In the conventional posterior approach to the lumbar spine for transforaminal lumbar interbody fusion (TLIF), the paravertebral muscles are stripped from the spinous process. The authors developed a novel surgical procedure in which TLIF was performed via a modified spinous process–splitting (SPS) approach that enabled the preservation of the attachment of the paravertebral muscles to the spinous process. The SPS TLIF group comprised 52 patients with lumbar degenerative or isthmic spondylolisthesis who underwent surgery using a modified SPS TLIF technique, whereas the control group comprised 54 patients who underwent conventional TLIF. Compared with the control group, the SPS TLIF group had a significantly shorter operation time, smaller intra- and postoperative blood loss volumes, and shorter hospital stay and time to ambulation (p < 0.05). The SPS TLIF group had a lower mean visual analog scale score for back pain than the control group on both postoperative day 3 and at 2 years postoperatively (p < 0.05). Follow-up MRI showed changes in the paravertebral muscles in 46 of 54 patients (85%) in the control group and 5 of 52 patients (10%) in the SPS TLIF group (p < 0.001). This novel technique may be a useful alternative to the conventional posterior approach for TLIF.