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.

Posterior cruciate ligament a twisted and flat structure, and the tibio-femoral ligament

Posterior cruciate ligament is twisted and flat structure: new prospective on anatomical morphology, by Kato et al. KSSTA (2018) 26(1):31–39

Abstract:

Purpose
This cadaveric study aimed to elucidate PCL morphology by observing the anatomical relationship with other structures and the fibre layers of the PCL in cross section for remnant preserving PCL reconstruction.

Methods
Seventeen fresh-frozen cadaveric knees were studied, using the clock-face method to analyse the anatomical relationship between the PCL and Humphrey’s ligament. The width and thickness of the PCL, Humphrey’s and Wrisberg’s ligaments were measured. The PCL was cut sharply perpendicular to the tibia shaft, and the fibre layers were observed in cross section.

Results
The PCL was located between 12 and 4 o’clock in the right knee (8 and 12 o’clock in the left), while Humphrey’s ligament was located between 2 and 4 o’clock in the right knee (8 and 10 o’clock in the left). Humphrey’s ligament at femoral insertion, midsubstance and lateral meniscus insertion averaged 8.7 ± 2.3, 5.9 ± 2.1 and 6.1 ± 2.0 mm, respectively, while the thickness at each level averaged 2.0 ± 1.2, 1.6 ± 0.6 and 1.9 ± 0.6 mm. The width of the PCL at midsubstance and at medial meniscus level averaged 13.3 ± 2.0 and 11.0 ± 1.6 mm, respectively, while the thickness of the PCL averaged 5.4 ± 0.8 and 5.5 ± 1.4 mm. In cross section, multiple, interconnected layers were observed which could not be divided. The main layers at each level were aligned from the posterolateral to the anteromedial aspect and formed a C-shape at the medial meniscus level.

Conclusion
The PCL at midsubstance is flat. PCL appears as a twisted ribbon composed of many small fibres without clearly separate bundles. When remnant preserving PCL reconstruction is performed, it is necessary to take account of not only PCL morphology but also the ligaments of Humphrey and Wrisberg. These findings may affect the PCL footprint and the graft shape in the future remnant preserving PCL reconstruction.

kato2017-Wrisberg-tibio-femoral-ligament
The variability of Wrisberg’s ligament. The “tibio-femoral” ligament.

Interesting excerpts:

Frequency of the ligaments of Humphrey and Wrisberg
Humphrey’s ligament alone was found in 6 out of 17 specimens (35.3%), while Wrisberg’s ligament alone was found in 3 out of 17 specimens (17.6%). Both were observed in 8 out of 17 specimens (47.1%).

The clock‑face method and the angle measurement for the ligaments of Humphrey and Wrisberg
All right PCLs were located between 12 and 4 o’clock; meanwhile, all right Humphrey’s ligaments were located between 2 and 4 o’clock. All left PCLs were located between 8 and 12 o’clock; meanwhile, all left Humphrey’s ligaments were located between 8 and 10 o’clock. The angle of the PCL averaged 86.4 ± 4.4°, whereas the angle of Humphrey’s ligament averaged 45.2 ± 8.7°. The angle of Wrisberg’s ligament averaged 34.1 ± 4.4°.

The variability of Wrisberg’s ligament
The “tibio-femoral” ligament, a posterior medial oblique ligament, covered the PCL like Wrisberg’s ligament in four specimens (Fig. 3a). This posterior ligament was superficial to the PCL and attached to the tibia more laterally than the PCL in spite of the same femoral attachment of Wrisberg’s ligament. Because the layer was obviously different from the PCL, it was recognized that this ligament did not form part of the PCL. This ligament was observed in the knees that did not have the typical Wrisberg’s ligament. It was named the “tibio-femoral” ligament, distinct from the PCL.

Morphology of the PCL and the fibre layers in cross section
The PCL is composed of many small fibres (Fig. 1). A relatively flat structure could be observed at the midsubstance (Fig. 4a), while multiple layers were observed in cross section. The layers connected with each other and could not be divided. The main layers observed in the cross section were aligned from the posterolateral to the anteromedial direction at the midsubstance, but formed a C-shape at the level of the medial meniscus (Fig. 4b). The axis of the arc was aligned in a similar direction at midsubstance.

Preoperative MRI predicts eligibility for arthroscopic primary ACL repair

ACL-tear-tipe-II

Preoperative magnetic resonance imaging predicts eligibility for arthroscopic primary anterior cruciate ligament repair, by van der List and DiFelice, KSSTA (2018), 26(2):660–671

Abstract:

Purpose
To assess the role of preoperative magnetic resonance imaging (MRI) on the eligibility for arthroscopic primary anterior cruciate ligament (ACL) repair.

Methods
All patients undergoing ACL surgery between 2008 and 2017 were included. Patients underwent arthroscopic primary repair if sufficient tissue length and quality were present, or they underwent single-bundle ACL reconstruction. Preoperative MRI tear locations were graded with the modified Sherman classification: type I (>90% distal remnant length), type II (75–90%), or type III (25–75%). MRI tissue quality was graded as good, fair, or poor. Arthroscopy videos were reviewed for tissue length and quality, and final treatment.

Results
Sixty-three repair patients and 67 reconstruction patients were included. Repair patients had more often type I tears (41 vs. 4%, p < 0.001) and good tissue quality (89 vs. 12%, p < 0.001). Preoperative MRI tear location and tissue quality predicted eligibility for primary repair: 90% of all type I tears and 88% of type II tears with good tissue quality were repaired, while only 23% of type II tears with fair tissue quality, 0% of type II tears with poor tissue quality, and 14% of all type III tears could be repaired. Conclusions This study showed that tear location and tissue quality on preoperative MRI can predict eligibility for arthroscopic primary ACL repair. These findings may guide the orthopaedic surgeon on the preoperative assessment for arthroscopic primary repair of proximal ACL tears. Level of evidence Level IV.

ACL-tear-MRI-repair-flowchart
Flowchart, based on preoperative MRI tear location and tissue quality, shows the percentage of patients that were repaired per tear location and tissue quality

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.