Small-Diameter Awls Improve Articular Cartilage Repair After Microfracture Treatment in a Translational Animal Model

Background: Microfracture is the most commonly applied arthroscopic marrow stimulation procedure. Hypothesis: Articular cartilage repair is improved when the subchondral bone is perforated by small-diameter microfracture awls compared with larger awls. Study Design: Controlled laboratory study. Methods: Standardized rectangular (4 x 8 mm) full-thickness chondral defects (N = 24) were created in the medial femoral condyle of 16 adult sheep and debrided down to the subchondral bone plate. Three treatment groups (n = 8 defects each) were tested: 6 microfracture perforations using small-diameter awls (1.0 mm; group 1), large-diameter awls (1.2 mm; group 2), or without perforations (debridement control; group 3). Osteochondral repair was assessed at 6 months in vivo using established macroscopic, histological, immunohistochemical, biochemical, and micro-computed tomography analyses. Results: Compared with control defects, histological cartilage repair was always improved after both microfracture techniques (P < .023). Application of 1.0-mm microfracture awls led to a significantly improved histological overall repair tissue quality (7.02 0.70 vs 9.03 0.69; P = .008) and surface grading (1.05 +/- 0.28 vs 2.10 +/- 0.19; P = .001) compared with larger awls. The small-diameter awl decreased relative bone volume of the subarticular spongiosa (bone volume/tissue volume ratio: 23.81% +/- 3.37% vs 30.58% +/- 2.46%; P = .011). Subchondral bone cysts and intralesional osteophytes were frequently observed after either microfracture treatment. Macroscopic grading, DNA, proteoglycan, and type I and type II collagen contents as well as degenerative changes within the adjacent cartilage remained unaffected by the awl diameter. Conclusion: Small-diameter microfracture awls improve articular cartilage repair in the translational sheep model more effectively than do larger awls. Clinical Relevance: These data support the use of small microfracture instruments for the surgical treatment of cartilage defects and warrant prolonged clinical investigations.