Front squats may be more suitable for those with knee problems

Both exercises, front and back squats, are as effective in terms of overall muscle recruitment. The significant difference is that the front squat causes significantly less compressive forces and extensor moments than the back squat. This result suggest that front squats may be advantageous compared with back squats for individuals with knee problems such as meniscus tears, and for long-term joint health.

The squat is a full body, compound exercise that involve the muscles of the thighs, hips, buttocks, quadriceps and the hamstrings. It also has effects on the bones, strengthening them, as well as ligaments and insertion of the tendons throughout the lower body.

Source:

Gullett JC. A biomechanical comparison of back and front squats in healthy trained individuals. J Strength Cond Res. 2009 Jan;23(1):284-92.