Abstract
Peri-prosthetic fractures above a TKA are becoming increasingly more common, and typically occur at the junction of the anterior flange of the femoral component and the osteopenic metaphyseal distal femur. In the vast majority of cases the TKA is well-fixed and has been functioning well prior to fracture. For loose components, revision is typically indicated. Often, distal femoral mega prostheses are required to deal with metaphyseal bone loss. Good results have been reported in small series, however, complications, including infection remain concerning, and these implants are incredibly expensive. Although performing a mega prosthesis in the setting of a well-fixed TKA is not unreasonable due to immediate full weight bearing, in my opinion, prosthetic replacement should be limited to cases of failed ORIF (rare), or in cases where fixation is likely to fail (i.e., severe osteolysis distally). For the majority of fractures above well-fixed components, internal fixation is preferred for the main reason that the overwhelming majority of these fractures will heal. Fixation options include retrograde nailing or lateral locked plating. Nails are typically considered in arthroplasties that allow intercondylar access (“open box PS” or CR implants) and have sufficient length of the distal fragment to allow multiple locking screws to be used. This situation is rare, as most distal fragments are quite short. If a nail is chosen, use of a long nail is preferred, since it allows the additional fixation and alignment that diaphyseal fill affords. Short nails should be discouraged since they can “toggle” in the meta-diaphysis and do not engage the diaphysis to improve coronal alignment. Plates can be used with any implant type and any length of distal fragment. The challenge with either fixation strategy is obtaining stable fixation of the distal fragment while maintaining length, alignment, and rotation. Fixation opportunities in the distal fragment can be limited due to obstacles caused by femoral component lugs, boxes, stems, cement mantles, and areas of stress shielding or osteolysis. Modern lateral locked plates can be inserted in a biologically friendly submuscular extra-periosteal fashion. More recent developments with polyaxial locked screws (that allow angulation prior to end-point locking) may offer even more versatility when distal fragment fixation is challenging. The goal of fixation is to obtain as many long locked screws in the distal fragment as possible. High union rates have been reported with modern locked plating techniques, however, biplanar fluoroscopic vigilance is required to prevent malalignments, typically valgus, distraction, and distal fragment hyperextension.
