Strontium ranelate (SR) and alendronate (ALN) are anti-osteoporotic
agents with antifracture efficacy against vertebral and non-vertebral
fractures. Whereas ALN is a pure bone resorption inhibitor, SR,
in vitro, increases bone formation and decreases bone resorption.
For the first time, we non-invasively evaluated and compared the effects
of SR and ALN on bone microstructure, a component of bone
quality, hence of bone strength, in osteoporotic women.
Eighty-eight women ≥50 years with postmenopausal osteoporosis
were randomised to SR 2g/day or ALN 70mg/week for 2
years. Microstructure of weight-bearing bone distal tibia was assessed
by high-resolution computerized tomography (HR-pQCT)
after 3, 6, 12, 18 and 24 months of treatment. A planned interim
statistical analysis was performed after 1 year in the intention-totreat
population (patients with a baseline and post-baseline HRpQCT
value, n=85). Primary endpoint was HR-pQCT variables
relative changes from baseline, secondary endpoints included
lumbar spine hip areal BMD and bone turnover markers.
Baseline characteristics were similar in both groups: age:
63.7±7.4 years; lumbar and hip T-Score: ‑2.7±0.9 g/cm² and -
2.0±0.8 g/cm², respectively. After 1 year of treatment, aBMD increases
were similar to results from pivotal trials (L1-L4: +5.7%
and +5.1%; total hip: +3.3% and +2.2%, in SR and ALN groups,
respectively). For bone microstructure, mean increases of +5.3%
(p<0.001) for C.Th, +2.0% (p=0.002) for BV/TV and +2.1%
(p=0.002) for trabecular density were found in SR group, compared
to no change in ALN group (1.3% p=0.130; 0.6% p=0.725
and 0.6% p=0.645, for corresponding variables, respectively),
with thus a significant between-group difference in favour of SR
(p=0.045, p=0.048 and p=0.034, for C.Th, BV/TV and trabecular
density, respectively). Improvement in microstructure was associated
in SR group with significant decrease in heterogeneity of
trabecular network (-3.6±8.6%, p=0.007). No between-group difference
was observed in cortical density. For bone turnover markers,
between-group differences were statistically significant at all
time-points, with a +5% increase in bALP and a -7% decrease in
sCTX in the SR group, compared to decreases of -35% and -58%
in the ALN group.
In conclusion, strontium ranelate had significantly higher effects
than alendronate on distal tibia microstructure including
cortical and trabecular variables, in women with postmenopausal
osteoporosis after one year of treatment.