Let me first put your mind at rest - this is quite probably nothing to do with not having done enough PT or been 'good enough' in what you did.
Here is my standard mini-lecture on the subject so read and absorb ...
All the structures in the body, muscles, tendons, ligaments, even gut and lungs, need to be able to glide over one another smoothly to let our bodies work. To do this, the body produces a special viscous fluid that acts like the oil in your car engine and lubricates everything with great efficiency.
Now when the surgeon opens up any part of our body, the internal stuff gets exposed to the air which is, by comparison to the inside of the body, cool and dry. The natural reaction is that fluids evaporate and tissues cool. This makes the organs and structures dry so when the wound is closed, part of the healing process is for the body to go into overdrive, producing extra fluid to replace what is lost. This is one reason why you need IV fluids during and after an operation.
Now as a general rule, 95% of people manage to make up this fluid loss and normality is restored quite quickly. But in the other 5%, for a variety of reasons some known, most unknown, their bodies are deficient in making up this loss and lacking the necessary lubrication, the ligaments and muscles lose their 'glide-ability' and begin to stick or adhere to one another. This is why they are often refered to as 'adhesions'.
NB: Some people (and surgeons!) often refer to this as scar tissue which is a bit of a misnomer. Scar tissue is abnormal or fibrous tissue that's grown in a place as a result of trauma like an incision. Adhesions are just normal tissues stuck together. Difference is that scar tissue won't split or seperate easily whilst adhesions will except it's a bit like trying to pull velcro apart by pulling on the opposite ends of each tape - not easy!
Anyway, if this occurs and the function of the joint is affected, the answer is to work the joint with some force, thereby freeing the structures from their locked-in state. Much as you would if you got a sticky or rusty lock and put some oil in it, you'd work it back and forth to free it up. That's all a manipulation is.