Lucas Smolders | University of Zurich, Switzerland (original) (raw)

Papers by Lucas Smolders

Objective: To assess pedicle screw-rod fixation (PSRF) of the canine lumbosacral junction (LSJ) e... more Objective: To assess pedicle screw-rod fixation (PSRF) of the canine lumbosacral junction (LSJ) ex vivo and in vivo. Study Design: Ex vivo cadaver study and in vivo pilot study. Sample Population: Six canine cadaveric lumbosacral spinal specimens and 3 Greyhound dogs diagnosed with degenerative lumbosacral stenosis (DLSS). Methods: Ex vivo study: PSRF of the LSJ was performed in 6 spinal specimens using guidelines and was evaluated by radiography, computed tomography, and magnetic resonance imaging. In vivo study: 3 Greyhounds diagnosed with DLSS had dorsal laminectomy and partial discectomy combined with PSRF of the LSJ. Curettage of the endplates with insertion of an autologous cancellous bone graft was performed to promote spinal fusion. During 18-month follow-up, dogs were monitored by clinical evaluation, diagnostic imaging, and force plate analysis. Dogs were euthanatized for reasons unrelated to PSRF or their lumbosacral disease , and postmortem imaging and histopathologic investigations of the LSJ were performed. Results: Ex vivo study: Sixteen of 24 inserted screws had an acceptable placement. In vivo study: Ten of 12 inserted screws had acceptable placement. Clinical signs of " lower " back pain resolved at 4 weeks after surgery. Diagnostic imaging and histopathology showed no bony spinal fusion of the LSJ. Force plate analysis revealed a trend toward improved pelvic limb function relative to preoperative function. Conclusions: PSRF of the LSJ of large breed dogs is technically possible. Improvements to the surgical technique to induce spinal fusion and assessment in a larger sample size are required before it can be recommended.

Intervertebral disc (IVD) degeneration is common in dogs and can lead to serious disorders. Curre... more Intervertebral disc (IVD) degeneration is common in dogs and can lead to serious disorders. Current treatments can relieve clinical signs of disease, but do not restore IVD function. The development of regener-ative strategies for IVD dysfunction requires detailed knowledge of the pathogenesis of IVD degeneration and its underlying mechanisms. Histological examination of IVDs at different stages of degeneration might provide this knowledge, but as there is currently no histological grading scheme for canine IVD degeneration, the aim of this study, which is the first of a two-part series, was to design and validate an appropriate scheme. Three independent observers evaluated 35 IVDs at different stages of degeneration using the scheme. Glycosaminoglycan contents of the nucleus pulposus and macroscopic grading according to Thompson, which are considered 'gold standards' for IVD degeneration, were used to validate the scheme. Reproduc-ibility was assessed by analysing the inter-observer reliability of all individual variables of the grading scheme, using a weighted j analysis. Significant correlations were found between Thompson grading and total histological score (r = 0.94; P < 0.01) and between glycosaminoglycan content and total histo-logical score (r = À0.72; P < 0.01). Most individual histological variables showed 'moderate' to 'almost perfect' inter-observer reliability. The high correlation with the gold standards in combination with the high reproducibility indicates that the proposed histological grading scheme is reliable and objective for classification of IVD degeneration in both chondrodystrophic and non-chondrodystrophic dog breeds.

A hydrogel nucleus pulposus prosthesis (NPP) was designed to swell in situ, have intrinsic radiop... more A hydrogel nucleus pulposus prosthesis (NPP) was designed to swell in situ, have intrinsic radiopacity, and restore intervertebral disc height and biomechanical function-ality. These features were examined using an ex vivo canine lumbar model. Nine NPPs were implanted in five spines and their visibility was assessed on radiography, computed to-mography (CT), and magnetic resonance imaging (MRI). The NPPs were visible on all imaging modalities and 8/9 NPPs stayed intact and in situ. Six other NPPs were tested biome-chanically in six canine lumbar spines. Removal of the nucleus pulposus (nuclectomy) caused significant changes in biomechanical parameters. After implantation and swelling of the NPP, values were not significantly different from the native state for range of motion (ROM) of flexion-extension (FE) and lateral bending (LB), the neutral zone (NZ) of all motion directions, and the NZ stiffness (NZS) of FE. Biome-chanical restoration by the NPP compared with the nuclec-tomized state was significant for the ROM of FE and axial rotation, the NZ of FE and LB, and the NZS of FE and LB. Disc height was significantly restored and 6/6 NPPs stayed intact and in situ. In conclusion, the NPPs swell in situ, have intrinsic radiopacity and restored disc height and aforemen-tioned biomechanical properties. V

Objective: To investigate, noninvasively, the soft tissue artifact (STA) in canine kinematic gait... more Objective: To investigate, noninvasively, the soft tissue artifact (STA) in canine kinematic gait analysis. Study Design: Experimental study. Animals: Labrador retrievers (n = 4). Methods: Kinematic study: Reflective markers were glued to the skin over bony landmarks, with the distance between 2 markers representing the length of the underlying scapula, humerus, ulna, femur, and crus. The distance between these markers (marker distance [MD]) was measured with infrared cameras while the dogs stood still or walked on a treadmill. Fluoroscopy study: Radiopaque markers were glued on the skin over the spinous process of the L6 vertebra and the stifle to allow fluoroscopic observation of the markers and underlying skeletal segments while the dogs walked on the treadmill. The position of the markers was compared with the position of the underlying skeletal segments during different phases of the step cycle. Results: Kinematic study: Significant differences were found between MD during standing and walking for all bones investigated. Mean percentage differences in MD ranged from –18% to +6%. Fluoroscopy study: Significant displacements relative to the bony landmarks were found ranging from 0.4 to 1.2 cm. Conclusions: Analysis of the motion of skeletal structures with the use of markers attached to the skin showed that the skin moves relative to underlying skeletal structures. When working with a 3-D motion-capture system using skin markers, researchers should be aware that the STA could significantly influence their results.

The notochordal cell (NC) of the nucleus pulposus (NP) is considered a potential NP progenitor ce... more The notochordal cell (NC) of the nucleus pulposus (NP) is considered a potential NP progenitor cell, and early interverte-bral disk (IVD) degeneration involves replacement of NCs by chondrocyte-like cells (CLCs). Wnt/b-catenin signaling plays a crucial role in maintaining the notochordal fate during embryogenesis, but is also involved in tissue degeneration and regeneration. The canine species, which can be subdivided into non-chondrodystrophic and chondrodystrophic breeds, is characterized by differential maintenance of the NC: in non-chondrodystrophic dogs, the NC remains the predominant cell type during the majority of life, with IVD degeneration only occurring at old age; conversely, in chondrodystrophic dogs the NC is lost early in life, with concurrent degeneration of all IVDs. This study investigated Wnt/b-catenin signaling in the healthy, NC-rich NP and early degenerated, CLC-rich NP of both breed types by immunohistochemistry of b-catenin and relative gene expression of brachyury and cytokeratin 8 (notochordal markers) and Wnt targets axin2, cyclin D1, and c-myc. Both NCs and CLCs showed nuclear and cytoplasmic b-catenin protein expression and axin2 gene expression, but b-catenin signal intensity and Wnt target gene expression were higher in the CLC-rich NP. Primary NCs in monolayer culture (normoxic conditions) showed Wnt/b-catenin signaling comparable to the in vivo situation, with increased cyclin D1 and c-myc gene expression. In conclusion, Wnt/b-catenin signaling activity in the NC within the NC-rich NP and in culture supports the role of this cell as a potential progenitor cell; increased Wnt/b-catenin signaling activity in early IVD degeneration may be a reflection of its dual role.

Purpose Dogs are often used as an animal model in spinal research, but consideration should be gi... more Purpose Dogs are often used as an animal model in spinal research, but consideration should be given to the breed used as chondrodystrophic (CD) dog breeds always develop IVD degeneration at an early age, whereas non-chondrodystrophic (NCD) dog breeds may develop IVD degeneration, but only later in life. The aim of this study was to provide a mechanical characterization of the NCD [non-degenerated intervertebral discs (IVDs), rich in notochordal cells] and CD (degenerated IVDs, rich in chondrocyte-like cells) canine spine before and after de-compressive surgery (nucleotomy). Methods The biomechanical properties of multisegment-ed lumbar spine specimens (T13–L5 and L5–Cd1) from 2-year-old NCD dogs (healthy) and CD dogs (early degeneration) were investigated in flexion/extension (FE), lateral bending (LB), and axial rotation (AR), in the native state and after nucleotomy of L2–L3 or dorsal laminectomy and nucleotomy of L7–S1. The range of motion (ROM), neutral zone (NZ), and NZ stiffness (NZS) of L1–L2, L2– L3, L6–L7, and L7–S1 were calculated. Results In native spines in both dog groups, the greatest mobility in FE was found at L7–S1, and the greatest mobility in LB at L2–L3. Surgery significantly increased the ROM and NZ, and significantly decreased the NZS in FE, LB, and AR in both breed groups. However, surgery at L2–L3 resulted in a significantly larger increase in NZ and decrease in NZS in the CD spines compared with the NCD spines, whereas surgery at L7–S1 induced a significantly larger increase in ROM and decrease in NZS in the NCD spines compared with the CD spines. Conclusions Spinal biomechanics significantly differ between NCD and CD dogs and researchers should consider this aspect when using the dog as a model for spinal research.

Degeneration of the intervertebral disc (IVD) is associated with a loss of notochordal cells (NCs... more Degeneration of the intervertebral disc (IVD) is associated with a loss of notochordal cells (NCs) from the nucleus pulposus (NP) and their replacement by chondrocyte-like cells. NCs are known to maintain extracel-lular matrix quality and stimulate the chondrocyte-like NP cells, making NCs attractive for designing new tissue engineering approaches for IVD regeneration. However, optimal conditions, such as osmolarity and other characteristics of the culture media, for long-term culture of NCs are not known. The purpose of this study was to investigate the effects of different culture media and osmolarity on the physiology of NCs in vitro. NC clusters isolated from canine IVDs were suspended in alginate beads and cultured at 37°C under normoxic conditions for 28 days. Three different culture conditions were investigated; (1) Dulbecco's modified Eagle's medium (DMEM)/F12 (300 mOsm/L), (2) a-MEM (300 mOsm/L), and (3) a-MEM adjusted to 400 mOsm/L to mimic a hyperosmolar environment. NC morphology, expression of genes related to NC markers, matrix production and remodeling, and DNA-and glycosaminoglycan (GAG) analyses were performed on 1, 7, 14, and 28 days in culture. Large, vesicle-containing cells organized in clusters, characterized as NCs, remained present during 28 days for all culture conditions. However, the proportion of the NC clusters decreased over time, whereas the proportion of spindle-shaped cells increased. Gene expression profiling at 7, 14, and 28 days in culture compared to day 1 indicated a initial loss of NC phenotype followed by some recovery of brachyury and aggrecan gene expression after 28 days of culture supporting a potential recovery of NC phenotype. NCs cultured in a-MEM adjusted to 400 mOsm/L showed the highest gene expression of brachyury, cytokeratin 18, and aggrecan, the highest GAG production, and the lowest collagen 1a1 gene expression. In conclusion, NCs cultured in alginate in native cell clusters, partially retained their characteristic morphology and recovered their phenotype in long-term culture. The type of culture medium and medium osmolarity appear to be important factors for culturing NC clusters. These findings provide additional information concerning the maintenance of NCs in vitro that may aid further mechanistic inquiry into the biology of NCs.

A nucleus pulposus prosthesis (NPP) made of the hydrogel N-vinyl-2-pyrrolidinone copolymerized wi... more A nucleus pulposus prosthesis (NPP) made of the hydrogel N-vinyl-2-pyrrolidinone copolymerized with 2-(4 0-iodobenzoyl)-oxo-ethyl methacrylate has recently been developed. The special features of this NPP, i.e. intrinsic radiopacity and its ability to swell in situ to fill the nucleus cavity and restore disc height, were investigated ex vivo in canine spinal specimens. L7-S1 intervertebral discs were isolated from three canine spinal specimens, and the dimensions of the nuclei pulposi were measured. Based on these averaged measurements, the NPP prototype was made and inserted in its dry form (xerogel) into a canine cadaveric spinal segment and allowed to swell overnight at 38 C. The integrity of the NPP and the filling of the nucleus cavity were assessed before and after swelling, using radiography, computed tomography, and magnetic resonance imaging. The ability of the NPP to restore disc height was assessed on radio-graphs of 10 spinal specimens. Thereafter the NPP was macroscopically assessed in situ by dissection of the spinal specimen. Both on imaging and macroscopically, 9/10 NPPs appeared to have a near perfect fit and disc height was restored in 8/10 spinal segments. The NPP may thus be an acceptable treatment option for low back patients meeting the requirements for NPP treatment.

Partial disc replacement is a new surgical technique aimed at restoring functionality to degenera... more Partial disc replacement is a new surgical technique aimed at restoring functionality to degenerated intervertebral discs (IVDs). The aim of the present study was to assess biomechanically the behaviour of a novel nucleus pulposus prosthesis (NPP) in situ and its ability to restore functionality to the canine IVD after nuclectomy alone or after combined dorsal laminectomy and nuclectomy. Nine canine T13–L5 specimens (L2L3 group) and 10 L5–Cd1 specimens (LS group) were tested biomechanically in the native state, after nuclectomy (L2L3 group) or after combined dorsal laminectomy and nuclectomy (LS group), and after insertion of the NPP. Range of motion (ROM), neutral zone (NZ), and neutral zone stiffness (NZS) were determined in flexion/extension, lateral bending, and axial rotation. Nuclectomy alone and combined dorsal laminectomy and nuclectomy caused significant instability in all motion directions. Implantation of the NPP resulted in significant restoration of the parameters (ROM, NZ, and NZS) towards the native state; however, fragmentation/herniation of the NPP occurred in 47% of the cases. In conclusion, the NPP has the ability to improve functionality of the nuclectomized canine IVD. The high rate of NPP failure requires modifications directed at the integrity of the NPP and its confinement to the nuclear cavity.

Introduction: Early degenerative changes in the nucleus pulposus (NP) are observed after the disa... more Introduction: Early degenerative changes in the nucleus pulposus (NP) are observed after the disappearance of notochordal cells (NCs). Thus, it has been suggested that NCs play an important role in maintaining the NP and may have a regenerative potential on other cells of the NP. As the number of resident NP cells (NPCs) decreases in a degenerating disc, mesenchymal stromal (stem) cells (MSCs) may be used for cell supplementation. In this study, using cells of one species, the regenerative potential of canine NCs was assessed in long-term three-dimensional coculture with canine NPCs or MSCs. Methods: Canine NCs and canine NPCs or MSCs were cocultured in alginate beads for 28 days under hypoxic and high-osmolarity conditions. Cell viability, cell morphology and DNA content, extracellular matrix production and expression of genes related to NC markers (Brachyury, KRT18) and NP matrix production (ACAN, COL2A1, COL1A1) were assessed after 1, 15 and 28 days of culture.

Study Design. Prospective observational and analytic study. Objective. To investigate whether spo... more Study Design. Prospective observational and analytic study. Objective. To investigate whether spontaneous intervertebral disc degeneration (IVDD) occurring in both chondrodystrophic (CD) and nonchondrodystrophic dogs (NCD) can be used as a valid translational model for human IVDD research. Summary of Background Data. Different animal models are used in IVDD research, but in most of these models IVDD is induced manually or chemically rather than occurring spontaneously. Methods. A total of 184 intervertebral discs (IVDs) from 19 dogs of different breeds were used. The extent of IVDD was evaluated by macroscopic grading, histopathology, glycosaminoglycan content, and matrix metalloproteinase 2 activity. Canine data were compared with human IVD data acquired in this study or from the literature. Results. Gross pathology of IVDD in both dog types (CD and NCD) and humans showed many similarities, but the cartilaginous endplates were signifi cantly thicker and the subchondral cortices signifi cantly thinner in humans than in dogs. Notochordal cells were still present in the IVDs of adult NCD but were not seen in the CD breeds or in humans. Signs of degeneration were seen in young dogs of CD breeds (< 1 year of age), whereas this was only seen in older dogs of NCD breeds (5–7 years of age). The relative glycosaminoglycan content and metalloproteinase 2 activity in canine IVDD were similar to those in humans: metalloproteinase 2

Introduction: Early degeneration of the intervertebral disc (IVD) involves a change in cellular d... more Introduction: Early degeneration of the intervertebral disc (IVD) involves a change in cellular differentiation from notochordal cells (NCs) in the nucleus pulposus (NP) to chondrocyte-like cells (CLCs). The purpose of this study was to investigate the gene expression profiles involved in this process using NP tissue from non-chondrodystrophic and chondrodystrophic dogs, a species with naturally occurring IVD degeneration. Methods: Dual channel DNA microarrays were used to compare 1) healthy NP tissue containing only NCs (NC-rich), 2) NP tissue with a mixed population of NCs and CLCs (Mixed), and 3) NP tissue containing solely CLCs (CLC-rich) in both non-chondrodystrophic and chondrodystrophic dogs. Based on previous reports and the findings of the microarray analyses, canonical Wnt signaling was further evaluated using qPCR of relevant Wnt target genes. We hypothesized that caveolin-1, a regulator of Wnt signaling that showed significant changes in gene expression in the microarray analyses, played a significant role in early IVD degeneration. Caveolin-1 expression was investigated in IVD tissue sections and in cultured NCs. To investigate the significance of Caveolin-1 in IVD health and degeneration, the NP of 3-month-old Caveolin-1 knockout mice was histopathologically evaluated and compared with the NP of wild-type mice of the same age.

The Veterinary Journal, 2013

Biomaterials, 2010

A nucleus pulposus prosthesis (NPP) made of the hydrogel N-vinyl-2-pyrrolidinone copolymerized wi... more A nucleus pulposus prosthesis (NPP) made of the hydrogel N-vinyl-2-pyrrolidinone copolymerized with 2-(4 0 -iodobenzoyl)-oxo-ethyl methacrylate has recently been developed. The special features of this NPP, i.e. intrinsic radiopacity and its ability to swell in situ to fill the nucleus cavity and restore disc height, were investigated ex vivo in canine spinal specimens. L7-S1 intervertebral discs were isolated from three canine spinal specimens, and the dimensions of the nuclei pulposi were measured. Based on these averaged measurements, the NPP prototype was made and inserted in its dry form (xerogel) into a canine cadaveric spinal segment and allowed to swell overnight at 38 C. The integrity of the NPP and the filling of the nucleus cavity were assessed before and after swelling, using radiography, computed tomography, and magnetic resonance imaging. The ability of the NPP to restore disc height was assessed on radiographs of 10 spinal specimens. Thereafter the NPP was macroscopically assessed in situ by dissection of the spinal specimen.

Proceedings 3rd International Congress Biotechnologies For Spinal Surgery Biospine 3, 2010

European Spine Journal, 2010

Eur Spine J, 2010

Introduction: Due to advancements in veterinary care and veterinary diets in the last four decade... more Introduction: Due to advancements in veterinary care and veterinary diets in the last four decades, dogs that are kept as companion animals have reached a life expectancy of 10 to 15 years. Together with intensive breeding of chondrodystrophic and non-chondrodystrophic dogs canine intervertebral disc degeneration (IVDD) has become an increasingly important veterinary disorder. Methods: IVDD occurs as a clinical entity

Objective: To assess pedicle screw-rod fixation (PSRF) of the canine lumbosacral junction (LSJ) e... more Objective: To assess pedicle screw-rod fixation (PSRF) of the canine lumbosacral junction (LSJ) ex vivo and in vivo. Study Design: Ex vivo cadaver study and in vivo pilot study. Sample Population: Six canine cadaveric lumbosacral spinal specimens and 3 Greyhound dogs diagnosed with degenerative lumbosacral stenosis (DLSS). Methods: Ex vivo study: PSRF of the LSJ was performed in 6 spinal specimens using guidelines and was evaluated by radiography, computed tomography, and magnetic resonance imaging. In vivo study: 3 Greyhounds diagnosed with DLSS had dorsal laminectomy and partial discectomy combined with PSRF of the LSJ. Curettage of the endplates with insertion of an autologous cancellous bone graft was performed to promote spinal fusion. During 18-month follow-up, dogs were monitored by clinical evaluation, diagnostic imaging, and force plate analysis. Dogs were euthanatized for reasons unrelated to PSRF or their lumbosacral disease, and postmortem imaging and histopathologic investigations of the LSJ were performed. Results: Ex vivo study: Sixteen of 24 inserted screws had an acceptable placement. In vivo study: Ten of 12 inserted screws had acceptable placement. Clinical signs of "lower" back pain resolved at 4 weeks after surgery. Diagnostic imaging and histopathology showed no bony spinal fusion of the LSJ. Force plate analysis revealed a trend toward improved pelvic limb function relative to preoperative function. Conclusions: PSRF of the LSJ of large breed dogs is technically possible. Improvements to the surgical technique to induce spinal fusion and assessment in a larger sample size are required before it can be recommended.

The Veterinary Journal, 2013

Biomaterials, 2010

A nucleus pulposus prosthesis (NPP) made of the hydrogel N-vinyl-2-pyrrolidinone copolymerized wi... more A nucleus pulposus prosthesis (NPP) made of the hydrogel N-vinyl-2-pyrrolidinone copolymerized with 2-(4 0 -iodobenzoyl)-oxo-ethyl methacrylate has recently been developed. The special features of this NPP, i.e. intrinsic radiopacity and its ability to swell in situ to fill the nucleus cavity and restore disc height, were investigated ex vivo in canine spinal specimens. L7-S1 intervertebral discs were isolated from three canine spinal specimens, and the dimensions of the nuclei pulposi were measured. Based on these averaged measurements, the NPP prototype was made and inserted in its dry form (xerogel) into a canine cadaveric spinal segment and allowed to swell overnight at 38 C. The integrity of the NPP and the filling of the nucleus cavity were assessed before and after swelling, using radiography, computed tomography, and magnetic resonance imaging. The ability of the NPP to restore disc height was assessed on radiographs of 10 spinal specimens. Thereafter the NPP was macroscopically assessed in situ by dissection of the spinal specimen.

Proceedings 3rd International Congress Biotechnologies For Spinal Surgery Biospine 3, 2010

European Spine Journal, 2010

Eur Spine J, 2010

Objective: To assess pedicle screw-rod fixation (PSRF) of the canine lumbosacral junction (LSJ) e... more Objective: To assess pedicle screw-rod fixation (PSRF) of the canine lumbosacral junction (LSJ) ex vivo and in vivo. Study Design: Ex vivo cadaver study and in vivo pilot study. Sample Population: Six canine cadaveric lumbosacral spinal specimens and 3 Greyhound dogs diagnosed with degenerative lumbosacral stenosis (DLSS). Methods: Ex vivo study: PSRF of the LSJ was performed in 6 spinal specimens using guidelines and was evaluated by radiography, computed tomography, and magnetic resonance imaging. In vivo study: 3 Greyhounds diagnosed with DLSS had dorsal laminectomy and partial discectomy combined with PSRF of the LSJ. Curettage of the endplates with insertion of an autologous cancellous bone graft was performed to promote spinal fusion. During 18-month follow-up, dogs were monitored by clinical evaluation, diagnostic imaging, and force plate analysis. Dogs were euthanatized for reasons unrelated to PSRF or their lumbosacral disease, and postmortem imaging and histopathologic investigations of the LSJ were performed. Results: Ex vivo study: Sixteen of 24 inserted screws had an acceptable placement. In vivo study: Ten of 12 inserted screws had acceptable placement. Clinical signs of "lower" back pain resolved at 4 weeks after surgery. Diagnostic imaging and histopathology showed no bony spinal fusion of the LSJ. Force plate analysis revealed a trend toward improved pelvic limb function relative to preoperative function. Conclusions: PSRF of the LSJ of large breed dogs is technically possible. Improvements to the surgical technique to induce spinal fusion and assessment in a larger sample size are required before it can be recommended.