Introduction: Lumbar spinal instability is an important factor in the treatment of lumbar degenerative diseases, and dynamic slip (DS) is generally evaluated by comparing extension and flexion positions (DS [EF]) and is particularly important in relation to the adaptation for fusion surgery. Preoperative DS comparing supine and standing positions (DS [US]) is considered a potentially missed indicator. However, the association of DS (US) with reoperation and postoperative residual symptoms after single-level decompression surgery has not been reported.
This study aimed to determine whether preoperative DS (US) is associated with reoperation and with postoperative residual symptoms after single-level decompression surgery for lumbar degenerative disease.
Methods: Multicenter retrospective study. Patients who underwent initial single-level decompression surgery for lumbar degenerative disease between 2008 and 2021 and were available for follow-up for at least three years were included. Patients with spinal metastasis, pyogenic vertebral osteomyelitis, and degenerative lumbar scoliosis were excluded. Our indications for decompression surgery with respect to lumbar segmental instability were preoperative DS (EF) <3 mm and segmental kyphosis in flexion position <5 degrees. Demographic data, surgical information (decompression level, detailed surgical procedure), and spinal alignment were measured. Preoperative lumbar segmental instability was evaluated with static vertebral slip in the neutral-standing position, DS (EF) in the difference in vertebral slip between the extension and the flexion radiographs, and DS (US) in the difference in vertebral slip between the standing and the supine radiographs. We evaluated other instability indicators such as facet joint opening, facet joint effusion, facet joint vacuum phenomenon, facet joint orientation, and tropism using spinal computed tomography and magnetic resonance imaging. Visual analogue scale (low back pain, lower extremity pain, and numbness) and Oswestry disability index (ODI) were evaluated preoperatively, three months, one, two, and three years postoperatively.
Results: Overall, 179 patients (age, 64.5 ± 21.0 years; male, 97) were included. Reoperation was required in 12 patients. Preoperative DS (EF) was smaller than DS (US) (0.9 ± 0.9 mm vs 1.4 ± 1.3 mm, p<0.001). Patients with preoperative DS (US) >3 mm had significantly greater static slip (1.4 ± 2.9 mm vs 3.6 ± 3.4 mm,p=0.001), required reoperation significantly more frequently (11 out of 12 cases, p<0.001), and showed significantly greater ODI at three months, one, two, and three years postoperatively (p=0.04, 0.002, 0.02, 0.02). Logistic regression analysis showed that DS (US) is an independent risk factor for reoperation (odds ratio, 3.7; 95% confidence interval [2.1-6.5]; p<0.001), and the cutoff for reoperation for DS (US) was 3.0 mm (area under the curve: 0.91). Other instability indicators were not associated with reoperation and residual symptoms.
Discussion: Patients with DS (US) ≥3.0 mm were also present in the group with DS (EF) <3.0 mm and were associated with reoperation. DS (US) is an important and possible missed indicator of lumbar segmental instability related to reoperation and postoperative residual symptoms.
Conclusion: Preoperative DS (US) was a factor associated with reoperation and postoperative residual symptoms after lumbar single-level decompression surgery, and the cutoff of DS (US) was 3.0 mm.