2015 ISAKOS Biennial Congress ePoster #1504

Medial Femoral Condyle Cartilage Defect Biomechanics: Effect of Obesity, Defect Size, and Cartilage Thickness

Kyle William Lacy, MD, MS, Detroit, MI UNITED STATES
Allison Cracchiolo, BS, Madison Heights, MI UNITED STATES
Stephen Yu, MD, Garden City, MI UNITED STATES
Henry Thomas Goitz, MD, St. Clair Shores, MI UNITED STATES

Detroit Medical Center - DMC Sports Medicine, Detroit, MI, USA

FDA Status Not Applicable

Summary: In a cadaver knee model simulating single-stance weight bearing, full-thickness cartilage defects of the medial femoral condyle sustained significantly greater force at the base of the defect for obese loads (BMI > 30), defect sizes > 2 cm2, and cartilage rim thickness < 2mm; these three factors may therefore lead to biomechanically unfavorable environments in the setting of microfracture.

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Abstract:

Introduction

Full-thickness cartilage defects of the medial femoral condyle (MFC) are a common source of knee pain; when indicated, microfracture can be used to treat these defects. Containment, the ability of the rim cartilage to protect the base of the defect from load, is favorable in microfracture, as the superclot is shielded from force. Post-operative weight bearing protocols after microfracture, as well as indications for microfracture in the obese patient, are controversial. The amount of force sustained at the base of full-thickness cartilage defects during weight bearing loads, and the influence of obesity, defect size, and cartilage thickness on these forces remains yet to be determined.

Methods

8 human cadaver knees were statically loaded in 15° of flexion to simulate 20, 30, and 40 BMI single-stance weight bearing. Full-thickness cartilage defects of diameters 6, 8, 10, 12, 14, 16, 18, and 20 mm were made on the MFC at the point of maximum contact force. A medial compartment sensor measured force transmission and area of containment. For defects 14, 16, 18, and 20 mm in diameter, a sensor quantified force at the subchondral bone. Surrounding rim cartilage thickness was quantified for each size defect using digital calipers. Repeated measures ANOVA was used to compare area of containment data and base of defect force data between BMI groups.

Results

Larger BMI loads (BMI > 30) led to significant decreases in the area of containment for all defects > 14 mm diameter (p < 0.038). Base of defect force increase was significant for defects > 16 mm diameter (2 cm2 in area) between loaded and unloaded states (p < 0.042), and for BMI > 30 loads (p < 0.045). Cartilage rim thickness < 2 mm resulted in significantly higher force at the base of the defect than for cartilage thickness > 2 mm, for all BMI groups (p < 0.025).

Conclusion

Biomechanically unfavorable environments were observed for MFC cartilage defects in the setting of obesity, size > 2 cm2, and rim thickness < 2 mm. The resultant decrease in area of containment, and increase in force sustained at the base of the defect, expose the superclot to potentially detrimental forces in the setting of microfracture. Our findings correlate with clinical studies showing decreased cartilage fill rates, and poorer knee functional outcome, after microfracture in patients with BMI > 30. Clinical studies are needed to compare microfracture with other more structurally stable treatment options (osteochondral autograft, osteochondral allograft) for femoral condyle cartilage defects in the obese patient population.