Development and Efficacy Testing of a “Hollow Awl” That Leads to Patent Bone Marrow Channels and Greater Mesenchymal Stem Cell Mobilization During Bone Marrow Stimulation Cartilage Repair Surgery

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To investigate whether microfracture with a cannulated hollow awl can yield more patent marrow channels and allow greater mobilization of the reparable cells to the defect compared to the conventional awl with blunt end in human knee joints. Patients who were planned for 1-stage bilateral total knee arthroplasty due to degenerative osteoarthritis with well-preserved lateral femoral condylar cartilage were retrospectively included. A 10-mm× 20-mm, rectangular, full-thickness chondral defect was made on the lateral femoral condyle on each knee joint. The 6-holed microfracture procedure, each at 9mm depth and 3mm separation of perforations, was followed using a hollow awl in one knee and using a conventional awl in the other knee, respectively. The bleeding through the microfracture holes was observed and collected using an absorbable gelatin sponge and was analyzed microscopically by colony forming unit-fibroblast assays and automated cell counting method. The representative 3 bony samples of the distal lateral femoral condyles obtained were also scanned with micro-computed tomography (micro-CT) for morphometric analysis (percent bone volume, trabecular separation, and total porosity) of subchondral bone microarchitecture of the microfracture holes. Twenty-two patients were enrolled, and the mean age was 70.8 ± 6.1 (58-83) years. Compared with the conventional awl group, the hollow awl group had a significantly greater amount of bleeding (1.8 ± 0.2g vs 1.1 ± 0.1g; P< .001) and a greater number of mesenchymal stem cells in the blood clot (21,474.0 ± 3,911.1 vs 13,329.7 ± 3,311.0; P= .004). The hollow awl group also showed overall more patent marrow channels around the adjacent subchondral bone of the microfracture hole, with greater trabecular separation on micro-CT analysis (P < .001). Compared to the conventional awl, microfracture with a cannulated hollow awl can yield more patent marrow channels at the adjacent subchondral bone of the microfracture hole and result in greater mobilization of the reparable cells to the defect in human knee joints. Level III, therapeutic case control.