Osmotic pump with potential for bone lengthening distracts continuously in vitro and in vivo.

BACKGROUND: In pediatric orthopedics, long bone lengthening procedures are routinely performed using manual, motorized or magnetically controlled implants. This study aims to prove expansion of a newly designed osmotic pump prior to long bone lengthening in living organisms and to rule out any complications related to in vivo conditions, such as congestion of the semipermeable membrane, local infection, or lack of water to drive the osmotic pump, as well as to compare in vivo and in vitro expansion data. METHODS: Osmotic pumps, which were designed to distract a plate osteosynthesis, were inserted in the dorsal paraspinal musculature of four piglets. To compare the performance of the pumps in in vivo and in vitro conditions, another set of pumps was submerged in physiologic saline solution at different temperatures. The lengthening progress was measured radiographically and sonographically in the study animals. RESULTS: Both, in vitro and in vivo tested osmotic pumps started distraction after an intended rest phase of four days and distracted evenly over the following twelve days. No complications, clogging or damages occurred. However, we observed a temperature dependency of the distraction rate ranging from 0.98 mm/day at 39°C to 1.10 mm/day at 42°C. With a second setup, we confirmed that the distraction rate differed by 72% within a measured temperature interval of 14° C. CONCLUSIONS: The data presented here confirm that the novel osmotic pump showed comparable lengthening characteristics in vivo and in vitro. No complications, such as congestion of the semipermeable membrane, local infection, or lack of water to drive the osmotic pump were observed. Thus, osmotic pumps may have great potential in future applications such as long bone lengthening procedures, where continuous distraction probably provides a better bone quality than intermittent lengthening procedures. The fact that one pump failed to elongate in each condition, highlights the importance of technical improvement, but also demonstrates that this was not due to different circumstances within the in vivo or in vitro condition.

Influence of Paraspinal Growth-Friendly Spinal Implants in Children with Spinal Muscular Atrophy on Parasol Deformity, Rib-Vertebral Angles, Thoracic, and Lung Volumes.

INTRODUCTION: Children with spinal muscular atrophy (SMA) and progressive neuromuscular scoliosis often require early growth-friendly spinal implant (GFSI) treatment for deformity correction with implant fixation either through pedicle screws or bilateral to the spine using ribto pelvis fixation. It has been proposed that the latter fixation may change the collapsing parasol deformity via changes in the rib-vertebral angle (RVA) with a positive effect on thoracic and lung volume. The purpose of this study was to analyze the effect of paraspinal GFSI with bilateral rib-to-pelvis fixation on the parasol deformity, RVA, thoracic, and lung volumes. METHODS: SMA children with (n = 19) and without (n = 18) GFSI treatment were included. Last follow-up was before definite spinal fusion at puberty. Scoliosis and kyphosis angles, parasol deformity, and index, as well as convex and concave RVA, were measured on radiographs, whereas computed tomography images were used to reconstruct thoracic and lung volumes. RESULTS: In all SMA children (n = 37; with or without GFSI), convex RVA was smaller than concave values at all times. GFSI did not crucially influence the RVA over the 4.6-year follow-up period. Comparing age- and disease-matched adolescents with and without prior GFSI, no effect of GFSI treatment could be detected on either RVA, thoracic, or lung volumes. Parasol deformity progressed over time despite GFSI. CONCLUSION: Despite different expectations, implantation of GFSI with bilateral rib-to-pelvis fixation did not positively influence parasol deformity, RVA and/or thoracic, and lung volumes in SMA children with spinal deformity directly and over time.

Scoliosis Treatment With Growth-Friendly Spinal Implants (GFSI) Relates to Low Bone Mineral Mass in Children With Spinal Muscular Atrophy.

BACKGROUND: Children with spinal muscular atrophy (SMA) frequently develop neuromuscular scoliosis at an early age, requiring surgical treatment with growth-friendly spinal implants (GFSI), such as magnetically controlled growing rods. This study investigated the effect of GFSI on the volumetric bone mineral density (vBMD) of the spine in SMA children. METHODS: Seventeen children (age 13.2±1.2 y) with SMA and GFSI-treated spinal deformity were compared with 25 scoliotic SMA children (age 12.9±1.7 y) without prior surgical treatment as well as age-matched healthy controls (n=29; age 13.3±2.0). Clinical, radiologic, and demographic data were analyzed. For the calculation of the vBMD Z-scores of the thoracic and lumbar vertebrae, phantom precalibrated spinal computed tomography scans were analyzed using quantitative computed tomography (QCT). RESULTS: Average vBMD was lower in SMA patients with GFSI (82.1±8.4 mg/cm 3) compared with those without prior treatment (108.0±6.8 mg/cm 3 ). The difference was more prominent in and around the thoracolumbar region. The vBMD of all SMA patients was significantly lower in comparison with healthy controls, especially in SMA patients with previous fragility fractures. CONCLUSIONS: The results of this study support the hypothesis of reduced vertebral bone mineral mass in SMA children with scoliosis at the end of GFSI treatment in comparison with SMA patients undergoing primary spinal fusion. Improving vBMD through pharmaceutical therapy in SMA patients could have a beneficial effect on the surgical outcome of scoliosis correction while reducing complications. LEVEL OF EVIDENCE: Therapeutic Level III.

Isolated catatonia-like executive dysfunction in mice with forebrain-specific loss of myelin integrity.

A key feature of advanced brain aging includes structural defects of intracortical myelin that are associated with secondary neuroinflammation. A similar pathology is seen in specific myelin mutant mice that model 'advanced brain aging' and exhibit a range of behavioral abnormalities. However, the cognitive assessment of these mutants is problematic because myelin-dependent motor-sensory functions are required for quantitative behavioral readouts. To better understand the role of cortical myelin integrity for higher brain functions, we generated mice lacking Plp1, encoding the major integral myelin membrane protein, selectively in ventricular zone stem cells of the mouse forebrain. In contrast to conventional Plp1 null mutants, subtle myelin defects were restricted to the cortex, hippocampus, and underlying callosal tracts. Moreover, forebrain-specific Plp1 mutants exhibited no defects of basic motor-sensory performance at any age tested. Surprisingly, several behavioral alterations reported for conventional Plp1 null mice (Gould et al., 2018) were absent and even social interactions appeared normal. However, with novel behavioral paradigms, we determined catatonia-like symptoms and isolated executive dysfunction in both genders. This suggests that loss of myelin integrity has an impact on cortical connectivity and underlies specific defects of executive function. These observations are likewise relevant for human neuropsychiatric conditions and other myelin-related diseases.

Reduced Volumetric Bone Mineral Density of the Spine in Adolescent Rett Girls with Scoliosis.

In advanced Rett syndrome (RTT), limited or complete loss of ambulation, nutritional problems and scoliosis are unfavorable factors for bone mineral density (BMD). Still, there are few data available in this research area. Spinal quantitative computed tomography (QCT) allows an exact measurement of the volumetric BMD (vBMD) in this patient group. Two examiners measured vBMD of thoracic and lumbar vertebrae on asynchronous calibrated CTs that were acquired prior to surgical scoliosis correction (n = 21, age 13.6 ± 2.5 years). The values were compared to age- and sex-matched healthy controls to additionally derive Z-scores (n = 22, age 13.8 ± 2.0 years). The results showed the most significant reduction of vBMD values in non-ambulatory RTT patients, with p < 0.001 and average BMD-Z-score −1.5 ± 0.2. In the subgroup comparison, non-ambulatory patients with valproate treatment had significant lower values (p < 0.001) than ambulatory patients without valproate therapy, with an average BMD-Z-score of −2.3 ± 0.2. Comparison of the Z-scores to critical BMD thresholds of 120 and 80 mg/cm3 showed normal Z-scores in case of the ambulatory RTT subgroup, as opposed to BMD-Z-scores of the non-ambulatory RTT subgroups, which were partially below osteopenia-equivalent values. Furthermore, valproate treatment seems to have a direct effect on vBMD in RTT patients and when combined with loss of ambulation, BMD-Z-scores are reduced to osteoporosis-equivalent levels or even further.

A Preclinical Pilot Study on the Effects of Thermal Ablation on Lamb Growth Plates.

(1) Background: Thermal ablation has been demonstrated to affect the bone growth of osteoid osteoma in adolescents. Growth modulation due to thermal heat in children is conceivable, but has not yet been established. We used lamb extremities as a preclinical model to examine the effect of thermal ablation on growth plates in order to evaluate its potential for axial or longitudinal growth modulation in pediatric patients. (2) Methods: Thermal ablation was performed by electrocautery on eight different growth plates of the legs and distal radii of a stillborn lamb. After treatment, target hits and the physical extent of the growth plate lesions were monitored using micro-computed tomography (micro-CT) and histology. (3) Results: Lesions and their physical extent could be quantified in 75% of the treated extremities. The histological analysis revealed that the disruption of tissue was confined to a small area and the applied heat did not cause the entire growth plate to be disrupted or obviously damaged. (4) Conclusions: Thermal ablation by electrocautery is minimally invasive and can be used for targeted disruption of small areas in growth plates in the animal model. The results suggest that thermal ablation can be developed into a suitable method to influence epiphyseal growth in children.

Foot Typology, Dynamic and Static Weight Distribution, and Radiographic Changes After Subtalar Arthroereisis in Juvenile Symptomatic Flexible Flat Feet.

Flexible flatfoot is among the most common skeletal disorders in childhood. This study describes the dynamic and static correction effects of subtalar arthroereisis in adolescents with flexible symptomatic flatfeet in comparison to normal subjects as well as to results before and after removal of metal. Eighteen adolescents with 25 symptomatic flexible flatfeet were treated surgically with a subtalar arthroereisis at a mean of 12.5 (10-16) years. At follow-up (mean 3.9 years, range 0.4-8), patients filled out the American Orthopaedic Foot and Ankle Society questionnaire, received radiographs and were examined using dynamic and static pedobarography as well as static hindfoot axis examination. Results were compared to healthy controls (n = 13; 26 feet). Surgically treated feet (n = 25) had better questionnaire results after surgery than before, but lower scores than healthy feet. Radiological parameters improved significantly after surgery. Removal of metal did not influence post-surgical results (follow-up 2.8 years). Surgically treated feet had larger contact areas than normal feet with predominance to the midfoot region. The relative maximum force, relative peak pressure and contact time were higher in the midfoot of treated feet compared to controls. When comparing pedobarography data of treated versus untreated feet of the same patients (subgroup n = 11 feet), there were no differences. Subtalar arthroereisis was able to effectively treat symptomatic flexible flatfeet in this population. Results improved significantly evaluating a questionnaire, radiographs, dynamic and static weight distribution, but were still worse than results of healthy feet. There was no relapse after removal of metal.

Smaller Intervertebral Disc Volume and More Disc Degeneration after Spinal Distraction in Scoliotic Children.

In recent decades, magnetically controlled growing rods (MCGR) were established to treat progressive early-onset scoliosis. The aim of this investigation was to assess the effect of long-term MCGR with continuous distraction on intervertebral discs in scoliotic children. Magnetic resonance imaging (MRI) of 33 children with spinal muscular atrophy was analyzed by grading intervertebral disc degeneration (IDD) and measuring intervertebral disc volume. Cohort I (n = 17) were children who had continuous spinal distraction with MCGRs for 5.1 years and MRI before (av. age 8.1) and after (av. age 13.4) MCGR treatment. Cohort II (n = 16, av. age 13.7) were patients without prior surgical treatment. Lumbar intervertebral disc volume of cohort I did not change during 5.1 years of MCGR treatment, whereas disc volumes were significantly larger in age- and disease-matched children without prior treatment (cohort II). Cohort I showed more IDD after MCGR treatment in comparison to early MRI studies of the same patients and children without surgical treatment. MRI data showed a volume reduction and disc degeneration of lower thoracic and lumbar intervertebral discs in scoliotic children after continuous spinal distraction with MCGRs. These effects were confirmed in the same subjects before and after treatment as well as in surgically untreated controls.

Spinal Deformities after Childhood Tumors.

Childhood tumors of the central nervous system (CNS) and other entities affecting the spine are rare. Treatment options vary from surgical biopsy to partial, subtotal, and total resection, to radiation, to chemotherapy. The aim of this study is to investigate spinal deformity and subsequent surgical interventions in this patient cohort. A retrospective review at our institution identified children with CNS tumors, spinal tumors, and juxta-spinal tumors, as well as spinal deformities. Tumor entity, treatment, mobilization, and radiographic images were analyzed relative to the spinal deformity, using curve angles in two planes. Conservative or surgical interventions such as orthotic braces, growth-friendly spinal implants, and spinal fusions were evaluated and analyzed with respect to treatment results. Tumor entities in the 76 patients of this study included CNS tumors (n = 41), neurofibromatosis with spinal or paraspinal tumors (n = 14), bone tumors (n = 12), embryonal tumors (n = 7), and others (n = 2). The initial treatment consisted of surgical biopsy (n = 5), partial, subtotal, or total surgical resection (n = 59), or none (n = 12), followed by chemotherapy, radiotherapy, or both (n = 40). Out of 65 evaluated patients, 25 revealed a moderate or severe scoliotic deformity of 71° (range 21-116°), pathological thoracic kyphosis of 66° (range 50-130°), and lordosis of 61° (range 41-97°). Surgical treatment was performed on 21 patients with implantation of growth-friendly spinal implants (n = 9) as well as twelve dorsal spinal fusions (two with prior halo distraction). Surgical interventions significantly improved spinal deformities without additional neurological impairment. With the increasing number of children surviving rare tumors, attention should be focused on long-term problems such as spinal deformities and consequent disabilities. A significant number of children with CNS tumors, spinal tumors or juxta-spinal tumors required surgical intervention. Early information about spinal deformities and a close follow-up are mandatory for this patient group.

CMTM6 expressed on the adaxonal Schwann cell surface restricts axonal diameters in peripheral nerves.

The velocity of nerve conduction is moderately enhanced by larger axonal diameters and potently sped up by myelination of axons. Myelination thus allows rapid impulse propagation with reduced axonal diameters; however, no myelin-dependent mechanism has been reported that restricts radial growth of axons. By label-free proteomics, STED-microscopy and cryo-immuno electron-microscopy we here identify CMTM6 (chemokine-like factor-like MARVEL-transmembrane domain-containing family member-6) as a myelin protein specifically localized to the Schwann cell membrane exposed to the axon. We find that disruption of Cmtm6-expression in Schwann cells causes a substantial increase of axonal diameters but does not impair myelin biogenesis, radial sorting or integrity of axons. Increased axonal diameters correlate with accelerated sensory nerve conduction and sensory responses and perturbed motor performance. These data show that Schwann cells utilize CMTM6 to restrict the radial growth of axons, which optimizes nerve function.

Altered bone development with impaired cartilage formation precedes neuromuscular symptoms in spinal muscular atrophy.

Spinal muscular atrophy (SMA) is a fatal neurodegenerative disease of newborns and children caused by mutations or deletions of the survival of motoneuron gene 1 resulting in low levels of the SMN protein. While neuromuscular degeneration is the cardinal symptom of the disease, the reduction of the ubiquitously expressed SMN additionally elicits non-motoneuron symptoms. Impaired bone development is a key feature of SMA, but it is yet unknown whether this is an indirect functional consequence of muscle weakness or caused by bone-intrinsic mechanisms. Therefore, we radiologically examined SMA patients in a prospective, non-randomized cohort study characterizing bone size and bone mineral density (BMD) and performed equivalent measurements in pre-symptomatic SMA mice. BMD as well as lumbar vertebral body size were significantly reduced in SMA patients. This growth defect but not BMD reduction was confirmed in SMA mice by µCT before the onset of neuromuscular symptoms indicating that it is at least partially independent of neuromuscular degeneration. Interestingly, the number of chondroblasts in the hypertrophic zone of the growth plate was significantly reduced. This was underlined by RNAseq and expression data from developing SMA mice vertebral bodies, which revealed molecular changes related to cell division and cartilage remodeling. Together, these findings suggest a bone intrinsic defect in SMA. This phenotype may not be rescued by novel drugs that enhance SMN levels in the central nervous system only.

Children With Spinal Muscular Atrophy With Prior Growth-Friendly Spinal Implants Have Better Results After Definite Spinal Fusion in Comparison to Untreated Patients.

BACKGROUND: Almost all children with spinal muscular atrophy (SMA) develop a scoliosis during childhood and adolescence. In the last decades, growth-friendly spinal implants have been established as an interim solution for these patients until definite spinal fusion can be performed. The effect of those implants on the final outcome has yet to be described. OBJECTIVE: To assess the effect of prior growth-friendly spinal surgical treatment on the outcome after spinal fusion in SMA children in comparison to untreated SMA patients through the prospective study. METHODS: A total of 28 SMA patients with (n = 14) and without (n = 14) prior surgical treatment with growth-friendly implants were included. Average surgical treatment prior to definite spinal fusion was 4.9 yr. Scoliotic curve angle, pelvic obliquity, spinal length, kyphosis, and lordosis were evaluated for children with prior treatment and before and after dorsal spondylodesis for all children. RESULTS: The curve angle before definite spinal fusion averaged at 104° for SMA patients without prior treatment and 71° for patients with prior treatment. Spondylodesis reduced the scoliotic curve to 50° and 33°, respectively, which equals a correction of 52% vs 54%. Pelvic obliquity could be improved by spinal fusion in all patients with better results in the pretreated group. Results for spinal length, kyphosis, and lordosis were similar in both groups. CONCLUSION: These data show the positive effect of prior growth-friendly surgical treatment on radiographic results of spinal fusion in children with SMA. Both scoliotic curve angles and pelvic obliquity showed significantly better values when patients had growth-friendly implants before definite spinal fusion.

Maintenance of high proteolipid protein level in adult central nervous system myelin is required to preserve the integrity of myelin and axons.

Proteolipid protein (PLP) is the most abundant integral membrane protein in central nervous system (CNS) myelin. Expression of the Plp-gene in oligodendrocytes is not essential for the biosynthesis of myelin membranes but required to prevent axonal pathology. This raises the question whether the exceptionally high level of PLP in myelin is required later in life, or whether high-level PLP expression becomes dispensable once myelin has been assembled. Both models require a better understanding of the turnover of PLP in myelin in vivo. Thus, we generated and characterized a novel line of tamoxifen-inducible Plp-mutant mice that allowed us to determine the rate of PLP turnover after developmental myelination has been completed, and to assess the possible impact of gradually decreasing amounts of PLP for myelin and axonal integrity. We found that 6 months after targeting the Plp-gene the abundance of PLP in CNS myelin was about halved, probably reflecting that myelin is slowly turned over in the adult brain. Importantly, this reduction by 50% was sufficient to cause the entire spectrum of neuropathological changes previously associated with the developmental lack of PLP, including myelin outfoldings, lamellae splittings, and axonal spheroids. In comparison to axonopathy and gliosis, the infiltration of cytotoxic T-cells was temporally delayed, suggesting a corresponding chronology also in the genetic disorders of PLP-deficiency. High-level abundance of PLP in myelin throughout adult life emerges as a requirement for the preservation of white matter integrity.

Genetic dissection of oligodendroglial and neuronal Plp1 function in a novel mouse model of spastic paraplegia type 2.

Proteolipid protein (PLP) is the most abundant integral membrane protein in compact central nervous system myelin, and null mutations of the PLP1 gene cause spastic paraplegia type 2 (SPG2). SPG2 patients and PLP-deficient mice exhibit only moderate abnormalities of myelin but progressive degeneration of long axons. Since Plp1 gene products are detected in a subset of neurons it has been suggested that the loss of neuronal Plp1 expression could be the cause of the axonal pathology. To test this hypothesis, we created mice with a floxed Plp1 allele for selective Cre-mediated recombination in neurons. We find that recombination of Plp1 in excitatory projection neurons does not cause neuropathology, whereas oligodendroglial targeting of Plp1 is sufficient to cause the entire neurodegenerative spectrum of SPG2 including axonopathy and secondary neuroinflammation. We conclude that PLP-dependent loss of oligodendroglial support is the primary cause of axonal degeneration in SPG2.

Proteolipid protein modulates preservation of peripheral axons and premature death when myelin protein zero is lacking.

Protein zero (P0) is the major structural component of peripheral myelin. Lack of this adhesion protein from Schwann cells causes a severe dysmyelinating neuropathy with secondary axonal degeneration in humans with the neuropathy Dejerine-Sottas syndrome (DSS) and in the corresponding mouse model (P0(null)-mice). In the mammalian CNS, the tetraspan-membrane protein PLP is the major structural myelin constituent and required for the long-term preservation of myelinated axons, which fails in hereditary spastic paraplegia (SPG type-2) and the relevant mouse model (Plp(null)-mice). The Plp-gene is also expressed in Schwann cells but PLP is of very low abundance in normal peripheral myelin; its function has thus remained enigmatic. Here we show that the abundance of PLP but not of other tetraspan myelin proteins is strongly increased in compact peripheral myelin of P0(null)-mice. To determine the functional relevance of PLP expression in the absence of P0, we generated P0(null)*Plp(null)-double-mutant mice. Compared with either single-mutant, P0(null)*Plp(null)-mice display impaired nerve conduction, reduced motor functions, and premature death. At the morphological level, axonal segments were frequently non-myelinated but in a one-to-one relationship with a hypertrophic Schwann cell. Importantly, axonal numbers were reduced in the vital phrenic nerve of P0(null)*Plp(null)-mice. In the absence of P0, thus, PLP also contributes to myelination by Schwann cells and to the preservation of peripheral axons. These data provide a link between the Schwann cell-dependent support of peripheral axons and the oligodendrocyte-dependent support of central axons.