While at a recent soccer game, I noticed this gal standing on the side lines. Talk about knee problems waiting to happen ! Note the hyperextended posture of the knees with increase in lumbar lordosis and anterior carriage of the entire pelvis with an increase in the thoracic kyphosis and head forward carriage to match! You can imagine the anterior pelvic tilt as well as stretch weakness of the abdominal obliques creating "core instability". At least she is not wearing heels, although a negative inclination [negative ramp delta] shoe would probably help.
Think of the strain on her poor posterior cruciate ligaments with all of that anterior femoral translation! We remember that the popliteus acts as an "accessory PCL" at initial contact in the gait cycle. It fires at heel strike and again from loading response until toe off
Think about the forces on these knees while descending hills or stairs. The momentum will carry the femur forward (or anteriorly). There needs to be something to reststrain this; enter the PCL. Because of the laxity (and instability), the poplitues will need to fire to take up the slack. We wrote about that here and here.
Note, this is a mere thought experiment, don’t get bent outta shape, these things might not occur, or they might. Time will tell.