DIFFERENCE IN BONE INGROWTH AFTER ONE VERSUS 2 DAILY EPISODES OF MICROMOTION - EXPERIMENTS WITH TITANIUM CHAMBERS IN RABBITS

Mechanical stimulation has been shown to affect the differentiation an d development of mesenchymal tissue. In the present study, we compared the histological and histomorphometric results of tissue ingrowth int o micromotion chambers that were moved at 0 cycles per day, 20 cycles once per day, and 20 cycles twice per day over 20-30 sec, for 3 weeks. In each case, a chamber having a 1 X 1 X 5 mm square-holed groove for tissue ingrowth was used. The total amplitude of motion was 0.75 mm. Histological sections from nonmoved chambers contained extensive trabe cular bone, embedded in a fibrovascular stroma. Histomorphometric anal ysis disclosed that bone comprised a mean of 31 +/- 2% (mean +/- SEM) of the ingrown tissue. Twenty movements per day appeared to further st imulate bone ingrowth (46 +/- 5%). Extensive ingrowth of more immature woven and trabecular bone was noted in a more cellular stroma. In gen eral, increasing the degree of micromotion to 20 movements twice per d ay resulted in a decreased amount of bone formation (19 +/- 7%). In se veral of these specimens, little or no bone could be found. These expe riments have demonstrated that, for the parameters chosen in this stud y, a short daily period of low frequency, micromotion may facilitate b one ingrowth; however, when the same motion is delivered twice daily, bone ingrowth is depressed. Thus a ''window'' of externally applied st rain appears to exist, which may facilitate or discourage tissue diffe rentiation to bone. (C) 1993 John Wiley & Sons, Inc.