Finite element analysis of double-plate fixation using reversed locking compression-distal femoral plates for Vancouver B1 periprosthetic femoral fractures.

BACKGROUND: Internal fixation is recommended for treating Vancouver B1 periprosthetic femoral fractures. Although several fixation procedures have been developed with high fixation stability and union rates, long-term weight-bearing constructs are still lacking. Therefore, the aim of the present study was to evaluate the stability of a double-plate procedure using reversed contralateral locking compression-distal femoral plates for fixation of Vancouver B1 periprosthetic femoral fractures under full weight-bearing. METHODS: Single- and double-plate fixation procedures for locking compression-distal femoral plates were analysed under an axial load of 1,500 N by finite element analysis and biomechanical loading tests. A vertical loading test was performed to the prosthetic head, and the displacements and strains were calculated based on load-displacement and load-strain curves generated by the static compression tests. RESULTS: The finite element analysis revealed that double-plate fixation significantly reduced stress concentration at the lateral plate place on the fracture site. Under full weight-bearing, the maximum von Mises stress in the lateral plate was 268 MPa. On the other hand, the maximum stress in the single-plating method occurred at the defect level of the femur with a maximum stress value of 1,303 MPa. The principal strains of single- and double-plate fixation were 0.63 % and 0.058 %, respectively. Consistently, in the axial loading test, the strain values at a 1,500 N loading of the single- and double-plate fixation methods were 1,274.60 ± 11.53 and 317.33 ± 8.03 (× 10- 6), respectively. CONCLUSIONS: The present study suggests that dual-plate fixation with reversed locking compression-distal femoral plates may be an excellent treatment procedure for patients with Vancouver B1 fractures, allowing for full weight-bearing in the early postoperative period.

Finite Element Analysis of Optimal Positioning of Femoral Osteotomy in Total Hip Arthroplasty With Subtrochanteric Shortening.

BACKGROUND: Total hip arthroplasty with femoral shortening is frequently recommended for patients with high hip dislocation. However, the possibility of postoperative rotational deviation of the stem presents a challenge for surgeons. We aimed to determine the optimal position for osteotomy in total hip arthroplasty under full weight-bearing and turning torque by using finite element analysis. METHODS: Four models of femoral osteotomy with 30-mm transverse shortening at 30% (model 30), 40% (model 40), 50% (model 50), and 60% (model 60) from the proximal end of the full length of the Exeter stem were constructed. Using finite element analysis, the constructs were first analyzed under an axial load of 1500 N and then with an added torsional load of 10°. RESULTS: The analyses under torsional loading conditions revealed that the maximum von Mises stress on the stem in each model occurred at the proximal end of the distal fragment and the distal side of the stem. The maximum stress values at the stem were 819 MPa (model 30), 825 MPa (model 40), 916 MPa (model 50), and 944 MPa (model 60). The maximum stress values at the osteotomy site of the medullary cavity side of the distal bone fragment were 761 MPa (model 30), 165 MPa (model 40), 187 MPa (model 50), and 414 MPa (model 60). CONCLUSIONS: The osteotomy level should be around the proximal 40% of the full length of the Exeter stem, which is most suitable for rotation stability in the early postoperative period.

Design and optimization of the oriented groove on the hip implant surface to promote bone microstructure integrity.

We proposed a novel surface modification for an artificial hip joint stem from the viewpoint of maintenance and establishment of appropriate bone function and microstructure, represented by the preferred alignment of biological apatite (BAp) and collagen (Col). Oriented grooves were introduced into the proximal medial region of the femoral stem to control the principal stress applied to the bone inside the grooves, which is a dominant factor contributing to the promotion of Col/BAp alignment. The groove angle and the stem material were optimized based on the stress inside the grooves through a finite element analysis (FEA). Only the groove oriented proximally by 60° from the normal direction of the stem surface generated the healthy maximum principal stress distribution. The magnitude of the maximum principal stress inside the groove decreased with increasing the stem Young's modulus, while the direction of the stress did not largely changed. An in vivo implantation experiment showed that this groove was effective in inducing the new bone with preferential Col/BAp alignment along the groove depth direction which corresponded to the direction of maximum principal stress inside the groove. The anisotropic principal stress distribution and the oriented microstructure inside the groove are similar to those found in the femoral trabeculae; therefore, the creation of the oriented groove is a potent surface modification for optimizing implant design for a long-term fixation.