Low back pain is strongly associated with degeneration of the intervertebral disc (IVD). During degeneration, altered matrix synthesis and increased matrix degradation, together with accompanied cell loss is seen particularly in the nucleus pulposus (NP). It has been proposed that notochordal (NC) cells, embryonic precursors for the cells within the NP, could be utilized for mediating IVD regeneration. However, injectable biomaterials are likely to be required to support their phenotype and viability within the degenerate IVD. Therefore, viability and phenotype of NC cells were analysed and compared within biomaterial carriers subjected to physiological oxygen conditions over a four-week period were investigated.

Porcine NC cells were incorporated into three injectable hydrogels: NPgel (a L-pNIPAM-co-DMAc hydrogel), NPgel with decellularized NC-matrix powder (dNCM) and Albugel (an albumin/ hyaluronan hydrogel). The NCs and biomaterials constructs were cultured for up to four weeks under 5% oxygen (n=3 biological repeats). Histological, immunohistochemical and glycosaminoglycans (GAG) analysis were performed to investigate NC viability, phenotype and extracellular matrix synthesis and deposition.

Histological analysis revealed that NCs survive in the biomaterials after four weeks and maintained cell clustering in NPgel, Albugel and dNCM/NPgel with maintenance of morphology and low caspase 3 staining. NPgel and Albugel maintained NC cell markers (brachyury and cytokeratin 8/18/19) and extracellular matrix (collagen type II and aggrecan). Whilst Brachyury and Cytokeratin were decreased in dNCM/NPgel biomaterials, Aggrecan and Collagen type II was seen in acellular and NC containing dNCM/NPgel materials. NC containing constructs excreted more GAGs over the four weeks than the acellular controls.

NC cells maintain their phenotype and characteristic features in vitro when encapsulated into biomaterials. NC cells and biomaterial construct could potentially become a therapy to treat and regenerate the IVD.

Objectives

Low back pain is strongly associated with degeneration of the intervertebral disc (IVD). During degeneration, altered matrix synthesis and increased matrix degradation, together with accompanied cell loss is seen particularly in the nucleus pulposus (NP). It has been proposed that notochordal (NC) cells, embryonic precursors for the cells within the NP, could be utilized for mediating IVD regeneration. However, injectable biomaterials are likely to be required to support their phenotype and viability within the degenerate IVD. Therefore, viability and phenotype of NC cells were analysed and compared within biomaterial carriers subjected to physiological oxygen conditions over a four-week period were investigated.

Introduction and Objective

Intervertebral disc (IVD) degeneration accompanying with low back pain is a serious worldwide problem. Even though, surgical treatments are available for pain relief, there is an urgent need to establish enduring cell-based remedies. Notochordal (NC) cells as the ancestor of nucleus pulposus (NP) cells in human IVD are a promising therapeutic target. It has been reported that the loss of NC cells after childhood could promote the onset of disc degeneration. Thus, we firstly, aimed to optimise the culture of NC cells in vitro without using the FCS in alginate (3D) culture systems, secondly, investigate their behaviour in healthy and degenerate niche and lastly, co-culture these cells with degenerated NP cells to assess their regeneration potentials.

After anterior cruciate ligament (ACL) rupture, reconstructive surgery with a hamstring tendon autograft is often performed. Despite overall good results, ACL re-rupture occurs in up to 10% of the patient population, increasing to 30% of the cases for patients aged under 20 years. This can be related to tissue remodelling in the first months to years after surgery, which compromises the graft's mechanical strength. Resident graft fibroblasts secrete matrix metalloproteinases (MMPs), which break down the collagen I extracellular matrix. After necrosis of these fibroblasts, myofibroblasts repopulate the graft, and deposit more collagen III rather than collagen I. Eventually, the cellular and matrix properties converge towards those of the native ACL, but full restoration of the ACL properties is not achieved. It is unknown how inter-patient differences in tissue remodelling capacity contribute to ACL graft rupture risk. This research measured patient-specific tissue remodelling-related properties of human hamstring tendon-derived cells in an in vitro micro-tissue platform, in order to identify potential biological predictors for graft rupture.

Human hamstring tendon-derived cells were obtained from remnant autograft tissue after ACL reconstructions. These cells were seeded in collagen I gels on a micro-tissue platform to assess inter-patient cellular differences in tissue remodelling capacity. Remodelling was induced by removing the outermost micro-posts, and micro-tissue compaction over time was assessed using transmitted light microscopy. Protein expression of tendon marker tenomodulin and myofibroblast marker α-smooth muscle actin (αSMA) were measured using Western blot. Expression and activity of remodelling marker MMP2 were determined using gelatin zymography.

Cells were obtained from 12 patients (aged 12–51 years). Patient-specific variations in micro-tissue compaction speed or magnitude were observed. Up to 50-fold differences in αSMA expression were found between patients, although these did not correlate with faster or stronger compaction. Surprisingly, tenomodulin was only detected in samples obtained from two patients. Total MMP2 expression varied between patients, but no large differences in active fractions were found. No correlation of patient age with any of the remodelling-related factors was detected.

Remodelling-related biological differences between patient tendon-derived cells could be assessed with the presented micro-tissue platform, and did not correlate with age. This demonstrates the need to compare this biological variation in vitro - especially cells with extreme properties - to clinical outcome. Sample size is currently increased, and patient outcome will be determined. Combined with results obtained from the in vitro platform, this could lead to a predictive tool to identify patients at risk for graft rupture.

Novel biomaterials are being developed and studied, intended to be applied as bone graft substitute materials. Typically, these materials are being tested in in vitro setups, where among others their cytotoxicity and alkaline phosphatase activity (as a marker for osteoblastic differentiation) are being evaluated. However, it has been reported that in vitro tests correlate poorly with in vivo results and therefore many promising biomaterials may not reach the clinic as a bone graft substitute product. One of the reasons for the poor correlation, may be the minimal complexity of the in vitro tests, as compared to the in vivo environment. Ex vivo models, mimicking the natural tissue environment whilst maintaining control of culture parameters, may be a promising alternative to assess biomaterials for bone formation. Assess the possibility of an ex vivo culture platform to test biomaterials on their potential to stimulate new bone formation. Osteochondral plugs (cylinders n=10, Ø 10 mm, height 15 mm) were drilled from fresh porcine knees, from the slaughterhouse. A bone defect (Ø 6 mm) was created and which was filled with a biomaterial graft (S53P4 bioactive glass (n=3); collagen sponges loaded with BMP-2 (n=3, as positive control)) or kept empty (n=4). The explants were cultured in custom-made two-chamber bioreactors for six weeks (LifeTec Group BV). Cartilage and bone were physically separated, similar to the in vivo situation, by a sealing ring. The two tissues were cultured in separate compartments, allowing for specific culture medium for each tissue. Medium was changed every 2–3 days and weekly micro computed tomography (µCT) images were obtained to longitudinally monitor the formation of new bone. An MTT assay was performed on half of the samples after six weeks of culture. The other samples were fixed for histology, to determine which cells were present after six weeks. The MTT metabolic assay showed that a number of cells in the bone were viable after six weeks. The further away from the border, the fewer living cells were observed. The cells in the cartilage also survived. No significant bone formation was observed with µCT in either of groups, even though abundant bone formation was expected in the BMP-2 group. Explanations of the negative results of the positive group might be that too few viable cells remain after six weeks, or that the cells that are still present are not able to form bone. No significant bone formation was observed in the bone defects in osteochondral explants that were cultured with, or without, biomaterials for six weeks. However, the platform showed that it is capable to successfully culture osteochondral explants for six weeks.

Histology needs to be performed to evaluate which cells were present at the end of the culture and this will be compared to the cells present directly after drilling the explants.

Currently, between 17% of patients undergoing surgery for adult spinal deformity experience severe instrumentation related problems such as screw pullout or proximal junctional failure necessitating revision surgery. Cables may be used to reinforce pedicle screw fixation as an additive measure or may provide less rigid fixation at the construct end levels in order to prevent junctional level problems. The purpose of this study is to provide insight into the maximum expected load during flexion in UHMWPE cable in constructs intended for correction of adult spine deformity (degenerative scoliosis) in the PoSTuRe first-in-man clinical trial.

Following the concept of toppinoff, a new construct is proposed with screw/cable fixation of rods at the lower levels and standalone UHMWPE cables at the upper level (T11). A parametric FE model of the instrumented thoracolumbar spine, which has been previously validated, was used to represent the construct. Pedicle screws are modeled by assigning a rigid tie constraint between the rod and the lamina of the corresponding spinal level. Cables are modeled using linear elastic line elements, fixing the rod to the lamina medially at the cranial laminar end and laterally at the caudal laminar end. A Youngs modulus was assigned such that the stiffness of the line element was the same as that of the cable. An 8 Nm flexion moment was applied to the cranial endplate.

The maximum value of the force in the wire (80 N) is found at the T11 (upper) level. At the other levels, forces in the cable are very small because most of the force is carried by the screw (T12) or because the wires are force shielded by the contralateral and adjacent level pedicle screws (L2, L3).

The model provides first estimates of the forces that can be expected in the UHMWPE cables in constructs for kyphosis correction during movement. It is expected that this approach can help in defining the number of wires for optimal treatment.

When a knee flex deeply, the posterior side of thigh and calf contact. The contact force is unignorable to estimate the load acting on a knee because the force generates extensional moment on the knee, and the moment might be about 20–80% of the flexional moment generated by a floor reacting force. Besides, the thigh-calf contact force varies so much even if the posture or the test subject are the same that it is hard to use the average value to estimate the knee load. We have assumed that the force might change not only by the individual physical size but also by a slight change of the posture, especially the angle of the upper body. Therefore we tried to create the estimation equation for the thigh-calf contact force using both anthropometric sizes and posture angles as parameters.

The objective posture was kneeling, both plantarflexing and dorsiflexing the ankle joint. Test subjects were 10 healthy males. They were asked to sit on a floor with kneeling, and to tilt their upper body forward and backward. The estimation equations were created as the linear combinations of the parameters, determining the coefficient as to minimize the root mean square errors. We used the parameters as explanatory variables which could be divided into posture parameters and individual parameters. Posture parameters included the angle of upper body, thigh and lower thigh. Individual parameters included height, weight, axial and circumferential lengths of thigh and lower thigh. The magnitude of the force was normalized by a body weight, and the acting position was expressed by the moment arm length around a knee joint and normalized by a height.

As a result, the adjusted coefficient of determination improved and the root mean square error decreased when using both posture and individual parameters, though there were large errors when neglecting either parameters. The accuracy decreased little when using the same equation for plantarflexed and dorsiflexed kneeling in magnitude. The relation of measured and estimated values of the magnitude and acting position, using the common equation with all the parameters. It might be because the difference of the postures could be described by the inclination angle of a thigh. In both postures, the magnitude of a thigh-calf contact force was mainly affected by the posture and acting position by the individual parameters. When calculating the knee joint load, the errors would be about 8.59 Nm on the knee moment and 290 N on the knee load when using just an average, and they would decrease to 2.23 Nm and 74 N respectively using the estimation equation.

INTRODUCTION

Growth-guidance constructs are an alternative to growing rods for the surgical treatment of early onset scoliosis (EOS). In growth-guidance systems, free-sliding anchors preserve longitudinal spinal growth, thereby eliminating the need for surgical lengthening procedures. Non-segmental constructs containing ultra-high molecular weight polyethylene (UHMWPE) sublaminar wires have been proposed as an improvement to the traditional Luque trolley. In such a construct, UHMWPE sublaminar wires, secured by means of a knot, serve as sliding anchors at the proximal and distal ends of a construct, while pedicle screws at the apex prevent rod migration and enable curve derotation. Ideally, a construct with the optimal UHMWPE sublaminar wire density, offering the best balance between providing adequate spinal fixation and minimizing surgical exposure, is designed preoperatively for each individual patient. In a previous study, we developed a parametric finite element (FE) model that potentially enables preoperative patient-specific planning of this type of spinal surgery. The objective of this study is to investigate if this model can capture the decrease in range of motion (ROM) after spinal fixation as measured in an experimental study.

Background

Bio-Active Glass (BAG) is a promising bone graft substitute for large bone defect reconstruction because of its favourable osteoconductive, antibacterial and angiogenic properties. Potentially, it could also mechanically reinforce the defect, thus making it suitable for load-bearing defects. However, the mechanical properties of the reconstructive layer consisting of BAG/bone allograft mixtures are unknown. The goals of this study therefore were, first, to measure the mechanical properties of different BAG/bone graft mixtures and, second, to investigate to what extent such mixtures could reinforce distal tibial defects using micro-FE analysis and high-resolution CT scans.

Background

Finite element (FE) models have become a standard pre-clinical tool to study biomechanics of spine and are used to simulate and evaluate different strategies in scoliosis treatment: examine their efficacy as well as the effect of different implant design parameters. The goal of this study is to investigate, in a system of rods and laminar wires, the effect of the number of wires and their pre-stress on whole spine stiffness.

Thigh-calf contact force is the force acting on posterior side of the thigh and calf during deep knee flexion. It has been reported the force is important to analyze the kinetics of a lower limb and a knee joint. Some previous researches reported the measured thigh-calf contact force, however, the values varied among the reports. Furthermore, the reports indicated that there were large variations even in a single report. One of the reports tried to find the relationship between the magnitude of thigh-calf contact force and anthropometric measurement as height, weight or perimeter of the lower limb, however, there could not found clear correlations. We considered that the cause of the variations might be the difference of the posture. At heel-rise squatting posture, we can bend or stand upright the upper body. Therefore we tried to create the equation to estimate the thigh-calf contact force by multiple regression analysis, using the anthropometric and posture parameters as explanatory variables.

We performed the experiment to measure thigh-calf contact force, joint angles and anthropometric information. Test subjects were 10 healthy male. First we measured their height, weight, perimeter of the thigh and muscle mass of the legs and whole body. Muscle mass was measured by body composition meter (BC-118E, Tanita Co., Japan). Then, test subjects were asked to squat with their heels lifted and with putting the pressure distribution sensor between thigh and calf. And they bent their upper body forward and backward. The pressure sensor to be used was ConfroMat System (Nitta Co., Japan). After that, we measured the joint angles of the hip, knee and ankle, and the angle between the floor and upper body using the videos taken during the experiment. Then, we created the equation to estimate the thigh-calf contact force by linear combination of the anthropometric values and joint angles. The coefficients were settled as to minimize the average error between measured and estimated values.

Results are shown in Fig.1. Forces were normalized by the body weight of the test subjects. Because the horizontal axes show the measured and vertical axis show the estimated values, the estimation is accurate when the plots are near the 45-degree line. Average error was 0.11BW by using only physical values, 0.15BW by angles and 0.06BW using both values. And the maximum error was 0.69BW, 0.43BW and 0.32BW respectively. Thus we could estimate the thigh-calf contact force by multiple regressions, using both physical parameters and angles to indicate the posture. Using the equation, we would be able to analyze the kinetics of a lower limb by physical and motion measurement. Our future work might be increasing the number of subjects to consider the appropriateness, because the test subjects of this study were very limited.

Introduction: Over the last 10 years minimally invasive plate osteosynthesis (MIPO) has gained more and more popularity over the conventional open surgical approach (ORIF). Numerous clinical case collection studies reported the MIPO technique as a good, alternative method. While MIPO offers some advantages over ORIF, it also has significant drawbacks, such as more demanding surgical technique and increased radiation exposure. In an attempt to compare these approaches, a previous animal study 1 did not show any significant differences in fracture healing outcome. Using a new developed, standardised severe trauma model on the sheep femur 2, this study examines the effects of the surgical approaches on fracture healing.

Methods: 24 sheep (Merino wethers, mean age 5.6years, mean weight 39.1kg) underwent the trauma model 2 with a severe soft tissue damage and a multifragmentary, distal femur fracture as well as initial stabilisation with an external fixator. After five days of soft tissue recovery, the animals were definitively operated with an internal fixator (LCP) randomised either by a minimally invasive or open approach. The sheep were sacrificed after 4 and 8 weeks (two groups), mechanical testing performed and statistically analysed with ANOVA test.

Results: After 4 weeks, torsional rigidity is significantly higher in the MIPO group (30.1r10.6(SD)%) of fractured to intact bones, p< 0.05) compared to ORIF group (9.8r12.4(SD)%), while ultimate torque also shows increased values for MIPO technique (p=0.11). After 8 weeks, the differences in mechanical properties levelled out, but still higher values for the MIPO group (p=0.36/p=0.26).

Conclusion: In the early stage of fracture healing, minimally invasive plate osteosynthesis shows advanced healing pattern compared to open fixation technique. This advantage seems to level out over time.

Introduction: Osteoporosis, a major public health burden, is associated with increased fracture risk. Fracture healing in osteoporosis is altered with reduced callus formation and impaired biomechanical properties of newly formed bone leading to high risk of fixation failure. Experimental data have shown decreased healing potential in aged animals and in animal models of post-menopausal bone loss. It is unclear whether fracture healing is similarly impaired in senile osteoporosis. The objective of this study is to investigate fracture healing in a small animal model of senile osteoporosis, senescence-accelerated mouse prone 6 (SAMP6).

Materials & Methods: A mid-femur osteotomy was created in SAMP6-mice (n=24) and senescence-resistant inbred strains (SAMR1) (n=24) were used as controls. The osteotomy was rigidly fixed using a newly developed screw-plate-implant (MouseFix). Fracture healing was evaluated at 7, 14, 28 and 42 days after surgery using micro-CT and histomorphometry. Biochemical marker for bone formation (osteocalcin) and bone resorption (TRAP5b) were evaluated from serum samples. MSC were extracted from the femurs of mice and cultured in vitro and differentiated into either osteoblasts or adipocytes using standard induction media.

Results: Studies carried out in vitro confirmed that MSC isolated from the bone marrow of SAMP6 mice had a reduced tendency to differentiate toward the osteoblast cell lineage as previously reported in human osteoporotic patients. Although osteoblastogenesis was clearly impaired, the formation of new bone in SAMP6 mice was comparable to that observed in SAMR1 mice. Similar results were found for histomorphometry data analyzing the degree of bone mineralisation. Interestingly, osteocalcin levels were significantly increased in serum samples from osteoporotic mice at day 7 and 14 following fracture.

Discussion: The data presented here indicates that fracture healing proceeds normally in a mouse model for senile osteoporosis. This finding supports the clinical observation that although fracture fixation is difficult in osteoporosis, healing potential seems to be unchanged. MSC from osteoporotic patients as wells as from SAMP6-mice show reduced proliferation rate together with adipogenic rather than osteogenic differentiation pattern. However, decreased cell dynamics seems not to influence diaphyseal fracture healing. Other sources of MSC other than bone marrow-derived MSC may therefore be pivotal in determining the outcome of intramembranous bone repair in both normal and osteoporotic bone.

We have observed damage to the labrum as a result of repetitive acetabular impingement in non-dysplastic hips, in which the femoral neck appears to abut against the acetabular labrum and a non-spherical femoral head to press against the labrum and adjacent cartilage. In both mechanisms anatomical variations of the proximal femur may be a factor. We have measured the orientation of the femoral neck and the offset of the head at various circumferential positions, using MRI data from volunteers with no osteoarthritic changes on standard radiographs. Compared with the control subjects, paired for gender and age, patients showed a significant reduction in mean femoral anteversion and mean head-neck offset on the anterior aspect of the neck. This was consistent with the site of symptomatic impingement in flexion and internal rotation, and with lesions of the adjacent rim. Furthermore, when stratified for gender and age, and compared with the control group, the mean femoral head-neck offset was significantly reduced in the lateral-to-anterior aspect of the neck for young men, and in the anterolateral-to-anterior aspect of the neck for older women. For patients suspected of having impingement of the rim, anatomical variations in the proximal femur should be considered as a possible cause.

Since January 1993 we have carried out MR arthrography on 23 patients with clinical symptoms and signs of abnormality of the acetabular labrum. Most of the patients were young adults. Such symptoms are known precursors of osteoarthritis, and therefore early and accurate evaluation is required.

We assessed the value of MR arthrography of the hip as a minimally-invasive diagnostic technique, in a prospective study and compared the findings with those at subsequent operations. All the patients complained of groin pain; 22 had a positive acetabular impingement test and 15 had radiological evidence of hip dysplasia.

In 21 of the patients, MR arthrography suggested either degeneration or a tear of the labrum or both. These findings were confirmed at operation in 18 patients, but there was no abnormality of the labrum in the other three. In two of the patients, MR arthrography erroneously suggested an intact labrum. Both MR arthrography and intraoperative inspection located lesions of the superior labrum most often, and these appeared slightly larger on arthrography than at operation.

We consider that MR arthrography is a promising diagnostic technique for the evaluation of abnormalities of the acetabular labrum.