Finite element method evaluates strain of spine metastasis

Chapter Effects Breast and Prostate Cancer Metastases on Lumbar Spine Biomechanics: Rapid In Silico Evaluation, Lorkowski J., Grzegorowska O., Kozień M., Kotela I.In: Advances in Experimental Medicine and Biology (2018). Springer, New York, NY.

Abstract:

Metastases to distant organs are a frequent occurrence in cancer diseases. The skeletal system, especially the spine, is one such organ. The objective of this study was to apply a numerical modeling, using a finite element method (FEM), for the evaluation of deformation and stress in lumbar spine in bone metastases to the spine. We investigated 20 patients (10 women and 10 men) aged 38–81 years. In women, osteolytic lesions in lumbar spine accompanied breast cancer, in men it was prostate cancer. Geometry of FEM models were built based on CT scans of metastatic lumbar spine. We made the models for osteolytic metastases, osteosclerotic metastases, and metastases after surgery. Images were compared. We found a considerable concentration of strain, especially located in the posterior part of the vertebral body. In osteolytic lesions, the strain was located below the vertebral body with metastases. In osteosclerotic lesions, the strain was located in the anterior and posterior parts in and below the vertebral body with metastases. Surgery abolished the pathological strain. We conclude that metastases to the lumbar spine introduce a pathological strain on the lumbar body. The immobilization of the vertebral body around fractures abolished the strain.

ACL tibial footprint is elliptical or triangular shaped in healthy young adults (3-T MRI analysis)

Anterior cruciate ligament tibial insertion site is elliptical or triangular shaped in healthy young adults: high-resolution 3-T MRI analysis, Tashiro et al. KSSTA (2018) 26(2):485-490.

Abstract:

Purpose
To clarify the morphology of anterior cruciate ligament (ACL) tibial insertion site in healthy young knees using high-resolution 3-T MRI.

Methods
Subjects were 50 ACL-reconstructed patients with a mean age of 21.4 ± 6.8 years. The contralateral healthy knees were scanned using high-resolution 3-T MRI. The tibial insertion sites of the anteromedial (AM) and posterolateral (PL) bundle fibres, and the ACL attachment on the anterior horn of lateral meniscus (AHLM) were segmented from the MR images, and 3D models were reconstructed to evaluate the morphology. The shape of ACL footprint was qualitatively analysed, and the size of AM and PL attachments and AHLM overlapped area was measured digitally.

Results
Tibial AM and PL bundles were clearly identified in 42 of 50 knees (84.0%). Morphology of the whole ACL tibial insertion site was elliptical in 23 knees (54.8%) and triangular in 19 knees (45.2%), but not classified as C-shape in any knees. However, the AM bundle attachment was of C-shape in 29 knees (69.0%) and band-like in 13 knees (31.0%). Overlap of ACL on AHLM was found in 26 knees (61.9%), and the size of the overlapped area was 4.8 ± 4.7% of the whole ACL insertion site.

Conclusion
3D morphology of the intact ACL tibial insertion site analysed by high-resolution 3-T MRI was elliptical or triangular in healthy young knees. However, the AM bundle insertion site was of C-shape or band-like. A small lateral portion of the ACL was overlapped with the AHLM. As for clinical relevance, these findings should be considered in order to reproduce the native ACL insertion site sufficiently.

Level of evidence
III.

tashiro2017-ACL-footprint-bundles
If PL bundle was eliminated, AM bundle footprint looked C-shape (a) in 29 knees (69.0%) and band-like in 13 knees (31.0%) (b)

3D graft-bending angle measurement and finite-element analysis

3D-FEM-ACL-graft

Peak stresses shift from femoral tunnel aperture to tibial tunnel aperture in lateral tibial tunnel ACL reconstructions: a 3D graft-bending angle measurement and finite-element analysis, by Van Der Bracht et al. KSSTA (2018) 26(2): 508–517.

Abstract:

Purpose
To investigate the effect of tibial tunnel orientation on graft-bending angle and stress distribution in the ACL graft.

Methods
Eight cadaveric knees were scanned in extension, 45°, 90°, and full flexion. 3D reconstructions with anatomically placed anterior cruciate ligament (ACL) grafts were constructed with Mimics 14.12®. 3D graft-bending angles were measured for classic medial tibial tunnels (MTT) and lateral tibial tunnels (LTT) with different drill-guide angles (DGA) (45°, 55°, 65°, and 75°). A pivot shift was performed on 1 knee in a finite-element analysis. The peak stresses in the graft were calculated for eight different tibial tunnel orientations.

Results
In a classic anatomical ACL repair, the largest graft-bending angle and peak stresses are seen at the femoral tunnel aperture. The use of a different DGA at the tibial side does not change the graft-bending angle at the femoral side or magnitude of peak stresses significantly. When using LTT, the largest graft-bending angles and peak stresses are seen at the tibial tunnel aperture.

Conclusion
In a classic anatomical ACL repair, peak stresses in the ACL graft are found at the femoral tunnel aperture. When an LTT is used, peak stresses are similar compared to classic ACL repairs, but the location of the peak stress will shift from the femoral tunnel aperture towards the tibial tunnel aperture. Clinical relevance: the risk of graft rupture is similar for both MTTs and LTTs, but the location of graft rupture changes from the femoral tunnel aperture towards the tibial tunnel aperture, respectively.