A novel strategy for reconstruction of AORI type III proximal tibial defects : surface-type knee reconstruction...

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.

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.

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.

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.