The main mechanism underlying spontaneous resorption of LDH has been confirmed as contact of the nucleus pulposus perforate posterior longitudinal ligament with blood, which elicits an immune response [9]. Resorption of LDH takes 3–12 months [5]. Patient experience of pain, mood, and family support are important factors that influence whether a treatment plan can be implemented[13]. The treatments patients receive, as well as their lifestyle, type of work, and rehabilitation exercises, can also affect the disease course[14]. Methods to promote absorption of the herniated disc and shorten the disease course warrant exploration. Because most of LDH patients were treated with surgery, prospective research on resorption of LDH is difficult; therefore, we conducted a retrospective analysis of patients with spontaneous absorption of LDH.
Physical and mental health parameters in patients undergoing conservative treatment
Although surgery has advantages in relieving early or mid-term pain and promoting early recovery in patients with LDH, its long-term efficacy does not differ from that of conservative treatment [15–17]. The main purpose of conservative treatment is to alleviate pain, increase motor function, improve quality of life, and provide adequate time for reabsorption to occur. Intensive conservative treatment can reduce the number of surgeries required for patients with non-contained LDH within 1 month of onset [18]. During hospitalization, patients in this study received a mean of 5.90 treatment methods each. Most patients (67.74%) also received intensive treatment during the rehabilitation period, with a mean of 1.91 outpatient treatments per patient. In this study, the majority of patients agreed that timely treatment, oral medicine, and hot compress were factors that enabled spontaneous absorption.
Early physical therapy can improve pain relief efficacy, function, and disability indices of patients with low back pain [19]. Acute pain management of non-specific chronic low back pain is conducive to recovery and return to work, and also reduces costs [19, 20]. Our data show that early treatment is beneficial to herniated disc absorption in patients with extrusion or sequestration.
For patients with chronic diseases, especially chronic low back pain, a good doctor-patient relationship is essential to treatment adherence [21]. The impact of the doctor-patient relationship is more obvious in the medium term (6 months after recovery) than in the short term [22]. A good doctor-patient relationship is conducive to recovery via spontaneous absorption in patients with LDH [23]. In this study, doctors and patients could communicate to ensure effective treatment according to patient symptoms during hospitalization, and during rehabilitation, 29 (93.55%) patients received subsequent visit(s) and follow-up by phone or WeChat. Patients also considered effective doctor-patient communication a favorable factor for recovery.
Anxiety or depression are common in patients with chronic low back pain; in one study, 56 (61.5%) such patients were reported to suffer from anxiety or depression before surgery [24]. Further, the prevalence rates of mood change and anxiety in 149 patients with LDH were 16.6% and 35.8%, respectively[25]. The most common specific diagnoses were major depression (16.9%) and generalized anxiety disorder (12.8%) [25]. Higher pain intensity and longer disease duration are independent risk factors for depression [26]. The use of microsurgery to remove the intervertebral disc can relieve pain, while also reducing physical anxiety and depression [27].
Family support for patients with chronic pain is also an important factor affecting mood. Patients with family support reported significantly lower pain intensity, drug dependence, and higher physical activity levels than those without [28]; for example, patients with knee arthritis who have strong family and spousal support had significantly fewer depression symptoms, and pain levels decreased with increasing family support [29]. In this study, although only 9.68% of patient family members did not agree with long-time conservative treatment, none firmly opposed this therapy option. Ten patients (32.26%) in this study experienced emotional distress, which is a lower rate than that in previous report[25]. This may be related to the fact that patients were hospitalized and received daily professional help from a physician. A good doctor-patient relationship has an important impact on rehabilitation [30], and 29 (93.55%) patients received follow-up visits via telephone or WeChat during rehabilitation; thus, they had access to professional help.
Symptoms and associated factors
Fourteen subjects (45.16%) were sensitive to factors such as prolonged walking, prolonged sitting, excessive weight bearing, and cold, which provoked waist discomfort, affected limb discomfort, numbness of the affected shank, and sacrococcygeal discomfort. Although patients with LDH exhibit a degree of fear avoidance [31], such beliefs are more common among patients with chronic low back pain than those with acute low back pain [31]; however, fear avoidance cannot explain patient sensitivity to factors such as prolonged sitting, fatigue, and cold. Inflammatory mediators released at the herniated disc can alter the expression of sodium, potassium, and calcium ion channels on the surface of the dorsal root nerve, causing ectopic and continuous discharge [32], which is related to sensitization of spinal dorsal horn cells and consequent hyperalgesia [33]. Simultaneously, spinal dorsal horn microglia are activated, and the expression of phosphorylated SRC family kinases up-regulated [34]. Long term nociceptive signals input caused by the herniated disc alters the morphology and/or cell structure of the anterograde projection area [35]. Functional MRI shows that the right dorsolateral prefrontal cortex and left anterior cingulate cortex of the pain-related area are activated in patients with chronic low back pain [36]. Further, patients with chronic low back pain have central sensitization, with sensitivity to noxious stimulus [37], as well as innocuous stimuli [38]. Lower than normal pressure levels can produce mild and severe pain in patients with chronic low back pain [36]. Further, patients with chronic low back pain have lower cold pain thresholds at the waist and in distal body parts [39]. Nevertheless, changes in weather temperature do not increase the risk of low back pain [40]. Since the autoimmune responses to herniated disc exceed 3 months, prolonged painful stimulation can cause central sensitization. Patient sensitivity to fatigue and cold may also be related to central sensitization.
Factors favorable for herniated disc absorption
Hernia type is an important factor affecting the occurrence of spontaneous resorption. Sequestered herniations have the highest proportion of spontaneous resorption, followed by transligamentous, with the lowest rates for subligamentous[8]. Further, the probability of sequestrated discs being fully resorbed is higher than that of extruded discs [5, 41]. Three hypotheses, including retraction, absorption, and dehydration, have been proposed to explain the resorption of herniated discs. Matrix metalloproteinases (MMPs) are the main metabolic enzymes involved in the process of apoptosis and self-absorption of intervertebral disc protrusions. Numerous mononuclear macrophages and MMP-3 have been detected in the herniated nucleus pulposus [42]. Levels of MMP-1, 3, and 13 in sequestered discs are significantly higher than those in contained discs [43]. In our study, the spontaneous resorption ratio of sequestration type hernia was significantly higher than that of extrusion type, confirming that the type of herniation is an important factor in spontaneous absorption.
The ruptured annulus fibrosus has reduced ability to fix the nucleus pulposus, and bed-rest can alleviate the load on spine intervertebral discs, thereby reducing the chance of further nucleus pulposus protrusion [44, 45]. When resting in bed, the height and area of the intervertebral disc increase significantly; however, the water signal intensity does not alter [46]. A meta-analysis showed that bed-rest is effective in reducing pain and improving lumbar function in patients with acute low back pain [47]. In self-evaluation, patients recommended bed-rest during the acute period as a favorable factor. Further, our regression analysis supported early bed-rest for patients with sequestration or extrusion disc herniation. Although the optimal duration of bed-rest remains uncertain, it has been recommended that patients with LDH remain in bed for < 1 week [48], and 2 weeks has also been suggested [49]. Based on the mean bed-rest day of the 31 patients in this study, we advise that patients with sequestration or extrusion disc herniation should remain in bed for approximately 3 weeks, to alleviate the load on ruptured intervertebral discs. However, long-term bed-rest during the early stages of pain is associated with higher levels of long-term disability [50]. Moderate quality evidence suggests that there is little difference between patients with sciatica who undergo bed-rest and those who stay active, in terms of pain reduction and function improvement [47]. Another study also found that bed-rest does not improve sciatica [51] because radicular pain is caused by various factors, including mechanical compression, inflammatory stimulation, and autoimmunity [35]. Therefore, active symptomatic treatment, such as medication, nerve block, acupuncture, and moxibustion, is necessary [52].
For patients with non-specific low back pain, prolonged bed-rest during the initial stages of symptoms is associated with higher levels of long-term disability[50], and can cause major cardiovascular, respiratory, musculoskeletal, and neuropsychological changes, as well as bone loss, which may delay or prevent recovery from critical illnesses, including disuse muscle atrophy, joint contractures, thromboembolic disease, and insulin resistance [53] [54] [55]. In this study, regression analysis showed that prolonged bed-rest duration in rehabilitation was negatively correlated with the reabsorption ratio; hence, prolonged bed-rest should be avoided during the rehabilitation period.
MRI analysis showed that the cross-sectional area of the iliopsoas muscle was reduced on the 14th day of strict bed-rest, while the sartorius muscle was reduced on the 42nd day [56]. After living in space weightlessness for 6 months, lumbar lordosis was reduced by an average of 11%, when astronauts were supine, and the functional cross-sectional area of the multifidus muscle and erector spinae were reduced by 20%, with the cross-sectional area reduced 8–9%. These data suggest that prolonged bed-rest causes lumbar muscle atrophy and a decline in spinal stability [57]. Trunk extensor strength is beneficial in increasing spinal stability and improving its function [58]. Early functional exercises, including passive and autonomous activities, can improve patient physiological function following percutaneous transforaminal endoscopic discectomy for LDH, as well as improving emotional function, mental health, and quality of life [59]. Dynamic lumbar stabilization training can relieve pain, reduce functional disabilities, and decrease patient fear avoidance behavior following lumbar microdiscectomy [60]. Early strengthening exercises include Williams flexion exercises and/or McKenzie extension exercises, which can increase spine compression by 12–18% and stability by 34–64% [61]. Eight weeks of core stability training improves the static endurance of the trunk muscles of patients with LDH to a normal level [62]. Rehabilitation exercise was the enabling factor rated highest in patient self-evaluation in this study. Active improvement of trunk extensor strength can help to prevent adverse reactions to prolonged bed-rest, enhance patient mood, and improve and maintain spinal function.
Lumbosacral orthosis is widely used to relieve low back pain. Moderate evidence shows that lumbosacral orthosis is more effective in preventing low back pain and improving pain and function than lack of intervention and training [63] [64]. Home care workers who wore lumbosacral orthosis devices had a reduced number of days of pain, but no reduction in sick days[65]; however, another study showed that lumbosacral orthosis did not reduce the incidence of low back pain in workers [66]. Hence, lumbosacral orthosis is effective in improving pain, but ineffective as primary prevention [63]. Rupture of the annulus fibrosus and decreased pressure on the intervertebral disc increases spinal flexion and rotation instability [67]. Lumbosacral orthosis improves the stiffness and stability of the spine by increasing abdominal pressure. The results of this study suggest that lumbosacral orthosis is beneficial for the absorption of herniated discs that break through ligaments and prolapse. Wearing a lumbosacral orthosis device during the acute phase of LDH is a favorable factor, which may be related to increased spine stability and reduced pressure on the intervertebral disc. Nevertheless, lumbosacral orthoses may reduce back muscle activity, leading to a concern that long-term wear may cause trunk muscle weakness; however, wearing lumbosacral orthoses for 6-months does not cause weakening of the paravertebral muscles in patients with chronic low back pain [68]. Further, there is no scientific evidence that prolonged wearing of lumbosacral orthosis devices results in trunk muscle weakness [69].
BMI is positively correlated with pain and the Roland-Morris Disability and Oswestry Disability indices, and logistic regression analysis demonstrated that higher BMI is a risk factor for LDH recurrence [11]. Here, we did not identify a relationship between BMI and spontaneous regression ratio; however, this does not mean that weight loss is not beneficial for herniated disc regression.
Our survey had several limitations, as follows: first, there was selection bias, as all subjects included in the study were hospitalized patients from Henan Provincial Luoyang Orthopedic-Traumatological Hospital (Henan Provincial Orthopedic Hospital) who had severe symptoms, hence they are not representative of patients with mild or moderate symptoms; second, this is a retrospective study, spanning a period of 4 years 3 months, hence patients will have exhibited memory bias; third, due to the wide application of spinal surgery techniques, most patients with severe LDH received surgeries, meaning that the number of collected cases was small, leading to potential data bias; fourth, few of the included patients were underweight or overweight, making it difficult to determine the effect of weight on reabsorption; finally, as patients were hospitalized in a Chinese medicine hospital, they received more TCM treatment techniques, which may have resulted in a bias toward Chinese medicine culture and treatment techniques.