Intermittent PTH injections can be used to accelerate healing of stress fractures (SFx). It was shown that a single PTH injection 24 hours after loading of SFx accelerated healing after six weeks. The aim of this study is to investigate the effect of daily PTH injections for two weeks on healing of SFx.
SFx was induced in 36 female Wistar rats. Daily PTH (8 μg/100g/day) or an equivalent vehicle (VEH) saline injections was administered to the rats 24 hours after loading of SFx for 14 days. Rats were divided into two equal groups and their ulnae were collected after 2 or 6 weeks. Two Toluidine Blue as well two TRAP stained slides showing the middle point of the SFx were examined for histomorphometric analysis using Osteomeasure™ software.
Woven bone area, woven bone perimeter, woven bone width (P<0.05) and woven bone apposition rate decreased significantly (P < 0.01) in the daily PTH injections group when compared to the single PTH injection after 6 weeks. Osteoclasts were retained for a longer period of time in the daily PTH injections groups (P < 0.01). There was also evidence of more osteoclast trails in the daily injection groups when compared to the single injection indicating past osteoclastic activity. Because osteoclasts were retained for a longer period of time, porosity or Basic Multicellular Unit (BMU) areas and perimeters were significantly higher in the daily PTH injections after 6 weeks when compared to 2 weeks (P < 0.01). There were no significant differences in healing parameters between single and daily injection groups, however, the erosion (unhealed) perimeter decreased significantly in the daily PTH injections group when compared to the single injection after 2 weeks.
Daily PTH injections are not superior to single injection in accelerating healing of SFx. They improve woven bone parameters and availability of osteoclasts.