After an accident, a patient lost the position and vibration sense from his lower half of the body. It is seen in the lesion of:

Dorsal column tracts are pa of the medial lemniscal system, convey well-localized sensations of fine touch, vibration, two-point discrimination, and proprioception (position sense) from the skin and joints; they ascend, without crossing, in the dorsal white column of the spinal cord to the lower brain stem. Ref: Waxman S.G. (2010). Chapter 5. The Spinal Cord. In S.G. Waxman (Ed), Clinical Neuroanatomy, 26e.