Intervertebral Disc Height Changes After Weight Reduction in Morbidly Obese Patients and its Effect on Quality of Life and Radicular and Low Back Pain

Zvi Lidar, MD; Eyal Behrbalk, MD; Gilad J. Regev, MD; Khalil Salame, MD; Ory Keynan, MD; Chaya Schweiger, MS; Liat Appelbaum, MD; Yair Levy, MD; Andrei Keidar, MD

Disclosures

Spine. 2012;37(23):1947-1952. 

In This Article

Discussion

Both mechanical and systemic inflammatory effects may contribute to back pain in obese patients. Obesity is characterized by reduced range of motion of the spine, causing postural adaptation with an increased anterior pelvic tilt due to increased lumbar lordosis.[2] In addition, obesity can increase the mechanical load on the spine by causing a higher compressive force or increased shear stress on the lumbar spine.[2] Of note, osteoarthritis, estimated to affect 34% of the obese population, is significantly correlated with BMI.[2] Furthermore, obesity may cause LBP by low-grade systemic inflammation resulting from increased production of cytokines and acute-phase reactants and through activation of proinflammatory pathways in adipose tissue[3,13]

Reports on the prevalence of back pain in severely obese patients show varying results. Although 86% of our study population experienced back pain prior to the bariatric procedure, Shiri et al[4] reported only a 22% prevalence of axial back pain in overweight and obese patients. The discrepancy may stem from differences in studied population because they included patients with BMI more than 24 kg/m2, whereas our cohort was heftier, with BMI more than 35 kg/m2 (mean, 42 kg/m2). Indeed, Urquhart et al[14] showed positive association between increased fat mass and intensity of back pain.

Previously, weight loss has been reported to improve back pain and quality of life. Khoueir et al[1] prospectively observed 38 patients treated by bariatric surgery and found significant improvement in the mental as well as in the physical component of the SF-36, a 24% reduction in the Oswestry Disability Index as well as a moderate reduction in back pain, 1 year after surgery. These findings were corroborated by Melissas et al,[6] who observed 29 patients after bariatric surgery. These results stand in contrast to the lack of improvement in the SF-36 components in this study. In this study, although pain reduction was significant, it is not the only parameter contributing to quality of life after bariatric surgery. The effects of weight reduction surgery, including the acquiring of new eating habits, changing old daily routines, psychosocial factors, reduction in cholesterol, diabetic control, and improvement of blood pressure levels and sleep apnea, may not be reflected in a general quality of life questionnaire such as the SF-36; indeed, the mental part showed no improvement but the physical part showed near significant improvement. The MA functional scale, which is an oriented, disease-specific, validated scale for obese patients, demonstrated a significant improvement after surgery.

Disc space changes, especially increase in disc space height in response to reduced axial loads, were documented in a few previous studies. The disc space was found to significantly change in height, volume, and morphology upon assuming recumbent and upright position.[15,16] Similar results were obtained when acute compressive forces were axially applied.[17] Kimura et al[18] measured a 1-mm height reduction at the L4–L5 disc level when loading the spine with 50% body weight. In this study, we found a clear correlation between the amount of weight loss and the degree of improvement in radicular pain, whereas back pain also improved significantly, albeit, not in linear correlation to the magnitude of weight reduction. Similarly, although disc height restoration after weight reduction was significant, a direct correlation to the extent of weight loss was lacking. These observations held true when comparing the absolute values as well as when comparing the percentages of weight reduction with disc height restoration. Hence, back pain and disc space height seem to behave as an "all or none" phenomenon.

Malko et al[19] performed a magnetic resonance imaging study exploring diurnal changes in disc space height in young patients, which may serve to explain this newly observed phenomenon. They showed that acute axial compression causes reversible disc height changes due to a water content shift, of approximately 70% to 80%, in and out the nucleus and the annulus.

Although we did not find a linear correlation between the amount of weight reduction and disc height increment, we think that the restoration of disc space height is a true occurrence as previous studies had shown and by the fact that our patients served as their own control group.

The nonlinear "all or nonphenomena" may be explained by the observation that in severely obese patients, the disc and facet joints are exposed to long years of considerable axial loads, combined with normal aging and dehydration of the disc. These changes, in turn, may lead to a reduction in the elasticity of the disc and ligaments, causing them to behave in a stepwise rather than in a linear fashion.[20]

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