Consequences Following Distal Femoral Growth Plate Violation in an Ovine Model With an Intramedullary Implant: A Pilot Study.

BACKGROUND

Retrograde femoral nailing in skeletal immature patients would broaden the surgical options for fracture care and reconstructive procedures but involves violation of the open, active distal femoral physis with the potential for growth disturbance. The tolerance for putting a large diameter metal implant across the physis is largely unknown. The purpose of this pilot investigation was to define the upper limit of cross-sectional violation with a metal implant before causing premature growth arrest or inhibition using a sheep model.

METHODS

Eighteen sheep underwent placement of a retrograde, intramedullary implant at 3-months of age through an open distal femoral physis. The cross-sectional area of the physis was measured preoperatively and implants were selected that violated 3% to 8% of the cross-sectional area of the physis. Growth across the distal femoral physis was examined radiographically following surgery. Following euthanasia, both operative and no operative femurs were removed to compare differences in maximal lengths.

RESULTS

The distal femora grew an average of 10.6±2.2 mm radio graphically after implantation. When compared with control specimens, only operative specimens with 8% of physeal violation demonstrated significant growth discrepancy with operative femurs measuring <2.1 mm in length compared with the contralateral control femur. Histologic analysis did not demonstrate any significant physeal bars formation.

CONCLUSION

Distal femoral growth continues across the physis when 3% to 7% of the cross-sectional area of the physis is violated using a retrograde intramedullary implant. Specimens with 8% of growth violation demonstrated significant growth inhibition. As such, retrograde nailing through the distal femoral physis appears safe up to 7%. On the basis of previous anatomic data in humans and average nail sizes, violations of >6% of the physis with pediatric retrograde nailing would be uncommon. These findings suggest that retrograde nailing may be a viable option and merits further study.

LEVEL OF EVIDENCE: Level IV-case series.