Yes, very interesting indeed.
Bakers cyst fluid can take 2 paths.
With a superficial rupture the fluid is in the subcutaneous space, so NOT deep to the muscle fascia.
With a deep rupture the fluid tracks down the aponeurotic space between the medial gastrocnemius and soleus in the same potential space that the plantaris tendon lives in.
In the case you show I don’t believe this is a Bakers cyst rupture as the fluid is not in the typical location. I think this is a bleed that has happened due to muscle injury or compression and the blood has accumulated in the sub-muscle fascia space. I agree you can only measure the haematoma, it is impossible to estimate the tear size. This is the case with most muscle injuries !
You do have to also remember that a bakers cyst can have another unusual path where is becomes intramuscular and I have seen them in medial gastric as well as soles. In fact I did a case of the week a while back you can watch exploring this topic.
I think the way you have described it is excellent.
Great work,
Thanks for such an interesting post and great images,
Steve.