Introduction

In patients with spinal disorders that warrant spinal decompression, the goal of intervention is to enhance function and reduce pain. In the past, outcomes were commonly assessed based on the results of imaging as well as the interventionalist’s subjective views; however, studies have shown that these frequently do not correlate with patient satisfaction. ^, In one study, Schwartz et al. reported an astonishing 24% mismatch in physician–patient perceived outcomes after spinal surgery. Patient-reported outcome measures (PROM) were created out of necessity to derive quantitative data from a patient’s perceived health. More recently, several questionnaires have been developed and validated to evaluate the severity of a condition and response to intervention. Such data aim to help providers develop a treatment plan and follow the patient to determine treatment efficacy. PROMs have a place not only in the clinical setting but also in research to help advance the field of interventional spine care ( Table 10.1 ).

Indications for use of each instrument

Many clinicians utilize the familiar numeric pain rating system (NRS) and/or the visual analog scale (VAS) to quickly assess pain intensity. The NRS is an 11-point numerical rating scale used to measure pain intensity. The patient is asked to choose a number between 0 and 10 that best represents how much pain they are feeling that day. Zero generally represents “no pain at all” whereas ten represents “the worst possible pain.” Alternatively, the VAS has many different versions. Examples of the most commonly used ones include a VAS of faces that asks patients to identify a face that best represents their perception of their pain. Alternatively, a metric VAS is one in which the patient marks a point on a 100-mm horizontal line that represents zero pain on one end and the highest amount of pain on the other. One then measures the distance from the beginning of the line to the marked point and the pain intensity is computed in millimeters. Although widely used and validated to show high correlation with other pain assessment tools, the NRS and VAS have been criticized for being unable to capture the complex, multifactorial, and functional burden of pain. As a result, more sophisticated patient-reported outcome (PRO) instruments have been developed over time. This chapter will focus on instruments for measuring outcomes in spinal decompression.

The most widely used measurement tool for assessing health-related quality of life is the Medical Outcomes Study Short Form questionnaire (SF-36). The SF-36 was derived from the Medical Outcomes Study, a multi-year study performed to elucidate variations in patient outcomes and to develop functional tools for monitoring patient outcomes and their determinants. The survey is composed of 36 questions that are organized into eight domains. The questions focus on the degree of limitation caused by the patient’s health on numerous activities. The results are expressed on a scale ranging from 0 to 100 with higher values representing better function. It is easy to see why it is a widely used instrument, as it is a generic tool that has been validated for a broad spectrum of spine pathologies and procedures including discectomy, decompressive laminectomy, and fusion. The SF-12 and SF-6 are shortened versions of the SF-36, created to reduce the burden of response. There are data showing that the SF-12 is a valid alternative to the SF-36 for preoperative and postoperative assessments of health status in patients with lumbar surgical disorders undergoing decompression surgery for a predominant symptom of radiating leg pain. When compared with the SF-36, the SF-12 and SF-6 scores were similar but almost always had larger standard errors. The RAND-36 (distributed by RAND corporation) includes the same set of eight domains that were developed in the SF-36 and Medical Outcomes Study. The scoring of the domains yields equivalent results for six out of eight of the domains; however, scoring differences exist for the pain and general health subscales. The detailed differences in scoring are summarized by Hays, Sherbourne, and Mazel.

Another generic tool for measuring health-related quality of life across a variety of chronic diseases is the Patient-Reported Outcomes Measurement Information System (PROMIS). The PROMIS-29 profile assesses pain intensity using a 0 through 10 numeric rating system over seven health domains (physical function, fatigue, pain interference, depressive symptoms, anxiety, ability to participate in social roles and activities, and sleep disturbance). Scores are standardized against United States normative population data. PROMIS has been compared with the SF-12 and Neck Disability Index (NDI) and is validated for patients treated surgically for degenerative cervical spine disorders. It has additionally been compared with the Oswestry Disability Index (ODI) and Zurich Claudication Questionnaire (ZCQ) and is additionally validated for patients treated surgically for lumbar spinal stenosis.

Unlike the generic tools discussed earlier, there are numerous disease-specific outcome measures unique to spine that link functional impairment reported by the patient to spine pathology. The ODI is the scale most commonly used to assess disability in low back pain and lumbar spine pathologies. There are 10 questions, each scored from 0 to 5, with 5 representing the most significant disability. The maximum score is 50 and can be multiplied by 2 to produce a percentage score. Scores between 0%–20% indicate minimal disability; 20%–40% indicate moderate disability; 40%–60% indicate severe disability; 60%–80% indicate crippling back pain; and 80%–100% describe patients who are bed-bound or exaggerating their symptoms. Generally, patients who score in the mild and moderate disability range can be treated with conservative measures, which include improved posture as well as general health and physical activity advice. Patients who score in the severe and crippling back pain ranges require further investigation and likely intervention. It is recommended that the ODI be administered to the patient to obtain an original baseline and then every two weeks after the intervention to measure progress. The ODI is considered the gold standard outcome tool for assessing function in activities of daily living in low back pain. It has been repeatedly validated in patients with lumbar spine pathologies.

Other instruments that assess disability due to lower back disorders include the Roland-Morris Disability Questionnaire (RMDQ) and Quebec Back Pain Disability Scale (QBPDS). The RMDQ is more appropriate for the assessment of patients with mild-moderate disabilities whereas the ODI may be more valid at measuring higher disability levels. The RMDQ consists of 24 statements that assess the impact of low back pain in daily life and work activities. The results vary from 0 (no impairment) to 24 (severe impairment). There are over 50 translations and adaptations available for application. Alternatively, the QBPDS is a measure that was described by Kopec and colleagues in 1995 to measure disability caused by back pain. The scale is composed of 20 activities and asks patients to rate their perceived amount of difficulty in performing each activity from 0 (not difficult at all) to 5 (unable to do). The responses are summed for a total score between 0 and 100 with a higher score representing a greater degree of disability.

The first tool designed to assess disability in patients with neck pain is the NDI. Similar to the ODI, the NDI has 10 questions with each one scored from 0 to 5 with 5 representing the most significant disability. The maximum score is 50 and can be multiplied by two to produce a percentage score. It has been validated for those undergoing cervical fusion for degenerative spine disorders.

Alternatively, the ZCQ is a tool designed for patients with lumbar spinal stenosis. There are 12 questions for all patients and an additional 6 for patients who have undergone intervention. The score is expressed as a percentage, with a higher score representing a greater degree of disability.

Perioperative considerations

Perioperative psychological evaluation is important in the preoperative and postoperative period. The presence of depression and anxiety in the preoperative period is associated with increased failure rates after surgical decompression for degenerative diseases of the spine. ^, The most widely used psychological assessment tool is the Beck Depression Inventory (BDI). The BDI consists of 21 questions with scores ranging from 0 to 3. The instrument assesses sadness, pessimism, sense of failure, feelings of guilt, self-dislike, suicidal thoughts, weight loss, work inhibition, sleep disturbances, fatigability, and loss of libido. Total scores range from 0 to 63. Scores of 0 to 13 indicate no depression or minimal symptoms, scores of 14 to 19 indicate mild depression, scores of 20 to 28 indicate moderate depression, and scores of 29 to 63 indicate severe depression.

General considerations

Successful PRO instruments are reliable, validated, yield appropriate responsiveness, decrease administrative burden and cost, and have language adaptations. The aforementioned PROs are among the most common in use today and have been validated for a variety of spine disorders. Some instruments have truncated versions, such as the SF-12, that were created to reduce the burden of response. Others, such as PROMIS, have developed computer-adaptive testing in which the questions are tailored to each person under evaluation. Many of the above PROs are available in numerous languages as well as cultural versions, such as the ODI, which has over 31 adaptations.

Another attribute for a successful PRO is interpretability. When assessing the clinical utility of spine surgery, one must determine the amount of subjective change that is most important to the patient. This is best expressed as the Minimal Clinically Important Difference (MCID), which is the smallest change that a patient would rate as meaningful. The two most widely used approaches to determine the MCID are anchor-based and distribution-based methods. We will avoid getting into the heavy details of statistics in this chapter, however it is important to note that limitations exist in the determination of the MCID. Schwartz et al. provide an exemplary paraphrase of such limitations. They note that “each method [of determining MCID] produces an MCID value different from the other methods. MCID definitions do not take into account the cost of treatment to the patient, and the change in PRO scores depends on the patient’s initial baseline status”. Some studies report the percentage of “responders” to a certain intervention. A responder is any patient who reaches the MCID threshold, and although not perfect, it serves as an important data point for clinicians in anticipating what portion of patients can be expected to benefit from an intervention. A range of the most agreed-upon MCIDs are expressed in the table above.

In general, there are many validated PRO instruments available that measure different clinical and functional outcomes, and it is essential for spine care providers to have good command and use of the PRO instruments.