A muscular tear such as in the quadriceps can cause a defect in the tissue and thus a dent seen externally. These though tend to be painful. Alternatively, what you perceive to be a dent may actually be due to soft tissue
lump (such as fairly common, benign lipoma
, a fatty tissue lump) creating uneven contours.
Eiher way, having an Ultrasound
scan by a Musculoskeletal Radiologist
is my advice.