Pedal float & release
There is no quick fix pedal for knee issues. Speedplay's non-centering wide float allows the least amount of outside force working on your knee while clipped in but requires more rotation and some force to exit the pedal regardless.

An ACL issue may be more harmed by the extra rotation and the angle at which release force is required, than it is helped by the non centering, wide float. I've listed several pedals and the float options and release tensions below. (Feel free to add others, if anybody has details. I will as I find them.)


  "Float" is defined as the degree of movement offered by the cleat
  within the pedal before release begins. This can be highly important
  to prevent damage to knees, as most peoples' legs do not remain in a
  single plane as they pedal.


Look:

Keo Easy/Max/Carbon System:
Offers Zero(black cleat), 4.5 degree(grey cleat), and nine degree(red cleat) float, adjustable only by cleat replacement. No release tension adjustment. 

Keo Blade system:
Offers Zero(black cleat), 4.5 degree(grey cleat), and nine degree(red cleat) float, adjustable only by cleat replacement. Release tension is either 12Nm or 16Nm. Stock is 12Nm, and adjustment requires changing the carbon leaf spring in the pedal. (Specific tools required.)

Look Delta:
Offers Zero(black cleat) and nine degree(red cleat) float, adjustable only by cleat replacement. Pedal design obsoleted but still common on older bikes. 

Shimano:

Shimano SPD-SL (Current Shimano road pedals):
Offered in Yellow/Black 6 degree float or red/black zero float. All SPD-SL pedals from Tiagra level to Dura Ace offer adjustable release tension, from 1Nm to between 12Nm and 16Nm depending on pedal component level. 

Speedplay:

Speedplay pedals are unique in that they do not rely on spring tension for cleat retention in the pedal. There is a spring, but is only active during pedal entry and release. This means there is no "centering" action on the pedal. This is the reason that they are often offered to, and can have some benefit for persons with knee trouble. They do require more rotation to reach the point of engaging the release spring, and the release requires some force.

Zero:
Float adjustable on cleat from zero to fifteen degrees. Release tension approximately 8Nm.

Light Action:
Fifteen degrees non-centering float. No adjustment possible. Release tension approximately 6Nm.

X-Series:
Fifteen degrees non-centering float. No adjustment possible. Release tension approximately 10Nm. Obsolete, replaced by light action pedal. Cleats still available.

I hope this is helpful.