instruction: How many patients of white russian ethnicity had a procedure for dorsal and dorsolumbar fusion of the posterior column posterior technique?
response: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN procedures ON demographic.hadm_id = procedures.hadm_id WHERE demographic.ethnicity = "WHITE - RUSSIAN" AND procedures.long_title = "Dorsal and dorsolumbar fusion of the posterior column, posterior technique"