Femur can be lengthened over nail, along its mechanical axis : a modified lengthening over nail technique.

The theoretical risk of medialisation of the knee joint and the lateral shift of the lower extremity mechanical axis, due to achievement of lengthening along the anatomical axis is present in the process of lengthening with elongation nails and the "lengthening over nail" technique. With this new technique described in this study we aimed to prove that lengthening over nail can be performed along the mechanical axis of the femur. Six lower-limb models were used to perform three different lengthening techniques. In group 1, lengthening was achieved along the anatomical axis with an external fixator. In group 2, the clamps of the external fixator were adjusted at 6° to achieve lengthening along the mechanical axis. In group 3, eight different sized nails were applied with an external fixator (angle adjustable clamps were at 6°) to achieve lengthening along the mechanical axis by LON technique. Photographs were taken after each cm of lengthening and the distance from the mechanical axis line were measured. The modified LON technique described in this study provided lengthening along the mechanical axis. One of the main advantages of the procedure described in our study is the chance for reconsideration and revision of unforeseen angulations and malalignments, via the help of the distal angular adjustable clamps; during the time of the surgery for external fixator removal before application of the poller screws.