Transplantation of activated nucleus pulposus cells after cryopreservation: efficacy study in a canine disc degeneration model.

Transplantation of activated nucleus pulposus (NP) cells obtained by coculturing NP cells and bone marrow mesenchymal stromal cells having cell-to-cell contact has been shown to be effective in animal models and, more recently, in human clinical trials. If the NP cells can be cryopreserved, then autologous cell transplantation could be offered to patients as and when required. In a previous study, we confirmed that activated NP cells can be obtained by coculturing with mesenchymal cells after cryopreservation. However, the in vivo effects of cell transplantation therapy using activated NP cells prepared from cryopreserved cells are not known. In this in vivo canine model, we compared indicators of disc degeneration in animals that received transplanted activated normal NP cells, transplanted cryopreserved NP cells, and no cell transplantation after induction of disc degeneration. The intervertebral disc height on radiographs and T2-weighted magnetic resonance imaging were significantly higher in both cell transplantation groups compared with the degenerated disc group. Macroscopic and histological findings demonstrated attenuated disc degeneration in the two transplanted groups. Intense staining of proteoglycan and collagen type II was seen in green fluorescent protein-labelled transplanted cells, which suggested that the cells had survived and were functioning after transplantation. No significant differences were observed between the two transplanted groups. Transplanted activated cryopreserved NP cells induced a similar attenuation of intervertebral disc degeneration as that of conventionally activated NP cells. These findings suggest that the use of cryopreserved cells specific to a patient's condition has potential in transplantation therapy.

3D ultrasound biomicroscopy for assessment of cartilage repair tissue: volumetric characterisation and correlation to established classification systems.

Objective and sensitive assessment of cartilage repair outcomes lacks suitable methods. This study investigated the feasibility of 3D ultrasound biomicroscopy (UBM) to quantify cartilage repair outcomes volumetrically and their correlation with established classification systems. 32 sheep underwent bilateral treatment of a focal cartilage defect. One or two years post-operatively the repair outcomes were assessed and scored macroscopically (Outerbridge, ICRS-CRA), by magnetic resonance imaging (MRI, MOCART), and histopathology (O'Driscoll, ICRS-I and ICRS-II). The UBM data were acquired after MRI and used to reconstruct the shape of the initial cartilage layer, enabling the estimation of the initial cartilage thickness and defect volume as well as volumetric parameters for defect filling, repair tissue, bone loss and bone overgrowth. The quantification of the repair outcomes revealed high variations in the initial thickness of the cartilage layer, indicating the need for cartilage thickness estimation before creating a defect. Furthermore, highly significant correlations were found for the defect filling estimated from UBM to the established classification systems. 3D visualisation of the repair regions showed highly variable morphology within single samples. This raises the question as to whether macroscopic, MRI and histopathological scoring provide sufficient reliability. The biases of the individual methods will be discussed within this context. UBM was shown to be a feasible tool to evaluate cartilage repair outcomes, whereby the most important objective parameter is the defect filling. Translation of UBM into arthroscopic or transcutaneous ultrasound examinations would allow non-destructive and objective follow-up of individual patients and better comparison between the results of clinical trials.

Intervertebral disc repair with activated nucleus pulposus cell transplantation: a three-year, prospective clinical study of its safety.

Degeneration of the lumbar intervertebral discs is irreversible, with no treatment currently available. Building upon experimental studies that demonstrated the importance of the nucleus pulposus (NP) in preserving disc structure, we demonstrated that reinsertion of NP cells slowed further disc degeneration and that direct cell-to-cell contact co-culture with mesenchymal stromal cells (MSCs) significantly upregulated the viability of NP cells in basic and pre-clinical studies in vitro and in vivo using animal models and human cells. Here, we report a 3-year result of a prospective clinical study, aimed to assess the safety and efficacy of activated NP cell transplantation in the degenerate lumbar intervertebral disc. Candidates were 9 patients aged 20-29 years who had Pfirrmann's grade III disc degeneration at the level adjacent to the level scheduled for posterior lumbar intervertebral fusion. Viable NP cells from the fused disc were co-cultured in direct contact with autologous bone marrow-derived MSCs. One million activated NP cells were transplanted into the degenerated disc adjacent to the fused level at 7 d after the first fusion surgery. No adverse effects were observed during the 3-year follow-up period. Magnetic resonance imaging did not show any detrimental effects to the transplanted discs and revealed a mild improvement in 1 case. No cases reported any low back pain. Our clinical study confirmed the safety of activated NP cell transplantation, and the findings suggest the minimal efficacy of this treatment to slow the further degeneration of human intervertebral discs.

CCL5/RANTES is a key chemoattractant released by degenerative intervertebral discs in organ culture.

Release of chemotactic factors in response to tissue damage has been described for different musculoskeletal tissues, including the intervertebral disc (IVD). This study investigated the chemoattractants that are released by induced degenerative IVDs and may be involved in recruiting mesenchymal stem cells (MSCs). Bovine caudal discs were cultured within a bioreactor and loaded under conditions that mimicked physiological or degenerative settings. Between days 4-6, medium was replaced by PBS, which was subsequently used for proteomic, ELISA and immunoprecipitation analyses of secreted chemokines and cytokines. A Boyden chamber assay was used to observe human MSC migration towards native and chemokine depleted media. Gene expression levels of chemokine receptors in human MSCs were analysed, and CCL5 was localised in bovine and human IVD by immunohistochemistry. Proteomic analysis revealed the presence of CCL5 and CXCL6 within conditioned media. Higher concentrations of CCL5 were found in the degenerative media, and a relationship was found between interleukin-1ß and CCL5 concentration. Chemokine immunoprecipitation showed that MSCs had a significantly reduced chemotactic migration towards CCL5-immunoprecipitated and CCL5/CXCL6 co-immunoprecipitated media, whilst CXCL6 depletion did not change MSC chemotaxis. MSCs showed a significant increase in mRNA expression of the CCL5 receptors, CCR1 and CCR4, upon culture in degenerative media. Furthermore, CCL5 was identified in bovine and human disc tissue by immunohistochemistry. Hence, CCL5 may be a key chemoattractant that is produced and released by the intervertebral disc cells. Therefore, these factors could be used to enhance stem/progenitor cell mobilisation in regenerative therapies for early stages of disc degeneration.

Endoplasmic reticulum stress response in the rat contusive spinal cord injury model-susceptibility in specific cell types.

STUDY DESIGN: Focus group study. OBJECTIVE: To investigate cell-specific endoplasmic reticulum (ER) stress reactions in contusive spinal cord by evaluating the expression of the glucose-regulated protein 78 (GRP78) and C/EBP homologous transcription factor protein (CHOP) using immunohistochemical staining. SETTING: Data were analysed at Tokai University School of Medicine in Japan. METHODS: The authors generated rat spinal cord injury (SCI) models using an IH-Impactor (100 kdyne(LI), 200 kdyne (HI)). Rats were killed at 1, 3, 5, 7 and 14 days post operation (dpo). Spinal cord sections were prepared and the expression ratio of GRP78 and CHOP was evaluated in oligodendrocyte precursor cells (OPCs) (NG2+), oligodendrocytes (OLs) (APC+), neurons (NeuN+) and astrocytes (GFAP+) using double immunohistochemical staining. We examined an area 8 mm distal from SCI-epicenter. RESULTS: Compared with the sham group, both injured groups had higher GRP78 expression ratio in contused spinal cord at 1 dpo. GRP78 expression ratio was highest in GFAP+ cells of both groups, and lowest in NG2+ cells. Although GRP78 was expressed strongly immediately after SCI in the both groups, increased CHOP expression was observed only in the HI group. The CHOP expression in NG2+ cells was significantly higher than that observed in GFAP+ cells at 5 dpo. CONCLUSION: Although the ER stress response contributes to cell survival in the low-stress SCI conditions, the ER stress response induces an apoptotic cascade in high-stress SCI conditions. The ER response varies according to cell type, with the highest observed in astrocytes, and the lowest observed in oligodendrocyte precursor cells.

Transplantatation of scaffold-free spheroids composed of synovium-derived cells and chondrocytes for the treatment of cartilage defects of the knee.

Autologous chondrocyte implantation (ACI) is the treatment of choice for osteoarthritis. However, to regenerate articular cartilage using this method, the procedure paradoxically demands that the cell source of the articular chondrocytes (ACs) for ex vivo expansion be from the patient's own healthy cartilage, which can result in donor site morbidity. Accordingly, it is essential to develop a substitute for AC. In the present study, we investigated whether synovium-derived cells (SYs) could be used as a partial replacement for ACs in ACI. ACs and SYs from the knees of rabbits were isolated and cultured, and the growth rates of the cells were compared. To manufacture the cellular transplants, we developed a high-density suspension-shaking culture method (HDSS), which circulates the cells in culture media, promoting self-assembly of scaffold-free cellular aggregates. ACs and SYs were mixed in various ratios using HDSS. Injectable cellular transplants were harvested and transplanted into full-thickness osteochondral defects. Simultaneously, histological evaluations were conducted with toluidine blue and safranin O, and immunohistochemistry of collagen type I and II was conducted. Gene expression to evaluate chondrocyte-specific differentiation was also performed. We successfully prepared a large quantity of spheroids (spheroidal cell aggregates) in a short time using mixed ACs and SYs, for all cellular composition ratios. Our data showed that the minimal therapeutic unit for the transplants contributed to in situ regeneration of cartilage. In summary, SYs can be used as a replacement for ACs in clinical cases of ACI in patients with broad areas of osteoarthritic lesions.

Variations in gene and protein expression in human nucleus pulposus in comparison with annulus fibrosus and cartilage cells: potential associations with aging and degeneration.

OBJECTIVE: Regardless of recent progress in the elucidation of intervertebral disc (IVD) degeneration, the basic molecular characteristics that define a healthy human IVD are largely unknown. Although work in different animal species revealed distinct molecules that might be used as characteristic markers for IVD or specifically nucleus pulposus (NP) cells, the validity of these markers for characterization of human IVD cells remains unknown. DESIGN: Eleven potential marker molecules were characterized with respect to their occurrence in human IVD cells. Gene expression levels of NP were compared with annulus fibrosus (AF) and articular cartilage (AC) cells, and potential correlations with aging were assessed. RESULTS: Higher mRNA levels of cytokeratin-19 (KRT19) and of neural cell adhesion molecule-1 were noted in NP compared to AF and AC cells. Compared to NP cytokeratin-18 expression was lower in AC, and alpha-2-macroglobulin and desmocollin-2 lower in AF. Cartilage oligomeric matrix protein (COMP) and glypican-3 expression was higher in AF, while COMP, matrix gla protein (MGP) and pleiotrophin expression was higher in AC cells. Furthermore, an age-related decrease in KRT19 and increase in MGP expression were observed in NP cells. The age-dependent expression pattern of KRT19 was confirmed by immunohistochemistry, showing the most prominent KRT19 immunoreaction in the notochordal-like cells in juvenile NP, whereas MGP immunoreactivity was not restricted to NP cells and was found in all age groups. CONCLUSIONS: The gene expression of KRT19 has the potential to characterize human NP cells, whereas MGP cannot serve as a characteristic marker. KRT19 protein expression was only detected in NP cells of donors younger than 54 years.

Low-intensity pulsed ultrasound stimulates cell proliferation, proteoglycan synthesis and expression of growth factor-related genes in human nucleus pulposus cell line.

Low-intensity pulsed ultrasound (LIPUS) stimulation has been shown to effect differentiation and activation of human chondrocytes. A study involving stimulation of rabbit disc cells with LIPUS revealed upregulation of cell proliferation and proteoglycan (PG) synthesis. However, the effect of LIPUS on human nucleus pulposus cells has not been investigated. In the present study, therefore, we investigated whether LIPUS stimulation of a human nucleus pulposus cell line (HNPSV-1) exerted a positive effect on cellular activity. HNPSV-1 cells were encapsulated in 1.2% sodium alginate solution at 1x10(5) cells/ml and cultured at 10 beads/well in 6-well plates. The cells were stimulated for 20 min each day using a LIPUS generator, and the effects of LIPUS were evaluated by measuring DNA and PG synthesis. Furthermore, mRNA expression was analyzed by cDNA microarray using total RNA extracted from the cultured cells. Our study revealed no significant difference in cell proliferation between the control and the ultrasound treated groups. However, PG production was significantly upregulated in HNPSV cells stimulated at intensities of 15, 30, 60, and 120 mW/cm(2) compared with the control. The results of cDNA array showed that LIPUS significantly stimulated the gene expression of growth factors and their receptors (BMP2, FGF7, TGFbetaR1 EGFRF1, VEGF). These findings suggest that LIPUS stimulation upregulates PG production in human nucleus pulposus cells by the enhancement of several matrix-related genes including growth factor-related genes. Safe and non-invasive stimulation using LIPUS may be a useful treatment for delaying the progression of disc degeneration.

Cross talk between Smad transcription factors and TNF-alpha in intervertebral disc degeneration.

The transforming growth factor-beta (TGF-beta) and the tumor necrosis factor-alpha (TNF-alpha) families are known to play important roles in intervertebral disc degeneration (IVD). However, molecular interactions between the TGF-beta and TNF-alpha signaling pathways have yet to be elucidated. The purpose of this study was to analyze the expression patterns of Smad transcription factor signaling associated with IVDs with aging and to examine the modulation of Smad signaling by TNF-alpha in IVD cells using SD rats. According to these experimental results, BMP signals in the TGF-beta family were more likely to be a key factor in IVD degeneration by aging, and it was predicted that besides the involvement of catabolic factors like MMPs and ADAMS-TS, there may be a decrease in expression of anabolic factors through cross talk of signaling between TNF-alpha and TGF-beta pathway in pathogenesis of disc degeneration.

Stem cell applications in intervertebral disc repair.

There is increasing rise of interest in stem cell therapy, as it provides new options for treating a broad range of diseases. Several experimental methods are being explored for the use of stem cells in delaying or reversing the degenerative process of the intervertebral disc, a major cause of low back pain. In this article, we review the current strategies for stem cell applications in intervertebral disc repair and present three novel approaches. These are, first, the activation of nucleus pulposus cells by co-culture with mesenchymal stem cells for autologous disc cell reinsertion; second, the in vitro induction of nucleus pulposus-like or annulus fibrosus-like cells from mesenchymal stem cells; and third, the in vivo induction study by direct transplantation of mesenchymal stem cells to the intervertebral disc induced to degenerate experimentally. Although still untested, stem cell therapy may become a major option in the treatment of intervertebral disc degeneration.

Cultured articular chondrocytes sheets for partial thickness cartilage defects utilizing temperature-responsive culture dishes.

The extracellular matrix (ECM) of articular cartilage has several functions that are unique to joints. Although a technique for transplanting cultured chondrocytes has already been introduced, it is difficult to collect intact ECM when using enzymes to harvest samples. Temperature-responsive culture dishes have already been clinically applied in the fields of myocardial and corneal transplantation. Earlier studies have shown that a sheet of cultured cells with intact ECM and adhesive factors can be harvested using such culture dishes, which allow the surface properties of the dish to be reversibly altered by changing the temperature. Human chondrocytes were subjected to enzymatic digestion and then were seeded in temperature-responsive culture dishes. A sheet of chondrocytes was harvested by only reducing the temperature after the cultured cells reached confluency. A real-time PCR analysis of the chondrocyte sheets confirmed that type II collagen, aggrecan, and fibronectin were present. These results suggested that, although chondrocytes undergo dedifferentiation in a monolayer culture, multilayer chondrocyte sheets grown in a similar environment to that of three-dimensional culture may be able to maintain a normal phenotype. A histological examination suggested that multilayer chondrocyte sheets could thus prevent the loss of proteoglycans because the area covered by the sheets was well stained by safranin-O. The present experiments suggested that temperature-responsive culture dishes are useful for obtaining cultured chondrocytes, which may then be clinically employed as a substitute for periosteal patches because such sheets can be applied without a scaffold.

Studies of the humoral factors produced by layered chondrocyte sheets.

The authors aimed to repair and regenerate articular cartilage with layered chondrocyte sheets, produced using temperature-responsive culture dishes. The purpose of this study was to investigate the humoral factors produced by layered chondrocyte sheets. Articular chondrocytes and synovial cells were harvested during total knee arthroplasty. After co-culture, the samples were divided into three groups: a monolayer, 7 day culture sheet group (group M); a triple-layered, 7 day culture sheet group (group L); and a monolayer culture group with a cell count identical to that of group L (group C). The secretion of collagen type 1 (COL1), collagen type 2 (COL2), matrix metalloproteinase-13 (MMP13), transforming growth factor-ß (TGFß), melanoma inhibitory activity (MIA) and prostaglandin E2 (PGE2) were measured by enzyme-linked immunosorbent assay (ELISA). Layered chondrocyte sheets produced the most humoral factors. PGE2 expression declined over time in group C but was significantly higher in groups M and L. TGFß expression was low in group C but was significantly higher in groups M and L (p<0.05). Our results suggest that the humoral factors produced by layered chondrocyte sheets may contribute to cartilaginous tissue repair and regeneration.

Reinsertion of stimulated nucleus pulposus cells retards intervertebral disc degeneration: an in vitro and in vivo experimental study.

Reinsertion of autogenous nucleus pulposus, an innovative method to delay further disc degeneration, has been proved with an experimental animal model. This study examined whether coculture of nucleus pulposus cells with annulus fibrosus cells (a) activates annulus fibrosus cells and (b) retards disc degeneration when reinserted into the disc in a rabbit model of disc degeneration. Coculture of the two cell types stimulated proliferation of each, as indicated by increased DNA synthesis measured by increases in DNA polymerase alpha expression and uptake of 5-bromo-2'deoxy-uridine assessed by an enzyme-linked immunosorbent assay. In a model of disc degeneration in rabbits, reinsertion of activated nucleus pulposus cells delayed the formation of clusters of chondrocyte-like cells, the destruction of disc architecture, and the elaboration of type-II collagen as measured immunohistochemically compared with no treatment. The direct reinsertion of activated nucleus pulposus cells into the disc offers a promising line of investigation for delaying intervertebral disc degeneration, although these results obtained with notochordal cells may not necessarily apply when mature central nucleus pulposus cells are used.

Percutaneous nucleotomy in lumbar disc herniation. A prospective study.

The purpose of this article is to present the clinical results of the prospective series of studies on percutaneous nucleotomy (PN) for lumbar disc herniation and to introduce current criteria of patient selection for PN. Since 1983, 107 patients were treated with PN (Hijikata's method), 85 of whom had a follow-up period of more than 2 years. Of these 85 patients, 54 had successful results. Clinical findings and various imaging evaluations (eg, magnetic resonance imaging and computed tomography after discography) before PN, as well as operative findings, were used to study the surgical outcomes of both the successful and unsuccessful groups. The results yielded the following new criteria for patient selection for PN: 1) age less than 40 years; 2) no perforation of the posterior longitudinal ligament and no degenerative canal stenosis detected by computed tomography after discography; 3) no malformation of the neural structure; 4) more than Grade 4 on manual testing of innervated muscles; and 5) more than 6 months of conservative treatment before PN.

Histologic analysis of the lumbosacral nerve roots after compression in young and aged rabbits.

STUDY DESIGN: The histologic changes in the lumbosacral nerve roots of aged rabbits because of chronic (graded) and acute compression were compared with those seen in young rabbits. OBJECTIVES: To study differences in the process of recovery from nerve compression between the aged and the young. SUMMARY OF BACKGROUND DATA: Clinical findings often differ between nerve compressive lesions in young and aged patients. Little has been reported on the pathologic basis of this difference. METHODS: Forty-five Japanese white rabbits were used. The cauda equina and spinal nerve root were compressed with a device specifically designed for this purpose. Nerve compression was applied to the dura mater and nerve roots after partial laminectomy. The specimens were sampled at 1 month or 3 months after acute or graded nerve compression. RESULTS: An increase in small myelinated fibers, consistent with the process of regeneration, was observed by light microscopy; this difference was greater in the young group than in the aged group. Reactive degenerative changes, as seen by electron microscopy, were more often observed in the aged group than in the young group. CONCLUSIONS: These findings demonstrate the suppression of regeneration and the latent fragility of the aged neural tissue. This may explain the clinical findings observed in aged patients with degenerative lumbar lesions.

Percutaneous reinsertion of the nucleus pulposus. An experimental study.

STUDY DESIGN: An analysis of the histologic changes in intervertebral discs after percutaneous reinsertion of the nucleus pulposus in rats. OBJECTIVE: To devise a way to delay further disc degeneration resulting from spinal deformity and the adverse effects of various treatments. SUMMARY OF BACKGROUND DATA: The role of the nucleus pulposus of the intervertebral disc described by many investigators has not been fully clarified. METHODS: Disc herniation was induced in the tails of 112 Wistar rats, using a fixation device between the 5th and 8th coccygeal vertebrae. After percutaneous nucleotomy at coccygeal vertebrae 5-6 and 6-7, fresh nucleus pulposus, cryopreserved nucleus pulposus, or an artificial substitute was inserted into the intervertebral disc at coccygeal vertebrae 5-6. Two, 4, or 8 weeks after reinsertion, disc sections from each coccygeal level were studied histopathologically. RESULTS: In the groups with reinsertion of fresh or cryopreserved nucleus pulposus, degenerative changes of the disc with the reinserted nucleus at coccygeal vertebrae 5-6 were milder than those of the disc without reinsertion at coccygeal vertebrae 6-7. However, no apparent benefit from reinsertion was observed in the group with artificial substitutes. CONCLUSIONS: Early reinsertion of the nucleus pulposus (fresh or cryopreserved) delays degeneration of such disc materials as the anulus fibrosus, endplate, and remaining nucleus pulposus.

Posterior stabilization of degenerative lumbar spondylolisthesis with a Leeds-Keio artificial ligament. A biomechanical analysis in a porcine vertebral model.

STUDY DESIGN: The biomechanical characteristics of the Leeds-Keio artificial ligament (Neoligament LTD, England) were assessed in the posterior stabilization of degenerative lumbar spondylolisthesis in a porcine vertebral model. OBJECTIVES: To evaluate the biomechanical properties of this nonrigid system immediately after instrumentation and during cyclic loading. SUMMARY OF BACKGROUND DATA: Mochida et al reported an innovative method of posterior stabilization in which the Leeds-Keio artificial ligament was used as a nonrigid instrument. Since 1990, this system has been used successfully to treat a select group of patients with degenerative lumbar spondylolisthesis. METHODS: Five porcine motion segments (L4-L5) were tested in the intact, destabilized, and Leeds-Keio-instrumented conditions. Specimens were loaded in flexion and extension, and construct stiffness was measured during the initial loading cycle and at 250 cycle intervals for 1500 cycles. RESULTS: Biomechanical stability in the model of degenerative lumbar spondylolisthesis was inferior to that in the controls. The instability in the Leeds-Keio group significantly improved immediately after placement and after 1500 cycles. CONCLUSIONS: This system is effective in initially stabilizing an unstable degenerative lumbar spondylolisthesis model and maintains its stabilizing effect during cyclic loading. Therefore, it can offer patients with degenerative lumbar spondylolisthesis in the late static stage several advantages over other treatment methods.

Percutaneous nucleotomy in lumbar disc herniation. Patient selection and role in various treatments.

Patients in percutaneous nucleotomy who met our new criteria for patient selection in 1992 showed 73% successful results. The success rate was not satisfactory in comparison with that (88%) in the open surgery through posterior approach (herniotomy), however. The purpose of this report is to re-evaluate 70 patients with follow-up more than 2 years based on imaging and clinical findings before percutaneous nucleotomy. In results, supplementary criteria such as two types of the combination of computed tomography discogram and computed tomography myelogram, continuation of the contrast medium in lateral view of discogram, and clinical findings characterized by sciatic pain were obtained to improve the success rate. Eighty-one percent of patients who met the new criteria in 1992 and the supplementary criteria were identified in the successful group. The authors believe that percutaneous nucleotomy should be considered as an independent operative procedure with results similar to open surgery, if the patient is selected strictly based on these criteria and supplementary criteria.

Neuromorphometric changes in the ventral spinal roots in a scoliotic animal.

The morphologic changes were investigated in the ventral and dorsal spinal nerve roots in a strain of white leghorn chickens that genetically was predisposed to have idiopathic scoliosis. In the ventral spinal roots in chickens with scoliotic curves, small myelinated fibers were increased in number and appeared in clusters. The number of small fibers did not correlate with the degree or the duration of the deformity. In 8 of the 15 chickens of the genetic scoliotic strain that did not have spinal curves, changes in the myelinated fibers, similar to those in chickens with scoliotic curves, were seen. These findings suggest that abnormalities in the myelinated fibers of the ventral spinal nerve roots may be the primary genetic lesion that, with variable penetrance, influences the development of scoliosis.

The importance of preserving disc structure in surgical approaches to lumbar disc herniation.

STUDY DESIGN: This study examined the clinical and radiographic results in patients with lumbar disc herniation treated surgically with one of four procedures: two different methods of herniotomy using a posterior approach and two different methods of percutaneous nucleotomy. OBJECTIVES: The authors goal was to identify the structural changes in the disc after each of the procedures and to correlate them with the clinical outcome. SUMMARY OF BACKGROUND DATA: The details of herniotomy procedure via a posterior approach or by percutaneous nucleotomy as described by many authors have not been consistent. Furthermore, previous reviews of these studies have been less than satisfactory. METHODS: One hundred fifty-seven herniotomies using a posterior approach and 94 percutaneous nucleotomies were studied with a follow-up of at least 2 years. Each of these groups was divided into two subgroups to evaluate the role of the remaining nucleus pulposus in the central area of the disc. RESULTS: Changes seen in imaging studies, such as a decrease in disc height and an increase of intervertebral instability in plain radiographs and a decrease in signal intensity of the disc in magnetic resonance images, were significantly less common in the subgroups of herniotomy and percutaneous nucleotomy in which the nucleus pulposus in the central area of the disc was preserved when compared with the subgroups in which a complete removal of the disc was attempted. The changes seen in the imaging studies were significant in patients younger than 40 years of age and correlated closely with the clinical results. CONCLUSIONS: Preserving the nucleus pulposus during the surgical treatment of lumbar disc herniation in patients younger than 40 years of age resulted in better radiographic and clinical results.