[Translated article] Mechanical resistance of polylactic acid bone matrices developed by 3D printing for the reconstruction of bone defects.

INTRODUCTION: Bone defects are one of the main limitations in orthopaedic surgery and traumatology. For this reason, multiple bone replacement systems have been developed, either by prosthetic implant or by substitution with osteoforming substances, whose limitations are their survival and lack of structurality, respectively. The objective of this work is the generation of a new material for the creation of biologically active structures that have sufficient tensile strength to maintain the structure during remodelling. MATERIAL AND METHODS: A new filament based on the fusion of natural polylactide acid (PLA) powder was designed for the generation of pieces by means of fused deposition modelling (FDM) on which to carry out tensile mechanical tests of osteosynthesis material. A total of 13 groups with different cortical thickness, filling and layer height were carried out, with 10 tensile tests in each group, defining the tensile breaking limit for each group. The regression lines for each group and their mechanical resistance to traction on the filament used were determined. RESULTS: The filament ratio per contact surface unit with the osteosynthesis used was the main determinant of the mechanical resistance to traction, either at the expense of the increase in cortical thickness or by the increase in the percentage of cancellous bone filling. Layer height had a minor effect on tensile strength. The regression value was high for cortical thickness and cancellous filling, being elements with a predictable biomechanical behaviour. CONCLUSIONS: The new methodology allows the creation of personalised neutral and implantable PLA bone matrices for the reconstruction of large bone defects by means of 3D printing by FDM with a mechanical resistance to traction greater than that of current biological support structures.

Mechanical resistance of polylactic acid bone matrices developed by 3D printing for the reconstruction of bone defects. / Resistencia mecánica de matrices óseas de ácido poliláctico desarrolladas por impresión 3D para la reconstrucción de defectos óseos.

INTRODUCTION: Bone defects are one of the main limitations in orthopedic surgery and traumatology. For this reason, multiple bone replacement systems have been developed, either by prosthetic implant or by substitution with osteoforming substances, whose limitations are their survival and lack of structurality, respectively. The objective of this work is the generation of a new material for the creation of biologically active structures that have sufficient tensile strength to maintain the structure during remodeling. MATERIAL AND METHODS: A new filament based on the fusion of natural polylactide acid (PLA) powder was designed for the generation of pieces by means of fused deposition modeling (FDM) on which to carry out tensile mechanical tests of osteosynthesis material. A total of 13 groups with different cortical thickness, filling and layer height were carried out, with 10 tensile tests in each group, defining the tensile breaking limit for each group. The regression lines for each group and their mechanical resistance to traction on the filament used were determined. RESULTS: The filament ratio per contact surface unit with the osteosynthesis used was the main determinant of the mechanical resistance to traction, either at the expense of the increase in cortical thickness or by the increase in the percentage of cancellous bone filling. Layer height had a minor effect on tensile strength. The regression value was high for cortical thickness and cancellous filling, being elements with a predictable biomechanical behavior. CONCLUSIONS: The new methodology allows the creation of personalized neutral and implantable PLA bone matrices for the reconstruction of large bone defects by means of 3D printing by FDM with a mechanical resistance to traction greater than that of current biological support structures.

[Extensor mechanism allograft and radiotherapy in the treatment of soft tissue sarcomas around the knee: Presentation of two clinical cases]. / Homoinjerto de aparato extensor y radioterapia en el tratamiento de sarcomas de partes blandas del entorno de la rodilla. A propósito de 2 casos clínicos.

OBJECTIVE: Knee involvement of soft tissue sarcomas is rare and very difficult to treat. Reconstruction of the extensor mechanism of the knee is essential to restore the functionality. Functional outcome is compromised by poor soft tissue coverage, adjuvant local radiotherapy, and resection of the extensor apparatus. No results were found in the literature as regards treatment by resection and reconstruction of the extensor mechanism in combination with adjuvant radiotherapy. The effects of radiotherapy are also unknown in the allografts. MATERIAL AND METHOD: . Two cases are presented of soft tissue sarcoma around de knee treated by resection, reconstruction of the extensor mechanism with cryopreserved cadaver allograft, and local radiotherapy. RESULTS: After more than 3 years of follow up, both patients are free of disease and have a good joint balance. DISCUSSION AND CONCLUSIONS: Resection of the tumor with adequate safety margins and reconstruction using cadaveric allograft preserves the extensor mechanism and function of the limb. The soft tissue coverage is an added problem that can be solved by propeller fasciocutaneous flap coverage. After surgery, the limb must be immobilized with a knee brace locked in extension. Local radiotherapy contributes to local control of the disease. The reconstruction of the extensor mechanism of the knee with allograft is a functional alternative to amputation, and it does not contraindicate adjuvant radiotherapy to improve local control of the disease.

Surgical management of hand contractures and pseudosyndactyly in dystrophic epidermolysis bullosa.

The term epidermolysis bullosa refers to a group of disorders characterized by skin blistering following minor trauma. The hands, because of constant use during normal daily activity, are especially exposed to blistering, with secondary scarring leading to pseudosyndactyly, adduction contracture of the thumb, and flexion or extension contracture of the fingers. The standard surgical approach for the correction of these deformities is based on the incisional release of pseudosyndactyly and contractures, and split skin grafting of the secondary wounds. A simplified approach without skin grafting is presented in this paper. Four children (8 hands) underwent 25 operations over two decades. The results, in terms of postoperative healing and recurrence, were comparable with those of the standard approach involving skin grafting.