Rotating Hinge Distal Femur Replacement: A Turn for the Worse

The use of a rotating hinge distal femur replacement (DFR) for significant bone and soft tissue defects in the setting of total knee arthroplasty (TKA) revision has become increasingly more common. Although significant advancements have been made in modern DFR components, complications and failure rates remain high. The unanticipated early failure presented serves as the first reported case in the literature to our knowledge of a 180° rotation of a press-fit DFR.

Originally, DFRs were used primarily for oncology patients with substantial bone loss following large mass excisions. The utility of DFRs has grown to include massive bone loss in the setting of TKA revision, periprosthetic fractures, and periprosthetic joint infections.^1-3 DFRs help restore the joint line in the setting of significant bone loss and contain a rotating hinge mechanism that provides functional movement despite the loss of soft tissue constraints around the knee.^1-3

DFRs have been associated with early postoperative mobilization and decreased need for ambulatory devices at 1 year in revision TKA and periprosthetic and geriatric distal femur fractures.^4-6 Advances in prosthetic design, biomechanics, and fixation technique have led to improved survival rates.³ Despite these improvements, the overall complication rate remains high at 30 to 40%.^3-7 Commonly reported complications after DFR include infection, aseptic loosening, soft tissue failure, and structural failure.^3,4,7 Recent case studies also have reported on dislocation or disengagement of the rotating hinge.^8-11

In this case report, we present a patient who had a DFR as the second stage of a 2-stage TKA revision due to a periprosthetic joint infection with a postoperative complication of 180° rotation of the press-fit femoral component. Although this is a rare event, knowledge of this possible complication is important for arthroplasty surgeons.

Case Presentation

A patient with a history of hypertension, osteopenia, and rheumatoid arthritis underwent a primary right TKA in 2007. Ten weeks postoperatively, the patient had a ground-level fall that resulted in a right periprosthetic supracondylar distal femur fracture that was treated with a distal femur locking plate. The patient healed, however, with a significant golf club deformity (Figure 1). The patient did well for more than a decade but in 2019 was admitted with pelvic inflammatory disease and adnexal abscess that was treated with broad-spectrum IV antibiotics. Shortly after this admission, the patient developed a right knee periprosthetic infection with cultures positive for Ureaplasma parvum.

The patient then underwent a 2-stage revision of the infected TKA. Stage 1 consisted of explant of the TKA components as well as removal of the distal femur plate and screws and placement of an articulating antibiotic cement spacer (Figure 2). The patient completed 6 weeks of IV antibiotics. Following completion of the antibiotic course, we obtained a serum erythrocyte sedimentation rate, C-reactive protein level, and white blood cell count, which were all within normal limits. A knee aspiration was performed and did not show signs of residual infection. Frozen histopathology was sent during the second stage of the revision and did not show infection. After the results of the frozen histopathology returned, the antibiotic spacer was removed, and the femoral canal was thoroughly debrided. Cement and fibrous tissue in the femoral canal were carefully removed. In the setting of significant bone loss and soft tissue compromise due to the previous infection and distal femur fracture, the Zimmer Biomet Orthopedic Salvage System (OSS) with porous coated press-fit elliptical femoral stem was utilized.

The femoral canal was reamed until good cortical chatter was obtained at 16 mm. Per the Biomet OSS guide, “For bowed (curved) long and short press-fit stems, the final flexible reamer shaft diameter may need to be larger than the definitive trial and implant diameter.” After trialing, size 15.5 mm was selected for implantation. Intraoperatively the final stem was noted to have good interference fit after insertion and was stable throughout knee range of motion and varus/valgus stress testing. The patient did well with mobilization while in the hospital postoperatively and was discharged home (Figure 3).

Five days after discharge, the patient kicked the repaired knee onto a chair for rest and elevation and experienced extreme pain and was unable to flex the knee. On presentation to the emergency department, the X-rays showed 180° rotation around the longitudinal axis of the femoral component without any other obvious component failure or fracture (Figure 4). The patient was taken back to surgery the following day. Intraoperatively, the femoral stem was found to be loose and rotated 180° (Figure 5). No failure or dislocation of the tibial or rotating hinge components were identified. The press-fit femoral stem was removed and replaced with a cemented stem (Figure 6).

The postoperative course after the revision surgery was uneventful, and the patient is doing well clinically with no pain, functional range of motion of 5 to 105°, and has returned to regular activities without difficulty.