Tianjin Medical University, 22 Qixiangtai Road, Tianjin, People's Republic of China.
Department of Bone Oncology, Tianjin Hospital, 406 Jiefang Southern Road, Tianjin, People's Republic of China.
J Orthop Surg Res. 2020 Dec 9;15(1):589. doi: 10.1186/s13018-020-02025-6.
Aseptic loosening of distal femoral tumor implants significantly correlates with the resection length. We designed a new "sleeve" that is specially engaged in the metaphysis at least 5 cm proximal to the knee joint line to preserve as much bone stock as possible. This study investigates the influence of a metaphyseal sleeve on the stress-strain state of a bone tumor implant system in the distal femur.
Cortex strains in intact and implanted femurs were predicted with finite element (FE) models. Moreover strains were experimentally measured in a cadaveric femur with and without a sleeve and stem under an axial compressive load of 1000 N. The FE models, which were validated by linear regression, were used to investigate the maximal von Mises stress and the implanted-to-intact (ITI) ratios of strain in the femur with single-legged stance loading under immediate postoperative and osseointegration conditions.
Good agreement was noted between the experimental measurements and numerical predictions of the femoral strains (coefficient of determination (R) ≥ 0.95; root-mean-square error (RMSE%) ≈ 10%). The ITI ratios for the metaphysis were between 13 and 28% and between 10 and 21% under the immediate postoperative and osseointegration conditions, respectively, while the ITI ratios for the posterior and lateral cortices around the tip of the stem were 110% and 119% under the immediate-postoperative condition, respectively, and 114% and 101% under the osseointegration condition, respectively. The maximal von Mises stresses for the implanted femur were 113.8 MPa and 43.41 MPa under the immediate postoperative and osseointegration conditions, which were 284% and 47% higher than those in the intact femur (29.6 MPa), respectively.
This study reveals that a metaphyseal sleeve may cause stress shielding relative to the intact femur, especially in the distal metaphysis. Stress concentrations might mainly occur in the posterior cortex around the tip of the stem. However, stress concentrations may not be accompanied by periprosthetic fracture under the single-legged stance condition.
股骨远端肿瘤植入物的无菌性松动与切除长度显著相关。我们设计了一种新的“套管”，至少在膝关节线近端 5cm 处与骨干紧密结合，以尽可能多地保留骨量。本研究探讨了骨干套管对股骨远端骨肿瘤植入物系统的应力-应变状态的影响。
采用有限元（FE）模型预测完整和植入股骨的皮质应变。此外，在轴向压缩 1000N 载荷下，在有无套管和柄的尸体股骨上进行了实验测量。通过线性回归验证的 FE 模型用于研究单腿站立负荷下术后即刻和骨整合两种情况下股骨的最大 von Mises 应力和植入物与完整（ITI）比值。
股骨应变的实验测量值与数值预测值吻合良好（决定系数（R）≥0.95；均方根误差（RMSE%）≈10%）。术后即刻和骨整合条件下，骨干的 ITI 比值分别为 13%至 28%和 10%至 21%，而在术后即刻条件下，柄尖端周围后皮质和外侧皮质的 ITI 比值分别为 110%和 119%，骨整合条件下分别为 114%和 101%。术后即刻和骨整合条件下，植入股骨的最大 von Mises 应力分别为 113.8MPa 和 43.41MPa，分别比完整股骨（29.6MPa）高 284%和 47%。
本研究表明，骨干套管可能会导致相对于完整股骨的应力屏蔽，特别是在远端骨干。应力集中可能主要发生在柄尖端周围的后皮质。然而，在单腿站立状态下，应力集中可能不会伴有假体周围骨折。
