Multi-center Prospective Study Determining the Sustainability of Pain Relief and Psychosocial and Functional Responses When Utilizing a Multiple Waveform Enabled Neurostimulator

EQ5D is a standardized instrument for use as a measure of health outcome applicable to a wide range of health conditions and treatments. It provides a simple descriptive profile and a single index value for health status. The EQ5D-3L descriptive system comprises the following 5 dimensions: mobility, self-care, usual activities, pain/discomfort and anxiety/depression. Each dimension has 3 levels: no problems, some problems, extreme problems. A visual analog scale (VAS) for health is also included in the measure as a patient-reported estimate of overall health status. EQ5D Index scores range from - 0.594 (min) to 1 (max). An EQ-5D summary index is derived by applying a formula that attaches values (weights) to each of the levels in each dimension. Higher values represent better outcomes.

The PCS is a validated scale that measures the magnitude of catastrophizing (negative thoughts and feelings while a patient is experiencing pain). Subjects answer questions about how they feel and what they think about when they are in pain (i.e., not at the current moment). The scale includes 13 statements concerning pain experiences that are rated on a scale between 0 'not at all' and 4 'always'. The scale is self-administered and takes 5 minutes to complete. A higher score indicated a higher level of catastrophizing. PCS total scores range from 0 (min) to 52 (max). Three sub-scales consists of rumination, magnification, and helplessness. Rumination scores range from 0 (min) to 16 (max), Magnification scores range from 0 (min) to 12 (max), and helplessness scores range from 0 (min) to 24 (max). The total PCS score is the sum of the three subscales.

The State-Trait Anxiety inventory is a self-administered screening for anxiety. The STAI has 40 items, 20 items allocated to each of the S-Anxiety and T-Anxiety subscales. All items are rated on a 4-point scale from 1 to 4. It clearly differentiates between the temporary condition of "state anxiety" and the more general and long-standing quality of "trait anxiety" by providing a score for each. Higher scores suggest greater levels of anxiety. The range of possible scores for the STAI varies from a minimum score of 20 to a maximum score of 80 on both the trait and state subscales. The total score is the sum of the two subscales. STAI total scores range from 40 to 160.

The PHQ9 is a multipurpose, validated instrument for screening, diagnosing, monitoring and measuring the severity of depression. The questionnaire consists of 9 questions that rate the frequency of the symptoms of depression. A follow up non-scored question screens and assigns weight to the degree to which depressive problems have affected the patient's level of function. The responses range between 4 choices (0=not at all to 3=nearly every day). Higher scores indicate a higher likelihood of major depression. PHQ-9 scores range from 0 (min) to 27 (max).

The TSK is a 11-item self-report checklist using a 4-point Likert scale that was developed from the original 17-item checklist (Miller, Kopri \& Todd, 1991) as a measure of fear or movement or (re)injury. The scale is based on the model of fear avoidance, fear of work related activities, fear of movement and fear of re-injury. The TSK has also been linked to elements of catastrophic thinking. The scale can be useful in measuring unhelpful thoughts and beliefs about pain in people with chronic pain. Total TSK-11 scores range from 11-44 points. Higher scores represent worse outcomes.

The MOS sleep scale is intended to assess the extent of sleep problems and measures 6 dimensions of sleep, including initiation, maintenance, quantity, adequacy, drowsiness and respiratory impairments. It includes 12 questions with the first question assessing how long it takes the subject to fall asleep. The second question asks how many hours each night the subject slept. The remaining 10 questions have a range of 6 responses from 1="all of the time" to 6="none of the time". The scale is self-administered and validated. MOS Sleep scale scores range from 0 (min) to 100 (max). Higher scores represent worse outcomes.

The PROMIS Physical Function short form is an 8-item instrument designed to measure physical capability rather than actual performance of physical activities. The scale measures universal physical function rather than disease-specific impairment and assesses current function rather than function over a specified time period. Each question has five potential response options ranging in value from one to five to give a total score ranging from 8 to 40. Scores are converted into t-scores where the average for the general US population is 50 and the SD is 10. Higher scores indicate better physical function.