Intervertebral discs (IVD) provide flexibility to the back and ensure functional distributions of the spinal loads. They are avascular, and internal diffusion-dependent metabolic transport is vital to supply nutrients to disc cells1, but interactions with personalized IVD shapes and mechanics remain poorly explored. Poromechanical finite element models of seven personalized lumbar IVD geometries, with mean heights ranging from 8 to 16 mm were coupled with a reactive oxygen, glucose and lactate transport model linked with tissue deformations and osmosis . In previous studies, reduced formulations of the divergence of the solute flux (∇ .J = ∇ . (D∇ C) = ∇ D. ∇ C +D∇ 2C) ignored the dependence of the diffusion on the deformation gradients, ∇ D. ∇C. We simulated this phenomenon to explore its significance in mechano-metabolic -transport couplings, in the different geometries, over 24h of simulated rest (8h) and physical activity (16h). ∇ D. ∇ C affected the daily variations of glucose concentrations in IVD thinner than 12 mm but with neglectable variation ranges, while not considering ∇ D. ∇ C in taller discs only slightly overestimated the glucose concentration. Most importantly, tall IVD had nearly 60% less glucose than thin IVD, with local drops below the concentration of 0.5 mM, considered to be critical for disc cells3, in the anterior nucleus pulposus. On the one hand, previous reduced formulations for mechanometabolic-transport models of the IVD seem acceptable, even for patient-specific modelling. On the other hand, tall IVD might suffer from unfortunate combinations of deformation-dependent solute diffusion and large diffusion distances, which may favor early

Acknowledgements: Catalan Government and European Commission (2020 BP 00282; ERC-2021-CoG-O-Health-101044828)

This study investigates the relationships between Intervertebral Disc (IVD) morphology and biomechanics using patient-specific (PS) finite element (FE) models and poromechanical simulations.

169 3D lumbar IVD shapes from the European project MySpine (FP7-269909), spanning healthy to Pfirrmann grade 4 degeneration, were obtained from MRIs. A Bayesian Coherent Point Drift algorithm aligned meshes to a previously validated structural FE mesh of the IVD. After mesh quality analyses and Hausdorff distance measurements, mechanical simulations were performed: 8 and 16 hours of sleep and daytime, respectively, applying 0.11 and 0.54 MPa of pressure on the upper cartilage endplate (CEP). Simulation results were extracted from the anterior (ATZ) and posterior regions (PTZ) and the center of the nucleus pulposus (CNP). Data mining was performed using Linear Regression, Support Vector Machine, and eXtreme Gradient Boosting techniques. Mechanical variables of interest in DD, such as pore fluid velocity (FLVEL), water content, and swelling pressure, were examined. The morphological variables of the simulated discs were used as input features.

Local morphological variables significantly impacted the local mechanical response. The local disc heights, respectively in the mid (mh), anterior (ah), and posterior (ph) regions, were key factors in general. Additionally, fluid transport, reflected by FLVEL, was greatly influenced (r2 0.69) by the shape of the upper and lower cartilage endplates (CEPs).

This study suggests that disc morphology affects Mechanical variables of interest in DD. Attention should be paid to the antero-posterior distribution and local effects of disc heights. Surprisingly, the CEP morphology remotely affected the fluid transport in NP volumes around mid-height, and mechanobiological implications shall be explored. In conclusion, patient-specific IVD modeling has strong potential to unravel important correlations between IVD phenotypes and local tissue regulation.

Acknowledgments: European Commission: Disc4All-MSCA-2020-ITN-ETN GA: 955735; O-Health-ERC-CoG-2021-101044828

INTRODUCTION

Limb salvage surgery is a common treatment for patients who suffer from bone tumors. In the case of pelvic tumors this creates a challenge for the surgeon and the treatment remains controversial because the oncologic complications like local recurrence, dissemination and orthopaedic ones, like infection, haemorrhage, and mechanical problems of reconstructions Tumors affecting the acetabulum are a challenge for the surgeon because of the impact in the function of the extremity. There are many reconstruction techniques described in the literature like prosthesis, allograft systems, arthrodesis, etc…, but still there is not a gold standard due to the poor functional results at long term follow up, and the associated complications of all techniques. In this study we show the experience in our center on pelvic reconstructions after tumors affecting the acetabulum area (zone II).

Goals: Sarcomatous degeneration of giant cell tumours (GCT) occurs rarely. It occurs in less than 1% of the cases, and most of them are GCT previously treated with radiotherapy. The goal of this presentation is to review the CGT cases treated at our unit that have evolved towards malignization.

Methods: Retrospective study of 96 GCT treated at our Hospital between 1983 and 2005. 5 presented sarcomatous degeneration in their evolution. These were the cases of 3 men and 2 women with a mean age of malignization of 42 years (32 years – 54 years). The median follow-up period was 155 months (5 months – 209 months). 3 cases affected the distal femur, one case affected distal radius and one case affected proximal humerus, with a slight tendency to the right hemibody. The primary treatment for GCT in these patients was curettage and bone graft. Only one case had received previous radiotherapy. In the same period of time we had two cases of lung dissemination of CGT with typical histology, without previous malignization of tumour.

Results: Malignization takes place, on average, at the 1.8th recurrence (1.3). Histologically, we find 3 osteosarcomas and 2 indifferentiated tumours. Three patients developed distant dissemination; 2 patients died due to lung metastases, with a mean time between the first surgery and the sarcomatous degeneration of 90 months (40 monts – 183 months) and a mean time between malignization and mestastases of 22.3 months (9 months – 34 months) The treatment, once the malignization was diagnosed, consisted in wide resection and substitution with mega-arthroplasty in cases of distal femur and osteoarticular graft at the shoulder. 2 cases required amputation of the affected limb due to irresecable recurrence in soft tissues.

Conclusions: There is no predictive criteria of which type of primary typical CGT will evolve into sarcoma. The malignization always has as a result high grade sarcomas, with a high tendency to hematogenous dissemination. When lung metastases appear the survival prognosis is a number of months. We must suspect malignization of a benign CGT when one of the relapses shows a very rapid growth with radiologic aggressive characteristics; in these cases we prefer wide resection of the tumour instead of curettage and thus we prevent the possible sarcomatous degeneration.

Introduction and purpose: Hallux valgus is a pathological condition with a high incidence in adults. Both open and percutaneous surgical techniques have been developed for its treatment. The aim of our study is to retrospectively assess the validity of the minimally invasive surgical method used by our department and determine its rate of complications.

Materials and methods: We retrospectively studied 100 patients that underwent surgery for hallux valgus using the MIS technique between 2000 and 2005 in our department. These cases were operated by 2 experienced surgeons and had a maximum 2-year follow-up during which they were assessed both clinically and statistically to determine the outcome and complication rate of this surgical method.

Results: MIS osteotomy performed in our department (double osteotomy of the first toe, bunionectomy, tenotomy of the adductor of the first toe and osteotomies of the 2nd, 3^rd and 4^th metatarsals) for the treatment of hallux valgus resulted in a good degree of correction with an acceptable rate of recurrences and complications such as 2^nd metatarsal nonunion and superficial infections in less than 10% of cases. The majority of patients were completely satisfied with the clinical results with AOFAS assessment tests that were good or very good.

Conclusions: In spite of the fact that radiographically 35% of the patients suffered partial recurrences, more than 90% of the patients were clinically asymptomatic. Therefore we consider this a valid technique for the treatment of hallux valgus in adults.