I don't think they are spikes. My dens grow spikes from the top of the cane or from the side, just below the top leaves and the spikes are quite thin compared to the canes. I believe most dens put out basal keikis (under the potting mix) so I think what you have here, are new canes. I'm new to dendrobiums though, so hopefully someone with more experience will chime in.
Oh boy, looks like we're having babies. Gonna have to figure out what to do with them.
Keep the plant in good culture and let the keiki grow. They will add fullness to your plant. Imagine these keiki and the rest of the plant in bloom! Some folks separate them, but an undivided plant will produce a lovely bouquet.