We examined the growth-related changes in femoral geometry and torsion
al strength in BMP-5 deficient short-ear mice over a 22-week time inte
rval (''long-term'' changes). Four groups of female mice (n = 6 per gr
oup) were examined: short-ear animals and their heterozygous control l
ittermates at 4 and 26 weeks of age. In agreement with findings previo
usly observed in a mixed-gender group of adult mice (26 weeks), the fe
mora of short-ear animals were significantly smaller in length and cro
ss section at both ages, The magnitudes of the differences between gen
otypes were comparable at each age, indicating that the overall rates
of appositional and endochondral growth were similar for both genotype
s over the 22-week period, In the adult animals, short-ear femora were
27 +/- 7% weaker in torsional strength due to their smaller cross-sec
tional geometry, However, bone strength in adult short-ear mice appear
ed to be adequate for animal size: No significant difference was detec
ted in maximum femoral torque when normalized by body mass, In 4-week
old animals, BMP-5 deficiency was associated with a 27 +/- 6% lower bo
dy mass, but the torsional strength of the femur was not significantly
different from that of controls. Cross-sectional geometry was smaller
in 4-week old short-ear mice, but the apparent bone material ultimate
shear stress was elevated by 33 +/- 10%, thereby resulting in a whole
bone torsional strength equivalent to that of the larger control mice
, While the data suggest a higher material strength in the 4-week-old
short-ear animals, no significant difference in the level of bone mine
ralization was detectable between genotypes at either age.