J Neurosurg Spine 17:486–490, 2012 486 J Neurosurg: Spine / Volume 17 / November 2012 T he quality of research in spinal surgery has been greatly advanced in recent years by a transition from surgeon-driven assessment of clinical out- come to the use of patient-driven, validated, health-re- lated quality of life measures. 6 General recommendations for the assessment of clinical outcomes include the use of both condition-specifc and generic health outcomes measures. 1 Condition-specifc measures focus on signs and symptoms that refect a specifc medical condi- tion, such as low-back pain. Generic measures are more comprehensive measures that assess multiple areas of health-related functioning in a patient’s life. These types of measures provide different and often complementary information about a patient’s health status. In the feld of spinal surgery, the ODI has emerged as one of the most commonly used disease-specifc instruments, and the Medical Outcomes Study SF-36 has become the most widely used generic measure. 5 In general, disease-specifc measures such as the ODI trade breadth of coverage to explore specifc health domains that are most relevant to a certain disease. This ability to focus on domains most relevant to a specifc disease process allows them to be sensitive to more subtle changes in a patient’s health. Generic measures such as the SF-36 trade “depth” of assessment for “breadth,” in Changes in the Oswestry Disability Index that predict improvement after lumbar fusion Clinical article Mladen djurasovic, M.d., steven d. GlassMan, M.d., john r. diMar ii, M.d., charles h. crawford iii, M.d., Kelly r. Bratcher, r.n., c.c.r.P., and leah y. carreon, M.d., M.sc. Norton Leatherman Spine Center, Louisville, Kentucky Object. Clinical studies use both disease-specifc and generic health outcomes measures. Disease-specifc mea- sures focus on health domains most relevant to the clinical population, while generic measures assess overall health- related quality of life. There is little information about which domains of the Oswestry Disability Index (ODI) are most important in determining improvement in overall health-related quality of life, as measured by the 36-Item Short Form Health Survey (SF-36), after lumbar spinal fusion. The objective of the study is to determine which clinical elements assessed by the ODI most infuence improvement of overall health-related quality of life. Methods. A single tertiary spine center database was used to identify patients undergoing lumbar fusion for standard degenerative indications. Patients with complete preoperative and 2-year outcomes measures were included. Pearson correlation was used to assess the relationship between improvement in each item of the ODI with improve- ment in the SF-36 physical component summary (PCS) score, as well as achievement of the SF-36 PCS minimum clinically important difference (MCID). Multivariate regression modeling was used to examine which items of the ODI best predicted achievement for the SF-36 PCS MCID. The effect size and standardized response mean were calculated for each of the items of the ODI. Results. A total of 1104 patients met inclusion criteria (674 female and 430 male patients). The mean age at surgery was 57 years. All items of the ODI showed signifcant correlations with the change in SF-36 PCS score and achievement of MCID for the SF-36 PCS, but only pain intensity, walking, and social life had r values > 0.4 refecting moderate correlation. These 3 variables were also the dimensions that were independent predictors of the SF-36 PCS, and they were the only dimensions that had effect sizes and standardized response means that were moderate to large. Conclusions. Of the health dimensions measured by the ODI, pain intensity, walking, and social life best pre- dicted improvement in overall health-related quality of life, as measured using the SF-36 PCS. (http://thejns.org/doi/abs/10.3171/2012.8.SPINE12614) Key words • Oswestry Disability Index • outcomes • SF-36 • lumbar fusion Abbreviations used in this paper: MCID = minimum clini- cally important difference; ODI = Oswestry Disability Index; PCS = physical component summary; SF-36 = 36-Item Short Form Health Survey.