In this episode Dr. Weinstein explains osteogenesis, a process by which we provide a framework for the body to grow new bone. I’ll cover the historical development, Ilizarov’s tension-stress concept, the mechanics of external fixation, the biology of callotasis/distraction osteogenesis, clinical examples, complications, and where the field is going.
The core biology and historical framework are consistent with the orthopedic literature: Codivilla described early limb-lengthening work in the early 1900s, while Ilizarov's later work established distraction osteogenesis as a reproducible clinical method and characterized the importance of distraction rate and frequency.
Modern bone transport remains an important option for critical-sized defects, particularly when infection or major bone loss makes conventional grafting difficult.
Growing new bone by distraction is an extremely useful tool for repairing segmental defects, lengthening congenitally short segments, or where bone loss has occurred that exceeds the size of reasonable bone grafting. This method has routine use by surgeons with special training in the method. The classic apparatus used in the procedure is the circular or ring fixation, commonly called an 'Ilizarov' device. The purpose of the device is to anchor to bones internally while controlling their stability and motion externally.
Axial lengthening is the archetype for understanding the procedure. First, the device is mounted to the limb using thin tensioned wires or larger diameter pins. An osteotomy is performed at a specific location, and the procedure then stops there for a latency period. This is often a week, which corresponds perfectly with the conversion of the initial hematoma into a soft callous phase. I'd refer you back to the podcast on bone healing for more information about the cellular events occurring during this transition.
Once the latency period is complete distraction begins, often at the programmed target rate of 1mm per day. In numerous studies this rate was shown to be the ideal lengthening parameter for time and distance. The rhythm however must be monitored, as premature regenerate consolidation or failure of regenerate formation can be a result of too fast or too slow a distraction.
Distraction occurs until the target length is achieved. Then comes consolidation, where the bone converts from soft to hard callous and ultimately gains its structural integrity. Once consolidation is complete the apparatus is removed and unconstrained tension is applied to the limb to allow further strengthening and mineralization. It is important to remember than fixation, whether internal or external, shields the bone from some stress that is required for bone to reach its full mechanical and structural potential.
Axial lengthening is easy to understand. Angular deformity correction is simply distraction around an axis. The axis of deformity correction can be mathematically plotted on radiographs to establish an apex. The fixation is then constructed to work around this apex, with the end result being conversion of a crooked limb or bone into a straight limb segment after distraction is complete. This concept can be uniplanar or multiplanar. In these more complicated deformities hexapod ring systems and computer software may be employed for developing distraction schedules that result in all three planes being corrected simultaneously.
After performing hundreds of these procedures, the miracle of osteogenesis is still fascinating and rewarding each and every time.