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Five revision total knee arthroplasties (TKAs) involving severe femoral bone loss were performed in 1 994. Each had sufficiently severe femoral bone loss in which collateral ligament origins and posterior capsular attachments were violated. A paradoxical phenomenon was observed in each case. Unlike primary TKAs, in which larger distal femoral bone resection leads to laxity of the knee joint in extension, these cases with severe distal femora! bone loss, after initial component selection, developed the opposite situation, a flexion contracture. It was hypothesized that femoral bone loss involving collateral ligament origins would permit distraction of the tibia below the femur with the knee held in flexion, but when the knee was brought to full extension, intact posterior structures would maintain a normal tibia! position. To investigate this hypothesis, six fresh-frozen cadaveric lower limbs were tested in full extension and 45° and 90° of flexion after release of the femoral attachments of the collateral ligaments and the posterior capsule from the femur. Joint space changes were measured via a motion tracking device. Results showed that with loss of collateral attachments, 17.2±8.9 mm of joint space is created in 90° of flexion, whereas the joint space in full extension is conserved (1.5±1.7 mm). With additional loss of the posterior capsule, the joint space at 90° of flexion increased to 26.2±6.1 mm, with minimal changes in the extension gap (3.4±0.8 mm). Distal femoral bone loss was associated with an increase in the flexion gap compared to the extension gap.

Reconstruction of the femur depends on the quantity of bone loss and the quality of the remaining bone stock. Multiple classifications and reporting systems can be used to characterize the bone defect. We present a simple algorithmic approach for proximal femoral bone loss reconstruction during revision total hip arthroplasty. Quantity of bone loss is assessed using radiographs based on different classification systems, whereas quality of the remaining bone stock is assessed intraoperatively. Based on the type of proximal bone loss and the quality of the available bone, we describe our preferred reconstruction technique. For minor bone loss, the metaphysis is expanded but intact with partially absent calcar. There is minimal bone loss anteriorly and posteriorly, and the diaphysis is intact. For significant bone loss, the metaphysis is compromised, and there is no calcar. There is minimal bone loss anteriorly and posteriorly. The available proximal bone may be thin, sclerotic, and incapable of support. However, the diaphysis is intact. For massive bone loss, there is complete circumferential bone loss in the metaphysis, extending to the diaphysis. The anterolateral bone and supporting subtrochanteric metaphyseal bone are absent. The metaphysis is not stable and will not offer rotational stability. There is massive bone loss anteriorly and posteriorly. The stability of the implant is dependent on distal diaphyseal fixation. For complete proximal bone loss, there is extensive circumferential segmental bone loss proximally and extensive cavitary loss involving the entire diaphysis. Additionally, there is extensive ectasia of the diaphysis.

During preparation for uncemeted femoral arthroplasty, a phenomenon has been observed that it in dicates thinning of anterior metaphyseal bone to a critical level light can be seen from within the canal passing through the anterior cortex. This skylight sign alerts the surgeon that a cortical defect or fracture can occur on reaming broaching, or component insertion. In 420 consecutive anthroplasties, a skylig sign was remoted in 97 (23%) hips. In 5 of those hips an oval cortical detect was created and in 3 hips a fracture occured during broaching or inserticon. Loosening developed in 1 hip with fracture. No fractures or defects ocurred in hips without a skylight sign. If a skylight sign is present, the featur is at risk, and preventive measures should be taken.

Educational Objectives As a result of reading this article, physicians should be able to: 1. Identify the available types of reconstruction for failed total hip arthroplasty. 2. Summarize the preoperative workup of patients with failed total hip arthroplasty and massive proximal femoral bone loss. 3. Assess the surgical technique of proximal femoral replacement for failed total hip arthroplasty. 4. Recognize treatment complications, patient outcomes, and survival of proximal femoral megaprostheses for revision of failed total hip arthroplasty. Despite recent advances in device manufacturing and surgical techniques, the management of proximal femoral bone loss in revision total hip arthroplasty remains challenging. Currently, failed total hip arthroplasty in elderly and less active patients, nonunion of the proximal femur with multiple failed attempts at osteosynthesis, resection arthroplasty, and massive proximal femoral bone loss can be salvaged with proximal femoral replacement using a megaprosthesis. The procedure is technically demanding and requires careful preoperative planning. Instability and aseptic loosening are the major complications, especially in younger and more active patients. The new generation of modular proximal femoral replacement megaprostheses and the increased experience obtained with these surgeries have reduced complication rates and improved outcomes. [ Orthopedics. 2014; 37(10):691–698.]

Recently, 3-dimensional (3D) printing technology has been used in the development of titanium metaphyseal cones to manage severe bone loss in revision total knee arthroplasty (rTKA). This study assessed (1) radiographs; (2) functional outcomes; (3) complications; and (4) 2-year implant survivorship in patients receiving 3D-printed titanium metaphyseal cones for moderate-to-severe tibial and femoral bone loss in rTKA. A single institution, retrospective chart review was performed for patients with large bone defects treated with a 3D-printed femoral or tibial titanium metaphyseal cone between 2015 and 2017 during rTKA (N=54). Paired sample t tests analyzed Knee Society Scores (KSS). Kaplan–Meier analyses determined implant survivorship when the endpoint was cone revision for aseptic loosening, cone revision for any reason, and reoperation for any reason. The authors found that 51 (98.1%) of 52 available radiographs demonstrated well-fixed components without any evidence of loosening or migration. Mean postoperative KSS scores were significantly higher when compared with preoperative scores (80.4 vs 52.0; P >.001). One patient experienced aseptic loosening of their cone. Seven additional cones were explanted as a consequence of reinfection, 1 of which was removed prior to arthrodesis. Cone survivorship was 98.5% when the endpoint was cone revision due to aseptic loosening, 88.2% when cone revision was due to any reason, and 77.9% for any reoperation. Metaphyseal cones appear to be well-suited for large bone defects during rTKA and the authors' findings suggest that cones may be a viable option for metaphyseal fixation during rTKA. Future studies should focus on their durability during a longer time period. [ Orthopedics . 2021;44(1):43–47.]