Introduction: Plastic deformation of the regenerate bone is a complication noted soon after limb lengthening. However, less is known about the factors responsible for the development of plastic deformation.

Materials and Methods: Retrospective analysis of 35 X-rays of achondroplast children who had limb lengthening were reviewed. The study compared Monofocal Vs Bifocal and Long lengthenings(> 10 cms) Vs modest lengthenings(≤ 10 cms) of tibial lengthening. Other parameters included in study were Bone healing Index, total length gained and sagittal and coronal axial deformities. There were 20 females and 15 males, 21 long lengthenings and 14 modest lengthenings in the study. The joint orientation and diaphyseal angles(antero-posterior and lateral X-ray views) was used for the measurement of plastic deformation of the regenerate bone.

Results: The mean age at operation was 10 years (range; 6–16 years). There were 29 cases of monolateral fixator and 6 of Ilizarov ring fixator, Of which 26 had monofocal lengthening and 9 had bifocal lengthening (34 callotasis and 1 chondrodiastasis). The total average length gained was 10 cms (range; 23–152). The mean bone healing index and external fixation index/time were 41 days and 352 days respectively. Plastic deformation of the regenerate bone was seen in 26 cases in total. 24 out of 29 cases of monolateral fixator (82%) developed plastic deformation. 44%(4/9) of bifocal group and 84%(22/26) of monofocal group showed evidence of plastic deformation. The long lengthenings showed plastic deformation in 85% (18/21) of the cases, whereas only 57%(8/14) of the cases were positive in modest lengthening group. Most of the axial deviation was in the coronal plane in 92% (24/26) and the sagittal plane accounted to only 23%(6/26) requiring surgical correction.

Conclusions: Long lengthenings and monofocal techniques showed more plastic deformation than bifocal and short lengthenings. However, Ilizarov ring fixator with bifocal corticotomy seemed to be promising with less association with the above entity in our recent experience.