Analysis of factors contributing to postoperative spinal instability after lumbar decompression for spinal stenosis.
OBJECTIVE
Decompressive laminectomy is one of the most commonly used surgical methods for the treatment of spinal stenosis. We retrospectively examined the risk factors that induce spinal instability, including slippage (spondylolisthesis) and/or segmental angulation after decompressive laminectomy on the lumbar spine.


METHODS
From January 1, 2006 to June 30, 2010, 94 consecutive patients underwent first-time single level decompressive laminectomy without fusion and discectomy. Of these 94 patients, 42 with a follow-up period of at least 2 years were selected. We measured the segmental angulation and slippage in flexion and extension dynamic lumbar radiographs. We analyzed the following contributing factors to spinal instability: age/sex, smoking history, disc space narrowing, body mass index (kg/m(2)), facet joint tropism, effect of the lordotic angle on lumbar spine, asymmetrical paraspinal muscle volume, and surgical method and level.


RESULTS
Female patients, normal lordotic angle, and asymmetrical paraspinal muscle volume were factors more significantly associated with spondylolisthesis (p-value=0.026, 0.015, <0.01). Statistical results indicated that patients with facet tropism were more likely to have segmental angulation (p-value=0.046). Facet tropism and asymmetry of paraspinal muscle volume were predisposing factors to spinal instability (p-value=0.012, <0.01).


CONCLUSIONS
Facet joint tropism and asymmetry of paraspinal muscle volume are the most important factors associated with spinal instability; therefore, careful follow-up after decompressive laminectomy in affected patients is necessary.
Department of Neurosurgery, VHS Medical Center, Seoul, Korea.
Joo Chul
JC
Yang
Department of Neurosurgery, VHS Medical Center, Seoul, Korea.
Sung Gon
SG
Kim
Department of Neurosurgery, VHS Medical Center, Seoul, Korea.
Tae Wan
TW
Kim
Department of Neurosurgery, VHS Medical Center, Seoul, Korea.
Kwan Ho
KH
Park
Facet tropism; Instability; Paraspinal muscle; Spinal stenosis