Dropping a loadstone has a chance of producing the message “You drop the loadstone right on your foot!” and wounding your legs.

If you are wearing kicking boots, you can kick even when your legs are wounded.

Restore ability (potion or spell) also cures wounded legs, “restoring your ability” to jump, kick, carry, etc, and will cure most status ailments as well.

If you have at least Basic in martial arts, you cannot injure your leg by kicking.

Give a different message for when you injure your legs by kicking. Possibly as subtle as “Ouch! That really hurts!”, but could be more explicit like “Ouch! You injured your leg!”

Bear traps injure your legs like xans do.

Debilitating wound system that expands on wounded legs. Includes wounded arms and various types of disease and poison, all of which provide various debuffs. Quaffing any healing potion cures all of these at once on top of its usual HP healing.