Role of Distal Femoral Replacement for Periprosthetic Fractures Above a Total Knee Arthroplasty: When and How?

Abstract

Summary: 

With increasing incidence of total knee arthroplasty (TKA), a concurrent rise in periprosthetic fractures is also expected. Although many periprosthetic fractures about a TKA can be fixed through locked plating, retrograde intramedullary nailing, or both, some fracture patterns combined with poor bone stock and/or osteolysis can offer a loose femoral component requiring TKA revision. TKA revision in the setting of periprosthetic fracture can be challenging and, often, nearly impossible as fractures that extend proximally may not be amenable to standard revision components. Distal femoral replacement may offer a more efficient, facile approach to treating periprosthetic fractures about a loose TKA component. Here, the role of distal femoral replacement is reviewed, offering indications, salient technical points, and tips to avoid pitfalls while allowing for immediate, reliable weight bearing in this challenging patient population.

Periprosthetic fractures above a total knee arthroplasty (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 before fracture. For fractures above well-fixed components, internal fixation is preferred.^1–4 Fixation options include retrograde nailing or lateral plating. Nails are typically considered in arthroplasties that allow for intercondylar access (“open box posterior stabilized” or cruciate retaining implants) and have sufficient length of the distal fragment to allow for 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 because it allows for the additional fixation and alignment that diaphyseal fill affords. Short nails should be discouraged because they can “toggle” in the metadiaphysis 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 because of 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 extraperiosteal fashion. 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 and nailing techniques; however, biplanar fluoroscopic vigilance is required to prevent malalignments, typically valgus, distraction, and distal fragment hyperextension.^1–4

For certain fractures, distal femoral replacement (DFR) is a wise choice.^1–7 The author reserves DFR for situations where internal fixation is likely to fail (severe distal osteolysis and severe osteopenia) or for cases where it has already failed (nonunion, Figs. 1A–D). Obviously, if the femoral implant is loose, revision is indicated, and typically, the distal bone loss is so severe that a DFR is indicated. The remainder of this article will focus on technical tips and tricks to achieving a successful reconstruction while minimizing potential complications.

FIGURE 1.: A–D, Anteroposterior (A) and lateral (B) radiographs of an 80-year-old woman with a multiply operated periprosthetic fracture with nonunion after dual plating. Postoperative anteroposterior (C) and lateral (D) view of reconstruction and revision to DFR.

Preoperative medical optimization is recommended in these typically debilitated patients. Radiographs should include full-length femur films because femoral stems are used routinely. Having some assessment of femoral bow and diameter can facilitate stem choice. CT scanning can facilitate decision making by providing information about distal bone stock. For acute fractures, an infection workup is generally not needed; however, for multiply operated periprosthetic nonunions, a sedimentation rate, C-reactive protein, and joint aspiration are typically performed. Intraoperative frozen section pathology is routinely obtained from the synovium around the arthroplasty or the nonunion site. The author does not obtain pathology from the fracture site in the setting of an acute fracture, as it is common to have a false-positive result. If there is any evidence of infection, then the reconstruction is performed in a staged fashion. The management of infected periprosthetic fractures is beyond the scope of this article.

SURGICAL TIPS AND TRICKS

The patient is positioned supine on a radiolucent table. Intraoperative fluoroscopy is used, and the patient is prepped out up to the anterior superior iliac spine. A sterile tourniquet is applied to the thigh. This allows for some flexibility in proximal access, should it be required. Intravenous antibiotics are given, and the author commonly uses tranexamic acid to minimize intraoperative blood loss.

The incision used will vary based on the presence of previous hardware. For an acute periprosthetic fracture or a fracture around a loose femoral component, the standard medial parapatellar approach will suffice. In the setting of failed fixation with a laterally based plate, the author prefers a lateral subvastus approach. The mid-line incision is extended anterolaterally. A lateral arthrotomy is extended under the vastus lateralis. This allows for hardware removal and excellent access to distal fragment excision.

TIP: Rotation and length (and therefore joint line) remain challenging to accurately reconstruct. The author recommends measuring the length of the distal fragment before it is excised. A trial component can be used to mark the distal femur resection level while the leg is under gentle traction. This will grossly reduce the fracture and give the surgeon some idea of the length of the distal segment needed to reconstruct the femoral bone loss.

The distal fragment is carefully excised beginning with both collaterals and remaining cruciates. Placing a bone hook in the intercondylar notch and “lifting” the distal femur allows for excellent posterior exposure. Careful subperiosteal dissection along the posterior femur will minimize the risk of neurovascular injury. After the distal femur is excised, the tibia is approached. The tibial component will need to be revised to be compatible with the DFR hinge mechanism. A full discussion of tibial component revision is beyond the scope of this article. In general, the tibial reconstruction is completed and cemented into place before completing the femoral reconstruction.

After a stable tibial reconstruction is completed, attention is turned back to the femur. Careful reaming of the femoral diaphysis is performed. A stem of appropriate diameter and length is chosen. The author prefers cemented stems in these typically elderly patients with osteopenic, capacious femoral canals. A trial is built and evaluated for length, rotation, alignment, and proximal stem bypass. This is the most challenging aspect of the procedure.

TIP: Fluoroscopy is used to evaluate the amount of proximal stem bypass. The author generally prefers longer, diaphyseal stems in the 120-mm range. If in doubt, choose the longer stem, especially in osteopenic patients. Leg lengths can be assessed by lining up the heels on the supine patient and comparing with the contralateral limb. Fluoroscopy can also be used to measure from the tip of the trochanter to the lateral joint line, then comparing the measurement to the contralateral limb (similar to the technique used when nailing a highly comminuted femoral shaft fracture).

TIP: Femoral component rotation is challenging to ascertain. The linea aspera provides some guidance to the posterior femur. Patellar tracking is a common problem with DFRs, so careful attention to rotation is important. Careful trialing is performed, evaluating patellar tracking, and the correct rotation is marked on the femoral diaphysis. If in doubt, add a bit more external rotation.

When the appropriate length and rotation of the femoral component is determined, the construct is cemented into place. Careful irrigation and drying of the canal is indicated to minimize embolic potential. The author routinely adds vancomycin powder (1 g per 40 g batch of cement) to these reconstructions because of the high reported rate of infection.

After cementation and choosing the appropriate polyethylene insert, patellar tracking is re-evaluated. It is not uncommon to need a lateral release or medial imbrication to optimize tracking. Patellar complications are the most common problems after DFR, so vigilance is recommended to optimize tracking. The knee is closed in the typical fashion over a suction drain. Liberal use of incisional negative-pressure wound therapy is recommended. Deep venous thrombosis prophylaxis is used in all patients. Postoperatively, patients are allowed full weight bearing with a walker for 6 weeks until soft-tissue recovery and quadriceps function allow transition to a cane.

TIP: Immobilizing the knee for a few weeks postoperatively can assist with soft-tissue recovery and extensor mechanism healing. DFRs typically do not get stiff and achieve motion very quickly. If extensive extensor mechanism realignment was performed, the author immobilizes the knee for 6 weeks. For more routine cases, immobilization until suture removal is adequate.

The published results of DFR for acute periprosthetic fracture and failed fixation are generally good. Complications, not surprisingly, are common. Infection and extensor mechanism problems are the most problematic.

In summary, for the vast majority of periprosthetic fractures of the distal femur, internal fixation is indicated, either with a retrograde nail or with a laterally based locking plate. DFR has a role in fractures where open reduction and internal fixation is likely to fail or already has. Careful attention to the extensor mechanism and taking measures to minimize infection is recommended. These reconstructions can provide durable functional improvement.