Subsidence Performance of the Bioactive Glass-Ceramic (CaO-SiO2-P2O5-B2O3) Spacer in Terms of Modulus of Elasticity and Contact Area: Mechanical Test and Finite Element Analysis.

OBJECTIVE: The objective of this study is to evaluate the subsidence performance of a bioactive glass-ceramic (CaO-SiO2-P2O5-B2O3) spacer in terms of its modulus of elasticity and contact area using mechanical tests and finite element analysis. METHODS: Three spacer three-dimensional models (Polyether ether ketone [PEEK]-C: PEEK spacer with a small contact area; PEEK-NF: PEEK spacer with a large contact area; and Bioactive glass [BGS]-NF: bioactive glass-ceramic spacer with a large contact area) are constructed and placed between bone blocks for compression analysis. The stress distribution, peak von Mises stress, and reaction force generated in the bone block are predicted by applying a compressive load. Subsidence tests are conducted for three spacer models in accordance with ASTM F2267. Three types of blocks measuring 8, 10, and 15 pounds per cubic foot are used to account for the various bone qualities of patients. A statistical analysis of the results is conducted using a one-way Analysis of variance and post hoc analysis (Tukey's Honestly Significant Difference) by measuring the stiffness and yield load. RESULTS: The stress distribution, peak von Mises stress, and reaction force predicted via the finite element analysis are the highest for PEEK-C, whereas they are similar for PEEK-NF and BGS-NF. Results of mechanical tests show that the stiffness and yield load of PEEK-C are the lowest, whereas those of PEEK-NF and BGS-NF are similar. CONCLUSIONS: The main factor affecting subsidence performance is the contact area. Therefore, bioactive glass-ceramic spacers exhibit a larger contact area and better subsidence performance than conventional spacers.

Influence of fragment volume on stability of 3-part intertrochanteric fracture of the femur: a biomechanical study.

Complex unstable fracture can complicate the treatment outcome of intertrochanteric fracture of the femur, and fixation failure after surgery is a significant problem in elderly patients. This study aimed to evaluate the effect of fracture geometry on the stability of 3-part intertrochanteric fracture by assessing the fragment size. Four categories (group I: large greater trochanter, small lesser trochanter; group II: large greater trochanter, large lesser trochanter; group III: small greater trochanter, small lesser trochanter; and group IV: small greater trochanter, large lesser trochanter) of a 3-part intertrochanteric fracture model were designed. Three-dimensional computer tomography scanning was performed to measure the volume of each fragment. After fixation with a dynamic hip screw, a cyclic loading study was conducted using a servohydraulic machine. There was a significant difference in fatigue failure between each group. After all specimens had endured 10,000 cycles with a range of loads (100-1,000 N), the mean number of cycles until fixation failure with a load range of 200-2,000 N was 1,467.67 ± 199.92 in group I; 579 ± 93.48, group II; 398.17 ± 37.92, group III; and 268.67 ± 19.92, group IV. Fixation strength was approximately 5 times greater in group I than in group IV. In 3-part intertrochanteric fracture, the sizes of the greater and lesser trochanteric fragments are important factors for determining stability after dynamic compression screw fixation. This study supports our hypothesis that the volumetric ratio of ∆lesser trochanter/∆greater trochanter can be used to predict stability of intertrochanteric femoral fracture.

Effect of repair of radial tears at the root of the posterior horn of the medial meniscus with the pullout suture technique: a biomechanical study using porcine knees.

PURPOSE: Our purpose was to evaluate the result of radial tears at the root of the posterior horn of the medial meniscus (PHMM) in terms of tibiofemoral contact mechanics and the effectiveness of pullout sutures for such tears. METHODS: Eleven mature pig knees each underwent 15 different testing conditions with an intact, simulated (incised) radial tear at the root of the PHMM and placement of pullout sutures in the radial tears of the medial meniscus at 5 different angles of flexion (0 degrees, 15 degrees, 30 degrees, 60 degrees, and 90 degrees ) under a 1,500-N axial load. A K-Scan pressure sensor (Tekscan, Boston, MA) was used to measure medial tibiofemoral contact area and peak tibiofemoral contact pressure. Data were analyzed to assess the difference in medial contact area and tibiofemoral peak contact pressure among the 3 meniscal conditions at various degrees of knee flexion. RESULTS: The mean contact area was significantly lower, and the peak tibiofemoral contact pressure was significantly high in knees with simulated radial tears at all angles of knee flexion compared with knees with intact menisci (P < .0001). The peak tibiofemoral contact pressure after the pullout suture technique was significantly high at 0 degrees and 15 degrees of flexion (P < .0001) compared with intact knee specimens. Failure of sutures occurred in 45% of the specimens at 0 degrees of flexion. CONCLUSIONS: Radial tears at the root of the PHMM in a porcine model significantly increased medial tibiofemoral contact pressure and decreased contact area. Although repair of tears of the PHMM with the pullout suture technique aids in significantly reducing tibiofemoral peak contact pressure between 30 degrees and 90 degrees , it remains significantly high at 0 degrees and 15 degrees of flexion. CLINICAL RELEVANCE: Pullout sutures for radial tears at the root of the PHMM may lead to an increase in peak medial tibiofemoral contact pressure and may be prone to mechanical failure, especially during the stance (loading) phase of gait (mean, 15 degrees of flexion).