Dear Marylou

I empathize with your situation, tendon tears like that can be painful and you seem quite worried. It sounds like you are under good care especially from a physio who would request for another US since you failed the Thompson's test twice. Kudos to her for being thorough.

Before I give any advice, I would try to explain possibly why you may have failed a thompson test inspite of further investigations suggesting only a partial tear.
The anatomy of the calf muscles include two (or three) major muscles, the lateral and medial heads of the gastroc and the soleus. You mentioned that on re-examination, the size of the tear had changed (you didnt mention whether it was larger or smaller). Perhaps the images were not clear at the time of investigating because of swelling?

One possibility is the technique of the THompson test carried out.

This test is often done by squeezing the muscle belly of the calf to elicit passive plantarflexion. It is possible that your TA tear could have involved one of these muscles and not the other, therefore testing with these test high up or too superficially in the muscle bulk alone may falsify results giving false negative. You mentioned that your tear is 15 cm above the calcaneal bone that indicates largely within the gastroc tendon (if my mental picture of measurements is right, i have never been good in maths...infact i flunked it many times...to make matters worse my parents suggested i went for "further" maths classes..go figure). It sounds to me that the major tear is within the gastroc tendon not the soleus. Maybe your therapist needs to explore the entire bulk of the calf area to see if passive plantarflexion can be elicited?
Having no gap between the tendons is not always a reliable method...because this can be filled with fluid giving the impression of an intact tendon

the other possibility could be with the imaging used...some studies have shown that Ultrasound though it is highly accurate can give false positive results in a very very very few cases often for the worse i.e suggesting a full tear when things are infact partial tears...this is not the case with you...

Studies have shown the thompson test to be quite sensitive and specific in clinically evaluating traumatic TA injuries ....

Both aspects seem contradictory...I know...so we will use some clinical reasoning

One basic question, are you in pain? were you in pain after the injury? if after the injury all you felt was pain then and not after...then it could be a rupture...
Being able to move you ankle by pointing your toes does not tell you anything to be honest simply because you have other muscles that help with this action...

As physiobob has suggested trying another imaging technique such as an Wikipedia reference-linkMRI may clarify things...

If it is a partial tear, I would advise you to be very patient because poor rehab can mean a full rupture in the future especially if you go back into sports early... (your rehab sometimes can run into months for a sporting candidate)...only because the tendon needs to strong and flexible again to be able to withstand the rigors of sports...remember that tendons generally have a low blood supply so they heal rather slowly.

I would worry that being a partial tear much of the reliability of that tendon is already in question, because scar tissue forms generally reducing the strength of the tendon, this scar tissue will in time resemble the structure of the tendon but may not enquire all its properties. Secondly with a partial tear, you already have a gap in the overall tendon structure causing some abnormal lengthening and weakness. In my mind a full rupture is more likely to have a better outcome because with surgery you knit the ends of the tendon together enhancing the tensile strength. So rather than worry about a full rupture, I think there is more to worry with a partial rupture really.

be patient and work with your physio to get very good outcomes

Good luck with your rehabilitation