Impact of transphyseal intramedullary nailing on tibial distraction regenerate and subsequent tibial growth in sheep: an experimental study
Authors: Kononovich N. A. , Leonchuk S. S. , Gorbach E. S. , Gorbach E. N. , Popkov D. A. 
Published: December 2024

Introduction In lengthening of limbs in children, the combination of elastic intramedullary reinforcement and  external fixation has advantages over standard techniques, but requires the removal of elastic nails and does not provide the possibility of their locking, that could significantly reduce the period of external fixation.

The purpose of the work was to study the features of tibial distraction regenerate formation and residual growth of the lengthened segment in lambs under the conditions of external fixation combined with a transphyseal rigid titanium rod.

Materials and methods In vivo experiments were performed on lambs (n = 7) during their growth period. In the control group, the right tibia was lengthened using transosseous distraction osteosynthesis for 28 days. In the study group, the segment was additionally reinforced with an intramedullary rigid rod. The following were measured in radiographs: the height of the distraction gap between the fragments, the transverse dimensions of the distraction regenerate, the height of the bone sections of the regenerate and the growth zone, the length of the tibia; the anatomical angles of the proximal articular end of the tibia. To determine the intrinsic growth dynamics of the segment under lengthening, the size of the distraction regenerate was subtracted from the length of the tibia.

Results In the main group, the transverse dimensions of the distraction regenerate were larger, and the height of the growth zone was smaller than in the control group. Consolidation of the regenerate in the main group occurred after 30 days, and in the control group 60 days after the cessation of lengthening. No slowdown in  the  longitudinal growth of the elongated segment was noted compared to the contralateral one, the orientation angles of the inclination of the proximal articular surfaces did not change.

Discussion Transphyseal implants should be located centrally to reduce the risk of epiphysiodesis, their area should not exceed 7 % of the growth zone. These conditions were met in the study. The reduction in the time of distraction regenerate corticalization and early termination of external fixation was associated with  pronounced periosteal osteogenesis and increased bone fragments stability. The location of the rod in the growth plate does not lead to epiphysiodesis and does not interfere with normal growth of the segment.

Conclusion Pronounced periosteal osteogenesis and additional stabilization of the bone fragments with a transphyseal rigid titanium rod contribute to the faster bone regenerate formation and maturation. There are no signs of inhibition of spontaneous growth of the segment under lengthening and radiographic signs of epiphysiodesis at the transphyseal level. The central location of the transphyseal rod relative to the growth zone plane and its cross-sectional area of less than 5 % of the physis area can be considered conditions under which epiphysiodesis does not develop.