Fonseca F, Sousa A, Completo A
Orthopaedic Surgery Department, Coimbra University Hospitals, Coimbra, Portugal.
Mechanical Engineering Department, University of Aveiro, 3810-193, Aveiro, Portugal.
J Exp Orthop. 2020 Apr 26;7(1):24. doi: 10.1186/s40634-020-00242-w.
Although metaphyseal sleeves are usually used with stems, little is known about the exact contribution/need of the stem for the initial sleeve-bone interface stability, particularly in the femur, if the intramedullary canal is deformed or bowed. The aim of the present study is (1) to determine the contribution of the diaphyseal-stem on sleeve-femur interface stability and (2) to determine experimentally the strain shielding effect on the metaphyseal femur with and without diaphyseal-stem. It is hypothesised that diaphyseal-stem addition increases the sleeve-femur interface stability and the strain-shielding effect on the metaphyseal femur relatively to the stemless condition.
The study was developed through a combined experimental and finite-element analysis approach. Five synthetic femurs were used to measure cortex strain (triaxial-rosette-gages) behaviour and implant cortex micromotions (Digital Image Correlation) for three techniques: only femoral-component, stemless-sleeve and stemmed-sleeve. Paired t-tests were performed to evaluate the statistical significance of the difference of cortex strains and micromotions. Finite-element models were developed to assess the cancellous bone strain behaviour and sleeve-bone interface micromotions; these models were validated against the measurements.
Cortex strains are significantly reduced (p < 0.05) on the stemmed-sleeve with a 150 μstrain mean reduction at the medial and lateral distal sides which compares with a 60 μstrain mean reduction (p > 0.05) on the stemless condition. Both techniques presented a mean cancellous bone strain reduction of 700 μstrain (50%) at the distal region and a mean increase of 2500 μstrain (4x) at the sleeve proximal region relative to the model only with the femoral component. Both techniques presented sleeve-bone micromotions amplitude below 50-150 μm, suitable for bone ingrowth.
The use of a supplemental diaphyseal-stem potentiates the risk of cortex bone resorption as compared to the stemless-sleeve condition; however, the stem is not essential for the enhancement of the initial sleeve-bone stability and has minor effect on the cancellous bone strain behaviour. Based on a purely structural point view, it appears that the use of a diaphyseal-femoral-stem with the metaphyseal sleeve is not mandatory in the revision TKA, which is particularly relevant in cases where the use of stems is impracticable.
尽管干骺端套筒通常与柄一起使用，但对于柄在初始套筒-骨界面稳定性方面的确切作用/需求知之甚少，尤其是在股骨中，当髓腔变形或弯曲时。本研究的目的是：（1）确定骨干柄对套筒-股骨界面稳定性的作用；（2）通过实验确定有无骨干柄时对干骺端股骨的应变屏蔽效应。假设相对于无柄情况，添加骨干柄可提高套筒-股骨界面稳定性以及对干骺端股骨的应变屏蔽效应。
本研究通过实验与有限元分析相结合的方法开展。使用五根合成股骨来测量三种技术的皮质骨应变（三轴应变片）行为和植入物与皮质骨的微动（数字图像相关技术）：仅股骨组件、无柄套筒和有柄套筒。进行配对t检验以评估皮质骨应变和微动差异的统计学显著性。建立有限元模型以评估松质骨应变行为和套筒-骨界面微动；这些模型通过测量数据进行验证。
有柄套筒的皮质骨应变显著降低（p < 0.05），在内侧和外侧远端平均降低150微应变，而无柄情况下平均降低60微应变（p > 0.05）。相对于仅使用股骨组件的模型，两种技术在远端区域的松质骨应变平均降低700微应变（50%），在套筒近端区域平均增加2500微应变（4倍）。两种技术的套筒-骨微动幅度均低于50 - 150微米，适合骨长入。
与无柄套筒情况相比，使用补充性骨干柄会增加皮质骨吸收的风险；然而，柄对于增强初始套筒-骨稳定性并非必不可少，且对松质骨应变行为影响较小。从纯粹的结构角度来看，在翻修全膝关节置换术中，使用带有干骺端套筒的骨干柄似乎并非必需，这在无法使用柄的情况下尤为重要。
