6.1 Background

Low back pain is ranked as the leading cause of disability worldwide in the latest Global Burden of Disease Study. In 2010 alone, low back pain resulted in 83 million years of life lived with disability. Perhaps not unexpectedly, estimates of prevalence of back pain and spinal disorders in the United States and Canada showed higher rates for the older adult. Martin estimated the cost of treating low back and neck pain at $86 billion dollars in 2005, an increase of 65% from just eight years prior. This trend is predicted to continue. The “silver tsunami” has been termed the growing proportion of the U.S. population over 65, which is expected to increase to 20% by 2040, from 13% in 2010. Complicating all this is the vast array of treatment options and strategies for spinal disorders. Given the cost, prevalence, and wide range of treatment strategies available for spinal disorders, there is a strong need to define value in spine care, especially in the aging population.

6.2 Measures of Outcomes in Spinal Surgery

The concept of a quality-adjusted life year (QALY) is a tool to help in decisions regarding resource allocation. It quantifies health using life years weighted by their quality. One QALY is equal to one year in perfect health. To be dead is to have 0 QALYs. Time spent in less than optimal health is a QALY ranging from 0 to 1, with greater value associated with greater health. Acknowledging that there are states worse than death, negative QALYs are possible as well. More compactly, QALY = quality of life x quantity of life. Cost-effectiveness (CE), therefore, is defined as CE = cost/QALY. The World Health Organization has defined a cost-effective intervention as three times the per-person average income per quality adjusted life (QALY) year gained. In the United States, where the average per-person income is about $40k, any intervention that costs less than $120k per QALY gained, is said to be cost effective. ¹

Various organizations, including the Panel on Cost-Effectiveness in Health and Medicine, have recommended that QALY be used to compare the economic impact of alternative health care interventions. This can be done using the incremental cost-effectiveness ratio (ICER) and has the advantage that it can be used across health care domains, to compare the value of a certain hip replacement to heart surgery, for example. ICER is defined as the change in cost divided by the change in effectiveness, ICER = [(cost_a-cost_b)/(QALY_a-QALY_b].

For any intervention to be cost-effective, however, it must first be efficacious. Qualitative measures of patient function, such as reduction in painful symptoms, do not fully describe the functionality of the patient and his/her ability to return to gainful employment or have a fulfilling life. As a result, multiple scales have been developed to evaluate health-related quality of life (HRQOL) with more validity. These surveys are administered in the clinical setting in the preoperative and postoperative settings. The most commonly utilized surveys are the Short Form-36 (SF-36) and the Oswestry Disability Index (ODI). They are reviewed briefly below.

6.3 Short Form – 36

SF-36 consists of eight scaled sections relating to vitality, physical functioning, bodily pain, perceptions of health, physical role functioning, emotional role functioning, social role functioning, and mental health. The scoring system ranges from 0 to 100 with a lower score representing worse health and higher grades representing better health. This survey is unique because it combines both physical and mental components into its scoring. Given its broad range of questions, it is frequently utilized in a variety of conditions, including acute coronary syndrome, total knee arthroplasty, and a variety of spine topics. ^{2 , 3}

6.4 Oswestry Disability Index

Originally derived from the Oswestry Low Back Pain Questionnaire, the most recent version of the ODI was published in 2000. ⁴ This validated questionnaire contains 10 topics: pain, lifting, the ability to care for oneself, the ability to walk, the ability to sit, sexual function, the ability to stand, social life, sleep quality, and traveling ability. The scores for these topics are summed and multiplied by two in order to reach a maximum score of 100, which represents complete disability.

6.5 Clinically Important Differences in Outcomes

While the creation of HRQOL surveys have made it easier to quantitatively evaluate the factors that significantly improve the lives of patients, minor changes in these factors may cause a significant clinical difference. The purpose of the minimum clinically importance difference (MCID) measurement is to establish a threshold in which improvement is identified as significant, regardless of what health-related quality of life survey is utilized. It can be considered as the smallest amount of improvement that a patient would identify as being important in their life. By condensing health-related quality of life surveys into a more simplistic result, clearly defined thresholds can be created.

Several methods are used to identify the MCID: distribution-based, anchor-based, and the delphi method. The anchor-based method is currently the most utilized method. This method provides a standard or “anchor” question that is general in nature in order to determine whether the patient feels that he/she is better, worse, or about the same since his/her intervention. These results are then cross-referenced with their posttreatment survey results. In addition to the HRQOL survey, the patient is also asked to decide whether overall their symptoms are “about the same,” “somewhat better,” or “much better”. The MCID is then identified as the difference between those who respond “somewhat better” vs. those who respond “about the same.”

Similar to the MCID is the substantial clinical benefit (SCB). SCB is the change in the healthy-related quality of life survey that the patient perceives as substantially better or markedly improved. This value denotes the difference between those who report themselves as “much better” vs. “about the same.” While the MCID may be the minimum amount of improvement necessary to be found, the SCB is considered to be the ultimate goal of any therapy.

A study conducted in 2008 by Carreon et al. utilized 454 patients from the Lumbar Spine Study Group and demonstrated a MCID value of 12.8 for ODI and 4.9 points for SF-36. ^{5 , 6} A similar study conducted in 2010 by Anderson et al demonstrated that for degenerative cervical spine conditions the MCID was 4.1 on SF-36, and the SCB was found to be 6.5. ⁷ While a variety of other scales exist to determine outcomes, many are not consistently used to evaluate for value of care. When using these outcome measures to assess value measures, it is important to note that the efficacy of MCID and SCB have been validated by multiple studies.

6.6 Healthcare Economics and Spine Surgery

When considering economics in healthcare, limitations exist as to what treatments are considered to be cost- and value-efficient. Value is defined as the benefit received compared to the cost of the surgical or medical intervention. The most important factor used to evaluate how much benefit is gained from the treatment is consistently assessed by the quality-adjusted life years (QALY). The goal of the QALY is to condense the treatment options into a single common score, for which a variety of disease states and interventions can be assessed by their effect on minimizing morbidity and mortality. The QALY is calculated by measuring the number of years until death with and without treatment in conjunction with the health-related quality of life survey (HRQOL) of the patient. After obtaining a value for this treatment, the cost per QALY can be calculated. The cost-effectiveness of the treatment can then be compared with other commonly implemented therapies.

There has been much debate over what is considered an acceptable cost per QALY. The most commonly used threshold cutoff for therapy efficiency is $50,000 per QALY. The rationale for this value is not based on science, but is rooted in the initial cost-effectiveness literature of end-stage renal disease. ⁸ The first introduction of a $50,000 QALY threshold was in an article from 1992 regarding HIV interventions. ⁹ While most authors in the 1990s openly acknowledged that this was an arbitrary choice, it slowly became common practice. One of the most highly cited articles was from 1998,; it ultimately concluded that no true cost-per-QALY threshold could ever be completely agreed upon due to the variability between decision makers, what their values are, and what the available resources are. ¹⁰ In addition to these limitations, comparisons between surgical and nonsurgical interventions are not clear.

Due to the limitations of a cost-per-QALY analysis when considering surgical and nonsurgical management, another commonly used measure is the incremental cost-effectiveness ratio (ICER). The ICER is defined as the overall difference in cost between two potential treatment options for a specific pathology. This value can be calculated by taking the cost-per-QALY gained from the procedure in question subtracted by the cost-per-QALY gained by the conservative/nonoperative therapy choice.