Aims Managing large medial tibial bone defects during total knee arthroplasty (TKA) remains technically demanding, particularly in elderly patients. This study quantitatively compares two reconstructive strategies: 'bridging' the defect using an asymmetric metaphyseal cone versus 'anatomical reconstruction' employing a symmetrical cone with a metallic block augment, and assesses their sensitivity to osteoporotic bone quality. Methods A finite element model of a tibia with a standardized medial defect (Anderson Orthopaedic Research Institute (AORI) Type 2a) was adapted to simulate both configurations under physiological loading cycles in healthy and severe osteoporotic bone. Cumulative interface micromotion was quantified using a coordinate-based post-processing algorithm that decouples normal separation from tangential shear. A parametric sweep of the tangential contact clearance evaluated near-surface biological interaction zones without additional simulations. Results In healthy bone, both strategies demonstrated adequate stability with micromotions predominantly below 50 μm. In osteoporotic bone, the asymmetric cone exhibited a loss of stability, characterized by intermittent lift-off during walking and excessive tangential shear during stair descending. This instability induced a toggle effect at the distal stem. The augmented symmetrical cone maintained stable fixation regardless of bone quality. Expanding the tangential contact clearance revealed considerable unrecognized shear risk surrounding the asymmetric cone, while the augmented construct remained insensitive to this parameter in the high-risk range (> 100 μm). Conclusion Asymmetric cones are viable in good bone stock but exhibit instability in osteoporosis due to the cantilever effect. Anatomical reconstruction with a modular augment and central cone provides a predictable, load-sharing structural column, making it the preferred strategy for large medial defects in osteoporotic patients.
Aims Managing large medial tibial bone defects during total knee arthroplasty (TKA) remains technically demanding, particularly in elderly patients. This study quantitatively compares two reconstructive strategies: ‘bridging’ the defect using an asymmetric metaphyseal cone versus ‘anatomical reconstruction’ employing a symmetrical cone with a metallic block augment, and assesses their sensitivity to osteoporotic bone quality. Methods A finite element model of a tibia with a standardized medial defect (Anderson Orthopaedic Research Institute (AORI) Type 2a) was adapted to simulate both configurations under physiological loading cycles in healthy and severe osteoporotic bone. Cumulative interface micromotion was quantified using a coordinate-based post-processing algorithm that decouples normal separation from tangential shear. A parametric sweep of the tangential contact clearance evaluated near-surface biological interaction zones without additional simulations. Results In healthy bone, both strategies demonstrated adequate stability with micromotions predominantly below 50 μm. In osteoporotic bone, the asymmetric cone exhibited a loss of stability, characterized by intermittent lift-off during walking and excessive tangential shear during stair descending. This instability induced a toggle effect at the distal stem. The augmented symmetrical cone maintained stable fixation regardless of bone quality. Expanding the tangential contact clearance revealed considerable unrecognized shear risk surrounding the asymmetric cone, while the augmented construct remained insensitive to this parameter in the high-risk range (> 100 μm). Conclusion Asymmetric cones are viable in good bone stock but exhibit instability in osteoporosis due to the cantilever effect. Anatomical reconstruction with a modular augment and central cone provides a predictable, load-sharing structural column, making it the preferred strategy for large medial defects in osteoporotic patients. Cite this article: Bone Joint Res 2026;15(10):1274–1287.
Aims For cases of Anderson Orthopaedic Research Institute (AORI) type III proximal tibial defects with intact medial collateral ligaments (MCLs), knee reconstruction is conventionally performed using semi-constrained prostheses with stemmed tibial components in conjunction with cones or sleeves. This study aimed to reconstruct AORI type III tibial defects using a 3D-printed extension-stem augment, followed by surface-type knee reconstruction to achieve long-term stability and promising clinical outcomes. Methods A patient-specific porous extension-stem augment was designed based on the defect morphology. The microporous structure allowed direct contact for osseointegration, the proximal portion supported tibial baseplate, while the distal stem achieved intramedullary fixation. Finite element analysis (FEA) assessed the biomechanical stability of the augment. A retrospective analysis was conducted between July 2021 and September 2023 on patients who underwent reconstruction of AORI type III proximal tibial defects with extension-stem augment and surface-type total knee prosthesis. Results FEA demonstrated favourable stress and strain distribution and micromotion at the prosthesis-bone interface, although localized high-strain regions were observed under higher-demand loading conditions. Four patients (0 male, 4 female) were included, with a minimum follow-up of 20.7 months (20.7 to 30) and a median age at surgery of 63.0 years (IQR 60.3 to 66.3). The mean Knee Society Score (KSS) improved significantly to 85 (82 to 87), and the mean Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score decreased by 18 (16 to 20). One patient developed periprosthetic joint infection on the femoral side at 20.7 months postoperatively and underwent revision surgery. Intraoperatively, the augment was securely integrated and could not be extracted. Radiological evaluation demonstrated satisfactory alignment and joint stability, with no evidence of prosthesis loosening or migration at the latest follow-up. Conclusion The extension-stem augment achieved anatomical reconstruction of AORI type III proximal tibial defects and provided stable support for the surface-type prosthesis, ensuring reliable knee stability after reconstruction. This represents a feasible option for revision of AORI type III tibial defects. Cite this article: Bone Joint Res 2026;15(10):1263–1273.
Aims Osteoporosis primarily results from age-related declines in bone marrow mesenchymal stem cell (BMSC) differentiation into osteoblasts; however, the regulatory mechanisms remain unclear. Methods Integrated analysis of Gene Expression Omnibus (GEO) and RNA sequencing (RNA-seq) data identified a key osteogenic regulator. Western blot, reverse transcription quantitative polymerase chain reaction (RT-qPCR), RNA-seq, immunohistochemistry (IHC), alkaline phosphatase (ALP), and alizarin red S (ARS) staining were employed to elucidate the functional and mechanistic aspects of modulating osteogenic differentiation. A C57 mouse tibial drill-hole model was used to evaluate therapeutic potential. Results RNA-seq identified baculoviral inhibitor of apoptosis (IAP) repeat-containing protein 3 (BIRC3) as a potential regulator of BMSC osteogenesis, showing significant upregulation during BMSC osteogenic differentiation and upon monocyte stimulation. BIRC3 positively correlated with ALP and ARS staining intensity and significantly enhanced the expression of (runt-related transcription factor 2) RUNX2 and ALP proteins. RNA-seq, RT-qPCR, and western blot data indicated that BIRC3 positively regulates the expression of nerve growth factor receptor (NGFR). NGFR also promoted the osteogenic differentiation of BMSCs. Further experiments demonstrated that BIRC3 regulates BMSC osteogenesis through NGFR. Through XAV939 treatment, we demonstrated that both BIRC3 and NGFR promoted BMSC osteogenesis by enhancing β-catenin expression and nuclear translocation, thereby defining the functional role of the BIRC3/NGFR/β-catenin axis in BMSCs. In C57 mouse tibial bone defect models, BIRC3 overexpression group exhibited significantly enhanced callus formation and ossification compared to the control group. Conclusion BIRC3 regulates BMSC osteogenic differentiation via NGFR/β-catenin signalling in vitro and promotes bone healing in vivo, suggesting therapeutic potential for osteoporosis and bone defects. Cite this article: Bone Joint Res 2026;15(10):1248–1262.
