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We examined the effect of periosteal devascularisation upon the early healing of osteotomies of sheep tibiae held in an instrumented external fixation system with an axial stiffness of 240 N/mm. At 14 days, cortical blood flow measured by the microsphere technique was 19.3 ml/min/100g in the well-vascularised osteotomies, but only 1.7 ml/min/100g in the devascularised osteotomies, despite an increase in medullary flow (p less than 0.0005). Delay in healing of the devascularised osteotomies was suggested by an in vivo monitoring system and confirmed by post-mortem mechanical testing. We suggest that the osteogenic stimulus of dynamic external fixation is dependent on the early restoration of cortical blood flow in devascularised fractures.

Several letters to the editors are presented in response to articles in previous issues including one on the death of Pope John Paul I in the October 9, 1978 issue, one on the prohibition of the Public Works Bill by U.S. President Jimmy Carter in the October 16, 1978 issue and "Innovation Recession," which appeared in the October 2, 1978 issue.