The effect of age and body mass index on cost of spinal surgery

Complex shifts in demography combined with drastic advancements in spinal surgery have led to a steep increase in often expensive spinal interventions in older and obese patients. A cost analysis, based on hospital charges, was performed retrospectively on the spinal surgery of 787 randomly selected patients who were operated at The Medical Center of Central Georgia, a large urban hospital in Central Georgia. The types of surgery included anterior cervical decompression and fusion (ACDF), lumbar decompression and fusion (LDF), and lumbar microdiscectomy (LMD). The distribution of patient age followed a Gaussian form. The peak age for patients was 50-59 years (28.8%), and there was no statistical difference in age between men and women. The body mass index (BMI) differed (p<0.01) between males (28.86 kg/m(2); range: 18-47 kg/m(2)) and females (30.69 kg/m(2); range: 17-58 kg/m(2)). The BMI data did not follow a Gaussian distribution for either gender. The hospital cost for spinal surgery increased with age except for male patients who underwent ACDF. For male patients who underwent LDF, the increase in hospital cost was statistically significant between the 40-49-year and the ≥ 70-year age groups. Univariate analysis with type of surgery as a covariate showed that age was a significant determinant of hospital cost (p=0.000), and BMI was not (p=0.110); however, the interaction between age and BMI was significant (p=0.000). Older patients undergoing spinal surgery had lower BMI, more so in males (r=-0.047, p=0.426) than in females (r=-0.038, p=0.485). There were linear trends in all gender-spinal surgery categories between age, BMI and hospital cost. Older female patients who underwent LDF tended to have a lower BMI but higher hospital cost, confirming that age was more important than BMI in determining hospital cost in these patients. The increments in cost of spinal surgery in relation to age especially and BMI were, nevertheless, small. We believe that spinal surgery in the elderly should be viewed as a public investment, as the modern concept of retirement involves people working intermittently up to their 80s. Thus, where clinical research on medical costs is to be conducted, cost analysis needs to be expanded to include returns to government in the form of taxes.