TiNbSn stems with gradient changes of Young's modulus and stiffness reduce stress shielding compared to the standard fit-and-fill stems.

BACKGROUND: The difference between Young's moduli of the femur and the stem causes stress shielding (SS). TiNbSn (TNS) stem has a low Young's modulus and strength with gradient functional properties during the change in elastic modulus with heat treatment. The aim of this study was to investigate the inhibitory effect of TNS stems on SS and their clinical outcomes compared to conventional stems. METHODS: This study was a clinical trial. Primary THA was performed using a TNS stem from April 2016 to September 2017 for patients in the TNS group. Unilateral THA was performed using a Ti6Al4V alloy stem from January 2007 to February 2011 for patients in the control group. The TNS and Ti6Al4V stems were matched in shape. Radiographs were obtained at the 1- and 3-year follow-ups. Two surgeons independently checked the SS grade and appearance of cortical hypertrophy (CH). The Japanese Orthopaedic Association (JOA) scores before and 1 year after surgery were assessed as clinical scores. RESULTS: None of the patients in the TNS group had grade 3 or 4 SS. In contrast, in the control group, 24% and 40% of patients had grade 3 and 4 SS at the 1- and 3-year follow-ups, respectively. The SS grade was lower in the TNS group than in the control group at the 1- and 3-year follow-ups (p < 0.001). The frequencies of CH in both groups were no significant difference at the 1- and 3-year follow-ups. The JOA scores of the TNS group significantly improved at 1 year after surgery and were comparable to control group. CONCLUSION: The TNS stem reduced SS at 1 and 3 years after THA compared to the proximal-engaging cementless stem, although the shapes of the stems matched. The TNS stem could reduce SS, stem loosening, and periprosthetic fractures. TRIAL REGISTRATION: Current Controlled Trials. ISRCTN21241251. https://www.isrctn.com/search?q=21241251 . The date of registration was October 26, 2021. Retrospectively registered.

ß-type TiNbSn Alloy Plates With Low Young Modulus Accelerates Osteosynthesis in Rabbit Tibiae.

BACKGROUND: Ti6Al4V alloy, which is commonly used for biomedical applications, has a Young modulus (110 GPa) that is higher than that of human cortical bone (11 to 20 GPa). Using an implant with a material with a low Young modulus that enhances load sharing by the bone even more than those made of Ti6Al4V could be beneficial for bone healing and further reduce the potential for stress shielding. A new ß-type TiNbSn alloy has a low Young modulus of approximately 40 to 49 GPa. However, whether the new titanium alloy with a lower Young modulus is advantageous in terms of fracture healing has not been assessed, and a small-animal model seems a reasonable first step in its assessment. QUESTIONS/PURPOSES: To assess the impact of a TiNbSn alloy plate with a lower Young modulus compared with a Ti6Al4V alloy plate on fracture healing, we evaluated: (1) bony bridging and callus volume, (2) new bone formation and remaining cartilage tissue, (3) osteoblast activity in the callus, and (4) mechanical strength and stiffness of the callus in bending. METHODS: Fracture plates manufactured from TiNbSn and Ti6Al4V alloys, which have Young moduli of 49 GPa and 110 GPa, respectively, were compared. The main reason for using rabbits was the high reliability of the three-point bending mechanical test of the rabbit tibia. Forty-two male Japanese white rabbits weighing 2.8 to 3.4 kg were anesthetized. A 5-cm skin incision was made on the medial side in the mid-diaphysis of the right tibia. Eight-hole plates were used, which were 42 mm long, 5 mm wide, and 1.2 mm thick. Plate fixation was performed using three proximal and three distal screws. After the plate was installed, an osteotomy was performed using a 1-mm-wide wire saw to create a standardized tibial transverse osteotomy model with a 1-mm gap. Bone healing was quantitatively assessed by two nonblinded observers using micro-CT (bony bridging and callus volume), histomorphometry (new bone formation and remaining cartilage tissue), immunohistochemistry (osteoblast activity), and mechanical testing (mechanical strength and stiffness in bending). Measurements on nondemineralized specimens were descriptive statistics due to their small number. Four weeks after osteotomy and fixation, 30 rabbits were euthanized to undergo micro-CT and subsequent mechanical testing (n = 12), histomorphometry and immunohistochemistry with demineralized specimens (n = 12), and histomorphometry with a nondemineralized specimen (n = 6). Eight weeks postoperatively, 12 rabbits were euthanized for micro-CT and subsequent mechanical testing. RESULTS: Intramedullary fracture calluses treated with TiNbSn alloy plates had larger bone volumes and more numerous bridging structures than those treated with Ti6Al4V alloy plates at 4 weeks after osteotomy (Ti6Al4V alloy versus TiNbSn alloy: 30 ± 7 mm 3 versus 52 ± 14 mm 3 , mean difference 22 [95% CI 9 to 37]; p = 0.005; ICC 0.98 [95% CI 0.95 to 0.99]). Histologic assessments demonstrated there was greater new bone formation (total callus: Ti6Al4V versus TiNbSn: 16 ± 4 mm 2 versus 24 ± 7 mm 2 , mean difference 8 [95% CI 1 to 16]; p = 0.04; ICC 0.98 [95% CI 0.93 to 0.99]; intramedullary callus: Ti6Al4V versus TiNbSn: 6 ± 4 mm 2 versus 13 ± 5 mm 2 , mean difference 7 [95% CI 1 to 13]; p = 0.02; ICC 0.98 [95% CI 0.95 to 0.99]) and a higher number of osteocalcin-positive cells (Ti6Al4V alloy versus TiNbSn alloy: 1397 ± 197 cells/mm 2 versus 2044 ± 183 cells/mm 2 , mean difference 647 [95% CI 402 to 892]; p < 0.001; ICC 0.98 [95% CI 0.95 to 0.99]) in the TiNbSn alloy group than in the Ti6Al4V alloy group. At 4 weeks after osteotomy, both bone strength and stiffness of the healed bone in the TiNbSn alloy group were higher than those in the Ti6Al4V alloy group (maximum load: Ti6Al4V alloy versus TiNbSn alloy: 83 ± 30 N versus 127 ± 26 N; mean difference 44 [95% CI 8 to 80]; p = 0.02; stiffness: Ti6Al4V alloy versus TiNbSn alloy: 92 ± 43 N/mm versus 165 ± 63 N/mm; mean difference 73 [95% CI 4 to 143]; p = 0.047). Eight weeks after osteotomy, no between-group differences were observed in the strength and stiffness of the healed bone. CONCLUSION: The results of this study indicate that TiNbSn alloy plate with a lower Young modulus resulted in improved bone formation and stiffer callus during the early phase (4 weeks after surgery) but not the later phase (8 weeks after surgery) of bone healing. CLINICAL RELEVANCE: An overly stiff plate may impair callus formation and bone healing. The TiNbSn alloy plate with a low Young modulus improves the early formation of new bone and stiff callus at the osteotomy site compared with the Ti6Al4V alloy plate in the healing process, which may promote bone repair. TiNbSn alloy may be a promising biomaterial for fracture treatment devices. Further research to address concerns about the strength of TiNbSn alloy plates, such as fatigue life and plate fracture, will be necessary for clinical applications, including mechanical tests to verify fatigue life and validation in larger animals with greater body weight.

Mid-term results of a new femoral prosthesis using Ti-Nb-Sn alloy with low Young's modulus.

BACKGROUND: This study was performed to investigate the mid-term results of Ti-Nb-Sn (TNS) alloy stem with a low Young's modulus. METHODS: This study was a multicenter prospective cohort study. A total of 40 primary total hip arthroplasties performed between April 2016 and September 2017 was enrolled in this study. With the unique functional gradient properties by heating treatment, the strength of the proximal portion was enhanced, while the distal portion maintained a low Young's modulus. The surgeries were performed through the posterolateral approach using the TNS alloy stems. Radiographs were taken from immediately after surgeries until 3 years, and stress shielding and subsidence of the stems were evaluated. The incidences of the stem breakage were also assessed. Clinical assessments were performed using Japanese Orthopaedic Association (JOA) and Japanese Orthopaedic Association Hip Disease Evaluation Questionnaire (JHEQ) scores. RESULTS: Among the 40 enrolled patients, 36 patients were female and 4 were male. At 3 years after surgery, there were no radiologic signs of loosening, subsidence, or breakage of the stem. Stress shielding was observed in 26 hips (65%). Of 26 hips, 16 hips (40%) were grade 1 and 10 hips (25%) were grade 2. There was no advanced stress shielding. The JOA and JHEQ scores significantly improved compared with the preoperative scores. CONCLUSION: The current study using a new TNS alloy femoral stem showed good clinical outcomes at 3-year follow-up. Radiologically, there was no loosening or subsidence of the stem. The mild stress shielding was observed in 65% of patients. TRIAL REGISTRATION: Current Controlled Trials ISRCTN21241251 . The date of registration was October 26, 2021. Retrospectively registered.