Low back pain (LBP) is the second most common source of disability in the United States, affecting more than 80% of the population during their lifetime [1
]. This can lead to costs reaching $
200 billion annually [3
]. Depending on the type of LBP, several types of treatment exist for reducing pain, including medication, exercise therapy, massage therapy, spinal manipulation, temperature treatment, transcutaneous electrical nerve stimulation, acupuncture, and spinal steroid injection [4
]. Regardless of the type of intervention, evidence is needed to show the effect of any treatment in the clinic and at home, and whether immediate improvement in post-treatment physical function leads to improvement in daily physical activity (DPA). In the current study, we investigated how the effect of spinal injection, a common minimally-invasive pain reduction intervention, can reduce LBP symptoms and pain caused by lumbar facet joint arthrosis, and how these effects may enhance DPA.
Among its many causes, lumbar facet joint pain accounts for up to 75% of the patients who present with LBP [6
]. One specific cause of LBP is lumbar degenerative facet osteoarthropathy, which is characterized by cartilage degradation and sclerosis in the subchondral bone at the synovial joint, leading to impingement of nerve roots as the cause of pain [6
]. Among the most common treatments, paravertebral spinal injection (PSI) is often utilized to manage chronic LBP [7
]. Spinal injections are categorized as epidural steroid (interlaminar or caudal), transforaminal epidural (selective nerve block), and paravertebral facet blocks (intra-articular or extra-articular medial or intermediate branch block). We investigated the utilization of paravertebral facet blocks and included both extra-articular and intra-articular as a PSI in order to encompass the medial and intermediate branch.
Although PSI has been commonly implemented for LBP treatment, there are few clinical trials pertaining to the use of lumbar PSI, and among those available, no consensus regarding effectiveness has been reached [8
]. One study investigated transforaminal or caudal fluroscopically guided epidural steroid injections for lumbar spinal stenosis, which found that 32% of the patients reported pain relief beyond two months post-injection, along with 53% who confirmed functional ability improvement at an average of 1.5 years post-injection [9
]. In another study specifically focusing on pain measures, 9 out of 30 patients who underwent fluoroscopically guided transforaminal epidural steroid injections for lumbar disc herniation reported complete pain relief after 24 weeks from the beginning of the study, which allowed for one injection every two weeks with a maximum of three injections [10
]. In another study, functional disability measured by the Roland-Morris Disability Questionnaire was insignificantly improved after six weeks of fluoroscopically guided transforaminal or interlaminar epidural steroid injections for lumbar spinal stenosis compared to baseline [11
]. Interestingly, one study assessed pain, disability, and physical impairment one week post-injection for lumbar spinal stenosis, but found that improvements in pain and function compared to baseline measurements did not positively correlate with the objective assessment of total activity over a period of seven days; no significant changes in physical performance were discovered with treatment using fluoroscopically guided epidural steroid injections [12
]. Within our recent investigation, we showed that fluoroscopy guided PSI for LBP improved motor performance between one and three months, but most notably at one month post-injection [13
]. According to these previous studies, decrease in pain is often observed after PSI but for varying lengths of time [9
]. Inconsistency also exists in the reported functional ability and physical performance status following PSI [9
]. Additionally, no study has compared changes in subjective and objective parameters, especially greater than or equal to a 30-month period after the treatment.
The primary aim of this study was to investigate the efficacy of paravertebral facet injection for degenerative facet osteoarthropathy, both subjectively and objectively over a period of one month, using wearable sensor technology to track DPA. Notable differences separating this study from previous investigations were the inclusion of previously unreported measures, the comparison of pain-related subjective and objective measures (both in-clinic and in-home measures), as well as the inclusion of patients with more diverse etiologies of LBP, which most accurately reflects the typical patient population. Specifically, we investigated: (1) how objectively measured DPA would change over the one-month period following spinal injection treatment; and (2) if and how much DPA measurement would be associated with post-treatment alterations in pain, disability, and objective in-clinic measures of gait and Timed Up and Go (TUG).
4.1. Differences between Subjective and Objective In-Clinic and In-Home LBP Improvements
We investigated how removal of LBP using PSI resulted in decreased disability and improved mobility in performing daily activities. Our results suggested that although participants claimed reduced pain and showed improvements in in-clinic function measures (gait and TUG) post-injection, similar trends of improvements were not observed in DPA measures.
Pain in general decreases patients’ quality of life depending on its extent, duration, and intensity [30
]. With regard to LBP, pain and disability are often measured using subjective self-assessments and their relationships with a patient’s quality of life is significant albeit weak due to other psychosocial factors [31
]. LBP manifests in altered movement patterns when walking or changing positions, and may interfere with both activities of daily living and work-related functions [31
]. Along with in-clinic measures of function that have been extensively studied for LBP treatments [33
], measures of daily activities can be utilized to objectively evaluate disability due to pain. We previously showed that fluoroscopy guided PSI for LBP improved in-clinic motor performance, which could last between one to three months [13
Considering subjective evaluations of PROMs, pain and disability, as measured by the visual analog scale and the Oswestry Disability Index, were significantly improved in patients after PSI (see Table 1
). This result was consistent with previous work investigating transforaminal or caudal fluoroscopically guided epidural steroid injection for lumbar spinal stenosis, which reported 32% pain relief beyond two months post-injection, along with 53% of patients who confirmed functional ability improvement within an average period of 1.5 years post-injection [9
Although several studies have reported subjective pain reduction after spinal injection, few investigated both subjective and objective measures. One study assessed pain, disability, and physical impairment one week post-injection for lumbar spinal stenosis. Although a different type of spinal disorder was targeted in that study, interestingly, and similar to our findings, they found that improvements in pain and function compared to baseline measurement did not positively correlate with the objective assessment of total DPA over a period of seven days [12
]; no significant changes in physical performance including daily steps, maximum minutes of continuous activity, and percentage of total counts in the light, moderate, and high range of intensity were discovered with treatment using fluoroscopically guided PSI [12
]. In contrast to our study, however, they did not measure in-clinic gait parameters nor did they measure parameters at one month post-injection.
According to current results, while immediate in-clinic assessments of gait and TUG revealed significant differences regarding gait speed, gait cycle time, and total TUG duration, no significant change in DPA for a duration of two days was observed at baseline, at the immediate follow-up, or at the one-month follow-up after the treatment (see Table 2
and Table 3
). This disparity between in-clinic and at-home measures may be explained by the fear-avoidance phenomenon, in which patients defer from performing movement or activity because of change in muscle activity, deconditioning, or guarded movement as a result of chronic pain [35
]. These immediate changes occur to avoid pain, and can become long-lasting and difficult to modify, as fewer opportunities might exist to change this acquired adaptation to prevent physical harm when it is chronic [35
]. Interestingly, previous work showed that fear-avoidance is more strongly correlated with disability and work loss in the past year when compared with pain measures such as pain severity and duration [36
]. Although we did not directly measure fear-avoidance in this study, our results suggest that while in-clinic motor performance (measured by gait and TUG parameters) and the level of pain do improve, individuals may be conditioned to maintain a modified level of physical performance due to persistent fear-avoidance.
4.2. Limitations and Future Directions
The study is limited by its sample size as well as the duration of follow-up. In future studies, more patients of disparate ages with diverse origins of LBP should be included to increase generalizability of the current findings. Specifically, follow-up should extend to a minimum duration of one year post-injection to better understand the time lag between pain relief and improvements in DPA. Several factors may positively or negatively skew the amount of DPA, such as weather conditions, special daily events, or daily personal mood. Therefore, in addition to quantitative measures of DPA, future studies with more reliable parameters related to quality of daily activities should be investigated, such as walking symmetry, variability, and regularity. Furthermore, a control group with patients who have no LBP could be used to determine if the severity of the chronic LBP correlates with the amount of time it takes to improve DPA. Additionally, in future studies, changes in DPA due to other types of neuromuscular disorders should be investigated.
4.3. Clinical Implications
Subjective measures of pain and disability or even in-clinic measures of motor function (gait and TUG) after PSI for chronic LBP may not correlate with short-term (one-month) improvements in DPA. Clinically, chronic LBP patients may not expect an immediate increase in DPA immediately post-injection. Hypothetically, differences between in-home activity and in-clinic measures of motor function may be related to fear of pain (psychological pain) and could affect patients’ ability to perform activities of daily living. Future studies should include measures of fear-avoidance to better understand the underlying mechanism of DPA improvements. In addition, consideration of adjunctive cognitive behavioral therapy with therapists or coaches could help address thoughts, emotions, and behaviors related to LBP by examining unhelpful thinking patterns and devising new ways of reaching optimal DPA goals for patients undergoing PSI for LBP.