Biology of Limb Lengthening

A dogs bone before and after lengthening A dogs bone before and after lengthening. Notice that the bone on the left looks identical to the one on the right except that it is longer. (reproduced with permission from Ilizarov). Limb lengthening regenerates a segment of bone as an organ. It is a form of limb regeneration.

X-rays showing the lengthening process X-rays showing the lengthening process. On the left is a tibia with an Ilizarov frame in place and the bone is broken. In the middle the bone is shown at the end of the distraction phase with a bone gap in place. On the right the bone is shown after it is fully healed.

Distraction End Distraction Consolidation Remodelling Phase Phase Histologic sections and drawings showing the new bone formation during the distraciton (lengthening) phase. At the end of the distraction phase the interzone where the bone is formed is still seen but the cortex of the bone is forming. During the consolidation phase the interzone heals across with bone and the bone is removed from the medullary canal at both ends and the cortex gets thicker. In the remodelling phase the cortex is now of nearly normal thickness and the medullary canal is reconstituted. (Histology courtesy of Ilizarov) Distraction Phase End Distraction Consolidation Phase Remodelling Phase

Interzone Pluripotential cells Histologic section with Inida Ink injection during the distraction phase and an artist rendition of the same. A histologic enlargement of the tip of one bone trabeculum at the site of the interzone showing the bone forming cells (osteoblasts surrounding the central bone trabeculum.

X-ray section of bone during the lengthening X-ray section of bone during the lengthening. The Interzone is clearly seen (left). Histologic section of the new bone (middle) and India ink injection of the vessels between the trabeculae of bone (right)

Intramembranous Ossification Since the new bone formation occurs without a cartilage intermediary this is called Intramembranous Ossification. This is different than the way bone forms to heal a fracture (endochondral ossification)

2 Phases of lengthening: Distraction phase (1mm/day) Consolidation phase There are two phases of limb lengthening: Distraction and Consolidation. Lengthening is usually performed at about 1mm/day during the distraction phase.

Normotrophic: Stable Histologic section and x-ray at the end of consolidatation.

Atrophic-Unstable Histologic section and x-ray in a case of failure of bone formation. This is typical of unstable fixation during the lengtheniing with fibrous tissue instead of bone between the bone ends.

Metaphyseal better than Diaphyseal Stable Fixation Low Energy Osteotomy Metaphyseal better than Diaphyseal Stable Fixation No Initial Separation between bone ends Latency Period before distraction Rate of distraction </= 1mm/day Rhythm of distraction ¼ mm 4X/day or greater Limb Lengthening Criteria for successful bone formation. 1. Low energy minimally invasive osteotomy. 2. Metaphyseal bone heals better and faster than diaphyseal bone. 3. Stable external or internal fixation. 4. No Initial separation between the bone ends. 5. Latency period before distraction of 3-7 days. 6 Rate of lengthening should be controlled. 1mm/day is average and ideal for bone formation but in some cases it should be slower. 7. Rhythm of distraction should be multiple doses a day instead of 1mm once a day.

CONSOLIDATION TIME vs DISTRACTION GAP How does the bone healing time relate to the amount of lengthening.

In as study we performed we showed that there was a linear relationship between bone healing time and distraction gap. There was however a minimum bone healing time of about 3 months.

The femur healed faster than the tibia as shown in this study.

Lengthening through metaphyseal bone healed faster than diaphyseal bone.

Patients under age 20 healed faster than those over age 20.

OSTEOTOME GIGLI SAW We also compared cutting the bone with an osteotome vs with a Gigli saw.

osteotome Lengthening with an osteotome osteotomy is shown on the top row. Lengthening with a Gigli saw osteotomy is shown in the lower row. Gigli saw

There was no difference between the healing time per distraction gap between the two osteotomy methods when the osteotomy was performed through metaphyseal bone.

IIizarov (canines) 1mm , 1 X/day (worst) ¼ mm, 4 X/day (better) 1/60mm, 60 X/day (best) CORR Vol. 239, 1989 Ilizarov claimed that lengthening with a motorized device gave the best results.

Birch (goats) No difference manual versus motorized ASAMI MTG, 1994. Birch did not find any difference with manual vs motorized lengthening in a goat experiment.

We compared our results of manual lengthening with the Ilizarov device to motorized Ilizarov device.

Materials Manual: 43 tibiae in 40 pts. Motorized: 27 tibiae in 26 pts. We compared 43 manual lengthenings to 27 motorized lengthenings.

Surgical Technique Percutaneous prox. tibia osteotomy Ilizarov ex.fix. Bone lengthened at 1mm/day: Manual: ¼ mm, 4 X/day Motorized: 1/1, 440mm, 1,440 X/day Manual was performed 1/4mm 4X/day. Motorized was 1/1440 mm, 1440 X/day.

For patients under age 20 there was no difference between manual and motorized.

For patients aged 20 and greater there was no significant difference between manual and motorized.