Centrifugal Cleansing of the Subchondral Bone of Osteochondral Grafts
- Drake, Rebecca L
- Advisor(s): Sah, Robert L
Transplantation of an osteochondral allograft (OCA) is a generally effective treatment for large chondral or osteochondral lesions. The effectiveness of OCAs is enhanced by the removal of marrow from the subchondral bone and facilitated by the maintenance of viable chondrocytes. Cleansing of OC is currently performed by pulsatile fluid lavage alone or in combination with high-pressure gas/air, but limited by depth of removal, need for user manipulation, and collection and disposal of large volumes of cleansing fluid. Centrifugation is an alternative method that has been applied to massive, previously-frozen allografts, and large osteochondral fragments including whole femoral heads, but has not been studied for osteochondral cylinders (OCs).The aim of the present study was to determine if centrifugation could be used to cleanse the marrow space of osteochondral cores (OCs) while maintaining viable chondrocytes. The effects of centrifugation duration (0-900 s) and centrifugal force (RCF, 0-10,000×g) were assessed on OCs from total knee arthroplasty (6 mm diameter, TKA) or OCA (8 mm diameter) tissue. Pellet mass and OC mass were measured after centrifugation and after additional trypsin treatment to loosen residual marrow. OC trabecular bone and marrow structure was characterized quantitatively by micro-computed tomography (µCT), without and with Hexabrix contrast, and qualitatively by photography and histology. Chondrocyte viability was assessed by live/dead imaging. Centrifugation at 10,000×g for 300s removed most of the marrow from TKA-OC based on estimates from pellet mass (88%) and µCT (73%), and from OCA-OC (72% and 86%, respectively). Release from TKA-OC was lower at 3,000xg/300s (64% and 45%) or shorter duration 10,000xg/30s (54%, pellet mass). The spatial variation in µCT images indicated that release progressed from the bone base up toward the subchondral plate. Release from OCA-OC was not affected by extending 10,000xg duration to 900s. Pellet mass correlated identically to OC mass decrease, and also correlated strongly with empty marrow volume by µCT. Histology with Oil Red O and Hematoxylin and Eosin confirmed the relative presence or absence of marrow. TKR and OCA donors differed in age (71 vs 20 yr), and their OC bone varied in volume faction (28% vs 38%), trabecular thickness (0.167 mm vs 0.188 mm), and trabecular separation (0.442 mm vs 0.371 mm). Chondrocyte viability throughout the cartilage was high for samples subjected to no centrifugation (95%) and only slightly diminished by 10,000xg centrifugation for 300 s (to 90%). Centrifugation provides a method of cleansing OCs that is similarly effective as the current pulsatile lavage standard method in terms of marrow cleansing (~70%) while maintaining chondrocyte viability (~90%). Centrifugation provides a controlled treatment, avoiding manual manipulation with pulsatile lavage. Centrifugation also avoids the need to collect and dispose of large volumes of lavage fluid. Additionally, with pellet mass measurement, centrifugation allows a simple assessment of the degree of marrow cleansing. Finally, by varying centrifugation RCF and duration, the extent of cleansing can be varied. Thus, centrifugation may provide a new effective method of cleansing OCAs that provides similar degrees of marrow cleansing and chondrocyte viability, while allowing convenient assessment by pellet mass and modulation of the degree of cleansing by varying RCF or duration.