RESUMO

Total hip arthroplasty stem fracture is an important contributor to morbidity rate and increases the cost of revision surgery. Failure is usually caused by issues related to overload, inadequate stem support, inappropriate stem design or dimensions and material processing. In this study, the role of the relationship between material characterization and biomechanical performance in the fracture of retrieved stems was explored. The stems were manufactured with forged stainless steel, had the same length, 12/14 trunnion, and 28-mm head. These stems were evaluated by macroscopic and microscopic examination to identify the causes of premature failure. Each stem was sectioned into four regions, and the cross-sections were used for the microhardness and grain size analysis. Finite element analysis (FEA) was carried out, considering the stem positioned at the femur, a musculoskeletal model, and biomechanical loading. All stems had fractured through a fatigue mechanism, mainly a unidirectional bending loading condition, with crack nucleation on the lateral side and propagation on the medial side. The numerical analysis revealed maximum mechanical stress on the lateral side of the stem neck, but this was below the yield stress calculated via the hardness. The use of a shorter head neck length could reduce the maximum mechanical stress at the neck. At a cross-section near the plane of the stem fracture, the hardness was lower than that normally reported by the ASM, and there were heterogonous and coarse grain sizes on the lateral side. The main cause of failure of the two stems analyzed was a combination of low hardness and coarse grain size, due to inappropriate materials processing, worsen by a high level of stress on the lateral side of the neck due to the large stem-head offset selected by the orthopedic surgeon.

Assuntos

Artroplastia de Quadril , Prótese de Quadril , Artroplastia de Quadril/efeitos adversos , Fêmur/cirurgia , Humanos , Desenho de Prótese , Falha de Prótese , Reoperação

RESUMO

BACKGROUND: High-energy tibial plateau fractures are challenges in treatment with controversy over operative stabilisation, especially for fractures with metaphyseal-diaphyseal dissociation. Treatment with percutaneous or minimally invasive direct reduction techniques, usually associated with circular external fixation, has generated interest although there is no consensus regarding the type of external fixation to be used. AIM: This study aims to compare the two hybrid circular external fixation mountings used to treat the high-energy tibial plateau fractures. METHODS: Two different groups of hybrid circular external fixation frame mountings were assembled using composite tibiae with proximal metaphyseal osteotomies simulating tibial plateau fractures with metaphyseal-diaphyseal dissociation. The standard all-wire frame mounting was assembled, and the comparison frame mounting had the distal K-wires replaced with half-pins. Both groups were tested through cyclic loading between 300 and 1000 N for 10,000 cycles. Interfragmentary linear and rotational displacements were analysed. RESULTS: The standard frame mounting behaved similarly to a classic Ilizarov frame, allowing greater axial movement (mean, 3.76 ± 0.26 mm in the standard group and 3.02 ± 0.23 mm in the test group) and smaller mediolateral displacement compared with the test frame (mean, 0.17 ± 0.16 mm compared to 0.56 ± 0.12 mm). The test frame behaved more similarly to a linear external fixator and provided greater axial stability, similar anteroposterior displacement, and lower mediolateral stability. Despite these differences, in both groups the axial displacement was greater than the prejudicial nonaxial movements. CONCLUSION: Increasing the number of half-pins and decreasing the number of K-wires in hybrid circular external fixation generate frames that tend to behave more similarly to the linear external fixators. HOW TO CITE THIS ARTICLE: Cardoso GS, Amorim R, Penha FM, et al. Biomechanical Analysis of the Behaviour at the Metaphyseal-Diaphyseal Junction of Complex Tibial Plateau Fractures Using Two Circular Fixator Configurations. Strategies Trauma Limb Reconstr 2020;15(3):138-145.