A thigh strain or quadriceps strain is a tear in one of the quadriceps muscles at the front of the thigh. It can range from a mild discomfort to a full blown tear of most of the muscle resulting in severe pain and inability to walk.
The breakage of the stitches starts within 2 weeks of the stitching but if you want the complete stitches to disappear then the process of hydrolysis or the enzymes in our body do that in a period of 60 days and therefore it approximately takes up to 2 months for the stitches to get dissolved.
It usually varies on types of suture but in general, if your stitches are dissolvable, they should start to break down within four weeks. When I had gum surgery, my surgeon advised me to continue taking salt water rinses, especially after eating, until those stitches got dissolve.