“Segmental Risk Profile” (SRP) for Lumbar Disk Degeneration
Authors: Samartzis D. , Karppinen J. , Luk K. , Cheung K. 
Published: June 2012

Introduction Disk degeneration (DD) is associated with low back pain. Previous studies have addressed various determinants of DD. Observations have noted that the prevalence and severity of disk degeneration varies throughout the lumbar spine. However, the influence of individual characteristics of risk factors upon segmental variation of lumbar disk levels is unknown. As such, this study addressed the role of known risk factors upon segmental DD of the lumbar spine and introduces the segmental risk profile (SRP) for DD. Materials and Methods A radiologic and clinical cross-sectional study of 2599 Southern Chinese volunteers was performed. Sagittal MRIs were utilized to assess the overall presence of DD and end-stage DD with disk space narrowing (DD-DSN) from L1 to S1. Assessment of DD was based on the Schneiderman et al criteria. Subject demographics included gender, age, body mass index (BMI), smoking, workload, and history of lumbar injury. Subject age at the time of MRI assessment was further stratified into age-specific categories as follows: 20 to 29, 30 to 39, 40 to 49, >50 years of age. Radiological determinants were noted as the presence of Schmorl's nodes and vertebral marrow changes. The lumbar spine was further stratified by regions: upper (L1-L2), mid (L2-L4), and lower (L4-S1). Results There were 1040 males and 1559 females with a mean age of 41.9 years (range: 21.0 to 63.3; ± SD: 9.4 years). Overall DD and DD-DSN were noted in 72.7 and 23.8% of individuals, respectively. Segmentally from L1 to S1, the presence of disk degeneration and DD-DSN was noted in 9.2% (2.6%), 16.2% (3.2%), 28.9% (3.8%), 49.0% (10.2%), and 52.0% (12.6%), respectively. Gender was not associated with DD-DSN at the upper (OR: 1.41; 95% CI, 0.83–2.39) and mid (OR: 0.94; 95% CI, 0.65–1.35) lumbar regions, but males were noted to have a significantly higher risk than females of DD-DSN in the lower lumbar region (OR: 1.36; 95% CI, 1.09–1.70). Age-specific categories presented similar risk of DD-DSN at the lower lumbar region, but presented with an exponential increase risk in the upper and mid lumbar regions with increasing age. Past injury to the lumbar spine was associated with DD-DSN at the lower lumbar region (OR: 2.19; 95% CI, 1.76–2.72), but not at the upper (OR: 1.20; 95% CI, 0.71–2.04) and mid (OR: 1.13; 95% CI, 0.79–1.62) lumbar regions. The impact of Schmorl's nodes decreased from the upper to the lower lumbar regions, but were significantly associated with DD-DSN at the upper (OR: 7.48; 95% CI, 4.51–12.43) and mid (OR: 2.06; 95% CI, 1.36–3.13) lumbar regions but not at the lower region (OR: 1.01; 95% CI, 0.74–1.38). The significance of vertebral bone marrow changes in relation to DD-DSN increased from the upper (OR: 2.30; 95% CI, 1.12–4.71), mid (OR: 3.98; 95% CI, 2.53–6.25) to lower (OR: 13.44; 95% CI, 9.05–19.94) lumbar regions. BMI was significantly associated with DD-DSN only at the lower ( p = 0.011) lumbar region. Obesity presented the greatest likelihood for having DD-DSN at the lower lumbar region (OR: 1.82; 95% CI, 1.28–2.60). Smoking and workload were not associated with DD or DD-DSN at any level ( p > 0.05). Assessing such factors based on the overall presence of disk degeneration, the impact of individual factors upon the lumbar spine behaved similarly as with DD-DSN. Conclusion This large-scale study broadens the understanding of how various determinants affect disk degeneration throughout the lumbar spine. Based on this understanding, the segmental risk factor (SRF) of disk degeneration may provide further insight in the prognosis of future biologic therapies for disk repair/regeneration, further assessment of the role of genetic factors, and environmental interaction effects related to the disk's integrity and temporal progression of disk disease. I confirm having declared any potential conflict of interest for all authors listed on this abstract Yes Disclosure of Interest None declared