A Comparative Evaluation of Third-Generation Advanced High-Strength Steels for Automotive Forming and Crash Applications.

While the third generation of advanced high-strength steels (3rd Gen AHSS) have increasingly gained attention for automotive lightweighting, it remains unclear to what extent the developed methodologies for the conventional dual-phase (DP) steels are applicable to this new class of steels. The present paper provides a comprehensive study on the constitutive, formability, tribology, and fracture behavior of three commercial 3rd Gen AHSS with an ultimate strength level ranging from 980 to 1180 MPa which are contrasted with two DP steels of the same strength levels and the 590R AHSS. The hardening response to large strain levels was determined experimentally using tensile and shear tests and then evaluated in 3D simulations of tensile tests. In general, the strain rate sensitivity of the two 3rd Gen 1180 AHSS was significantly different as one grade exhibited larger transformation-induced behavior. The in-plane formability of the three 1180 MPa steels was similar but with a stark contrast in the local formability whereas the opposite trend was observed for the 3rd Gen 980 and the DP980 steel. The forming limit curves could be accurately predicted using the experimentally measured hardening behavior and the deterministic modified Bressan-Williams through-thickness shear model or the linearized Modified Maximum Force Criterion. The resistance to sliding of the three 3rd Gen AHSS in the Twist Compression Test revealed a comparable coefficient of friction to the 590R except for the electro-galvanized 3rd Gen 1180 V1. An efficient experimental approach to fracture characterization for AHSS was developed that exploits tool contact and bending to obtain fracture strains on the surface of the specimen by suppressing necking. Miniature conical hole expansion, biaxial punch tests, and the VDA 238-100 bend test were performed to construct stress-state dependent fracture loci for use in forming and crash simulations. It is demonstrated that, the 3rd Gen 1180 V2 can potentially replace the DP980 steel in terms of both the global and local formability.

Risk Factors for Nonunion After First Metatarsophalangeal Joint Arthrodesis With a Dorsal Locking Plate and Compression Screw Construct: Correction of Hallux Valgus Is Key.

First metatarsophalangeal joint (MTPJ) arthrodesis is currently the gold standard technique for advanced hallux rigidus. This retrospective study aimed to identify the risk factors for nonunion after first MTPJ arthrodesis with a dorsal locking plate and compression screw construct. Between April 2014 and April 2019, 165 consecutive patients (28 men and 137 women; mean age, 60 (range, 28-84) years) who underwent 178 primary first MTPJ arthrodeses were retrospectively reviewed. All arthrodeses were performed using either a dorsal locking plate with an integrated compression screw (Anchorage CP plate, Stryker, n = 97) or a dorsal locking plate (Anchorage V2 plate, Stryker, n = 81) with a separate compression screw (4 mm cannulated ACE screw). Union was defined as bone bridging across the fusion site on at least 2 of the 3 standard foot radiographs (anteroposterior, lateral, oblique) and no MTPJ movement or pain during clinical examination. Potential risk factors for nonunion were analyzed with the use of univariate and multivariate analyses. The overall nonunion rate was 6.2% (11 of 178 cases). The risk factors identified in the univariate analysis included preoperative hallux valgus deformity, postoperative residual hallux valgus deformity, and diabetes (p < .05). Multivariate analysis confirmed that postoperative residual hallux valgus deformity (odds ratio 6.5; p= .015) and diabetes (odds ratio 7.4; p = .019) are independent risk factors for nonunion after first MTPJ arthrodesis. Diabetes is the most important independent risk factor for nonunion after first MTPJ arthrodesis with a dorsal locking plate and compression screw construct. A residual postoperative hallux valgus deformity is associated with a significantly increased risk for nonunion. It is therefore crucial to correct the hallux valgus deformity to a hallux valgus angle of less than 20°.

Single-photon-emission computed tomography in painful total ankle replacements.

BACKGROUND: The use of single-photon-emission computed tomography (SPECT) in identifying unexplained pain in the foot and ankle has been described, where other imaging modalities have failed. The investigation of a painful total ankle replacement (TAR) is difficult, often not delineating a definitive cause. Our aim in this study was to investigate the use of SPECT-CT imaging in painful TARs. METHODS: We performed a retrospective analysis of SPECT imaging performed for painful TARs in our department between October 2010 and December 2014. There were 14 patients identified who had undergone SPECT-CT imaging for a painful TAR. The mean age was 63.1 years, with a male/female sex ratio of 2:3 and a minimum time from surgery to imaging of 18 months. RESULTS: Of the 14 patients, 13 were positive for increased osteoblastic activity in relation to the periprosthetic area consistent with implant loosening. The most common finding was tracer activity in relation to the talar component in 13 cases. There was additional tracer activity localized to the tibial component in 5 of these cases. In 10 of the 13 cases with prosthetic loosening/failure of bony ongrowth, there was no evidence of loosening on the plain radiographs. Infection was ruled out by using joint aspiration as clinically indicated. CONCLUSION: In our series, SPECT-CT imaging revealed a high incidence of medial sided talar prosthesis activity consistent with loosening. The finding of a high incidence of talar nonintegration illustrates the limitations of conventional radiology in follow-up of total ankle replacements, as this was not apparent on plain radiographs. We therefore conclude that there should be a high index of suspicion for talar prosthesis nonintegration in patients with otherwise unexplained ongoing medial pain in total ankle replacements. LEVEL OF EVIDENCE: Level IV, retrospective case series.