To compare between bifocal and trifocal external bone transport by ilizarov ring external fixator as a treatment method for posttraumatic bone defects more than 5cm in lower extremities regarding:

• External fixation index .
• The need of any further surgical procedures as debridement at docking site , the need of cancellous bone graft or the use of internal fixation.
• Functional outcome, complication rate as well as limb length discrepancy.

Distraction osteogenesis is formation of new bone(regenerate bone) when bone segments undergo gradual, controlled separation.

There are three treatment approaches by ilizarov ring external fixator according to number of bone osteotomies. First one is the monofocal approach with closure of defect without any osteotomies. Second one is the bifocal approach with a single osteotomy to create one transported bone segment between the osteotomy and the defect. Third one is the trifocal approach with two osteotomies creating two separate transported bone segments.

Hypothetically, trifocal approach has shorter treatment time than bifocal one as it is a double level bone transport so closes the defect faster. However, there are other considerations as complications that may occur and the need of further surgical procedures and this is what will be discussed in this research.

Inclusion Criteria:

• 1)Age from 18-60ys . 2)Posttraumatic bone defects more than 5 cm. 3)Lower extremity bone defects.

Exclusion Criteria:

• 1)Young pts <18 or old pts>60. 2)Post infectious or post-resection of a tumor bone defects. 3)Upper extremity bone defects.