the number of patients who have been treated with drsl/drslumb fus ant/ant since 4 years ago.
select count( distinct admissions.subject_id ) from admissions where admissions.hadm_id in ( select procedures_icd.hadm_id from procedures_icd where procedures_icd.icd9_code = ( select d_icd_procedures.icd9_code from d_icd_procedures where d_icd_procedures.short_title = 'drsl/drslumb fus ant/ant' ) and datetime(procedures_icd.charttime) >= datetime(current_time,'-4 year') )