Intramuscular pressure of the multifidus muscle and low-back pain after posterior lumbar interbody fusion: comparison of mini-open and conventional approaches

Object. This randomized study was designed to elucidate the time course of the perioperative development of intramuscular multifidus muscle pressure after posterior lumbar interbody fusion (PLIF) and to investigate whether the route of pedicle screw insertion affects this pressure and resultant low-back pain. Although several studies have focused on intramuscular pressure associated with posterior lumbar surgery, those studies examined intramuscular pressure generated by the muscle retractors during surgery. No study has investigated the intramuscular pressure after PLIF. Methods. Forty patients with L4-5 degenerative spondylolisthesis were randomly assigned to undergo either the mini-open PLIF procedure with pedicle screw insertion between the multifidus and longissimus muscles (n = 20) or the conventional PLIF procedure via a midline approach only (n = 20). Intramuscular pressure was measured 5 times (at 30 minutes and at 6,12,24, and 48 hours after surgery) with an intraoperatively installed sensor. Concurrently, the FACES Pain Rating Scale score for low-back pain and the total dose of postoperative analgesics were recorded. Results. With the patients in the supine position, for both groups the mean pressure values were consistently 40-50 mm Hg, which exceeded the critical capillary pressure of the muscle. With the patients in the lateral decubitus position, the pressure decreased over time (from 14 to 9 mm Hg in the mini-open group and from 20 to 10 mm Hg in the conventional group). Among patients in the mini-open group, the pressure was lower, but the difference was not statistically significant. Postoperative pain and postoperative analgesic dosages were also lower. Conclusions. To the authors' knowledge, this is the first study to evaluate postoperative intramuscular pressure after PLIF. Although the results did not demonstrate a significant difference in the intramuscular pressure between the 2 types of PLIF, mini-open PLIF was associated with less pain after surgery.