Abstract
Large cartilage lesions in younger patients can be treated by fresh osteochondral allograft transplantation, a surgical technique that relies on stable initial fixation and a minimum chondrocyte viability of 70% in the donor tissue to be successful. The Missouri Osteochondral Allograft Preservation System (MOPS) may extend the time when stored osteochondral tissues remain viable. This study aimed to provide an independent evaluation of MOPS storage by evaluating chondrocyte viability, chondrocyte metabolism, and the cartilage extracellular matrix using an ovine model.
Femoral condyles from twelve female Arcott sheep (6 years, 70 ± 15 kg) were assigned to storage times of 0 (control), 14, 28, or 56 days. Sheep were assigned to standard of care [SOC, Lactated Ringer's solution, cefazolin (1 g/L), bacitracin (50,000 U/L), 4°C storage] or MOPS [proprietary media, 22-25°C storage]. Samples underwent weekly media changes. Chondrocyte viability was assessed using Calcein AM/Ethidium Homodimer and reported as percent live cells and viable cell density (VCD). Metabolism was evaluated with the Alamar blue assay and reported as Relative Fluorescent Units (RFU)/mg. Electromechanical properties were measured with the Arthro-BST, a device used to non-destructively compress cartilage and calculate a quantitative parameter (QP) that is inversely proportional to stiffness. Proteoglycan content was quantified using the dimethylmethylene blue assay of digested cartilage and distribution visualized by Safranin-O/Fast Green staining of histological sections. A two-way ANOVA and Tukey's post hoc were performed.
Compared to controls, MOPS samples had fewer live cells (p=0.0002) and lower VCD (p=0.0004) after 56 days of storage, while SOC samples had fewer live cells (p=0.0004, 28 days; p=0.0002, 56 days) and lower VCD (p=0.0002, 28 days; p=0.0001, 56 days) after both 28 and 56 days (Table 1). At 14 days, the percentage of viable cells in SOC samples were statistically the same as controls but VCD was lower (p=0.0197). Cell metabolism in MOPS samples remained the same over the study duration but SOC had lower RFU/mg after 28 (p=0.0005) and 56 (p=0.0001) days in storage compared to controls. These data show that MOPS maintained viability up to 28 days yet metabolism was sustained for 56 days, suggesting that the conditions provided by MOPS storage allowed fewer cells to achieve the same metabolic levels as fresh cartilage. Electromechanical QP measurements revealed no differences between storage methods at any individual time point. QP data could not be used to interpret changes over time because a mix of medial and lateral condyles were used and they have intrinsically different properties. Proteoglycan content in MOPS samples remained the same over time but SOC was significantly lower after 56 days (p=0.0086) compared to controls. Safranin-O/Fast Green showed proteoglycan diminished gradually beginning at the articular surface and progressing towards bone in SOC samples, while MOPS maintained proteoglycan over the study duration (Figure 1).
MOPS exhibited superior viability, metabolic activity and proteoglycan retention compared to SOC, but did not maintain viability for 56 days. Elucidating the effects of prolonged MOPS storage on cartilage properties supports efforts to increase the supply of fresh osteochondral allografts for clinical use.
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