February 19, 2014
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Surgeons find risk factors responsible for neurological deficits after interbody fusion

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Researchers identified a number of risk factors that raised the risk of postoperative neurological deficit in patients who underwent lateral lumbar interbody fusion with a retroperitoneal transpsoas approach, according to a recent study.

“The level of fusion, multilevel lateral lumbar interbody fusion, female gender, as well as the use of bone morphogenetic protein-2 [BMP-2] were associated with a higher risk of developing a postoperative neurological deficit and pain,” Alexander Aichmair, MD, a spine research fellow at New York’s Hospital for Special Surgery, said in a presentation.

According to Aichmair, the incidence of postoperative neurological deficit following lateral lumbar interbody fusion (LLIF) ranges from 0.7% to 23% in the current literature. To identify the risk factors associated with these deficits and test whether they are transient or persistent in nature, the researchers studied 451 patients who underwent LLIF and were treated at a total of 919 levels, with an average of two levels treated per patient.

The researchers included patients with a degenerative spine condition, at least 6 postoperative months of follow-up and no previous thoracolumbar spine surgery, according to Aichmair. The most frequently treated levels were L3-4 and L4-5. The average age at surgery was 63 years, and the average follow-up was 15 months.

The researchers performed an initial analysis of neurological function in the entire study population and multiple subanalyses in study subcohorts. “In order to differentiate between a mechanical and neurological muscle injury, we defined a motor nerve injury as a weakness of grade 4 if it persisted for more than 6 months, or grade 3 or lower independent from the duration.” Aichmair said.

In the initial analysis, the rates for motor and sensory deficits in all patients at the last clinical follow-up were 24.1% and 17.3%, respectively.

“[The initial] analysis also included patients with a preoperative deficit, so these results cannot be considered as the true incidence of LLIF-related postoperative deficits” Aichmair said.

After excluding patients with preoperative neurological deficits, they found a motor deficit rate of 3.2% and a sensory deficit rate of 9.3% at the last follow-up. A third analysis with only standalone patients who did not have posterior supplemental instrumentation revealed a motor deficit of 3.7% and a sensory deficit of 11.2% at the last follow-up. An analysis of 87 patients with a follow-up of at least 18 months showed rates of 2.3% for a persistent motor deficit, 9.6% for a sensory deficit, and 5.8% for anterior thigh and groin pain, which were present at the last follow-up visit. A multivariate analysis showed female gender, surgeon experience, the L2-3 level, multilevel surgery and BMP-2 use were associated with an increased risk of postoperative neurological deficits and/or pain.

“This is the largest series of lateral lumbar interbody fusion in current literature with 919 levels, and we also have a large number of patients with a follow-up of at least 18 months, which allowed us to differentiate between transient and persistent deficits,” Aichmair said. “We defined the incidence of those deficits, which is important for pre-operative patient counseling and surgical decision-making. We also confirmed that most of these deficits, although high in the immediate postoperative setting, are transient in nature.”

BMP-2 being a risk factor for postoperative neurological deficits after LLIF was further confirmed by a matched cohort study comparing patients with and without BMP-2 use in LLIF, Aichmair said about previous work he and his colleagues did in this area. – by Renee Blisard Buddle

Disclosure: Aichmair has no relevant financial disclosures.