Third-Generation Flexible Metaphyseal Cones in Revision Total Knee Arthroplasty: Minimum Two-Year Follow-up

Porous metal cones are commonly utilized in revision total knee arthroplasty (rTKA) to manage severe bone loss. Flexible metaphyseal cones (FMCs) allow for macrodeformation, more uniform stress distribution, and diminished peak stresses to the compromised cortical bone, potentially reducing fracture risk during impaction. This study aimed to evaluate the early outcomes of FMCs used to treat severe bone loss in rTKA.

There were 241 FMCs inserted during 200 rTKAs. A combination of femoral and tibial FMCs was used in 41 knees. The most common reasons for revision were flexion instability (90 cases), aseptic loosening with or without osteolysis (55 cases), and reimplantation postinfection (27 cases). The mean age at operation was 68 years (range, 37 to 82). The Anderson Orthopaedic Research Institute bone loss classification was used. Serial radiographs were reviewed for evidence of loosening or osseointegration, and survivorship was determined. The mean follow-up was 3 years (range, 2 to 4.5).

At final follow-up, no radiolucent lines were identified around the FMCs. Survivorship was 98% for any revision, 99% for aseptic revision, and 100% for aseptic loosening. Excluding infection, all remaining FMCs (240 cones) demonstrated evidence of stable fixation. There were two intraoperative fractures (1%) that occurred (one femur and one tibia), both in knees with type 2B defects, with only one fracture associated with cone insertion (0.5%). There were three re-revisions (1.5%). There was one knee (0.5%) that was explanted for a recurrent infection at 6 months; one underwent irrigation and debridement with polyethylene exchange for infection (postreimplantation), and a third was revised with polyethylene exchange for arthrofibrosis.

To our knowledge, this is the first study evaluating the clinical results exclusively for noncustomized, third-generation FMCs in rTKA. The FMCs provide stable fixation at early follow-up, and their ability to deform during impaction appears advantageous with a low rate of intraoperative fracture.