Sciatica and Disk Degeneration

Paul L. Reller L.Ac. / Last Updated: August 03, 2017

A number of studies have addressed the outcomes of the treatment choices for lumbar disc degeneration and sciatic nerve pathology. The latest study of 472 patients lead by Dartmouth Medical School's Dr. James Weinstein and supported by the National Institute of Health "for the first time showed very significant improvement in the patients who ended up with nonoperative treatment (exercises and NSAIDS)." This study failed to address the treatment success when standard physical therapy exercises are combined with skilled soft tissue mobilization, acupuncture and herbal prescription, though, and many intelligent patients are choosing to incorporate these therapies into the overall treatment strategy today, utilizing Complementary and Integrative Medicine (CIM) and the Licensed Acupuncturist, or TCM physician, with these skills. In 2013, the U.S. National Institutes of Health (NIH) initiated the first serious randomized controlled human clinical trial (RCT) of acupuncture for lumbar spinal stenosis, sponsored by the Korean Medicine Hospital of Pusan National University. Acupuncture is now widely used, thoroughly proven, and endorsed for chronic low back pain, yet there is still no standard evidence to really assess objectively if it does stimulate effective healing and repair of degenerative lumbar conditions. To date, there is a discounting in standard medicine of acupuncture in this regard because of the difficulty in study design. This RCT will measure both functional improvement and pain reduction when combined with standard care, meaning physiotherapy and pain medication.

While skepticism of needle stimulation as a sound medical treatment has been widespread in standard medicine, thousands of scientific studies, including stage 3 human clinical trials that are randomized and controlled, do confirm the effectiveness of acupuncture stimulation. In 2012, Dr. Andrew Vickers, a renowned health outcomes researcher at Memorial Sloan-Kettering in New York, published a definitive meta-review of these studies in the Annals of Internal Medicine. Dr. Vickers chose only the human clinical studies with the highest possible rating, and found that in these 29 studies, involving more than 18,000 patients with chronic pain, that acupuncture stimulation definitely outperforms the chosen sham or placebo significantly, and more importantly, outperforms standard therapy for chronic pain even more significantly than it outperforms placebo. Dr. Vickers stated that this meta-review should change the attitude in standard medicine and prompt M.D. referrals for patients with chronic pain. There is no longer any scientific doubt of efficacy. It is expected that this new RCT of acupuncture in the treatment of subacute and chronic lumbar degenerative disease will also provide sound evidence to support the integration of acupuncture. Of course, traditionally, acupuncture is combined with soft tissue mobilization in TCM, which is called Tui na, as well as safe and effective herbal and nutrient medicine to speed tissue healing and growth and reduce inflammatory dysfunction. This holistic package of care delivers a better outcome than needle stimulation alone, and is also traditionally combined with patient instruction in therapeutic routines, which generally falsl into the category of Qi gong. Of course, even the newer single-blinded RCT designs that assess the treatments within a broader scope of integrated care do not allow for a real assessment of this traditional holistic protocol, as the parameters and variables are too broad for the RCT design. Clinical evidence is overwhelming, though, which many patients and physicians can attest to.

Recent studies of the Traditional Chinese Medicine (TCM) practice of soft tissue mobilization, commonly called 'acupressure' but actually called Tuina in Chinese, which literally means mobilization or manipulation of the soft tissue, have showed proven benefits in RCTs. A Taiwanese doctor, Dr. Hsieh, published results of a randomized controlled trial showing significant benefit from 'acupressure and physical therapy', or Tuina, in 2006, in the treatment of low back pain. Few such manual treatments have ever been analyzed with the RCT design. The United States congress Office of Technology Assessment concluded in 2005 that "only 10-20% of all procedures currently in use in medical practice have been shown to be efficacious by controlled trial." Controlled trials have produced consistent evidence of the treatment success from Tuina and acupuncture, though, because of the challenge to prove medical efficacy. Today, most of the proof of efficacy of manual therapies with the standard of double-blinded placebo-controlled human trials concern acupuncture. There are still almost no RCTs that show evidence for manual procedures such as surgery and physical therapy. Surgical costs for lumbar disc repair average more than $10,000, and carry considerable risks, whereas the cost of acupuncture and soft tissue therapies is small, and carries little or no risk of harm. This implies that first trying acupuncture and soft tissue physiotherapy for a majority of cases of degenerative lumbar disease, and especially when the diagnosis is unclear as to the cause of the 'sciatica' symptoms, is both practical and sensible. The immediate relief of symptoms when utilizing surgery may be quicker than with conservative therapies, but the long term outcome often involves multiple surgeries and 'failed back syndrome', a commonly seen syndrome of chronic debility despite multiple surgeries. This may occur because the patient is not given proper rehabilitative treatment after the surgery. Although the tissue causing the worse symptoms is surgically corrected, the entire problem is not addressed. The solution would be to first try conservative care with acupuncture and physiotherapy, and if needed, proceed to the more radical surgical solutions, and then follow-up the surgery with conservative care and rehabilitation integrating acupuncture and physiotherapies. When numerous large studies have proven that the long-term outcomes with lumbar surgery are on the average no better than just a short course of physical exercise and pain medication, this solution is a no-brainer. Complementary and Integrative Medicine and Traditional Chinese Medicine (CIM/TCM) should be a part of the better solution to this widespread and debilitating health problem.

A number of recent studies have supported the conservative care approach of acupuncture, physiotherapy, and instruction in targeted stretch and exercise coupled with correction of body mechanics and posture that I utilize in my practice. Increased utilization of this approach could have a significant effect on reducing health care costs in the United States, both reducing the cost of insurance, and saving the government a lot of money. This can only be achieved with patient support. An analysis of clinical trials in 2008 by the Oregon Health and Science University, published in the the Lancet medical journal, found that the typical path of prescription pain medications, X-ray and MRI imaging did not result in improvement over conservative care, but did add a tremendous cost burden to overall health expenditure and the price of health care coverage. To see a BBC report on these studies, click here:

The cost of treatment for chronic or recurrent low back pain syndromes, which are quite common, is now a serious consideration for both the patient and the provider of care. Not only quality of care and reduction of adverse outcomes, but savings in healthcare, and affordability, are a primary concern as healthcare costs skyrocket and out-of-pocket expenses increase, and Complementary and Integrative Medicine, with a combination of acupuncture, physiotherapy and herbal/nutrient medicine, and patient instruction in therapeutic activities, is now proven to be cost effective. For example, a 2013 meta-review of such QALY studies of CIM (Complementary and Integrative Medicine) by researchers at Harvard Medical School and Charite' University Medical School, and published in the esteemed British Medical Journal (see link to the study below in Additional Information), found that of 28 sound cost-utility comparisons of Complementary Medicine, that Incremental Cost-Effectiveness Ratios (ICER) of up to $10,000 QALY were clearly demonstrated for treatment by Licensed Acupuncturists in private practice in the United Kingdom for low back pain, by acupuncture therapies in the hospital setting in South Korea for low back pain, by physicians trained in acupuncture therapy in the treatment of dysmenorrhea (severe menstrual cramps) in Germany, by osteopathic spinal manipulation, chiropractic therapy, and other soft tissue physiotherapies (e.g. Tui Na in TCM) in the United Kingdom, with or without integration of a protocol to instruct patients in targeted therapeutic exercise. The one study that did not show cost-effectiveness was simple massage therapy for back pain. The authors stated that: "Details of the 31 recent higher-quality full economic evaluations indicate potential cost-effectiveness and cost savings across a wide variety of CIM (Complementary and Integrative Medicine) therapies applied to different conditions." (Patricia M. Herman, Beth L. Poindexter, Claudia M. Witt, and David M. Eisenberg; BMJ Open 2012; (2) e001046).

It is wise to utilize imaging studies when conservative care strategy has not provided sufficient relief. A short course of conservative care, utilizing acupuncture and soft tissue therapies, should be tried first to evaluate functional improvement. Sometimes the tissue probems are too severe for conservative care alone and surgery is needed. While lumbar surgeries have had a dismal record of success in the past, recent advances in less invasive surgical techniques have proven quite promising. In the past, laminectomies, or full incision of the lumbar lamina, which is the surrounding support tissues, often resulted in chronic tissue problems from incision of so many delicate tissues. Likewise, insertion of metal supports, and disc replacement or removal, also had poor longterm outcomes. Today, many surgeons have become skilled in lumbar surgeries that utilize endoscopy, microsurgery, arthrodesis with small support implants, etc. Studies are finding that it is the quality of comprehensive care after these surgeries that determines ultimate success. It is wise to consider integrating proven conservative care into your strategy no matter whether you choose surgery or not. Improvement in tissue health before surgery, and utilization of acupuncture and soft tissue therapies after surgery, will improve the chances of the best possible outcome. A lasting outcome depends upon correcting all of the problems and not just upon temporary relief of symptoms. Ask me about the package of care that I utilize to help you achieve the best outcome and prevent future problems.

Understanding sciatica and degenerative lumbar pathology

The term sciatica has long become a catch-all phrase in medicine to refer to any pathology of lumbar pain that produces radiating symptoms to the lower extremities (also see the article Piriformis Syndrome on this website). Often, the actual pathology, when explored, involves myofascial pain patterns and nerve irritation of nerves other than the sciatic proper. Proper treatment involves attention to all the structures that could be causing symptoms of "sciatica", aggravating the sciatic nerve itself, or contributing to the sciatic pathology. The sciatic nerve arises from the sacral plexus, or tailbone, just below the lumbar vertebrae, and is part of a broad collection of nerve fibers commonly called the cauda equina, or horse tail, because the number of nerve fibers is thick like a horse's tail, and includes all of the nerve fibers emerging from the lumbar. Tissue problems of the lumbar, such as bulging or herniated discs, or inflammatory tissue and scarring, can affect various parts of these nerve roots, or the cauda equina itself. Often there is an underlying degenerative disc or joint condition, with an acute injury leading to sudden pain and paresthesia radiating to the buttocks and thigh. Disc herniation will often cause constant pressure to sustain nerve related symptoms, while a degenerated bulging disc will cause pressure, or impingement, on the nerve depending on the position of the lumbar. Degenerative or acute inflammatory conditions may cause nerve related symptoms by irritating the nerve with inflammatory chemicals, or by decreasing the lumbar stability, which may lead to mechanical pressure on the nerve.

These impingement and inflammatory problems may affect the sciatic nerve portion directly, or indirectly. Identifying correctly the exact area of nerve irritation of the nerve bundle is not easy. An X-ray will only show the bony material, and is insufficient to diagnose soft tissue, such as intervertebral disc, joint capsule, ligament, tendon and muscle. Often, the MRI images show some disc bulging or broad-based degeneration, as well as inflammatory scarring, called hypertrophy, usually of the facet joints, which are the vertebral joinings which are close to the roots of the nerves at the foramina, or spaces that the nerve root emerges from. The question of whether these findings of disc bulge or inflamed scar tissue are causing your pain is difficult to answer. Many patients studied with disc bulging or joint degeneration experience little of no pain. The pain could be caused from myofascial tissue farther away from the spine, or the myofascial contractures could be causing nerve irritation further along the nerve pathway. Chronic inflammation of the muscle and connective tissue could also be causing pain and nerve irritation from buildup of inflammatory mediators along the path of the nerve. MRI studies give valuable information, but do not answer these questions of pathology definatively. This is the reason that medical experts now recommend months of conservative care before considering imaging and surgery.

The sciatic nerve emerges from the broad bundle of nerves at the sacrum and goes through a notch on the pelvic girdle near the sacroiliac joint, and then takes either of three paths through the deep muscles of the buttock. The typical path of the sciatic goes through the piriformis muscle, which is the hip adductor, whose chief job is to stabilize the leg in the hip. This muscle is frequently contracted chronically, and often the leg is rotated laterally resulting in outtoe, or lateral pointing of the foot when standing. In these cases, hip flexion is also limited, and sometimes bending forward or rising from a seat is painful. Another typical path of the sciatic nerve through the buttock is under or over the piriformis, and here too, contracture or weakness can cause sciatic irriation with position or movement. The third type of path in one where the thick sciatic nerve takes two paths, with half of the nerve through the piriformis, and half around it. Often, myofascial release of the gluteal muscles and piriformis provides much improvement of the sciatic irritation. Clearing of the muscle tissues of accumulated inflammatory mediators also improves the condition.

As the sciatic nerve continues out of the buttock region, is travels deep along the biceps femoris, or lateral hamstring. Here too, hamstring problems can cause irrittion of the sciatic nerve. The hamstring need not be contracted in total to cause problems. Imbalance of the stresses of the medial and lateral muscles and tendons of the hamstring can cause significant irritation with common activities. Often, the muscles are strained, and the patient has not learned the proper way to stretch the hamstrings. Irritation of the head of the hamstring muscles at the tendons attaching to the pelvis can also cause a sciatic-like pain pattern, or irritate the sciatic nerve itself. This pathology can result from prolonged sitting with poor posture, or from a strain of the muscles with physical exercise or sports.

Just below and behind the knee, the sciatic nerve branches to two distinct pathways, one lateral on the calf, and one posterior, which are called the peroneal and tibial nerves, although on a percentage of patients, the branching occurs above the knee. Here too, myofascial pathology can irritate the nerve lower on the leg and cause pain symptoms above, contributing to chronic hip and back pain. A thorough musculoskeletal assessment will look for possible myofascial contributors as well as the typical problems at the spine.

To fully address the subject of sciatica, a comprehensive and holistic approach to physiotherapy should be utilized. The allopathic M.D. has the job of assessing the possibility of a serious tissue problem at one point of the sciatic path. If this one area shows severe injury, surgery may be warranted. The allopathic approach is not adequate to address the broad number of problems that can accumulate and cause sciatica. Here, the Complementary Medicine physician enters the picture to provide the patient with an expanded perspective and address the whole array of tissue problems. Choose this physician wisely. Only a small percentage of the Complementary physicians have developed the specialties and skills to address this problem in the most comprehensive and informed manner. As in standard medicine, the patient that chooses the correct specialist achieves the best results.

Understanding degenerative disc and joint disease

Degeneration of the intervertebral lumbar discs is a problem that nearly all of us will face, leading to a variety of scenarios of bulging and herniation. These degenerative disc pathologies may present with no symptoms to severe constant symptoms of pain, muscle weakness, numbness, paresthesia, and/or neurological dysesthesia. A wide variety of symptom presentations are seen clinically, oftened partially relieved with change of position, rest, or activity modification. The lower lumbar spine is the most common location for symptomatic disc herniation, accounting for nearly 80 percent of all disc herniations. The disc is a cushion between the large bodies of the vertebrae, and plays an important part in vertebral mobility as well as separation and positioning. The disc is composed of an outer ring of hard tissues, similar to ligament tissue, and an inner core that is more fluid, called the nucleus pulposa. It has no blood vessels, and nutrition of the disc depends upon fluid being pushed in and out of the disc, mainly through the intervertebral endplate. As we age, the inner pulposa of the disc gradually hardens, and mobility decreases. This also helps us as we age, though, as a fully hardened disc cannot bulge or herniate. Disc herniations and degenerative bulging commonly occur between the age of 30 to 50, when the disc still has a high fluidity. Bulging and herniation occur when the inner fluid pulposa pushes out through the harder layers of outer rings. The outer rings may experience small tears and degeneration, allowing the disc center to bulge, usually to the rear, as sitting and lumbar flexion opens the vertebrae this way. Prolonged sitting usually increases the pain with bulging discs. When the discs bulge to the rear and side of the vertebrae, the bulge may impinge upon the opening, or foramen, where the nerve root emerges. This is called positional impingment of the nerve root, or radiculopathy.

If the degenerative disc experiences sufficient trauma, the disc may herniate, meaning that the inner fluid pulposa sac emerges through a large tear, and usually causes a constant impingment if the herniation is posterior and lateral into the nerve root opening. Disc herniations may occur through the endplates or through the anulus fibrosum, or sides of the disc, usually through the posterior wall. Fragments of the disc may be contained or extruded, causing a variety of irritations of other tissues and nerve endings. The MRI will be very useful to diagnose these conditions, although bulging discs may not impinge as much when the patient is lying supine in the MRI machine. This is why newer MRI devices may examine the patient in a standing or moving position. Another problem that may eventually cause impingement upon the nerve root is disc narrowing, or stenosis. Sufficient disc height, or thickness, is needed to provide a sufficient space for the nerve root to exit the spinal cord. The discs need to rehydrate each day to maintain their height. This usually occurs when we sleep, but when tight muscles and tendons keep the lumbar vertebrae compressed at night, the discs may have trouble hydrating. Eventually, severe disc stenosis may lead to a sciatic pathology, or radiculopathy. Disc stenosis may also decrease joint mobility, contributing to degenerative joint disease. Therapy to release deep muscles and mobilize lumbar joints is often necesary to prevent or reverse these conditions.

Decades of research have still not identified the one physiological mechanism that causes degenerative disc disease. This is because a group of mechanisms is responsible. Allopathic medicine is still looking for the one type of surgical correction, or one drug, that will correct lumbar degenerative disease. The intelligent patient realizes that a more thorough and holistic approach is necessary. Inflammatory processes must become healthier, creating healthy new tissues, and clearing degenerative tissues. For this to be possible, increased circulation must be established. Deep stabilizing muscles must be released from chronic contracture if the circulation is to be restored. Chronic contracture will also add mechanical impingement with movement that wears down joint tissues. If postural habits have been acquired that contributes to muscle contracture and puts abnormal stress upon the lumbar joint tissues, these habits have to be corrected. A complete package of care is the sensible approach to restoration of healthy tissues at the lumbar. Research into inflammatory dysfunction is very useful to the herbalist as well. The more we learn about specific inflammatory dysfunction, the more we can apply specific herbal remedies to correct these problems.

Numerous studies have documented the matrix tissue degradation pathway in degenerative disc disease. The inflammatory mediators interleukin-1 beta (IL-1 beta) and TNFalpha have been shown to be overexpressed in degenerating discs, driving excess degradation enzymes. Novel antagonists of the IL-1 beta receptors have been created and tested in studies by the pharmaceutical industry, but side effects have made these drugs not well used at this time. The National Institute of Health (NIH) funded a study conducted at the University of Maryland Center for Integrative Medicine, with participation by Harvard Medical School and the University of Illinois at Chicago (Rui-Xin Zhang et al) in 2008, and found that a classic formula of Chinese Herbs, Boswellia carterii (ru xiang), Commiphora myrrha (mo yao), Angelica sinensis (dang gui), and Salvia miltiorrhiza (dan shen), modified with Notopterygium incisum (qiang huo), Paeonia lactiflora (chi shao), Corydalis yanhusuo (yan hu suo), Ligusticum chuanxiong (chuan xiong), Gentiana macrophylla (qin jiao), Cinnamomum cassia (gui zhi), and Glycyrrhiza uralensis (gan cao), effectively reduced IL-1 beta and TNFalpha in laboratory animals with induced arthritis. No observable adverse effects were noted, and with a 42 day course of treatment, the researchers concluded that the formula produces significant anti-arthritic effects by suppressing pro-inflammatory cytokines (Journal of Ethnopharmacology 121(2009) 366-371).

Besides inhibition of the inflammatory mediators that drive degeneration of the intervertebral discs and joint capsules, it has also been found that supplementation with the key nutrient chemicals needed to restore healthy tissue, and antioxidants that target joint tissues is very effective in treatment of arthritis and degenerative disc and joint disease. The nucleus pulposus, or fluid center, or the vertebral disc consists of collagen type 2 and proteoglycans, notably aggrecan, much like the tissues of the joint capsule and ligaments. Studies at Harvard Medical School have been completed utilizing specific extracts of collagen type 2 derived from chicken tissues that are bioidentical to human collagen. Human trials have been completed and signficant benefit has been proven utilizing this extract bound in a natural membrane so that it better survives digestion and is delivered to the joint tissues. An antioxidant that is proven very effective for joint tissues is derived from the whole pomegranate, and is rich in anthocyanins. These products complete a sensible course of therapy to achieve all the necessary goals in restoration of degenerative discs and joint capsules that cause sciatica, combining herbal formula, patented collagen type 2 extract, whole pomegranate extract, myofascial release, soft tissue mobilization, acupuncture, patient instruction in targeted therapies and correction of postural mechanics.

It is very important to obtain the right therapeutic products to achieve these goals. While pomegranate juice is beneficial, the chemicals extracted from the rind and calyx of the plant are what is needed to produce the desired effects. Many collagen extracts on the market are not made with the patented methods researched at Harvard. A professional herbalist can insure that the products used in therapy are the real thing, and medicinal products from professional herbal companies are sold through these physicians. Dependable quality is maintained for physicians who rely on this quality to get the results that they need in the clinic. Commercial products are often highly hyped in advertising and packaging, but the FDA does not enforce claims of quality and assurance of quantity in these products. When research proves effectiveness, and the patient does not see the positive results, the problem is probably the poor quality of the product.

Information Resources

  1. A 2010 review of sciatica by the University Francois Rabelais School of Medicine, in Tours cedex, France, explains that the term sciatica is a non-specific catch-all that denotes a symptom, not a diagnosis, usually referring to degenerative lumbar conditions with neuropathy that radiates down one leg, but often used to describe any low back and pelvic pain radiating down the leg. If nerve-related symptoms are involved, it is generally a combination of inflammation and compression, and thus needs a more holistic approach in therapy. These rheumatologists show that conservative care is indicated even in acute sciatica, and that long-term outcomes are about the same in studies when surgery is used and not, with only temporary relief resulting in most cases with surgery:
  2. In 2006 and 2007, German researchers found positive proof with blinded placebo studies comparing acupuncture to sham acupuncture and conventional therapy, that acupuncture provided more effective outcome. Thousands of patients were enrolled in these studies. These clinical trials and studies show that including acupuncture into the whole protocol is a smart choice:
  3. A 2012 meta-analysis of the cost effectiveness of Complementary and Integrative Medicine (CIM) by researchers affiliated with Oxford Medical School in the United Kingdom and Harvard Medical School in the United States (Dr. David M. Eisenberg MD), and published online in the esteemed British Medical Journal, found from careful analysis of the highest quality studies published on the established medical scientific databases in the West that treatment with acupuncture and physiotherapy by licensed physicians in CIM, including Licensed Acupuncturists, Chiropractors, and Osteopaths, was proven effective in a cost-benefit analysis, using standard measures of Incremental Cost-Effectiveness Ratio (ICER) and measured in Quality of Life Years (QALY):
  4. In the near future, various implants will be used in lumbar surgeries to promote bone and tissue growth that eventually replaces the implant. To insure that this process works well for you, decreasing mechanical stress with myofascial release and soft tissue mobilization, and promoting improved tissue healing with acupuncture and herbal/nutrient medicine is recommended. This protocol could result in a healthy spine for many patients with severe degenerative tissue problems in the future. Click here to review some of these promising surgical strategies:
  5. A 2010 meta-analysis of all published scientific studies of joint manipulation/mobilization by the Northwestern Health Sciences University, in Bloomington, Minnesota, U.S.A. found that this therapy was proven effective in randomized controlled human clinical trials of high quality for acute, subacute and chronic low back pain, cervical neck pain, headache, migraine and several extremity joint conditions. Studies were still inconclusive for chronic neck pain, sciatica, TMJ, tension headache, fibromyalgia and PMS, due to inadequate study design, but this does not mean that these treatments are not effective for these conditions. TCM therapy often combines joint mobilization with soft tissue therapies, myofascial release, neuromuscular reeducation, acupuncture and trigger point needling, providing greater success in this more thorough and holistic protocol, when the Licensed Acupuncturist is trained in Tui na:
  6. A 2014 study in China found that electroacupuncture stimulation at the point GB30, over the sciatic nerve in the piriformis muscle, upregulated nerve growth factor (NGF) and downregulated the inflammatory chemokine Fos-B to effect repair and improved function of the sciatic nerve in animal studies:
  7. A 2013 study in China found that electroacupuncture with alternating 2 Hz and 100 Hz stimulation, at ST36 and GB34, significantly improved neuropathic pain by downregulating neuronal nitric oxide synthase (nNOS) and cGMP-dependent protein kinase in the hippocampus, the center of pain modulation. Such effects are combined in standard acupuncture treatment, and are now proven and explained in scientific studies of effects. The combination of direct soft tissue mobilization (Tui na), acupuncture and electroacupuncture is an effective protocol for treatment of sciatic injury and irritation:
  8. A 2012 study at South-Central University in China showed that the Chinese herbal extract tree resin called Dragon's Blood exerts significant anti-inflammatory and analgesic effects via inhibition of Substance P and COX-2 induction of calcium ion concentration. Such herbal extracts are usually combined to improve tissue healing in Chinese Herbal Medicine, and can be included in a comprehensive treatment protocol with acupuncture, electroacupuncture and soft tissue mobilization:
  9. A 2011 controlled study at China Medical University, in Taichung, Taiwan, found that a chemical in the Chinese herb Ge gen (Pueria), called Puerarin, significantly increased regrowth of myelinated fibers and improved conduction velocity in peripheral nerves in study animals with injured nerves: