Periprosthetic Distal Femur Fracture After Total Knee Arthroplasty
A 79-year-old woman presents 3 weeks after a cemented cruciate-retaining total knee arthroplasty with a fall and inability to weight-bear. Radiographs show a comminuted supracondylar distal femur fracture, with a fracture line extending proximally, a well-fixed femoral component with no radiolucent lines, and severe osteopenia. The fracture is about 4 cm above the anterior flange of the femoral component, with no comminution around the peg or stem, and no evidence of loosening; the polyethylene insert appears intact. She lives alone, uses a walker, and has mild cognitive impairment. She is medically stable. Her distal femoral bone stock is poor, with a cortical thickness of about 2 mm on the lateral view. The on-call registrar has booked a distal femoral locking plate and asks whether a hinge knee replacement would be better.
1. How do you classify this fracture, and do you agree with the plan for a locking plate?
Read the worked answer
This is a periprosthetic distal femoral fracture around a total knee arthroplasty. The key classification questions are: is the femoral component well fixed, and is the fracture reducible with enough distal bone stock to hold fixation? Radiographs here suggest a well-fixed component with no radiolucent lines and an intact interface, and the fracture is supracondylar with proximal extension.
For a well-fixed implant with a reducible fracture and adequate distal bone stock, open reduction and internal fixation is the standard. The options are a distal femoral locking plate, a retrograde intramedullary nail if the intercondylar box allows and the fracture is not too distal, or a combination. A locking plate is reasonable here because the fracture extends proximally and the comminution and osteopenia make nail fixation less predictable, although a cruciate-retaining box may permit a nail.
Distal femoral replacement is reserved for a loose component, severe comminution with inadequate bone stock, or a fracture that cannot be reconstructed. This patient has severe osteopenia and comminution, which raises the failure risk of fixation, but the implant is well fixed and she is medically stable. I would proceed with a locking plate, with a low threshold to convert to replacement if intraoperative findings show a loose component or unreconstructable bone loss.
2. What are the technical points that determine success, and how would you counsel her about weight-bearing?
Read the worked answer
The technical keys are: restore length, alignment, and rotation; use a plate long enough to span the comminution with at least three or four bicortical screws proximally and multiple locking screws distally; avoid leaving a short distal segment held by only a few screws; and consider bone graft or substitute for the comminution. A bridging plate with indirect reduction preserves blood supply better than extensive stripping. If the fracture extends to the anterior flange, place the plate laterally and choose a distal screw trajectory that avoids the implant.
Weight-bearing: in an elderly patient with osteopenia and comminution, protected weight-bearing for 6–8 weeks is prudent, but prolonged non-weight-bearing is poorly tolerated and increases complications. I would aim for touch-down weight-bearing initially and progress as callus appears, with physiotherapy and a walking frame.
Counsel her that the fixation may fail - the reoperation rate after fixation in this group is around 10–20% - and that replacement remains an option if it does. Discuss the goals: return to walking, not high-demand function. Document the discussion, and ensure she has social support at discharge.
3. At surgery, the distal fragment is a single piece with a fracture line entering the trochlear notch, and the component is found to be loose. What now?
Read the worked answer
This changes the plan. A loose femoral component, particularly with a fracture extending into the trochlear notch, means fixation alone will not provide a stable construct - the implant-bone interface is the weak link. Distal femoral replacement with a hinged revision knee is the appropriate operation. The fracture is effectively a peri-implant fracture around a loose component, and reconstruction with a stemmed, hinged prosthesis addresses both the fracture and the loose implant.
Technical points: use a stemmed femoral component that bypasses the fracture zone by at least two cortical diameters, reconstruct the distal femur with a revision or tumor-type prosthesis, and address bone loss with augments or cement. Assess the tibial component; if it is well fixed and the insert is intact it may be retained, but a hinge requires a compatible tibial platform. Postoperatively, allow immediate weight-bearing as tolerated, which is an advantage in this patient.
Counsel about the higher risk of infection, loosening, and the need for long-term follow-up. Document the intraoperative findings and the rationale for changing the plan.