Abstract INTRODUCTION Because of the significant implications on hospital payment schedules, length of acute care remains an important discussion. The objective of this study was to identify predictors of inpatient hospitalization. METHODS A statewide collaborative quality initiative consisting of 26 hospitals for patients = 18 yr, the Michigan Spine Surgery Improvement Collaborative was queried for lumbar interbody fusions from January 1, 2016 to December 31, 2017 by a single surgeon. Because of the rightwardly skewed data, length of acute care stay was divided into routine discharge = 3 d (timeframe under the normally distributed portion of the curve) and prolonged discharge = 4 d (a time mark at the start of the rightwardly skewed data). The 30-d mean preoperative Morphine Milligram Equivalent (MME) was calculated by a statewide automated prescriber system. The modified Frailty Index (mFI) is a surrogate marker for comorbidity burden. Electronic medical records were queried for physical therapy notes. RESULTS Of the 73 patients, 10 (13%) remained in the hospital = 4 d. Interestingly, median day of ambulation with physical therapy was earlier in the routine discharge cohort (postoperative day 1) versus prolonged discharge cohort (postoperative day 2) (P = .003). The expected group ambulated a mean of 109 feet versus 56 feet in the prolonged group (P = .008). The 30-d preoperative MME did not differ between the cohorts and failed to predict prolonged hospitalization in the logistical regression, controlling for mFI (OR = 2.6, P = .006) and discharge to rehab (OR = 29.2, P = .004). CONCLUSION While the mFI and discharge to rehab expectedly predicted longer hospitalization, both time to and duration of ambulation with physical therapy did correlate with faster discharge. Surprisingly, preoperative opioid usage was equivalent between the groups. Preoperative optimization of comorbidities and early physical therapy increases the likelihood of routine discharge.