The tension-stress effect on the genesis and growth of tissues: Part II. The influence of the rate and frequency of distraction.

To assess the influence of both the rate and the frequency of distraction on osteogenesis during limb elongation, a canine tibia was used with various combinations of distraction rates (0.5 mm, 1.0 mm, or 2.0 mm per day) and distraction frequencies (one step per day, four steps per day, 60 steps per day). The distractions were performed after both open osteotomy and closed osteoclasis. Histomorphic and biochemical studies were conducted on the elongated osseous tissue, fascia, skeletal muscle, smooth muscle, blood vessels, nerves, and skin. It was determined that distraction at a rate of 0.5 mm per day often led to premature consolidation of the lengthening bone, while a distraction rate of 2.0 mm per day often resulted in undesirable changes within elongating tissues. A distraction rate of 1.0 mm per day led to the best results. It was also observed that the greater the distraction frequency, the better the outcome. With optimum preservation of periosseous tissues, bone marrow, and blood supply at the time of osteotomy, stability of external fixation, and 1.0 mm per day of distraction in four steps, osteogenesis within the distraction gap of an elongating bone takes place by the formation of a physislike structure, in which new bone forms in parallel columns extending in both directions from a central growth zone. The growth plate that forms under the influence of tension-stress has features of both physeal and intramembranous ossification, yet is neither; instead, the distraction regenerated bone is unique, providing numerous applications in clinical traumatology, orthopedics, and other medical disciplines.