While evaluating a client's health-history questionnaire, an ACE certified Personal Trainer learns that the client...

While evaluating a client's health-history questionnaire, an ACE certified Personal Trainer learns that the client had Knee surgery six month| ago. The client engaged in two weeks of physical therapy immediately after the procedure but has maintained a sedentary lifestyle since that time. The client reports that the knee now feels weak and unstable. Which of the following is MOST likely to have happened to the muscle tissue around the knee?