Impact of BMI, osteoporosis, and disc degeneration on post-UBE lumbar stability: a finite element analysis of nonlinear synergistic effects

This finite-element study demonstrated that the coexistence of disc degeneration, osteoporosis, and elevated body mass index markedly increases posterior-element loading and disc-internal stresses after unilateral biportal endoscopic decompression. Changes in range of motion were modest overall and tended to decrease when degeneration was combined with osteoporosis, creating a pseudo-stability state in which elevated internal stress is not reflected by gross segmental motion. These findings highlight the importance of considering body weight, bone quality, and disc health together when evaluating postoperative spinal stability and suggest that stress-based assessments may provide a more reliable indicator of hidden instability risk than motion measurements alone.