Hi Mike,
It is interesting you mention the Pet anserine as a topic this morning.
Last Saturday I worked at Anatomy day which is a wet lab protection learning day at Griffith University. We did lower limb and when I was working with the specimens it reminded me how lovely the design of the Pet really is.
The sartorius, gracilis and semitendinosus tendons look really small on ultrasound, however when you see them in the flesh they are indeed really thin, but they are really broad and strong. Like a broad strap of collagen. They blend together sharing an enthesis and this is why they are so strong.
The reason we need a bursa is that the 3 tendons of the Pes pass immediately over the distal end of the medial collateral ligament of the knee.
The bursa sits between the 3 pets tendons and the MCL.
The fluid and vascularity you can see does indeed link like it is coming from the Pes area and you might want to try a catabolic intervention in this area.
Has the patient has a prior anterior cruciate ligament repair? The reason I ask is that the distal exit point of the ACL repair tunnel is often close to the pes and may create an issue.
If there has not been a prior ACL repair you my be seeing some pes anserine bursitis.
As far as the click goes, I am not too sure what would cause the click unless the pes tendons are catching on the MCL below, but I have not seen this before.
Most clicks around this medial joint line are associated with meniscal tears / degeneration and OA changes.
As always in a knee with these type of symptoms an MRI is a better option than an ultrasound.
On your videos your MC-LS video looks entirely normal to me with the MCL seen in long xis and the pes anserine tendons in short axis.
The Pes-Ans-LS is a bit trickier for me to orientate but there is clearly some inflammatory change around the collagen structure like a synovitis of some sort.
The third one Pes-Ans TS is a bit harder for me to orientate.
I wonder if the muscle is the medial gastrocnemius and if the hypoechic area adjacent to it is the semimembranosus tendon.
Is the swelling associated with Semimembranosus ? as this is quite close to the pes.
Steve