While diffusion from joint space is perfusion limited, some work suggests ultrasound might increase that perfusion? By vasodilation and microvascular recruitment, from heating and shear stress on endothelial cells. With bubble vibration and cavitation as one source of stress.

Also, though perhaps not rate limiting, ultrasound might be able to mess with the N2 bubble boundary diffusion rate.

Caveats: Very not my field; no clinical practice; mostly animal studies; mostly musculature and not joint; and under-validated AI.

Meta: But I so very much enjoy surfing literature with AI. Even with AI's rich collection of interesting failure modes. They serve as fun added encouragement to keep you on your toes, and keep clear on the gradients of your confidence.