Symptomatic lumbar spondylolysis. Neuroimmunologic studies

Hallmarks of peripheral nerve function in bone regeneration

Skeletal tissue is highly innervated. Although different types of nerves have been recently identified in the bone, the crosstalk between bone and nerves remains unclear. In this review, we outline the role of the peripheral nervous system (PNS) in bone regeneration following injury. We first introduce the conserved role of nerves in tissue regeneration in species ranging from amphibians to mammals. We then present the distribution of the PNS in the skeletal system under physiological conditions, fractures, or regeneration. Furthermore, we summarize the ways in which the PNS communicates with bone-lineage cells, the vasculature, and immune cells in the bone microenvironment. Based on this comprehensive and timely review, we conclude that the PNS regulates bone regeneration through neuropeptides or neurotransmitters and cells in the peripheral nerves. An in-depth understanding of the roles of peripheral nerves in bone regeneration will inform the development of new strategies based on bone-nerve crosstalk in promoting bone repair and regeneration.

Lumbar spondylolysis - Current concepts review

Lumbar pars interarticularis (PI) injury or spondylolysis occurs only in humans. This represents a stress fracture of the PI. Excessive loading in repetitive hyperextension is a significant risk factor and occurs most commonly at L5 followed by L4. It is bilateral in 80% of symptomatic cases but can be unilateral defect as well which runs a more benign course. Symptoms of low back pain relating to this lesion are more common in young athletes involved in trunk twisting sports. Like other stress fractures, the pain may come on abruptly or more insidiously over time and only related to certain activities. The pathologic progression starts with a stress reaction in the pars, progressing to an incomplete stress fracture, and then a complete pars fracture. Diagnosis is dependent on clinical examination and radiological imaging studies (plain radiography, computed tomography (CT) scans and magnetic resonance imaging (MRI) scans). Treatment is dependent on symptoms as well as radiographic stage of the lesion. Conservative management is the mainstay of treating early lesions. A comprehensive rehabilitation program incorporates core spinal stabilization exercises. Athletes should not return to sports until pain free. Professional sporting individuals are at increased risk of failure of resolution of symptoms that may require early surgical repair of the PI defect. Modified Buck's technique & pedicle screw-hook constructs for direct repair has a high success rate in patients who have persistent low back pain. Minimally invasive lumbar pars defect repair has given similar successful outcome with added advantage of minimizing muscle injury, preserving the adjacent joint and reduced hospital stay. Functional outcome is evaluated using the Visual Analogue Scale (VAS) for back pain, Oswestry Disability Index (ODI) and 36-Item Short-Form Health Survey (SF-36). Preoperative ODI and SF-36 physical component scores (PCS) are significant predictor of a good functional outcome.

Is Microendoscopic Discectomy Effective for Patients With Concomitant Lumbar Disc Herniation and Spondylolysis?

STUDY DESIGN

A retrospective cohort study.

OBJECTIVE

Although it is controversial whether to choose only discectomy or fusion surgery in patients with disc herniation and spondylolysis, we expected that aggravation of the spondylolysis may be prevented if posterior supporting muscles can be well-preserved without extensive exploration. The purpose of this study was to investigate the influence of L5 spondylolysis on surgical outcomes following microendoscopic discectomy (MED) in patients with concomitant lumbar disc herniation and spondylolysis.

METHODS

We reviewed 811 patients who underwent MED for L4/5 or L5/S1 disc herniation. Patients with spondylolisthesis were excluded. We compared surgical outcomes of patients with and without L5 spondylolysis, whose age, sex, and surgical level were matched.

RESULTS

A total of 655 patients (80.7%) with complete data were considered eligible for the study. MED was performed at L4/5 and L5/S1 in 338 and 317 patients, respectively. A total of 20 patients (3.1%) had concomitant L5 spondylolysis and disc herniation at L4/5 (9 patients) or L5S1 (11 patients). As we compared each outcome of the 20 patients having L5 spondylolysis with 40 matched patients without L5 spondylosis, there were no significant differences in preoperative or postoperative outcomes between the 2 groups, and no patient with spondylolysis had undergone additional surgery during the mean follow-up period of 24 months.

CONCLUSIONS

MED demonstrated good surgical results regardless of the presence or absence of spondylolysis. In patients with sciatica with concomitant disc herniation and spondylolysis, but without spondylolisthesis, fusion surgery may not be always necessary.

No pain, no gain? The effects of pain-promoting neuropeptides and neurotrophins on fracture healing

Neuropeptides and neurotrophins are key regulators of peripheral nociceptive nerves and contribute to the induction, sensitization, and maintenance of pain. It is now known that these peptides also regulate non-neuronal tissues, including bone. Here, we review the effects of numerous neuropeptides and neurotrophins on fracture healing. The neuropeptides calcitonin-gene related peptide (CGRP), substance P (SP), vasoactive intestinal peptide (VIP), and pituitary adenylate cyclase-activating peptide (PACAP) have varying effects on osteoclastic and osteoblastic activity. Ultimately, CGRP and SP both accelerate fracture healing, while VIP and PACAP seem to negatively impact healing. Unlike the aforementioned neuropeptides, the neurotrophins nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) have more uniform effects. Both factors upregulate osteoblastic activity, osteoclastic activity, and, in vivo, stimulate osteogenesis to promote fracture healing. Future research will need to clarify the exact mechanism by which the neuropeptides and neurotrophins influence fracture healing. Specifically, understanding the optimal expression patterns for these proteins in the fracture healing process may lead to therapies that can maximize their bone-healing capabilities and minimize their pain-promoting effects. Finally, further examination of protein-sequestering antibodies and/or small molecule agonists and antagonists may lead to new therapies that can decrease the rate of delayed union/nonunion outcomes and fracture-associated pain.

Spinal dural arteriovenous fistula associated with L-4 isthmic spondylolisthesis

The authors describe a case of a 79-year-old man with a lumbar spinal dural arteriovenous fistula (DAVF) and isthmic spondylolisthesis at the same level. The patient's thoracic spine MRI study demonstrated swelling and increased T2 signal in the spinal cord and regional dilated perimedullary vessels. Lumbar spine MRI showed L-4 isthmic spondylolisthesis with severe bilateral L4–5 foraminal stenoses. Spinal angiography revealed a fistulous connection at the left L-4 nerve root sleeve between perimedullary veins and a dural branch of the L-4 radicular artery. Based on previous reports about secondary spinal DAVFs, the abnormal vascular communication likely developed secondary to the microtrauma and inflammation on the left L-4 nerve root sleeve, which was attributable to the isthmic spondylolisthesis. The authors performed disconnection of the arteriovenous shunt as well as an L4–5 decompression and posterior instrumented fusion with pedicle screws. The patient's postoperative course was uneventful, and he improved neurologically. It is important to bear in mind that a spinal DAVF may develop as a consequence of any sort of trauma or inflammation involving nerve roots. One should consider the concomitant treatment of both the spinal DAVF and the underlying pathology that may have given rise to the spinal DAVF.

Relationship between the histological findings of spondylolytic tissue, instability of the loose lamina, and low back pain

STUDY DESIGN

We investigated the histomorphological features of the tissue occupying the spondylolytic defect (spondylolytic tissue), which was similar to ligament, and then graded the complete enthesis structure and the density of the fibrous portion. The relationships between the features, instability of the loose lamina against the affected vertebra, and the severity of low back pain were studied.

OBJECTIVE

To elucidate the histomorphological features of spondylolytic tissue and the associations between the features, instability of the loose lamina, and low back pain.

SUMMARY OF BACKGROUND DATA

Spondylolysis is thought to be caused primarily by a fatigue fracture and spondylolytic tissue has been recognized as being a fibrocartilaginous mass. Recently, innervation of the spondylolytic tissue was reported to be one of the sources of low back pain.

METHODS

The spondylolytic tissue from 17 patients who underwent microscopic decompression of the pars defect was observed for histology including hematoxylin and eosin, elastica van Gieson, and immunohistochemical staining for S100 protein. Instability of the loose lamina against the affected vertebra was evaluated by flexion/extension radiographs.

RESULTS

The spondylolytic tissue had a ligamentous structure without innervation. The histomorphological findings, instability of the loose lamina, and low back pain had no relationship to one another.

CONCLUSION

Spondylolysis is a pseudarthorosis of the pars interarticularis and the spondylolytic tissue tends to develop noninnervated ligament-like tissue with an enthesis structure. The histomorphological features, instability of the loose lamina, and low back pain have no relationship to one another.

Evidence for overgrowth after midfemoral fracture via increased RNA for mitosis

Middiaphyseal femoral fractures in children and young rats stimulate linear femoral growth, a phenomenon commonly attributed to increased vascularity. To test for changes in mRNA expression of genes related to blood vessels, nerve fibers, cartilage, bone, and cell metabolism, we measured mRNA gene expression for all known rat genes in the physis at various times after diaphyseal fracture. Female Sprague-Dawley rats, 4 weeks of age at surgery, were subjected to a unilateral, simple, transverse, middiaphyseal femoral fracture stabilized with an intramedullary rod. At 0 (intact), 0.1, 0.4, 1, 2, 3, 4, and 6 weeks after fracture, the femoral head with the proximal physis was collected from fractured and intact femora. The RNA was extracted, processed to biotinlabeled cRNA, and hybridized to Affymetrix Rat 230 2.0 GeneChip microarrays. Transcripts from fracture-induced lengthening of the injured femora were compared to those of the intact contralateral femur. In the proximal physis, transcripts related to blood vessels and cartilage formation were down-regulated by fracture. Transcripts related to bone remodeling, nerve axon elongation, cell division, and protein synthesis were up-regulated by fracture. The data support increased mitotic activity in the physis after a midshaft fracture and not increased vascularity.

Direct Repair of Spondylolysis Using a New Pedicle Screw Hook Fixation: Clinical and CT-Assessed Study

OBJECTIVE

A prospective analysis of 19 consecutive cases of spondylolysis repair using a new hook screw device is presented. The objective of the study was to assess the clinical, radiologic, and computed tomography (CT) scan outcomes to establish the indications of isthmic repair in the treatment of spondylolysis.

METHODS

Nineteen patients treated with a new segmental pedicle screw hook fixation were followed up for a minimum of 2 years (mean 30 months, range 24-48 months). Mean age was 20.5 years (range 13-29 years). All lytic defects were bilateral and located at L5, except for one at L3. CT scans were obtained at 6 months and 1 year postoperatively. CT scans were performed using both traditional and reverse gantry angled cuts to assess the healing of the defect. Fusion was considered to be present when trabeculae passed across the lytic defect. CT scan images were not considered conclusive until 1 year after surgery, because in two cases, trabecular pass across the pars was observed on only one side after 6 months, becoming bilateral 1 year postoperatively.

CONCLUSIONS

Twelve of 13 patients who were 20 years or younger at the time of the study (average age 17.2 years) had fusion (92%), whereas in the group of 6 patients age 21 and older (average age 27.5 years), no cases of fusion were observed. Clinical outcome was excellent to good in 15 patients, fair in 3 cases, and poor in 1. The group of patients age 20 or younger had significantly better clinical results (84% excellent or good) (P = 0.00097) than those obtained in the group of patients age 21 and older (66% excellent or good) (P = 0.016). According to the current findings, the authors believe that segmental pedicle screw hook fixation is a useful alternative in the treatment of spondylolysis in adolescents but do not recommend this procedure in patients over age 20.

Altered mRNA expression of genes related to nerve cell activity in the fracture callus of older rats: A randomized, controlled, microarray study

Background

The time required for radiographic union following femoral fracture increases with age in both humans and rats for unknown reasons. Since abnormalities in fracture innervation will slow skeletal healing, we explored whether abnormal mRNA expression of genes related to nerve cell activity in the older rats was associated with the slowing of skeletal repair.

Methods

Simple, transverse, mid-shaft, femoral fractures with intramedullary rod fixation were induced in anaesthetized female Sprague-Dawley rats at 6, 26, and 52 weeks of age. At 0, 0.4, 1, 2, 4, and 6 weeks after fracture, a bony segment, one-third the length of the femur, centered on the fracture site, including the external callus, cortical bone, and marrow elements, was harvested. cRNA was prepared and hybridized to 54 Affymetrix U34A microarrays (3/age/time point).

Results

The mRNA levels of 62 genes related to neural function were affected by fracture. Of the total, 38 genes were altered by fracture to a similar extent at the three ages. In contrast, eight neural genes showed prolonged down-regulation in the older rats compared to the more rapid return to pre-fracture levels in younger rats. Seven genes were up-regulated by fracture more in the younger rats than in the older rats, while nine genes were up-regulated more in the older rats than in the younger.

Conclusions

mRNA of 24 nerve-related genes responded differently to fracture in older rats compared to young rats. This differential expression may reflect altered cell function at the fracture site that may be causally related to the slowing of fracture healing with age or may be an effect of the delayed healing.

Lumbar spine traction: evaluation of effects and recommended application for treatment

Despite the widespread use of traction, little is known of the mode of effect, and application remains largely anecdotal. The efficacy of traction is also unclear because of generally poor design of the clinical trials to date, and because subgroups of patients most likely to benefit have not been specifically studied. These observations prompted this review, the purposes of which are to evaluate the mechanisms by which traction may provide benefit and to provide rational guidelines for the clinical application of traction. Traction has been shown to separate the vertebrae and it appears that large forces are not required. Vertebral separation could provide relief from radicular symptoms by removing direct pressure or contact forces from sensitised neural tissue. Other mechanisms proposed to explain the effects of traction (e.g. reduction of disc protrusion or altered intradiscal pressure) have been shown not to occur. We conclude that traction is most likely to benefit patients with acute (less than 6 weeks' duration) radicular pain with concomitant neurological deficit. The apparent lack of a dose-response relationship suggests that low doses are probably sufficient to achieve benefit.

Neuropeptides and the puzzle of bone remodeling. State of the art

Bone metabolism is dependent on cells of the osteoblast and osteoclast lineage. These cells play a major role in the synthesis and degradation of osteoid and in its mineralization and demineralization. Bone cells are under the influence of various systemic and local auto/paracrine factors. One further regulatory element that can play both a sensory/ afferent and a regulatory/efferent role, consists of neuropeptide-containing nerves. In particular, the calcitonin gene-related peptide (CGRP) and vasoactive intestinal peptide (VIP) have been implicated; their distribution in bone and their molecular biology are discussed in some detail. Bone neuropeptides can function as direct bone cell regulators, with additional amplifying indirect effects mediated by vascular endothelial cells, monocyte/macrophages and mast cells and their mediators. Recent experimental and clinical work has implicated bone nerves in processes varying from normal remodelling to fracture healing and non-union. Apart from systemic endocrine influences on bone stock and osteoclast/ osteoblast coupling (activation-resorption-formation cycle) mediated by local auto/paracrine factors, bone nerves/neuropeptides may explain why various inputs/outputs are transformed in a meaningful way to altered mass and quality of bone.