PRG4 and osteoarthritis: As reported in the literature, TMJs and knees developed osteoarthritis‐like degenerative changes in Prg4‐/‐ mice.[32, 43] Our results revealed an increased neurovascular density in the Prg4‐/‐ mouse knee joint, confirming other studies (Figure 4d; Movie S10,S11, Supporting Information).[32, 43] Benefiting from whole joint mapping, we can see how the neurovascular architectures change with dense nerves and vessels radiating through the Prg4‐/‐ knee joint (Figure 4d).