[A nail for progressive lengthening. An animal experiment with a 2-year follow-up].

The elongation nail was experimented on 10 pure-breed Romanov ewes aged 9 to 12 month-old. It was implanted in a randomly chosen femur, the other femur being used as a control. After a superior and lateral approach to the femur, drilling and initial distraction averaging 26 mm, the nail was inserted and locked at both ends. Lengthening began at D1 by alternate inward and outward rotation maneuvers exerted on the pelvic limb. One ewe presented an intraoperative hip dislocation, another one unlocked the upper lock, with secondary shortening. The other 8 ewes underwent successful lengthening without apparently suffering (63-mm gain, i.e. 37% at the end of lengthening). Two ewes died at 9 months and their femura presented with a space remaining to fill smaller than 3 mm. Five of the other 6 ewes were followed up for an average of 10 months after bone healing and nail removal, over a total follow-up of 2 years. The femur is modified all over its diaphysis and widened at the level of the regenerated tissue, where cortical bone is thinner but has a normal lamellar appearance. Bone marrow is replaced by trabecular bone filled with fatty marrow. The pathology study of the last of the 6 ewes followed up for 2 years showed a bridge between both sites of incipient regeneration, indicating bone healing. The final gain as compared to the non-operated side is 27%. Progressive lengthening can be performed with an internal fixator in animals. The clinical trial in progress with allow evaluating this technique and establishing its field of application.