Objective: To evaluate the short-term in vivo dynamic motion characteristics of the lower lumbar spine (L3-S1) after unilateral pedicle screw fixation (UPSF) or bilateral pedicle screw fixation (BPSF) combined with TLIF for treatment of L4-5 lumbar degenerative disc diseases (DDD).
Methods: Twenty-eight patients were recruited (13 UPSF, 15 BPSF). Each patient was CT-scanned to construct 3D models of the L3-S1 vertebrae. The dual fluoroscopic imaging system (DFIS) was then used to image the lumbar spine while the patient performed seven functional activities (upright standing, maximum extension, flexion, left-right twist, and left-right bend). The in vivo vertebral positions were reproduced using the 3D vertebral models and DFIS images. The ranges of motion (ROMs) of L3-4, L4-5, and L5-S1 segments were analyzed.
Results: At the index L4-5 segment, the primary ROM of left-right twist of the UPSF group (2.11 ± 0.52°) was significantly larger (p = 0.000) than the BPSF group (0.73 ± 0.32°). At the proximal adjacent L3-4 segment, the primary ROMs of left-right twist, and left-right bend of the UPSF group (2.16 ± 0.73°, 2.28 ± 1.03°) were significantly less (p = 0.003, 0.023) than the BPSF group (3.17 ± 0.88, 3.12 ± 1.04°), respectively. However, at distal adjacent L5-S1 segment, no significant difference was found between the two groups during all activities.
Conclusions: The ROM in left-right twisting of UPSF group was significantly larger compared with BPSF group at the index level in the short term. The UPSF has less impact on the cranial adjacent level (L3-4) in left-right twisting and bending activities compared to the BPSF. The data implied that the UPSE and BPSF combined with TLIF would result in different biomechanics in the index and cranial adjacent segment biomechanics. Long-term follow-up studies are necessary to compare the clinical outcomes of the two surgeries.
Keywords: Adjacent segment; Bilateral pedicle screw fixation; In vivo ROM; Lumbar spine; Unilateral pedicle screw fixation.