A 24-year-old athletic male soccer player was brought to the Emergency Department with a history of having fallen hard during a game and twisting his knee after being tripped. On examination, he was lying with his left knee partially flexed. It was beginning to swell with fullness visible at the sides and above the patella, together with a slight patellar tap. All passive movements were painful. There was localized pain on deep pressure just medial to the patellar ligament over the joint line, and also severe pain over the joint line on the medial border of the knee. It became excruciating with firm medial-ward pressure applied over the lateral side of the joint at the same time as attempted abduction of the leg at the knee. A plain frontal radiograph, including a film taken while maneuvering the joint as described with attempted abduction of the leg at the knee, showed inequality of the femur/tibia joint line with widening on the medial side.

1. What is the anatomical basis for patellar tap?

2. What structure was injured to be the cause of pain on deep pressure medial to the patellar ligament?

3. What structure was injured to explain pain on the medial border of the knee, accentuated by pressure over the lateral side with concomitant abduction of the leg?

4. Which ligaments are extracapsular and which are intracapsular? What are their roles instabilizing the joint?