Sharp pain in big toe? A nerve problem or a joint problem?

Either. You need to see apodiatrist for a work up to determine the problem.
Joint. It depends if it crosses the joint. If it hurts when the joint is moved or palpated, it is the joint.

Related Questions

Woke up to 4th toe on left foot and big toe on right foot numb. Have either SI joint problem or pirifomis could this be related? No leg pain at the time

Could be . the nerves that go to those areas originate in the lower back. It is a bit odd that it is on both legs and in different dermatomes but injuring two parts of your lower back would explain that. Read more...