OK, lets look at some leg extensions as finishers to any good leg programming. The meat and potatoes to legs are always going to be squats but for endurance training such as hypertrophy with accessory work towards the end of your workout, you'll be able to finish off your legs with some isolate machine exercises.
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Inbound the leg extension. Although most hit the leg extension straight on there are other uses for targeting the specific muscle groups of the legs.
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Section 1). Inward Leg Extensions:
-With the toes pointed inward, now we are target the outer sweep of the leg.
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Section 2). Straight Leg Extensions:
-Its pretty "straight forward", HAHA, get it? OK bad joke but no really this is the most common and basically hits the whole leg in general, nothing fancy.
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Section 3). Outward Leg Extensions:
-With the toes pointed outward, we are now working the inner thighs and more of the teardrop portion of the leg.
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With that being said, if you have a preexisting knee issue, I would use your own caution.