Objective: This study investigates the impact of age and knee osteoarthritis (OA) on the coronal plane alignment of the lower extremity in Japanese males and females, utilizing the Coronal Plane Alignment of the Knee (CPAK) classification system. Methods: A cross-sectional analysis was conducted with 150 male and 150 female patients. Participants were divided into three groups according to age and OA progression. The mechanical lateral distal femoral angle (mLDFA) and mechanical medial proximal tibial angle (mMPTA) were measured using standard digital long-leg radiographs. Arithmetic hip-knee-ankle angle (aHKA) and joint line obliquity (JLO) were calculated, and the CPAK classification was performed to verify the distribution among the three groups. Results: The results showed increased varus alignment of the mean mLDFA correlated with OA in both genders and with aging in males. The mean mMPTA did not change in males but shifted toward varus in females with both aging and OA. Both genders demonstrated a constitutional varus alignment with the progression of osteoarthritis (males: 1.3 ± 2.4° to −3.5 ± 3.7°, p < 0.001; females: −1.2 ± 3.2° to −3.6 ± 2.9°, p < 0.001). However, this trend with aging was observed only in females (0.0 ± 2.5° to −1.2 ± 3.2°, p = 0.018). JLO maintained its apex distal position with aging and OA progression in all subjects. The study further revealed a notable transition from CPAK Type II to Type I with OA progression in both genders, additionally influenced by aging in females. Conclusions: Aging affects coronal alignment and CPAK classification differently across genders. With OA progression, there was a shift toward smaller aHKA, while JLO remained unchanged. Compared to other races, young Japanese people exhibit similar CPAK distributions, but distinct differences appear in OA-affected individuals, highlighting potential racial variations in CPAK classifications.

Introduction: Total knee arthroplasty (TKA) is a widely used treatment for advanced knee osteoarthritis. While cemented fixation is the standard technique, cementless fixation has demonstrated comparable long-term outcomes. However, the association between cement use and postoperative complications, including venous thromboembolism and surgical site infections, remains unclear, particularly in Japanese patients. This study aimed to investigate the incidence of postoperative complications in cemented and cementless TKA using a nationwide database. Methods: A nationwide cohort study was conducted using Japan’s DPC database from April 2016 to March 2023. Patients who underwent TKA were identified, and postoperative complications, including deep vein thrombosis, pulmonary embolism, pneumonia, cerebrovascular events, postoperative cognitive dysfunction, and surgical site infection, were analyzed. One-to-one propensity score (PS) matching was performed based on age, sex, body mass index, type of anesthesia, simultaneous bilateral surgery, Charlson comorbidity index, and comorbidities to ensure comparability. Statistical analyses included χ² tests, Student’s t-tests, and multivariate logistic regression analysis. Results: A total of 228,595 patients met the eligibility criteria, with 21,906 matched pairs in the cemented and cementless groups after PS matching. The incidence of deep vein thrombosis (OR: 1.231, 95% CI: 1.151–1.316, p < 0.0001) and surgical site infection (OR: 1.716, 95% CI: 1.420–2.073, p < 0.0001) was significantly higher in the cemented group. No significant differences were observed in pulmonary embolism or other complications. Conclusion: Cement application was associated with an increased risk of deep vein thrombosis and surgical site infection. These findings suggest that careful perioperative management may be warranted in patients undergoing cemented TKA.

Orthopedic implants such as arthroplasty prostheses, fracture plates, and intramedullary nails often use materials like Ti6Al4V alloy and commercially pure titanium (CP-Ti), which have Young's modulus significantly higher than that of human cortical bone, potentially causing stress shielding and inhibiting effective fracture healing. TiNbSn alloy, a β-type titanium alloy with a lower Young's modulus (40-49 GPa), has shown promise in reducing stress shielding and enhancing bone healing by promoting effective load sharing with bone. This study used 5-hole plates made from TiNbSn alloy and CP-Ti to investigate their effects on bone healing in a rat femoral fracture model. Micro-CT analysis and mechanical testing were performed six weeks postoperatively to assess bone healing. Additionally, Finite element method (FEM) analysis was employed to evaluate stress shielding and interfragmentary movement (IFM) at the fracture site. Micro-CT analysis revealed significantly higher bone volume and mineral density in the TiNbSn group than in the CP-Ti group. Mechanical testing showed increased maximum load and stiffness in the TiNbSn group (77.2 ± 10.0 N for the TiNbSn alloy plate group versus 53.3 ± 8.5 N for the CP-Ti group (p = 0.002)). FEM analysis indicated that TiNbSn plates reduced stress shielding and allowed for greater displacement and strain, promoting IFM conducive to bone healing. The findings suggest that TiNbSn alloy plates are more effective than CP-Ti plates in promoting bone healing by reducing stress shielding and enhancing IFM. The lower Young's modulus of TiNbSn allows better load distribution, facilitating bone regeneration and strengthening at the fracture site.

Background: Stress shielding (SS) after total hip arthroplasty (THA) leads to proximal femoral bone loss and increases the risk of complications such as implant loosening and periprosthetic fracture. While various low-stiffness stems have been developed to prevent SS, they often compromise mechanical stability. A novel femoral stem composed of Ti-33.6Nb-4Sn (TNS) alloy offers a gradually decreasing Young’s modulus from proximal to distal regions, potentially improving load distribution and reducing SS. This study aimed to evaluate the mid-term clinical and radiographic outcomes of the TNS stem, with a particular focus on its effectiveness in suppressing SS. Methods: A prospective clinical study was conducted involving 35 patients who underwent THA using the TNS stem, with a minimum follow-up of 7 years. Twenty-one patients with Ti6Al4V metaphyseal-filling stems served as controls. Clinical outcomes were assessed using Japanese Orthopaedic Association (JOA) scores, and radiographic SS was graded using Engh’s classification and analyzed in Gruen zones. Inter-examiner reliability and statistical comparisons between groups were performed using appropriate tests. Results: The TNS group showed significantly higher preoperative JOA scores than the control group, but no significant difference in final scores. Both groups demonstrated significant improvement postoperatively. Third-degree SS occurred in the TNS group, although the overall SS grade distribution was significantly lower than in the control group (p = 0.03). SS frequency was significantly reduced in Gruen Zones 2, 3, and 6 in the TNS group. Conclusions: The TNS stem demonstrated a significant reduction in SS progression compared to conventional titanium stems over a 7-year period, with comparable clinical outcomes. However, the occurrence of third-degree SS indicates that material optimization alone may be insufficient, highlighting the need for further design improvements.