P005 - Interfacial Shear Mechanical Properties of Commercially Available Osteochondral Allografts
Abstract
Purpose
In vivo failures of osteochondral allograft transplantation for the treatment of articular cartilage defects are often characterized by shear delamination of the cartilage from the underlying bone (Figure 1). Implanted allografts that are inherently weak at the osteochondral junction may be more prone to chondral delamination when subjected to shear loading in the postoperative period; however, the interfacial shear properties of commercially available osteochondral allografts are unknown. The objective of this study was to characterize the shear mechanical properties of the cartilage-bone interface in commercially available osteochondral allografts as a function of graft storage time, donor age and sex, and histologic characteristics.
Methods and Materials
Ten osteochondral allograft specimens from different donors were collected from a single commercial vendor. Graft storage time (at 4°C) and donor demographics were gathered from vendor allograft offering documents. The mean storage time was 21.2 days (range, 16-25 days), and the mean donor age was 25.9 years (range, 19-34 years). Histologic analysis included % cell viability, proteoglycan content, and collagen fiber organization. Biomechanical shear testing at the osteochondral interface was performed using a custom testing device until failure at the interface. Mixed-effect regression modeling was performed to evaluate for adjusted correlations between the shear mechanical properties and graft characteristics.
Results
Among all specimens, the mean shear strength, shear stiffness, and energy to failure were 2.9±1.4 MPa, 155.2±88.0 N/mm, and 0.08±0.04 J, respectively. Older donor age was correlated with increased interfacial shear strength and energy to failure. Longer storage time was correlated with decreased interfacial shear strength. Histologically, increased proteoglycan content loss was correlated with decreased shear strength and stiffness. There were no significant correlations between cell viability and interfacial shear properties (Table 1).
Conclusion
Due to the wide variation in shear properties among commercial osteochondral allograft specimens, the addition of mechanical testing to the graft screening process may be considered.
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