Figure Figure 3.

Load‐induced bone formation in thoracic limb long bones was most pronounced in the periosteal bone envelope. Neuronal mechanotransduction regulated the majority of adaptive bone formation in distant bones and a large proportion of bone formation in the loaded (right) ulna. (A) Formation of calcein‐labeled new bone in thoracic limb bones of Sprague‐Dawley rats in response to unilateral cyclic loading of the right ulna. In the high strain group, normalized periosteal labeled bone area (Ps.L.B.Ar) was increased in both the loaded (right) ulna and the contralateral (left) ulna. Similar but reduced responses were also seen in the humerii that were not directly loaded. Changes in total labeled bone area (Tt.L.B.Ar) in response to mechanical loading were less evident. Increased endosteal labeled bone area (Es.L.B.Ar) was only found in the right humerus after high strain loading. Bone formation in baseline and Sham control groups of rats was not significantly different. (B) Adaptive bone formation after brachial plexus blocking and loading at high strain was not significantly different from Sham control, except Ps.L.B.Ar in the loaded (right) ulna, which was reduced 45% by neuronal blocking. BC, baseline control; SC, Sham control; low, loading at −3.3 N, initial peak strain, −760 μϵ; med, loading at −10 N, initial peak strain = −2000 μϵ; high, loading at −18 N, initial peak strain = −3750μϵ; block + high, loading at high initial peak strain after brachial plexus blocking. *p < 0.05; **p < 0.01; ***p < 0.001; ^# p < 0.15 vs. the relevant Sham control. Differences between the group loaded at high strain and the blocked + loaded group are also indicated. Error bars represent SD. Loaded groups, n = 16; Sham control group, n = 12; blocked + loaded group, n = 8; baseline control group, n = 8.