Austin, Texas – October 24, 2007 – Surgeons continue to debate whether a link exists between adjacent segment hypermobility and lumbar spine segmental fusion. What complicates the issue is that generally, segmental mobility is measured with plain radiographs, which is an imprecise method.
 
Five-year radiostereometry results showed that adjacent segment hypermobility is not a general finding post-fusion, according to a study presented at the 22nd Annual North American Spine Society Meeting.
 
“There is a debate and insufficient knowledge on whether fusion in the lumbar spine creates/promotes degeneration and pain in segments adjacent to fusion,” Björn Strömqvist, MD, PhD, Department of Orthopedics, Lund University Hospital, Lund, Sweden. “Adjacent segment degeneration does occur, but whether this is an effect of the degenerative process that led to fusion in the individual patient or an effect of the fusion per se is difficult to deduce.
 
“If adjacent degeneration is related to the fusion procedure, it is thought to be related to changed kinematics of the spine and increased, compensatory mobility of the adjacent segment,” he said. “Our findings strongly contradict that increased mobility of the adjacent segment is a common development.”
 
The study included nine patients who failed conservative treatment and were scheduled for segmental lumbar fusion. Strömqvist and colleagues performed preoperative spinal radiostereometry and reassessed these patients five years after surgery. They scanned each patient in two standardized positions, supine and sitting. They also examined the patients with conventional radiography preoperatively and at the five-year follow-up.
 
All patients had painful degenerative disc disease at L4-L5 and/or L5-S1. Before their fusion, all patients had lumbar pain without sciatica with a mean duration of four years.
Three patients had posterolateral fusion without instrumentation and three had instrumented posterolateral fusion. The remaining three patients had anterior lumbar interbody fusion with two threaded cylindrical cages.
 
Strömqvist and colleagues measured mobility along transverse, vertical and sagittal axes. Preoperatively, the mean transverse, vertical and sagittal translation at the segment adjacent to fusion were 0.4 mm, 1.7 mm, and 1.8 mm. At five years, these measurements were 0.6 mm, 1.4 mm and 2.3 mm, respectively.
 
The researchers used radiostereometry for their study because the literature has shown that external measurements and radiographs are imprecise tools. Strömqvist noted that there are measurement errors of 2 mm to 8 mm along movement axes with plain radiographs. In contrast, the measurement error of radiostereometry is 0.2 mm to 0.6 mm.
 
“Radiostereometry, thus, is the most precise way to measure spinal mobility. It has also been used a lot for measuring the fixation and/or migration of hip and knee prostheses. … Further, other mobility measurement techniques are depending on patient cooperation, pain level, etc, whereas the mobility measurement in radiostereometry is standardized.”
 
Radiostereometry is invasive and costly, making it difficulty to use in large patient groups, Strömqvist said, which is why there were a small number of patients in the study. The conclusions drawn from it must be expressed carefully, he said.
 
“However, the three most common types of fusion techniques are included, and the patients are representative for a fusion material.”

Source: Abstract #7. Björn Strömqvist, MD, PhD. “Adjacent Segment Mobility Evaluated by Radiostereometry Before and Five Years After Fusion.”

FDA Device/Drug Status: This abstract does not discuss or include any applicable devices or drugs.

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