Thirty percent and 50 % responder rates were 61.7 % and 39.3 % in patients with pre-existing pain for < 6 months , 42.3 % and 23.3 % in patients with pain for 6 months to 2 years , 40.9 % and 21.6 % in patients with pain for > 2-10 years , and 32.3 % and 14.1 % in patients with pain for > 10 years .