Decreased osteoblast differentiation is progressive with disease development and age of the mice. (a) A representative example of histological section of osteoblasts at the tibial endo-cortical surface of Balb/c IL1ra-/- (32 to 33 weeks old) compared to WT age-matched control mice. A decrease in the number of osteoblasts over 6.5 mm of tibial endo-cortical surface in Balb/c IL1ra-/- affected by the disease for five weeks was observed and was found more prominent in older mice (aged 31 to 32 weeks, n = 3) than younger mice (aged 22 to 23 weeks, n = 5) despite they both had the disease for the same length of time. (b) X-ray micro CT scanning of tibia of Balb/c IL1ra-/- mice showed no significant difference in bone volume in the cancellous bone area with disease progression (n = 8). (c) No significant difference in osteoclast numbers was observed with the progression of disease in Balb/c IL1ra-/- mice which were 22 to 23 weeks of age (n = 5) or 31 to 32 weeks of the age (n = 3) compared to age matched WT control mice. All data are presented as means ± SEM and analysed by unpaired t test. *P < 0.05. WT, wild type mice; BV/TV, bone volume/tissue volume; Oc, osteoclasts; Ob, osteoblasts.