Injectable freeze-dried chitosan/PRP implants improve marrow stimulated cartilage repair in a chronic defect rabbit model.

Bone Marrow Stimulation (BMS) improves knee joint function but elicits incomplete repair. Liquid chitosan (CS)-glycerol phosphate/blood clots have been shown to improve BMS-based cartilage repair. Platelet-rich-plasma (PRP) - a rich source of growth factors and cytokines - improves recruitment and chondrogenic potential of subchondral mesenchymal stem cells. We hypothesized that repair response in a rabbit chronic defect model will improve when freeze-dried chitosan/PRP is used to augment BMS. Bilateral trochlear defects created in New Zealand White rabbits were allowed to progress to a chronic stage over 4 weeks. Chronic defects were debrided and treated by BMS in second surgery, then augmented with PRP (BMS + PRP) or freeze-dried chitosan/PRP implants (BMS + CS/PRP). The quality of 8 week repair tissue was assessed by macroscopic, histological and micro-CT analysis. ICRS macroscopic scores indicated fibrocartilaginous or fibrous repair in control defects that were improved in the BMS + CS/PRP group. An overall improvement in repair in BMS + CS/PRP group was further confirmed by higher O'Driscoll scores, %Saf-O and %Coll-II values. Micro-CT analysis of subchondral bone indicated on-going remodeling with repair still underway. Quality and quantity of cartilage repair was improved when freeze-dried chitosan/PRP implants were used to augment BMS in a chronic defect model.