Anatomical structures at risk with the proud retrograde femoral nail.

Background: Post-operative knee pain is common following retrograde nailing, with its etiology often multifactorial although a well-established cause is nail protrusion from the intercondylar notch. The aim of this study was to assess the structures at risk if the nail is left proud of the femoral articular surface.

Methods: A retrograde femoral nail (Synthes Distal Femoral Nail) was inserted into the distal femur of 15 cadaveric lower limbs using the standard technique. The nail was left 10 mm proud of the articular surface and locked in this position. The knee was then put through a full range of movement while recording the intra-articular structures that came into contact with the distal end of the nail as well as the position of the knee when this occurred. This was repeated with the nail 5 mm proud.

Results: With the nail 10 mm proud, it impinged on the anterior horn of the medial meniscus in 14 cases and the anterior horn of the medial meniscus as well as the tibial insertion of the ACL in one case at 15° of flexion. At 70° of flexion the nail came into contact with the distal margin of the patellar articular surface in the midline in all 15 cases. With the nail 5 mm proud, it impinged on the anterior horn of the medial meniscus in seven cases and the tibial insertion of the ACL as well as the anterior horn of the medial meniscus in eight cases as the knee was brought into full extension. In flexion the distal margin of the patellar articular surface in the midline came into contact with the nail at 70° of flexion in all 15 cases.

Conclusion: Correct positioning of a retrograde femoral nail is of paramount importance to avoid further iatrogenic injury to intra-articular structures.