Selective Dorsal Rhizotomy. Guide. Selective dorsal rhizotomy (SDR) is the most common nerve surgery for symptoms related to cerebral palsy (CP). During SDR, a surgeon cuts the skin over the lower part of the spinal cord.The surgeon then finds and cuts the nerves in the cord that are causing muscle tightness in the legs.elective Dorsal Rhizotomy. Guide. Selective dorsal rhizotomy (SDR) is the most common nerve surgery for symptoms related to cerebral palsy (CP). During SDR, a surgeon cuts the skin over the lower part of the spinal cord.