticular spongiosa was better restored after 1.0-mm drilling, indicated by significantly higher bone volume and more and thinner trabeculae. Moreover, the bone mineral density of the subchondral bone in 1.0-mm drill holes was similar to the adjacent subchondral bone, whereas it was significantly reduced in 1.8-mm drill holes. No significant correlations existed between cartilage and subchondral bone repair.ConclusionSmall subchondral drill holes that reflect the physiological trabecular distance improve osteochondral repair in a translational model more effectively than larger drill holes.Clinical RelevanceThese results have important implications for the use of subchondral drilling for marrow stimulation, as they support the use of small-diameter bone-cutting devices.© 2014 The Author(s).

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