Activation and localization of cartilage-derived morphogenetic protein-1 at the site of ossification of the ligamentum flavum

Thoracic ossification of the ligamentum flavum causing acute myelopathy in a patient with cervical ossification of the posterior longitudinal ligament: illustrative case

BACKGROUND

Ossification of the ligamentum flavum (OLF) has been well characterized as a distinct entity but also in tandem with ossification of the posterior longitudinal ligament (OPLL) in noncontiguous spinal regions. The majority of OLF cases are reported from East Asian countries where prevalent, but such cases are rarely reported in the North American population.

OBSERVATIONS

The authors present a case of a Thai-Cambodian American who presented with symptomatic thoracic OLF in tandem with asymptomatic cervical OPLL. A “floating” thoracic laminectomy, resection of OLF, and partial dural ossification (DO) resection with circumferential release of ossified dura were performed. Radiographic dural reexpansion and spinal cord decompression occurred despite the immediate intraoperative appearance of persistent thecal sac compression from retained DO.

LESSONS

Entire spinal axis imaging should be considered for patients with spinal ligamentous ossification disease, particularly in those of East Asian backgrounds. A floating laminectomy is one of several surgical approaches for OLF, but no consensus approach has been clearly established. High surgical complication rates are associated with thoracic OLF, most commonly dural tears/cerebrospinal fluid (CSF) leaks. DO commonly coexists with OLF, is recognizable on computed tomographic scans, and increases the risk of CSF leaks.

The role of vascularization on changes in ligamentum flavum mechanical properties and development of hypertrophy in patients with lumbar spinal stenosis

BACKGROUND CONTEXT

Ligamentum flavum (LF) induced lumbar spinal stenosis (LSS) is conditioned not only by its "gathering" but especially by hypertrophy. Previous studies have examined the pathophysiology and biochemical changes that cause the hypertrophy. Some studies have described a link between chronic LF inflammation and neovascularization but others have reported highly hypovascular LF tissue in LSS patients. Currently, there is no practical application for our knowledge of the pathophysiology of the LF hypertrophy. Considerations for future treatment include influencing this hypertrophy at the level of tissue mediators, which may slow the development of LSS. To our knowledge, there is no study of micromechanical properties of native LF to date.

PURPOSE

(1) To clarify the changes in vascularization, chondroid metaplasia, and the presence of inflammatory cell infiltration in LF associated with LSS. (2) To quantify changes in the micromechanical properties associated with LF degenerative processes.

STUDY DESIGN/SETTING

Vascular density analysis of degenerated and healthy human LF combined with measurement of micromechanical properties.

METHODS

The study involved 35 patients who underwent surgery between November 1, 2015 and October 1, 2016. The LSS group consisted of 20 patients and the control group consisted of 15 patients. LF samples were obtained during the operation and were used for histopathological and nanoindentation examinations. Sample vascularization was examined as microvascular density (L_v), which was morphometrically evaluated using semiautomatic detection in conjunction with NIS-Elements AR image analysis software. Samples were also histologically examined for the presence of chondroid metaplasia and inflammation. Mechanical properties of native LF samples were analyzed using the Hysitron TI 950 TriboIndenter nanomechanical testing system.

RESULTS

Vascular density was significantly lower in the LSS group. However, after excluding the effect of age, the difference was not significant. There was high association between L_v and age. With each increasing year of age, L_v decreased by 11.5 mm². Vascular density decreased up to the age of 50. Over the age of 50, changes were no longer significant and L_v appeared to stabilize. No correlation was observed between L_v and the presence of inflammation or metaplasia; however, LSS patients had a significantly increased incidence of chondroid metaplasia and inflammatory signs. The mechanical properties of control group samples showed significantly higher stiffness than those samples obtained from the LSS group.

CONCLUSION

This study showed that L_v changes were not dependent on LSS but were age-dependent. Vascular density was found to decrease up to the age of 50. A significantly higher incidence of chondroid metaplasia and inflammation was observed in LSS patients. The mechanical property values measured by nanoindentation showed high microstructural heterogeneity of the tested ligaments. Our results showed that healthy ligaments were significantly stiffer than LSS ligaments.

CLINICAL SIGNIFICANCE

Prevention of the loss of LF vascularization during aging may influence stiffness of LF which in turn may slow down the LF degenerative processes and delay onset of LSS.

Transforaminal en bloc resection for the treatment of thoracic ossification of the ligamentum flavum: Retrospective cohort study

BACKGROUND

Our purpose is to introduce transforaminal en bloc resection for the treatment of thoracic ossification of ligamentum flavum, and report outcomes of the procedure.

PATIENTS AND METHODS

The record of patients with symptomatic thoracic ossification of the ligamentum flavum who received transforaminal en block resection from October 2010 to September 2014 were retrospectively reviewed. Outcomes were Japanese Orthopaedic Association (JOA) lower extremity motor dysfunction and sphincter dysfunction scores.

RESULTS

Seventeen patients (10 males, 7 females) with a median age of 60 years were included in the analysis. Surgery was performed as planned without complications in all patients. One segment decompression was performed in 1 case, 2 segment in 9 cases, 3 segment in 3 cases, and 4 segment in 4 cases. The median lower extremity motor dysfunction score was significantly higher at 2 weeks, 3 months, and 6 months postoperatively, and the end of follow-up, than before surgery (median score: 2, 2, 3, 3, respective, vs. 1, all, p ≤ 0.008). There were no significant differences in JOA sphincter dysfunction score between the different time points.

CONCLUSION

Transforaminal en bloc resection is a safe and effective method for the treatment of thoracic ossification of the ligamentum flavum.

Ossification of the ligamentum flavum

Ossification of the ligamentum flavum (OLF or OYL: ossification of the yellow ligament) usually occurs at the lower thoracic level and causes various types of neurological symptoms in accordance with the compression level of the spinal cord, the nerve roots, the conus medullaris, and the cauda equina. Although the greatest compression level to the nerve tissues is thought to be the most pathognomonic one, it is difficult to diagnose it in some cases. The effectiveness of conservative treatment such as applying a corset is small. Early surgical treatment is strongly recommended for the patients with spastic gait, severe decrease of muscle power in the lower extremities, bladder-bowel disturbance, combined ossification of the posterior longitudinal ligament at the same level, and severe compression to the spinal cord due to thickly hypertrophied ossification. However, numbness of the lower extremities and spastic gait tend to remain even after surgery.

Recombinant human bone morphogenetic protein-2-induced ossification of the ligamentum flavum in rats and the associated global modification of histone H3

OBJECT

The primary object of this investigation was to study recombinant human bone morphogenetic protein-2 (rhBMP-2)-induced ossification of the ligamentum flavum and associated histone H3 modification in a rat model. In an additional set of studies the authors investigated spinal cord and behavioral changes in the same model.

METHODS

The authors report on 2 separate sets of studies. A total of 90 rats were used for the 2 sets of studies (45 each); in each study, a lyophilized rhBMP-2 and collagen mixture (20 μg rhBMP-2 and 200 μl collagen) was implanted in the lumbar extradural space in 18 rats; another 18 animals were used for a sham-operation control group and underwent implantation of lyophilized collagen without rhBMP-2 at the same level; an additional 9 animals were used as untreated controls. Lumbar spinal samples were harvested from the rhBMP-2 groups and the shamoperation control groups at 1 week, 3 weeks, and 9 weeks after the operation. Samples were also obtained from untreated controls at the same time points. All samples were scanned using micro-CT and then made into paraffinembedded sections. The sections from the first set of 45 rats were stained using elastica van Gieson and toluidine blue, and the expression of histone modifications (H3K9ac, H3K18ac, H3K4me3, and H3K36me3) and osteogenic transcription factors (osterix, Runx2) was detected by immunohistochemistry. In the second set of studies, hindlimb motor function was assessed at 1 week, 3 weeks, and 9 weeks after surgery. After behavioral evaluation, samples were harvested, scanned using micro-CT, and then made into paraffin-embedded sections. The sections were stained using Luxol fast blue. The expression of NeuN was also detected using immunohistochemistry.

RESULTS

Ossification was seen in the rhBMP-2 group from 1 week after insertion, and the volume of ossified mass increased at 3 and 9 weeks. There was no ossification seen in the sham-surgery and normal controls. The pathological changes of ossification involved ligament degeneration, cartilage formation, and, finally, bone replacement. Spinal cord evaluation showed a significant decrease in white matter content and number of neurons at 9 weeks after operation in the rhBMP-2-treated group (compared with findings in the sham-surgery and control groups as well as findings at the earlier time points in the rhBMP-2 group). Using immunohistochemical staining, histone modifications (H3K9ac, H3K18ac, H3K4me3, and H3K36me3) and osteogenic transcription factors (osterix, Runx2) all were found to be expressed in the fibrocartilage area of the rat ossified ligamentum flavum samples (rhBMP2 group).

CONCLUSIONS

This rhBMP-2-induced OLF is a typical endochondral ossification, which is similar to clinical OLF. The compressed spinal cord around the ossification site showed signs of a chronic degenerative process. Histone H3 modifications (H3K9ac, H3K18ac, H3K4me3, and H3K36me3) may play an important role in OLF.

Dural ossification in ossification of the ligamentum flavum: a preliminary report

STUDY DESIGN

A retrospective review.

OBJECTIVE

The aim of this study is to highlight one of the under recognized and under reported aspects of ossification of the ligamentum flavum (OLF), namely, dural ossification in OLF and to discuss the incidence, radiologic signs, causes as well as the surgical and prognostic implications of dural ossification in OLF.

SUMMARY OF BACKGROUND DATA

OLF is being increasingly recognized as a cause of myelopathy. One of the surgical pitfalls in the management of this condition is ossification of the dura mater in OLF. Preoperative identification of ossified dura mater will be helpful to the surgeon to modify the surgical technique and to counsel patients regarding the risks of surgery.

METHODS

A retrospective analysis of a database of OLF maintained by this author was done to identify cases of OLF where there was intraoperative evidence of dural ossification and dural laceration. Only those patients who had both computed tomography (CT) and magnetic resonance imaging (MRI) were included in the analysis. Patients with MR imaging alone were excluded from the analysis as CT evaluation was not done routinely in the earlier part of the study. Nurick's grading was used to assess the neurologic status before and after surgery. The CT and MR images of these patients were analyzed to identify radiologic signs of dural ossification. The pattern of dural ossification, if present, was noted. The intraoperative and postoperative complications were recorded.

RESULTS

During the study period from 1997 to 2006, there were 20 patients with OLF who had both CT and MR imaging evaluation. Of these 20 patients, 8 had intraoperative evidence of dural ossification and these patients also sustained dural laceration during surgery. Of these 8 patients, CT evidence of dural ossification was found in 7. In the remaining one patient, there was no radiologic evidence of dural ossification. The radiologic signs of dural ossification as depicted in the bone windows of CT were of 2 types: (1) the "tram track sign," where there was a hyperdense bony excrescence with a hypodense center and (2) the "comma sign," where there was evidence of ossification of one-half of the circumference of the duramater. Of these 7 patients, 4 developed cerebrospinal fluid (CSF) leak following surgery and 1 of these 4 patients developed meningitis. Neurologic function improved by one Nurick's grade in 5 of the 7 patients. In the remaining 2 patients, there was no change in the neurologic status.

CONCLUSION

Dural ossification is a common finding in OLF. There are 2 radiologic signs of dural ossification, namely, the "tram track sign" and the "comma sign." Preoperative identification of dural ossification might help the surgeon to anticipate and appropriately deal with dural laceration during surgery. This will also help to counsel patients regarding the risks of surgery for OLF. The surgical and prognostic implications of dural ossification are being discussed.

Bone morphogenetic protein-7 regulates differentially the mRNA expression of bone morphogenetic proteins and their receptors in rat achilles and patellar tendon cell cultures

Previous animal studies have suggested that certain bone morphogenetic proteins (BMPs) may be useful therapeutically in treating tendon healing. To better understand the relationship among the different BMPs in the healing process, we initiated the present study to examine the effects of a member of the BMP family, BMP-7 (also called Osteogenic Protein-1) on the temporal and spatial expression patterns of other BMPs and the BMP receptors in cell cultures of adult rat Achilles and Patellar tendons. Cultures from both tendon types expressed detectable but variable levels of biochemical markers characteristics of tendons. RNAs coding for type II collagen and transcription factors Six1, Scleraxis, and Tendin were detected in both types of cultures. Distinct patterns of expression of several BMP members and their receptors were observed in these cultured cells and BMP-7 exerted differential effects on their expression. The findings may have implications in the treatment of different tendon injuries with BMPs.

Hormones and growth factors in the pathogenesis of spinal ligament ossification

Ossification of the spinal ligaments (OSL) is a pathologic condition that causes ectopic bone formation and subsequently results in various degrees of neurological deficit, but the etiology of OSL remains almost unknown. Some systemic hormones, such as 1,25-dihydroxyvitamin D, parathyroid hormone (PTH), insulin and leptin, and local growth factors, such as transforming growth factor-beta (TGF-beta), and bone morphogenetic protein (BMP), have been studied and are thought to be involved in the initiation and development of OSL. This review article summarizes these studies, delineates the possible mechanisms, and puts forward doubts and new questions. The related findings from studies of genes and target cells in the ligament of OSL are also discussed. Although these findings may be helpful in understanding the pathogenesis of OSL, much more research needs to be conducted in order to investigate the nature of OSL.

Ossification of the Posterior Longitudinal Ligament: An Update on Its Biology, Epidemiology, and Natural History

SIGNIFICANT PROGRESS HAS been achieved in basic research during the past decade on the pathogenesis of ossification of the posterior longitudinal ligament (OPLL), a multifactorial disease in which complex genetic and environmental factors interact. A review of the literature was conducted to update recent findings on the biology, epidemiology, natural history, and related diseases of OPLL. Gene analysis studies found specific polymorphisms that may be associated with OPLL in several collagen genes, which encode for extracellular matrix proteins. Polymorphisms in the nucleotide pyrophosphate gene, which is involved in regulation of calcification in chondrocytes, may also be associated with OPLL. However, the results of the gene analysis studies have not always been consistent. Involvement of many growth factors and cytokines, including bone morphogenic proteins and transforming growth factor-β, has been demonstrated in various histochemical and cytochemical analyses. Several transcription factors involved in cellular differentiation may also have a role. Recent epidemiological studies reaffirmed an earlier finding that diabetes mellitus is a distinct risk factor for OPLL. The long-term follow-up studies of OPLL patients are disclosing the natural history, as well as the frequency and rate of progression, of OPLL after surgical intervention. Further knowledge on the factors responsible for progression of OPLL may predict its behavior in each patient, and treatment may be tailored accordingly. The coexistence of OPLL with other diseases of ectopic ossification of the spine, such as ossification of the ligamentum flavum and diffuse idiopathic skeletal hyperostosis, is not uncommon. Scientific breakthrough in those diseases may, in turn, give insights into the pathogenesis of OPLL.

Stimulatory effects of distinct members of the bone morphogenetic protein family on ligament fibroblasts

OBJECTIVE

To investigate effects of cartilage derived morphogenetic protein-1 and -2 (CDMP-1, CDMP-2), bone morphogenetic protein (BMP)-7 and BMP-6 on metabolism of ligament fibroblasts and their osteogenic or chondrogenic differentiation potential.

METHODS

Ligament fibroblasts were obtained from 3 month old calves, plated as monolayers or micromass cultures, and incubated with or without CDMP-1, CDMP-2, BMP-7, and BMP-6. Expression of the indicated growth factors was assessed by RT-PCR and western immunoblotting. The presence of their respective type I and II receptors, and lineage related markers, was investigated in stimulated and unstimulated cells by RT-PCR and northern blotting. Biosynthesis of matrix proteoglycans was assessed by [(35)S]sulphate incorporation in monolayers. Alcian blue and toluidine blue staining was done in micromass cultures.

RESULTS

CDMP-1, CDMP-2, BMP-7, and BMP-6 were detected on mRNA and on the protein level. Type I and II receptors were endogenously expressed in unstimulated ligament fibroblasts. The growth factors significantly stimulated total proteoglycan synthesis as assessed by [(35)S]sulphate incorporation. Toluidine blue staining showed cartilage-specific metachromasia in the growth factor treated micromass cultures. Transcription analysis of stimulated ligament fibroblasts demonstrated coexpression of chondrocyte markers but no up regulation of osteogenic markers.

CONCLUSION

CDMP-1, CDMP-2, BMP-7, and BMP-6 and their receptors were expressed in ligament tissue. These growth factors induced matrix synthesis in fibroblasts derived from bovine ligament. The preferential expression of cartilage markers in vitro suggests that CDMP-1, CDMP-2, BMP-7, and BMP-6 have the potential to induce differentiation towards a chondrogenic phenotype in ligament fibroblasts. Thus, fibroblasts from ligaments may serve as a source for chondrogenesis and tissue repair.

Acute quadriparesis caused by calcification of the entire cervical ligamentum flavum in a white female--report of an unusual case and a brief review of the literature: case report

STUDY DESIGN

Case report.

OBJECTIVES

To describe an extremely unusual case of acute quadriparesis in a white female caused by calcification of the ligamentum flavum (LF) from C1 to T2, and to review briefly the pertinent literature.

SUMMARY OF BACKGROUND DATA

Diseases characterized by abnormal calcium deposition on the spinal ligaments have an unclear etiology. The overwhelming majority of these cases has been reported in people of Asian descent and has a predilection for the thoracic spine. Multilevel involvement of the cervical LF in white patients is exceptionally rare. To our knowledge, complete calcification of the entire cervical LF has not been previously reported in the literature.

METHODS

The history, physical examination, and radiographic studies of a 64-year-old white female with a history of scleroderma are described. The patient presented with neck pain and acute quadriparesis caused by spinal cord impingement by calcified cervical LF from C1 to T2. The patient underwent emergent C3-C7 laminectomy and C2-C7 posterior spinal fusion.

RESULTS

Operative intervention resulted in marked neurologic improvement and relief from neck pain. Histopathologic examination of the calcified LF showed that the deposits consisted of hydroxyapatite crystals exclusively with no heterotopic bone. However, kyphosis did develop in the patient after laminectomy.

CONCLUSION

To our knowledge, this unusual case of complete calcification of the entire cervical LF has not previously been described. Multilevel laminectomy and fusion can improve neurologic function but may result in kyphosis.

Evaluation of HealosMP52 osteoinductive bone graft for instrumented lumbar intertransverse process fusion in sheep

STUDY DESIGN

HealosMP52 was evaluated in a sheep model of instrumented lumbar intertransverse process spine fusion and compared to autogenous bone graft.

OBJECTIVES

To determine the long-term efficacy and safety of HealosMP52 as a bone graft substitute in posterolateral instrumented spinal fusion.

SUMMARY OF BACKGROUND DATA

Although the standard intertransverse fusion method employs autogenous iliac crest bone, autograft has certain limitations. HealosMP52, an osteoinductive bone graft material, can facilitate noninstrumented posterolateral spine fusion in rabbits and nonhuman primates, but the long-term outcome of such fusions has not been evaluated.

METHODS

Eleven skeletally mature, female sheep were instrumented with pedicle screws and rods at L2-L3 and L5-L6. Each animal was treated with autograft bone at one fusion level and HealosMP52 at the other. At 6 and 12 months after surgery, bone formation was measured on contact microradiographs and by backscattered electron imaging. Bone core biopsies taken from 6-month and 12-month specimens were evaluated histologically for pathology indicative of osteosarcoma.

RESULTS

Grossly, all autograft- and HealosMP52-treated levels showed stable fusions at 6 and 12 months. HealosMP52 and autograft treatments resulted in equivalent mean percent bone volumes within fusion bodies; similar values were observed at 6 and 12 months. Fusion bodies contained cortical and trabecular bone with osteoid seams and fatty marrow, and fusion masses showed maturation from 6 to 12 months. HealosMP52 treatment was not associated with implant migration, ectopic bone formation, or pathologic abnormality. No histologic evidence of osteosarcoma was seen on bone core biopsies.

CONCLUSIONS

This long-term assessment of the use of HealosMP52 in posterolateral instrumented spine fusion indicates that HealosMP52 possesses safe and efficacious bone grafting properties and can potentially serve as anosteoinductive alternative to autograft bone.

A comparative dose-response study of cartilage-derived morphogenetic protein (CDMP)-1, -2 and -3 for tendon healing in rats

Cartilage-derived morphogenetic proteins (CDMPs), belonging to the bone morphogenetic protein (BMP) family, are known to be cartilage and bone inducers as well as to induce tendon and ligament-like tissue. In this study we investigated the influence of CDMP-1, -2 or -3 at four different doses (0, 0.4, 2 and 10 microg) on tendon healing in a rat model, as well as differences in osteogenesis between the different CDMPs and doses.In 110 rats, a 3 mm segment of the Achilles tendon was removed via a 2 mm skin incision. CDMP-1, -2 or -3 was injected into the defect 6 h postoperative. The rats were killed 8 days after operation. The tendon regenerates were tested biomechanically. There was a significant dose-related increase in strength and stiffness with all three CDMPs, but no difference between the CDMPs was found. Another 50 rats were used to compare the highest dose of the CDMPs with controls and osteogenic protein 1 (OP-1), as regards cartilage or bone formation after 4 weeks. Cartilage occurred in all groups, including the controls. Some specimens in all groups contained bone, except the controls. No difference between the CDMPs could be demonstrated. The CDMP-1, CDMP-3 and OP-1 groups contained significantly more calcium than controls. Only the CDMP-2 group and the controls contained significantly less calcium than the OP-1 group.In conclusion, the three CDMPs appeared similar as regards improvement of tendon repair and osteogenicity in this setting.

Tumoral calcium pyrophosphate dihydrate deposition disease of the ligamentum flavum

OBJECTIVE

Calcium pyrophosphate dihydrate (CPPD) deposition disease (CPPDD), also known as pseudogout, is rarely known to affect the spine. The purpose of this article is to report our experience with six cases involving massive focal deposition of CPPD crystals in the ligamentum flavum.

METHODS

Between January 1998 and June 2002, we treated six patients with CPPDD involving the ligamentum flavum of the cervical and thoracic spine. Their ages ranged from 45 to 70 years. There were five female patients and one male patient. The cervical spine was involved in two cases and the thoracic spine in four. All except one patient presented with an insidious onset of myelopathy. The remaining patient presented with paraplegia after trauma. None of the patients exhibited any systemic features of CPPDD or other metabolic conditions that can lead to CPPD deposition. Plain x-rays often yielded inconclusive results. Computed tomography and magnetic resonance imaging were useful in confirming the diagnoses. Decompressive laminectomy, with removal of the ossified ligamenta flava, was performed for all patients. Polarized-light microscopic examinations of the excised ligamenta flava revealed the characteristic rod-shaped, birefringent crystals.

RESULTS

Five of the six patients experienced significant improvements in their myelopathic symptoms after surgery. The remaining patient experienced improvements in sensations but no appreciable improvement in motor power. During the follow-up periods, which ranged from 7 months to 3 years, none of the patients presented with a recurrence of CPPD crystal deposition at the previously treated level. However, one patient who exhibited improvement after surgery presented 2 years later with a recurrence of myelopathic features attributable to ossification of the ligamentum flavum at a new level.

CONCLUSION

Tumoral CPPDD of the ligamentum flavum is rare. It commonly occurs among middle-age or elderly female patients and presents with progressive myelopathy. Computed tomography and magnetic resonance imaging are complementary in the diagnosis of this condition. Surgery, if performed early, leads to good improvement. However, long-term follow-up monitoring of these patients is necessary, because surgery provides only symptomatic relief and does not treat the underlying disease. With the increasing availability of magnetic resonance imaging, ossification of the ligamentum flavum is being more frequently recognized. In every case of ossified ligamentum flavum, the excised specimen should be examined with polarized-light microscopy. We think that this simple, inexpensive method will lead to the recognition of more cases of spinal CPPDD.