32. THE IN VIVO PERFORMANCE OF OSTEOCHONDRAL ALLOGRAFTS IN THE GOAT IS DIMINISHED WITH EXTENDED STORAGE AND DECREASED CARTILAGE CELLULARITY
Name: Andrea L Pallante
Grad Year: 2012
Purpose: Determine effect of allograft storage on structure, composition, and function of cartilage within osteochondral allografts (OCA) retrieved at 12months in the goat. Materials and Methods: Adult goats (n=15, 3yo) were OPerated in one knee, with two site-matched OCA (d=8mm, h=5mm) of different storage conditions (FROZEN, FRESH, 4°C/14d, 4°C/28d) implanted into alternating medial femoral condyle (MFC) and lateral trochlea (LT) sites. Contralateral knees were Non-OPerated controls. At 12months, gross-score (0-9) was assessed macroscopically (surface, fill, integration) and cartilage histopathology by modified-Mankin score (0-15). Cellularity was assessed with depth from the articular surface from fluorescently-labeled cell nuclei, normalized to cartilage volume. Fixed charge density (FCD) was assessed (inversely) with Hexabrix-enhanced-µCT (HE-µCT). Cartilage stiffness was assessed by indentation. Relationships between gross-score, histopathology-score, stiffness and FCD versus cellularity were assessed by linear regression. Effects of treatment and site were assessed by ANOVA. Results: Cellularity varied with treatment (p<0.001), and with zone (p<0.001), decreasing with depth. At MFC, for depth=0-50µm, cellularity was ~55% lower in 4°C/14d (p<0.05) and 4°C/28d (p=0.06) than FRESH (Fig.1). Gross-score and histopathology-score varied with treatment (each, p<0.001). At MFC, gross-score tended to increase with increasing 4ºC storage duration from 2.7±0.3 in FRESH to 3.5±0.6 in 4°C/14d and 4.0±0.6 in 4°C/28d (Fig.2). Cartilage health indices, including gross-score and histopathology-score, correlated negatively with cellularity (each, ρ2=0.7, p<0.001). Stiffness and %HE-µCT-absorption varied with treatment (p<0.001). At MFC, FCD was similar among treatments, but, at LT, tended to decrease with increasing 4ºC storage duration, indicated by ~30% increase in HE-µCT-absorption in 4ºC/28d versus FRESH (p<0.01). FCD and stiffness correlated positively with cellularity (R2=0.2, p<0.001, R2=0.4, p<0.01, respectively). Conclusions: Reduced cellularity at the articular surface, resulting from 4°C storage, was associated with variable long-term outcomes, versus consistently good repair by FRESH allografts. In human cartilage, with ~5x less cells than goat, repair outcomes may be more sensitive to 4°C storage duration.