Insufficient Stability of an Extramedullary Lengthening Device of the Tibia in Sheep

Author(s): Jäckle K, Becker A, Reupke V, Lorenz HM, Lippross S, Tsaknakis K, Lüders KA, Braunschweig L, Hell AK

Background: Congenital or acquired limb length discrepancy during childhood can be either treated by growth arrest or lengthening procedures. Lengthening with external fixation is usually associated with various complications. The more elegant method of bone lengthening via an intramedullary device is limited by the inner diameter of the tubular bone and the presence of open growth plates. Recently, extramedullary fixated intramedullary lengthening devices have been used off- label in children. To our knowledge, evaluation of this technique in humans as well as in animals is still pending.

Case Presentation: This study was designed to critically test a novel extramedullary fixated lengthening device at the tibia using a four months old lamb as a clinical model. The device was successfully tested for biomechanical stability up to 500 N before implantation. Although the positioning of the implant and the subsequent osteotomy went as planned, the sheep was not able to place a stable load on the leg after recovery from anesthesia. Radiological analysis and replacement of the device could not rescue leg stability so that the sheep had to be sacrificed.

Conclusions: The present case report indicates that an off-label used surgical treatment method for children with limb length discrepancy causes harmful secondary effects in lamb, which otherwise often represent preclinical subjects for human devices. Probably due to rotational load and the inability to relieve the leg, this novel extramedullary fixated lengthening device is not transferable to the anatomy of sheep.