Background

Metatarsus adductus is the most common forefoot deformity. Variable prevalence values were reported in literature using different techniques in different populations.

Numerous radiological measurements have been proposed to assess this deformity with a paucity of studies reporting the reliability of these methods.

The metatarsus adductus angle was shown to correlate with the severity of hallux abductovalgus in normal feet and preselected populations of juvenile hallux valgus.

Introduction: Acrylic bone cement (ABC) manufacturers vary their products by using different proportions of the principle ingredients to optimise handling time or mechanical properties. Surprisingly, there is limited research showing the effect of varying monomer/polymer and initiator/activator ratios (independent from other constituents) on thermal and mechanical properties of ABC.

Materials and Methods: The formula for CMW (DePuy) was reproduced using original ingredients obtained from different suppliers. The commercially available CMW monomer/polymer ratio is approximately (0.6 ml/gm). Six variants of CMW bone cement were prepared by varying the monomer/polymer ratio (0.4–1 ml/gm) and eight variants were prepared by varying the initiator/activator BPO/DMPT ratio (1.71–11.25). Specimens were stored in an incubator for 7 days at 37 °C. Thermal characteristics of the polymerisation reaction such as maximum polymerisation reaction temperature (Tmax) and setting time (Ts) were recorded using a thermocouple and Picolog digital data recorder. Compressive mechanical properties were measured using Zwick Roell All Round Testing System implementing ISO5833 recommendations. SPSS software was used to perform ANOVA and calculate Pearson correlation coefficient.

Results: Increasing monomer/polymer ratio resulted in prolongation of setting time (5.3–11.3 minutes) displaying a significant (p= 0.000) correlation (r=0.988); however, there was no significant correlation with Tmax (r=−0.123, p=0.792). Increasing the monomer/polymer ratio resulted in a significant reduction in yielding compressive strength (F=110.97, p=0.000) and modulus (F=16.1, p=0.000). Pearson correlation test showed that monomer/polymer ratio had a significant correlation with yielding compressive strength (r= −0.930, p=0.002) and a significant correlation with the corresponding modulus of elasticity (r= −0.827, p=0.022). An increase in the BPO/DMPT ratio did not display a significant (p= 0.172) correlation (r=−0.535) with Tmax; however, the setting time was prolonged by increasing the BPO/ DMPT ratio with a significant (p=0.002) strong positive correlation (r=0.903). Compression tests showed a significant (F=13.45, p=0.000) reduction in yielding compressive strength with a significant (p=0.04) inverse (r=−0.729) correlation with the BPO/DMPT ratio. Modulus of elasticity followed a similar pattern to a lesser degree displaying a significant (F=5.123, p=0.001) reduction in values which was moderately correlated (r=−0.619), though insignificant (p= 0.101) with BPO/ DMPT ratio.

Discussion and Conclusions: Varying the monomer/ polymer ratio independently from other constituents in acrylic bone cement significantly affects setting time and compressive mechanical properties. Setting time can be prolonged to increase handling time; however this will occur at the expense of a reduction in compressive stiffness and strength. Similarly, varying the BPO/DMPT ratio may result in optimised handling time; however, this will also cause a reduction in compressive strength and stiffness. These finding are paramount in clinical applications where compressive strength is essential e.g. percutaneous vertebroplasty.

Introduction: Acrylic bone cement (ABC) manufacturers vary their products by using different proportions of the principle ingredients to optimize handling time or mechanical properties.

There is limited research showing the effect that varying the monomer to polymer ratio (independent from other constituents) has on thermal and mechanical properties of ABC.

Materials and Methods: The formula for CMW1 (DePuy) was reproduced using original ingredients obtained separately from different suppliers. The commercially available CMW1 monomer/polymer ratio is approximately (0.6 ml/gm). Six variants of CMW1 bone cement were prepared with varying monomer/polymer ratio (0.4–1 ml/gm). The specimens were cured and aged in an incubator for 7 days at 37°C.

Thermal characteristics of the polymerization reaction such as maximum polymerization reaction temperature (Tmax) and setting time (ts) were recorded using a Picolog digital data recorder.

Compressive mechanical properties (Young’s modulus and yield stress) were measured using a TestexpertII Universal Testing System from Zwick Roell implementing ISO5833 test criteria.

SPSS 14 for Windows software was used for calculating statistics and data analysis.

Results: An increase in monomer/polymer ratio was associated with a significant (p= 0.00) increase in setting time (5.3–11.3 minutes) with a strong correlation (r2=0.988). However, there seemed to be no effect on Tmax (p=0.792).

Compression tests showed a significant (p=0.022) decrease in E-modulus (2.63 to 2.22 GPa) with a strong Pearson correlation negative coefficient (r2= −0.827).

Similarly, yield compressive stress showed a significant (p=0.002) decrease (121.83–101.19 MPa) with a strong negative correlation (r2= −0.93)

Conclusion: This experimental study shows that varying the ratio of monomer to polymer independently from other constituents in acrylic bone cement significantly affects setting time and compressive mechanical properties. Setting time can be prolonged to increase handling time; however this will occur at the expense of a reduction in compressive stiffness and strength.