Physical and chemical decay of prosthetic ACL after in vivo implantation

Massive foreign body reaction and osteolysis following primary anterior cruciate ligament reconstruction with the ligament augmentation and reconstruction system (LARS): a case report with histopathological and physicochemical analysis

BACKGROUND

Autologous hamstrings and patellar tendon have historically been considered the gold standard grafts for anterior cruciate ligament reconstruction (ACLR). In the last decades, the utilization of synthetic grafts has re-emerged due to advantageous lack of donor site morbidity and more rapid return to sport. The Ligament Augmentation and Reconstruction System (LARS) has demonstrated to be a valid and safe option for ACLR in the short term. However, recent studies have pointed out the notable frequency of associated complications, including synovitis, mechanical failure, and even chondrolysis requiring joint replacement.

CASE PRESENTATION

We report the case of a 23-year-old male who developed a serious foreign body reaction with wide osteolysis of both femoral and tibial tunnels following ACLR with LARS. During first-stage arthroscopy, we performed a debridement of the pseudocystic mass incorporating the anterior cruciate ligament (ACL) and extending towards the tunnels, which were filled with autologous anterior iliac crest bone graft chips. Histological analysis revealed the presence of chronic inflammation, fibrosis, and foreign body giant cells with synthetic fiber inclusions. Furthermore, physicochemical analysis showed signs of fiber depolymerization, increased crystallinity and formation of lipid peroxidation-derived aldehydes, which indicate mechanical aging and instability of the graft. After 8 months, revision surgery was performed and ACL revision surgery with autologous hamstrings was successfully carried out.

CONCLUSIONS

The use of the LARS grafts for ACLR should be cautiously contemplated considering the high risk of complications and early failure.

Topologically controlled tensile behaviour of braided prostheses for anterior cruciate ligaments

Anterior cruciate ligament (ACL) is one of the most susceptible ligaments of the knee that can suffer injury. These ruptured ligaments can be treated through surgical intervention using a braided structure that either acts as a substitute graft in isolation or an augmentation device alongside the biological tissue. Therefore, the main objective of the research work is to present an analytical model for predicting the complete set of tensile properties of braided prosthesis consisting of multifilament strands based upon predefined braid geometry and constituent material properties. The model has also accounted for the kinematical changes under defined loading conditions. The research findings have been confirmed by making a comparison between the theoretical and experimental results. The tensile properties of braided prostheses predicted via analytical route matched reasonably well with the experimental results.

Bioactive scaffolds for bone and ligament tissue

Bone and ligament injuries present the greatest challenges in connective tissue regeneration. The design of materials for these applications lies at the forefront of material science and is the epitome of its current ambition. Indeed, its goal is to design and fabricate reproducible, bioactive and bioresorbable 3D scaffolds with tailored properties that are able to maintain their structure and integrity for predictable times, even under load-bearing conditions. Unfortunately, the mechanical properties of today's available porous scaffolds fall short of those exhibited by complex human tissues, such as bone and ligament. The manipulation of structural parameters in the design of scaffolds and their bioactivation, through the incorporation of soluble and insoluble signals capable of promoting cell activities, are discussed as possible strategies to improve the formation of new tissues both in vitro and in vivo. This review focuses on the different approaches adopted to develop bioactive composite systems for use as temporary scaffolds for bone and anterior ligament regeneration.

Viscoelastic behavior of composite ligament prostheses

Despite the compelling need for artificial connective tissue replacements for orthopedic applications, to date, there is no material which can adequately reproduce the mechanical behavior of natural tissue with necessary long-term endurance. In this work, we introduce a novel soft composite material as a more suitable candidate for connective tissue replacement. The material proposed is based on a hydrogel-polymer matrix reinforced with poly(ethylene terephthalate) fibers wound helically to mimic the architecture of the collagen fibers in natural tissue. Macroscopic behaviors such as static stress-strain, stress relaxation, and dynamic frequency responses can be modulated with choice of the components and design of the composite structure. In doing so, the mechanical characteristics of natural ligaments can be qualitatively reproduced and sustained over time.

Composite hydrogels for implants

Hydrophilic composite structures are designed to mimic the transport and mechanical properties of natural soft tissue such as tendons, ligaments and intervertebral discs. Mechanical and viscoelastic behaviour of a soft composite material based on a hydrogel matrix reinforced with bundles of polyethylene therephthalate (PET) fibres is analysed. The typical J-shaped stress-strain behaviour, displayed by natural tendons and ligaments, is reproduced. The mechanical characteristics, such as the extent of the 'toe-in region' and the elastic modulus in the linear region, can be controlled by varying the winding angle of the fibres and the matrix composition. Dynamic mechanical analysis showed the dual behaviour of the composite systems due to the progressive contribution of the PET fibres. Different poly(2-hydroxyethylmethacrylate)/polycaprolactone (PHEMA/PCL) semi-interpenetrating polymer networks (IPNs) hydrogel composite systems reinforced with PET fibres have been investigated for potential use as intervertebral disc prostheses. Compression properties have been evaluated by static and dynamic tests. Uniaxial compression tests on the swollen samples showed an increase of the modulus and maximum stress with increasing content of PCL and PET fibres. Creep behaviour is also dependent on the hydrogel composition. The composite PHEMA/PCL hydrogels showed compression properties similar to those expressed by canine intervertebral discs in different spinal locations.

Mechanical behaviour of composite artificial tendons and ligaments

The mechanical behaviour of a soft composite material based on a hydrogel polymer matrix reinforced with bundles of poly(ethylene terephthalate) (PET) fibres is analysed. The composite reproduces the typical J-shaped stress-strain curves displayed by natural tendons and ligaments. The lamination composite theory was used to investigate the role of the fibres and the matrix properties, as well as the role of the winding angle and the volumetric fraction of fibres, on the mechanical response of this system. The results suggested that large variations in the mechanical behaviour can be obtained by changing the winding angle of the fibres in the composite which determines the extent of the 'toe' region and the sensitivity of the system to the rigidity of the fibres.