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 × 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.