Characteristics and mechanical mechanisms of intervertebral disc degeneration in old thoracolumbar fractures with kyphosis: clinical observations and finite element analyses.

BACKGROUND

Low back pain is a common complication in patients with old thoracolumbar fractures with kyphosis (OTLFK), and intervertebral disc degeneration (IDD) is a major contributor. Mechanical abnormalities are believed to play a key role in the development to IDD. This study aimed to investigate the characteristics of lumbar disc degeneration and underlying mechanical mechanisms in patients with OTLFK.

METHODS

A total of 52 patients with OTLFK were included from February 2017 to March 2023 as the observation group (OG). A control group (CG) of individuals with chronic low back pain were matched for age, body mass index, and gender. The disc degeneration grades and distribution in both groups were observed. Intact, 20°, 30°, and 40° kyphotic finite element (FE) models were established. Intervertebral disc pressures (IDPs) were calculated under standing, flexion, extension, lateral bending, and axial rotation conditions.

RESULTS

The overall IDD in the OG was higher than that in the CG. The grades from T11 to L3 were higher in the OG (p < 0.05), while there was no significant difference from L4 to S1. Degeneration levels IV and V were concentrated in the T11-L3 segment in the OG; whereas, in the CG, this was in L4/5 and L5/S1 (p < 0.05). The FE analysis results showed that, in the kyphotic model, the IDP was higher than the intact model in the standing position, flexion, lateral bending, and rotation, but lower in extension.

CONCLUSIONS

Patients with OTLFK exhibit higher-grade disc degeneration concentrated in the thoracolumbar segment. Abnormal mechanical stress may contribute to this degeneration, highlighting the importance of managing stress in kyphotic deformities.