Stress shielding remains a major concern in cementless total hip arthroplasty (THA) due to the stiffness mismatch between femoral stems and surrounding bone. This study investigated the biomechanical and clinical performance of a novel Ti-33.6Nb-4Sn (Ti-Nb-Sn) alloy stem with a graded Young’s modulus achieved through localized heat treatment. A finite element model (FEM) of the Ti-Nb-Sn stem, incorporating experimentally validated Young’s modulus gradients, was constructed and implanted into a patient-specific femoral model. Stress distribution and micromotion were assessed under physiological loading conditions. Clinical validation was performed by evaluating radiographic outcomes at 1 and 3 years postoperatively in 40 patients who underwent THA using the Ti-Nb-Sn stem. FEM analysis showed low micromotion at the proximal press-fit region (4.89 μm rotational and 11.74 μm longitudinal), well below the threshold for osseointegration and loosening. Stress distribution was concentrated in the proximal region, effectively reducing stress shielding distally. Clinical results demonstrated minimal stress shielding, with no cases exceeding Grade 3 according to Engh’s classification. The Ti-Nb-Sn stem with a gradient Young’s modulus provided biomechanical behavior closely resembling in vivo conditions and showed promising clinical results in minimizing stress shielding. These findings support the clinical potential of modulus-graded Ti-Nb-Sn stems for improving implant stability in THA.

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.

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Background: Total hip arthroplasty (THA) is a widely used surgical intervention for hip osteoarthritis (HOA), with a rising demand driven by an aging population. Osteoporosis is associated with increased risks of bone loss and implant loosening after THA. While medications such as bisphosphonates and denosumab have shown promise in mitigating these risks, the impact of preoperative osteoporosis treatment on postoperative outcomes remains unclear. This study investigates the effect of preoperative osteoporosis treatment intervention on stress shielding and clinical outcomes in THA patients. Methods: This retrospective study included 107 patients who underwent cementless THA between April 2019 and March 2022. Patients under 60 years old, with a follow-up period of less than one year, or with prior hip surgery were excluded. Participants were divided into two groups: a treatment group receiving osteoporosis medication preoperatively and a non-treatment group. The outcomes assessed included preoperative bone metabolism markers, Bombelli classification, stress shielding grade, and clinical scores. Statistical analysis was performed using the Mann–Whitney U test and Chi-squared test, with significance set at p < 0.05. Results: The preoperative osteoporosis treatment intervention rate was 28.9%. Stress shielding grades were significantly lower in the treatment group (p = 0.001). However, no significant differences were observed in clinical scores one year postoperatively. Conclusion: Preoperative osteoporosis treatment significantly reduced stress shielding incidence, potentially influencing long-term outcomes by preventing bone atrophy-related pain and fractures. Preoperative bone density assessment and osteoporosis treatment intervention are recommended to improve THA outcomes. Larger studies are needed for further validation.

Stress shielding (SS) after cementless total hip arthroplasty arises from the stiffness mismatch between conventional Ti-6Al-4V femoral stems (110 GPa) and cortical bone (10–30 GPa). The β-type Ti-33.6Nb-4Sn (TNS) alloy femoral stem addresses this limitation through a continuous Young’s modulus gradient (~70 GPa proximally to ~40 GPa distally) achieved by localized heat treatment of a single homogeneous alloy. This review synthesizes a translational research program encompassing material characterization, finite element modeling (FEM), preclinical animal studies, and prospective clinical follow-up of up to seven years. FEM demonstrated favorable proximal micromotion well below the osseointegration threshold, with physiological proximal stress concentration concordant with clinical outcomes. At seven years, SS grade distribution was significantly lower in the TNS group than in Ti-6Al-4V controls, with SS frequency reduced in Gruen Zones 2, 3, and 6, and no stem-related failures; however, third-degree SS was still observed in 11 of 34 evaluable cases (32%), indicating that modulus-gradient optimization alone is insufficient to fully prevent SS. TNS alloy is currently the only β-type titanium alloy clinically applied in joint prostheses. Remaining challenges include stem geometry optimization, additive manufacturing-based porous structures, and dual-energy X-ray absorptiometry-based bone density quantification. Future directions encompass long-term follow-up, cyclic fatigue FEM simulations, and expansion to fracture fixation devices and dental implants.

Background: This study aimed to evaluate short-term outcomes, including in-hospital complications, mortality, and medical costs, after total hip arthroplasty (THA) in super-elderly patients aged ≥85 years compared with elderly patients aged 70–84 years, using a nationwide database in Japan. Materials and Methods: We conducted a retrospective cohort study using the Japanese Diagnosis Procedure Combination (DPC) database from 2011 to 2023. Patients undergoing unilateral THA were divided into super-elderly and elderly groups. Propensity score matching (1:1) was performed based on demographics and comorbidities, including Charlson Comorbidity Index (CCI). Primary outcomes included in-hospital complications and mortality; secondary outcomes included hospital length of stay, Barthel Index, and medical costs calculated on a fee-for-service basis for the perioperative period (surgery day through postoperative day 7). Results: A total of 11,997 matched pairs were analyzed. The super-elderly group had significantly higher rates of cerebrovascular events (0.6% vs. 0.3%; OR: 2.125; 95% CI: 1.403–3.219) and in-hospital mortality (0.2% vs. 0.0%; OR: 5.565; 95% CI: 2.106–14.71), though absolute risk differences were small (0.0029 and 0.0017, respectively). Hospital stay was longer in the super-elderly group (32.6 ± 21.3 vs. 29.5 ± 19.5 days). No significant difference in perioperative medical costs was observed between groups. Conclusions: Although super-elderly patients demonstrated slightly higher in-hospital risks of cerebrovascular events and mortality, the absolute risk differences were minimal. These findings suggest that elective THA can be safely performed during hospitalization in this population, although further research is needed to evaluate post-discharge outcomes.