Extraction of total knee arthroplasty intramedullary stem extensions

Abstract

Intramedullary stem extensions will need to be extracted during total knee arthroplasty (TKA) revisions, especially repeated ones. These stems have various designs and lengths, can be straight or offset, cemented (partially or totally) or cementless, smooth or rough. This diversity adds to the difficult of extracting them, which the surgeon must anticipate before starting the revision procedure. Porous metaphyseal metal components (cones, sleeves) are being used increasingly during revision TKA. They pose specific extraction challenges and complicate the extraction of the stems with which they are often associated. The maneuvers used during extraction have a direct impact on the subsequent joint reconstruction methods. These procedures are always long and difficult, with an increased risk of bone-related complications (perforation, fracture) or infection. They must always be carried out at specialized centers by experienced surgeons. The reasons for re-revision are the same as those for TKA revision, mainly aseptic loosening, instability and infection-only the latter requires that all components be removed. The local conditions are often unfavorable: epiphyseal-metaphyseal bone defect, thin cortices, osteoporosis, and in some cases, stiffness. The type of implant to extract and its characteristics must be identified beforehand in case special instruments are needed. An imaging workup is done to specify the relationship of the stem with bone, quality of its fixation, bone lesions and gaps between stem and bone, knowing that extraction is harder when the gaps are smaller. A combination of extended radiolucent lines, purely metaphyseal fixation, and a thin smooth stem may mean that intramedullary extraction is feasible. The extensor mechanism must be released to achieve sufficient exposure. If a tibial tubercle osteotomy is needed, it must be sized to match the extraction. After disassembly of femoral and tibial components-which can be challenging-the epiphyseal components must be released. High performance instruments for cement extraction and metal cutting are essential. Other than simple cases (loosened or partially fixed implants), intramedullary extraction can be dangerous especially when the stem extension is well-fixed, whether cemented or not. A diaphyseal window may be sufficient, but in most cases, an extended osteotomy is needed. This includes detaching the tibial tubercle at the tibia. At the femur, this may require an anterior midline window, an anterior extended ostéotomy or an anterolateral oblique distal femoral osteotomy with fibrous hinge. The extraction of metaphyseal porous components is difficult. Their connection with the bone must be broken - which can be long and risky - before the associated stem is removed. While it is easier to extract when the stem can be removed first, it is not always feasible. Reconstruction depends intimately on the methods used to extract the existing implants. Any diaphyseal discontinuity must be bridged (long stem or plate). The extent of the resulting bone defect after extraction drives the revision methods, which are simplified by using porous metaphyseal metal components and shorter stems when possible.

Keywords: Intramedullary stem extensions; Revision; Total knee arthroplasty.