The influence of a new operative channel on water dynamics and its related factors in unilateral biportal endoscopic spine surgery: An in vivo human study

Background: In recent years, unilateral biportal endoscopic (UBE) surgery has become one of the most popular minimally invasive spine surgeries. Unlike traditional open surgery, UBE surgery is performed in isotonic saline solution. Therefore, comprehending the water dynamics involved in UBE surgery is crucial. Methods: This prospective study involved 29 patients with single-level lumbar instability or degenerative disk disease who underwent UBE surgery between April 2021 and March 2022. Water flow pressure was measured using a disposable pressure transducer. Multifidus muscle MRI images were analyzed by ImageJ software at intervertebral disc levels. Perioperative blood loss was estimated by the Gross formula. The obtained data were then analyzed with independent t tests, chi-squared tests, and Pearson’s correlation. Results: Height and weight were risk factors for increased water flow pressure during UBE surgery (r = 0.424, P = 0.022, r = 0.384, P = 0.040). The phenomenon of low water flow pressure led to escalations in perioperative total blood loss, hematocrit loss and hemoglobin loss (r=-0.369, P = 0.049, r=-0.424, P = 0.022, r=-0.405, P = 0.029). An excessive water flow pressure can worsen postoperative multifidus swelling and elevate the patient's leg pain visual analogue scale (VAS) score at 1 week (r = 0.442, P = 0.016, r = 0.394, P = 0.034). Conclusion: Both low and high water flow pressures can have deleterious effects. The water flow pressure should be controlled within a reasonable range during UBE surgery.