Effect of pore size on tissue ingrowth and osteoconductivity in biodegradable Mg alloy scaffolds.

Magnesium has mechanical properties similar to those of bone and is being considered as a potential bone substitute. In the present study, two different pore sized scaffolds of the Mg alloy LAE442, coated with magnesium fluoride, were compared. The scaffolds had interconnecting pores of either 400 (p400) or 500 µm (p500). ß-TCP served as control. Ten scaffolds per time group (6, 12, 24, 36 weeks) were implanted in the trochanter major of rabbits. Histological analyses, µCT scans, and SEM/EDX were performed. The scaffolds showed slow volume decreases (week 36 p400: 9.9%; p500: 7.5%), which were accompanied by uncritical gas releases. In contrast, ß-TCP showed accelerated resorption (78.5%) and significantly more new bone inside (18.19 ± 1.47 mm3). Bone fragments grew into p400 (0.17 ± 0.19 mm3) and p500 (0.36 ± 0.26 mm3), reaching the centrally located pores within p500 more frequently. In particular, p400 displayed a more uneven and progressively larger surface area (week 36 p400: 253.22 ± 19.44; p500: 219.19 ± 4.76 mm2). A better osseointegration of p500 was indicated by significantly more trabecular contacts and a 200 µm wide bone matrix being in the process of mineralization and in permanent contact with the scaffold. The number of macrophages and foreign body giant cells were at an acceptable level concerning resorbable biomaterials. In terms of ingrown bone and integrative properties, LAE442 scaffolds could not achieve the results of ß-TCP. In this long-term study, p500 appears to be a biocompatible and more osteoconductive pore size for the Mg alloy LAE442.

Monitoring Performance in Show Jumping Horses: Validity of Non-specific and Discipline-specific Field Exercise Tests for a Practicable Assessment of Aerobic Performance.

Show jumping is a highly specialized equestrian discipline that requires technical skill but also power and fitness. Monitoring the horses' aerobic performance is therefore essential in order to verify whether the training has induced the desired cardiovascular and muscular adaptations. This study therefore aimed at evaluating the validity of non-specific and discipline-specific field exercise tests for objective evaluation of aerobic performance in show jumpers. For this purpose, data obtained from horses competing at Junior and Young Rider level during show jumping competitions as well as field exercise tests were retrospectively analyzed. The effect of the level of difficulty, the horses' age, the penalty score and the horses' previous level of performance on blood lactate concentrations after show jumping competitions (100 observations in 49 horses) was evaluated by linear mixed effects models (horse as random effect). Estimated marginal means significantly increased from 140 (4.1 mmol/L) to 150 cm (5.2 mmol/L) classes (P = 0.02). Furthermore, post-exercise lactate values significantly increased with the horses' age (P = 0.001). Another group of 12 horses performed a standardized incremental field exercise test on a track (SETtrack), a standardized show jumping course (SETcourse) and a standardized grid exercise (SETgrid) each on three consecutive days. Indices of aerobic performance, derived from the SETtrack [velocity at a heart rate of 140 bpm (V140) and at a lactate concentration of 2 mmol/L (V La2 )] were highly correlated with heart rate (V140: r = -0.75, P = 0.005; V La2 : r =-0.66, P = 0.02) and lactate (V140: r = -0.73, P = 0.02; V La2 : r = -0.72, P = 0.02) in response to SETcourse as well as heart rate during SETgrid (V140: r = -0.73, P = 0.02; V La2 : r = -0.76, P = 0.01). Subjective rating of muscular fatigue was significantly correlated to the mean heart rate during SETcourse (r = -0.64, P = 0.05) and SETgrid (r = -0.74, P = 0.02) but not to the aerobic indices calculated from SETtrack. Besides non-specific incremental field tests, performance monitoring in show jumpers should therefore also include discipline-specific tests that more closely reflect the internal load induced by show jumping competitions.

Comparison of two pore sizes of LAE442 scaffolds and their effect on degradation and osseointegration behavior in the rabbit model.

The magnesium alloy LAE442 emerged as a possible bioresorbable bone substitute over a decade ago. In the present study, using the investment casting process, scaffolds of the Magnesium (Mg) alloy LAE442 with two different and defined pore sizes, which had on average a diameter of 400 µm (p400) and 500 µm (p500), were investigated to evaluate degradation and osseointegration in comparison to a ß-TCP control group. Open-pored scaffolds were implanted in both greater trochanter of rabbits. Ten scaffolds per time group (6, 12, 24, and 36 weeks) and type were analyzed by clinical, radiographic and µ-CT examinations (2D and 3D). None of the scaffolds caused adverse reactions. LAE442 p400 and p500 developed moderate gas accumulation due to the Mg associated in vivo corrosion, which decreased from week 20 for both pore sizes. After 36 weeks, p400 and p500 showed volume decreases of 15.9 and 11.1%, respectively, with homogeneous degradation, whereas ß-TCP lost 74.6% of its initial volume. Compared to p400, osseointegration for p500 was significantly better at week 2 postsurgery due to more frequent bone-scaffold contacts, higher number of trabeculae and higher bone volume in the surrounding area. No further significant differences between the two pore sizes became apparent. However, p500 was close to the values of ß-TCP in terms of bone volume and trabecular number in the scaffold environment, suggesting better osseointegration for the larger pore size.