Objective: With the advancement of digital orthopedics, the growing prevalence of medial compartment knee osteoarthritis (MCKOA) and the widespread adoption of knee‐preserving surgical techniques have heightened new interest in predicting the onset of MCKOA and promoting surgical outcomes. This study was to clarify the differences in kinematics and contact patterns between the MCKOA knee and its native sides during knee extension.Methods: From March 2023 to June 2024, thirty‐two patients who suffered from unilateral MCKOA, with their contralateral extremities asymptomatic and intact, were enrolled in this descriptive research. Three‐dimensional models were created from computed tomography scans, and all patients performed continuous stair climbing under the surveillance of a dual fluoroscopic imaging system (DFIS) to determine the accurate 6‐degrees‐of‐freedom (6‐DOF) of their medial OA knees and the contralateral knees. The volume penetration centers between tibial and femoral cartilage models were defined as contact centers. All measured parameters were tested for significant differences using the Wilcoxon Rank‐Sum test.Results: Compared to native knees, the MCKOA tibia showed increased flexion (mean 3.6°) and varus rotation (mean 1.6°), with more posterior (mean 1.4 mm), lateral (mean 1.2 mm) and proximal translations (mean 0.5 mm) relative to the femur during extension (p < 0.05). The tibiofemoral contact patterns on the medial and lateral tibial plateau of the MCKOA knee both shifted more medially (mean 1.4 mm and 1.3 mm, respectively, p < 0.05) than the native side, which was consistent with the lateral translations observed in 6‐DOF.Conclusion: Our findings offer valuable insights into the in vivo kinematics of MCKOA knee, its tibiofemoral joint (TFJ) and contact pattern. In MCKOA knees, the tibia exhibited increased flexion and varus rotation, along with more posterior, lateral, and proximal translation relative to the femur compared to the native side during extension. These changes aligned with the more medial shifts in contact patterns of the tibial plateau on the MCKOA side. These findings provide data support for the digital diagnosis and treatment of MCKOA.

The biomechanical mechanism of postoperative patellofemoral joint (PFJ) complications after open-wedge high tibial osteotomy (OWHTO) has not been investigated. This study was to determine the length changes in the patellar tendon (PT), medial patellotibial ligament (MPTL), medial patellofemoral ligament (MPFL), and quadriceps moment arm (QMA) during staircase motion before and after OWHTO. Computed tomography (CT) scans of 15 patients’ lower extremities were used to reconstruct three-dimensional models, and magnetic resonance imaging (MRI) of the knee and hip joints was used to mark the soft tissue footprints. Then, such soft tissue lengths were quantified by a dual fluoroscopic imaging system (DFIS). Additionally, function scores were used to assess patient outcome changes. The results showed that there was a contraction of the PT after OWHTO due to its adhesion to the osteotomy site, causing PT length to be negatively correlated to the open-wedge angle. In addition, the shortening of the MPTL and QMA caused patellar instability and an imbalance in the strength of the lower extremities. Additionally, most knee function scores improved after OWHTO, except the Feller scores. Multiple methods should be considered to optimize surgical procedures, postoperative rehabilitation, and physical therapy.