Developing a Method to Evaluate Interventions for Osteochondral Defects of the Talus

Osteochondral lesions of the talus (OLTs) are commonly caused by an acute traumatic ankle injury. Multiple treatment modalities are available for OLTs, with the size and location of the lesion informing treatment choice. Hydrogels provide an exciting possibility for future therapies for OLTs due to their tunable properties and similarities to native cartilage. However, there is a lack of understanding relating to the differences in clinical success seen with different lesions and a notable paucity in long term studies or appropriate ex vivo methods to assess the biomechanical changes within the tibiotalar joint. A functionalised hydrogel was developed as an injectable therapy for OLTs. Reproducible synthesis using sequential functionalisation of 4-vinylbenzyl chloride (4VBC) and methacrylamide (MA) on type I rat tail collagen was performed to create an injectable precursor material. Successful photocrosslinking of 4VBC-MA precursor was performed using vis-light photoinitiation in physiological conditions. Encapsulation of ATDC-5 immortalised chondrocytes and MSCs showed viability within the scaffolds for up to 7 days and maintenance of chondrogenic morphology. The subsequent studies aimed to develop a greater understanding by characterising the biomechanical changes associated with OLTs through changes in contact area, contact pressure, and frictional properties. Presence of a 10 mm defect within the human talar dome caused a significant increase to the coefficient of friction compared with that of native tibiotalar joint but did not significantly change the contact mechanics. Repair of the defect with the 4VBC-MA hydrogel was able to reduce the friction coefficient in the tibiotalar joint to a similar level as that seen using autologous matrix induced chondrogenesis (AMIC) and osteochondral allograft treatments (p < 0.05). None of the treatments were able to return the friction coefficient to the value seen in healthy tissue, with only the osteochondral allograft treatment allowing for loading to occur through the defect site. The outcomes of AMIC treatments varied depending on size, shape and lesion location. Stability of AMIC repair was dependent on shape, with square repairs performing poorer compared to circular repairs. AMIC treatment of kissing lesions is subject to material-material interactions which negatively impacts the tissue frictional properties, reducing the stability of the repair.