Temporal role of macrophages in cancellous bone healing.

Macrophages are important phagocytosing and cytokine producing cells with effects on fracture healing. We used clodronate-containing liposomes to reduce the number of macrophages, in order to study their role in the early phases of cancellous bone healing. Holes were drilled bilaterally into the cancellous bone of the proximal metaphysis of the tibia of 60 mice. A screw was inserted in the hole in the right tibia. The day of surgery was day 0. Clodronate-containing liposomes were injected intraperitoneally as a single injection either day -4 or -1 (before surgery) or day 1 or 3 (after surgery). A control group underwent surgery as above, but received no clodronate. The mice were killed day 7. The mechanical quality of the new formed cancellous bone holding the screw was evaluated by a pull-out test. The contents of the drill hole in the left tibia was analyzed by microCT. Another set of 20 mice received a drill hole in the metaphysis of the right tibia, and were given either clodronate or saline injections days -3 and -2. The animals were killed day 1 and 3. Flow cytometry was used to analyze the composition of macrophage subpopulations in the regenerating tissue. Flow cytometry showed that clodronate injections day -3 and -2 led to a decrease in mature monocytes day 1 together with an increase in immature monocytes. On day 3 this effect had mostly disappeared, suggesting that the effect of the injections lasted 3 to 5days. Mechanical testing revealed that the injections prior to surgery decreased the strength of the new formed bone, holding the screw, by about half. Bone density in the drill hole was similarly reduced. In contrast, the injections given day 1 and 3 had smaller and statistically insignificant effects. Since their depletion at later time points failed to produce a significant effect, it seems that the role of macrophages in cancellous bone is most crucial during the first two days after trauma.

Influence of a lower leg brace on traction force in healthy and ruptured Achilles tendons.

BACKGROUND: we investigated how ruptured Achilles tendons are loaded in a brace. There is an ongoing discussion whether patients should be recommended to bear weight on the injured limb. However, little is known about the effects of bracing on tensional loading of the healing Achilles tendon: it is uncertain if load-bearing actually stresses the Achilles tendon inside a brace. METHODS: we measured plantar flexion moment inside the brace, in order to estimate tensional loading of the tendon, by use of an insole with pressure transducers. RESULTS: after wearing the brace for 1 hour, young healthy individuals reduced their maximum flexion moment during gait by half. Patients with Achilles tendon rupture showed no measurable flexion moment during gait with the brace, 4 or 7 weeks after injury. Only when specifically instructed, they could produce a considerable plantar flexion moment. We noted that gait speed with the brace at 4 weeks correlated with a heel-raise functional test at 1 year: the higher the spontaneous gait speed, the less the functional difference between the injured and the uninjured leg (r(2)=0.68; p=0.002). CONCLUSION: the correlation with gait speed suggests that the patients' general physical aptness has an impact on the end result.