BACKGROUND:Lateral lumbar interbody fusion (LLIF) is commonly used to address various lumbar pathologies. LLIF using the prone transpsoas (PTP) approach has several potential advantages, allowing simultaneous access to the anterior and posterior columns of the spine. The aim of this study was to report the 1-year outcomes of LLIF via PTP. METHODS:This is a retrospective review of 97 consecutive patients who underwent LLIF via PTP. Radiographic parameters, including lumbar-lordosis, segmental-lordosis, anterior disc height, and posterior disc height, were measured on preoperative, initial-postoperative, and 1-year postoperative imaging. Patient-reported outcomes measures, including Oswestry Disability Index, visual analog scale (VAS), pain EQ5D, and postoperative complications, were reviewed. RESULTS:Ninety-seven consecutive patients underwent 161 levels of LLIF. Fifty-seven percent underwent 1-level LLIF, 30% 2-level LLIF, 6% 3-level LLIF, and 7% 4-level LLIF. The most common level was L4 to L5 (35%), followed by L3 to L4 (33%), L2 to L3 (21%), and L1 to L2 (11%). Significant improvements were noted at initial and 1-year postoperative periods in lumbar-lordosis (2° ± 10°, P = 0.049; 3° ± 9°, P = 0.005), segmental-lordosis (6° ± 5°, P < 0.001; 5° ± 5°, P < 0.001), anterior disc height (8 mm ± 4 mm, P < 0.001; 7 mm ± 4 mm, P < 0.001), and posterior disc height (3 mm ± 2 mm, P < 0.001; 3 mm ± 2 mm, P < 0.001). Significant improvements were seen in Oswestry Disability Index at 6 weeks (P = 0.002), 6 months (P < 0.001), and 1 year (P < 0.001) postoperatively; pain EQ5D at 6 weeks (P < 0.001), 6 months (P < 0.001), and 1 year (P < 0.001) postoperatively; and leg and back visual analog scale at 2 weeks (P < 0.001), 6 months (P < 0.001), and 1 year (P < 0.001) postoperatively. The average length of stay was 2.5 days, and the most common complications were ipsilateral hip flexor pain (46%), weakness (59%), and contralateral hip flexor pain (29%). CONCLUSION:PTP is a novel way of performing LLIF. These 1-year data support that PTP is an effective, safe, and viable approach with similar patient-reported outcome measures and complications profiles as LLIF performed in the lateral decubitus position. LEVEL OF EVIDENCE: 4: