My left thumbnail has been very lumpy for about 20 years. The lumps aren't "ridges" and can't be described as horizontal or vertical. They are irregularly-shaped, raised areas - as if the nail were mimicking rolling hills. Fine vertical ridges cover the whole nail and a deep, v-shaped furrow runs through center length of the nail. The lumps are not in the nail bed, but move upward from the bottom as the nail grows. Occasionally, thin, rust-colored, vertical stripes also appear and grow out with the nail.
Have you damaged or had trauma to your matrix (area under cuticle) this could be the result in having permanent ridges to your nail. To smooth out and make the nail more pleasing to the eye, i suggest buffing and applying cream to your nail plate every fortnight.
It sounds like the "matrix" has been damaged, this happens if the nail has been bashed or bumped and there isnt anything that can be done about it all you can really do is gentley file the ridges away and apply nail vanish to disguise it.