Review Question - QID 218932

This patient has a cruciate retaining (CR) total knee arthroplasty (TKA) implant. The femoral notch recess built in the femoral component often necessitates a more posterior start point for the retrograde nail, resulting in some degree of extension deformity.

Distal femur periprosthetic fractures can be managed similarly to native knee distal femur fractures with multiple implant options available. Retrograde nailing is an enticing option, given the minimal soft tissue damage when compared to open plating techniques. Surgeons need to be conscious of the underlying TKA implant, as not all can accommodate a retrograde nail. While all modern CR total knee implants can accommodate a retrograde nail (Illustration A), some posterior stabilized (PS) implants cannot (Illustration B). The PS implants have a box cut required to accommodate a cam post built into the polyethylene to assist in femoral rollback. Most of these boxes have an 8-12mm recess/opening to accommodate an intramedullary nail, however, some have a closed box which eliminates the ability to pass an intramedullary nail (Illustration B). In TKA implants that can accommodate a retrograde nail, surgeons must be aware that these implants force a more posterior start point, which ultimately results in an extension deformity (Illustration C). If performed properly, the deformity seen is minimal and inconsequential.

Hake and colleagues provided a comprehensive review regarding the treatment of distal femur fractures and implant-specific considerations. They review pearls and pitfalls of lateral locked plating, retrograde intramedullary nailing, and distal femur replacement. They conclude that the optimal implant choice for the treatment of distal femur fractures is still poorly defined, however, is best chosen based on patient- and surgeon-specific factors.

Davis and colleagues provided a technical overview of how to perform retrograde intramedullary nailing through a total knee arthroplasty. They provide a step-by-step approach and provide a supplementary video discussing the technical pitfalls. They emphasize ensuring the implants are well fixed and that the TKA can accommodate a retrograde nail before going back for surgery.

Ebraheim and colleagues performed a systematic review regarding distal femur periprosthetic TKA fractures and surgical treatment options. They found the most reported periprosthetic TKA fracture was classified as Rorabeck type II (displaced fracture with stable implant). This subgroup of patients had similar union rates when comparing locked plating (87%) to retrograde intramedullary nailing (84%), however, the retrograde nailing group had a higher revision surgery rate overall due to nonunion. The authors concluded that patients’ overall health, fracture morphology, and surgeon experience should guide the surgical treatment plan, as a gold standard has yet to be established.

Figure A shows lateral imaging of a TKA distal femur periprosthetic fracture (Rorabeck type II) in a patient with a CR implant. Illustration A displays CR implant design with a femoral notch recess which can accommodate a retrograde intramedullary nail. Illustration B displays PS implant designs and delineates the difference between open and closed-box designs. Only open-box PS TKA implants can accommodate a retrograde intramedullary nail. Illustration C shows this patient’s post-operative imaging with an appreciation of mild extension deformity.

Incorrect Answers:
Answer 2: Retrograde intramedullary nailing causes less soft tissue injury (i.e. dissection and periosteal stripping) compared to lateral locked plating.
Answer 3. There is no box in these CR TKA implants. There is a femoral notch recess (where the retrograde nail start point is placed) purposefully built into the implant to leave a sizable block of bone where the PCL origin lies posteriorly.
Answer 4: While retrograde nailing is an appropriate treatment option, there is a considerable (~15%) chance of requiring revision surgery (i.e. nonunion).
Answer 5: Retrograde intramedullary nails can be utilized in the vast majority of periprosthetic distal femur fractures. The most common absolute contraindications for a retrograde intramedullary nail include TKA femoral component that cannot accommodate the nail (i.e. closed box or stemmed implant), a loose femoral component, a pre-existing long antegrade cephalomedullary nail, or insufficient bone stock. This fracture is transverse and at the level of the anterior flange, which could accommodate multiple distal interlocking screws with modern implants.