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?