“BMI [body mass index] is associated with disc herniation and spinal stenosis. It is also associated with disc degeneration, but the coefficient is so small it’s unlikely to be clinically relevant,” lead investigator Dr. Anand Segar reported at the World Congress on Osteoarthritis.
“Age appears to be the most import factor in determining spinal degeneration,” he added. “Interestingly, smoking and work intensity were not associated with any outcomes.”
Although degenerative changes were worse and more prevalent at the lower lumbar levels, the associations of BMI with these changes were actually stronger at the upper three levels, according to Dr. Segar, who is a resident in the Nuffield Department of Orthopaedics, Rheumatology, and Musculoskeletal Sciences at the University of Oxford (England). Thus, “we further add to the thought of an upper spine phenotype, which has been described by other authors, and this needs further investigation,” he maintained.
Session comoderator Dr. Jeffrey N. Katz, professor of orthopedic surgery at Harvard Medical School and codirector of the Brigham Spine Center at Brigham and Women’s Hospital, Boston, asked, “Looking at the upper spine, were you able to exclude the possibility of scoliosis as a reason for transferring load to the upper rather than the lower spine? And in evaluating spinal stenosis and thinking about BMI as your primary predictor, did you make any accommodation for how you dealt with epidural fat in relation to spinal stenosis?”
The investigators did not specifically look at scoliosis, but it was uncommon in the study sample and therefore unlikely to have affected the findings, Dr. Segar replied. Similarly, they did not specifically evaluate epidural fat, “but my understanding from the literature is that epidural fat is not really associated with obesity, ... so I don’t think again it would have changed our results.”
The patients in Genodisc were recruited from tertiary spinal clinics in the United Kingdom, Hungary, Italy, and Slovenia.
They underwent MRI of the lumbar spine, and the scans were evaluated by a musculoskeletal radiologist. Disc degeneration was assessed with the 5-point Pfirrmann grading system, while disc herniation and spinal stenosis were simply scored as present or absent.
On average, the patients studied were 51 years old and had a BMI of 27.2 kg/m2, according to data reported at the meeting, which was sponsored by the Osteoarthritis Research Society International.
Results of multivariate analysis showed that each 5-kg/m2 increase in BMI was associated with a 0.04-unit increase in disc degeneration score, a 19% increase in the odds of disc herniation, and a 24% increase in the odds of spinal stenosis.
For comparison, each 10-year increment in age was associated with a 0.31-unit increase in disc degeneration score, a 30% decrease in the odds of disc herniation, and a more than a doubling of the odds of spinal stenosis.
The impact of BMI on the lumbar spine was greater at the upper three levels, reported Dr. Segar, who disclosed no relevant conflicts of interest. In analyses restricted to those levels, each 5-kg/m2 increase in BMI was associated with a 39% increase in the odds of disc herniation and a 65% increase in the odds of spinal stenosis.