A growth or just a part of the spine?

i have lower back pain and such and i'm going to physical therapy for my achilles tendonitis and walking problems. i was just sort of running my knuckles up and down my lower back around my lumbar spine and i noticed that as i went up my hand sort of dipped but before the dip was a smooth i dunno what it was.. my physical therapist has worked on that part of my back before so it's proabbly nothing right?