Abstract / Summary
Although unilateral biportal endoscopy (UBE) provides effective decompression for degenerative lumbar diseases, facet joint violation may occur and has been implicated in postoperative instability. This study aimed to establish a facet injury grading system and evaluate its association with postoperative lumbar stability using combined clinical and finite element analyses. 126 patients who underwent UBE decompression between June 2022 and June 2023 were enrolled. Patients were divided into four groups (0, I, II, III) based on the severity of facet joint injury. Clinical results were analyzed using the MacNab criteria, the visual analogue scale (VAS) for back and leg pain, the Oswestry Disability Index (ODI) and Japanese Orthopaedic Association (JOA) Scores. Radiological results were analyzed using the range of motion (ROM), disc height and flexion-extension X-rays. A three-dimensional finite element model of the L4/5 segment was constructed to simulate different degrees of unilateral facet joint resection. Segmental ROM, facet joint contact pressure, and von Mises stress in the intervertebral disc and endplate were analyzed. 126 patients successfully completed the surgery. There were 21 patients in the level 0 group, 75 in the level I group, 24 in the level II group, and 6 in the level III group. During postoperative follow-up, VAS, JOA scores, and ODI all showed significant improvement compared to preoperative values. Overall, 6 complications occurred, with an overall complication rate of 4.8% (6/126). At the 12-month follow-up, the excellent and good rate, based on the MacNab criteria, was 93.6% (118/126). Radiographic evaluation demonstrated significant differences in postoperative lumbar stability among the four groups at 7 days, 1 month, 3 months, 6 months, and 12 months after surgery ( P < 0.05). Finite element analysis showed that compared with M0, ROM increased by 17.6% in the 50% resection models, with the most prominent changes under right rotation. UBE surgery achieved satisfactory clinical outcomes for degenerative lumbar diseases. Clinical and finite element analysis suggested that facet joint injury exceeding 50% may be associated with a greater risk of lumbar instability, increased low back pain, greater segmental mobility.