Use of Activity Monitors in Enhancing Spine Surgery

Outcome Measurement: Present Practice and Standard of Care

How outcomes are determined after spine surgery has shifted from subjective and solely physician-based to patient-centered and patient-reported. The last few decades have seen the development and systematic validation of a wide variety of generic and disease-specific patient-reported outcome measures (PROMs). Those are usually administered to patients in the form of conventional pen-and-pencil or electronic questionnaires that produce a score or value to estimate the severity of a patient’s pain, disability, or restriction in health-related quality of life (HRQOL).

The benefits of these scales are evident. Firstly, they measure the patient’s own (subjective) perception of symptom severity and wellbeing—a key outcome any surgical treatment aims to address. Secondly, there are several specific PROMs available that measure different aspects of outcome and that can be chosen according to the leading complaints or pathology (e.g., back pain vs. radicular leg pain vs. painless weakness vs. myelopathy). Thirdly, for the more frequently used PROMs such as the Oswestry Disability Index (ODI), the Roland-Morris Disease Index (RMDI), the Core Outcome Measures Index (COMI) Back, the Zurich Claudication Questionnaire (ZCQ), or the Short-Forms 12/36 (SF-12/SF-36), there are large bodies of literature with disease-specific data, allowing the comparison and interpretation of individual patient scores.

However, there are certain downsides to subjective outcome measures. Those include restricted comparability, as every patient rates his/her subjective pain perception differently. Subjective outcome measures are influenced by educational, cultural, and motivational inter-individual differences. The questions included in PROM questionnaires can be misunderstood (especially in foreign-language patients/illiterate people) or misinterpreted, leading to reliability issues. Some questions contained in PROMs (e.g., questions about traveling or sex life) may not necessarily apply to the individual patient’s situation, which lowers validity on the patient level. Most PROMs focus on pain as major complaint and are insensitive to less painful conditions where, for example, hindering motor deficits or dexterity issues dominate the clinical picture. Lastly, patients do not like filling out questionnaires and typically remain unaware of the constructed score. Especially for detailed (multiple questionnaires) or repeated assessments over time, there are important compliance issues, which lead to low data quality resulting from missing data and very limited granularity.

The use of objective outcome measures has significantly increased, especially over the past two decades. This increase was caused by both technological advances and the recognition that objective tests can easily, accurately, and repetitively measure functions that are performed by virtually all ambulant humans daily. Additionally, these measured functions are essential for patients after spine surgery to maintain activities of daily living and quality of life. Those activities (e.g., standing up, walking, changing direction, and sitting down) can be measured by (wearable) accelerometers, global positioning systems (GPS), or simply modern smartphone devices. Some of the smartphones store activity data unobtrusively, rendering a possible retrospective analysis of longitudinal “big data” with high granularity and completeness. The options for physical performance tests range from brief evaluations at predefined time points, which can be performed by the physician or physician assistants during outpatient evaluation, to extensive and longitudinal patient self-measurements generating “big data”. The results from objective tests of function allow the estimation of frailty and prediction of perioperative complications of patients scheduled for spine surgery, which can be helpful for risk stratification and complication avoidance. Digital objective outcome measures can be self-measured and display an easily interpretable result. In doing this, patients are empowered to take a greater degree of interest and responsibility as an equal partner in their healthcare. Reported objective outcome measures for degenerative lumbar spine diseases were summarized in recent reviews. The available and validated options for activity monitoring are listed in Table 14.1 of this chapter.

The downsides to some objective outcome measures are their lack of thorough validation and the lack of normative data availability, although the test qualities of many including the Timed-Up-and-Go (TUG) test, the app-based 6-minute walking test (6WT), the 5-Repetitions-Sit-To-Stand (5R-STS), and Motorized Treadmill Tests (MTTs) have been studied extensively and are favorable. Moreover, there is little standardization in the test choice, conduction, and result interpretation, especially in view of the comorbidities that naturally impact mobility and can introduce significant bias (e.g., prior stroke, congestive heart failure, Parkinson disease, or hip/knee osteoarthritis). This underlines a need for agreement in order to facilitate future comparison of outcome results across cohorts, studies, and countries.

Two of the key advantages of objective activity monitoring are patient convenience and preference. Many spine surgeons are aware of the difficulties associated with questionnaire-based outcome evaluations, which are regarded as tedious and patients tend to avoid filling them out. Objective outcome measures are less prone to missing data, which is a huge problem for PROM-based database studies and is known to influence results. Compared to PROMs, objective tests of function were rated as superior by patients with lumbar degenerative spinal disorders to assess severity and change in spine-related symptoms, as well as significantly more convenient to perform. For repeated assessments, the shift in patient preference from PROM questionnaires to objective functional assessments is more pronounced. The authors of this chapter have encountered several patients who were fascinated by the fact that they were able to observe and measure themselves their positive change in functional impairment over time, for instance after epidural injections or surgical treatment. Many patients conducted notably more measurements than they were asked to provide; some patients even measured their objective functional conditions voluntarily on a daily basis. With PROMs (at least in the authors’ experience) this has never happened.

There are clinical scenarios where patient-specific features render a subjective, PROM-based evaluation less precise. For example, patients with depressive comorbidities are known to over-rate pain or disability on subjective scales, whereas in patients with radiculopathy and associated motor deficits, disability may be under-appreciated by PROMs. It has been shown that in cases where pain is subordinate to neurological deficits, PROMs are suboptimal to determine disability. Case 2 (see below) illustrates the benefit of activity monitoring in patient with motor deficits; hence, this topic is not expanded upon in this section.

Case Discussion: Benefits of Objective Outcome Measures

Regarding the benefits of objective outcome measures in patients with mental health issues, we would like to describe the case of a 27-year-old female who developed sciatica secondary to a relatively minor posterolateral LDH with preserved motor function and a history of depression. Her initial TUG test was 25.3 s (age- and sex-adjusted T-score 218.4), indicative of severe objective functional impairment (TUG T-scores of >123 indicate disability). After oral pain medication and epidural steroid injections were administered, she showed significant progressive improvement in the TUG test from 22.0 s (T-score 198.2) to 18.8 s (T-score 178.5), and down to 12.8 s (T-score 141.7). At the same time, she rated her subjective back and leg pain as unchanged, always ranging from 8 to 10 on the visual analog scale (VAS), and was requesting surgical treatment. When realizing the marked improvement in her TUG test T-score over time, however, she became motivated to pursue nonoperative treatment, which lead to complete alleviation within 4 weeks. We have the impression that patients, specifically those with depressive comorbidities, experience difficulties in realizing their rehabilitation progress. In these situations, objective activity monitoring, for example, by serial TUG tests, is useful to objectify improvement and reinforce motivation at the same time.

Case Description

Preoperative Assessment

Lumbar MRI revealed a recurrent disk herniation at the level L4/5 compromising the right-sided L5 nerve in the intervertebral recess (see Fig. 14.1A and B ). His baseline 6-minute walking distance (6WD) was below the age- and sex-adjusted healthy population reference (487 m; z-score –1.00), indicative of mild disability (see Fig. 14.1C ). For a screenshot of the “6WT app” depicting his baseline 6WT result, see Fig. 14.2 .