Activity Levels Amongst Patients With Lumbar Spinal Stenosis

Disease background:

While lumbar spinal stenosis (LSS) is one of the most common degenerative diseases of the spinal column, there is no universally accepted definition of LSS, and no accepted radiologic diagnostic criteria. LSS most often refers to a narrowing in the central canal of the vertebrae, the lateral recess, or the neural foramen. Changes to these can occur due to acquired degenerative spondylosis or spondylolisthesis, or more rarely due to conditions such as ankylosing spondylitis and space-occupying lesions, or congenital abnormalities. LSS can be classified according to anatomical location, etiology or severity of narrowing, though no validated classification has been published.

The lack of concrete definition has caused difficulties in estimating the prevalence of LSS. Studies using community-based sampling has shown a prevalence of acquired LSS, defined as a narrowing of the central canal to ≤ 10mm in the anterior-posterior (AP) direction, of 7.3%. The prevalence has been shown to rise with age, from 4.0% affected at < 40 years of age, to 14.3% amongst patients ≥ 60. No significant differences have been observed in overall prevalence according to gender, although there seems to be a slightly higher prevalence amongst elderly females than males.

Although LSS is often asymptomatic, common symptoms of LSS include low back pain, which worsens with prolonged ambulation, lumbar extension and standing, and which is relieved by rest and forward flexion, as well as lumbar radiculopathy. Patients may also complain of poor balance, and physical examination findings may include a wide-based gait and abnormal Romberg results. Symptoms are thought to occur due to compression of microvascular structures in the nerves, allowing for neural ischemia and defects in nerve conduction, and venous pooling resulting in inadequate oxygenation and metabolite accumulation.

Current treatment options for LSS range across both conservative and surgical management strategies. Conservative management has traditionally been regarded as first-line treatment, with a combination approach of physical therapy and pharmacological treatment with NSAIDs and analgesics. Epidural steroid injections have been used for symptom management, though with limited short and long-term benefits. Surgical management is often indicated in patients with ongoing pain despite attempts at conservative management for 3-6 months. Choice of surgical strategy to relieve the pressure on the neural structures depends on the anatomical location of stenosis and number of stenotic segments, as well as the intraoperative assessment of stability.

The effect of surgical decompression on disability, leg pain and back pain has been widely evaluated, but studies of the effect on postural control are sparse. The present study aims to investigate the effect of surgical decompression of symptomatic lumbar spinal stenosis on postural control by assessment of sway measures before and after surgery.

Activity levels:

Physical activity (PA) has been demonstrated to be correlated to physical and mental wellbeing, having been shown to offer significant benefits including preventing and managing cardiovascular disease, cancer, and diabetes, as well as reducing symptoms of depression and anxiety. A dose-response relationship has been observed, and while all PA can be beneficial, higher levels can have more positive effects. Likewise, the negative consequences of sedentary behaviour are well established, hereunder increasing risks of metabolic and musculoskeletal disorders as well as all-cause mortality. As such, PA as both an intervention tool and as a measurement of effect has been becoming increasingly prevalent in the literature.

It is currently recommended that adults should undertake regular PA, with a minimum of 150-300 min of moderate-vigorous physical activity (MVPA) every week. Adults who do not achieve this can be classified as physically inactive. It is worth keeping in mind though, that no definition of MVPA exists, as such a definition would need to be highly individualized.

Efforts have been made to quantify PA in the context of research; the doubly labelled water (DLW) technique has been shown to be highly accurate in measuring total daily energy expenditure and is considered the gold standard when measuring activity levels. However, as this technique is expensive, time-intensive and imposes a high degree of subject interference, it is not practical for large-scale studies.

Other measurements of activity have been developed and validated, including self-report questionnaires, self-report activity diaries, direct observation, and the use of devices such as accelerometers, pedometers, heart-rate monitors, and armbands. Among these, the use of accelerometers as an activity monitoring device has become increasingly prevalent due to the high frequency of measurements, large memory capacity, low subject interference and ability to differentiate between differing levels of activity. Accelerometer use has likewise been recommended as a clinical measurement of PA when undertaking intervention studies and has seen a rise in use in the field of orthopaedics.

Patients with LSS are often classified as physically inactive due to the ambulatory limitations that symptomatic LSS can present with, and rarely meet the abovementioned recommendations for PA, despite evidence suggesting the benefits of PA for LSS patients. Previous studies have not been able to prove a significant effect of decompressive surgery on activity levels for LSS patients six months post-operatively, measured by accelerometer. However, while comparable studies on patients undergoing total hip arthroplasty likewise found no significant improvement in activity levels after six months, studies with longer follow-up, up to a year post-operatively, have been able to show an activity level comparable to healthy control individuals. Likewise, studies measuring activity levels on LSS patients undergoing decompressive surgery using pedometer readings have been able to show a significant increase in activity after 12 months.

Activity monitoring device:

The ActiGraph wGT3X-BT is a triaxial accelerometer, recording inertia in three planes at a sampling rate up to 100 Hz. A proprietary filter can be applied to eliminate artifacts due to movement not caused by human activity, and data is summed as a total activity count per minute, which can then be used to estimate PAEE and MVPA. The wGT3X-BT has been widely validated against gold standard measurements such as DLW, and in appropriate patient groups such as the elderly, and has been shown to be valid and reliable in assessing physical activity intensity.

Rationale of the study:

This study will be the first to correlate the effects of decompressive surgery in patients with symptomatic LSS with activity levels, and associated quality of life increases. Previous studies have been hampered by low power due to sampling size limitations, and short follow-up regimes, both of which this study seeks to manage through multi-centre collaboration and inclusion, and a follow-up regime spanning two years from the time of surgery.

It is expected that the results of our study can facilitate an increased understanding of the role of activity when considering surgical management of symptomatic LSS patients, as well as enable targeted treatment of patients with LSS.

Research question:

Do elderly patients with symptomatic LSS, who have undergone decompressive surgery, show an improvement in activity level compared to pre-operative values?