Background: Treating critically sized defects (CSDs) of bone remains a significant challenge in foot and ankle surgery. Custom 3D-printed implants are being offered to a small but growing subset of patients as a salvage procedure in lieu of traditional alternates such as structural allografts after the patient has failed prior procedures. The long-term outcomes of 3D-printed implants are still unknown and understudied because of the limited number of cases and short follow-up durations. The purpose of this study was to evaluate the outcomes of patients who received custom 3D-printed implants to treat CSDs of the foot and ankle in an attempt to aid surgeons in selecting appropriate surgical candidates. Methods: This was a retrospective study to assess surgical outcomes of patients who underwent implantation of a custom 3D-printed implant made with medical-grade titanium alloy powder (Ti-6Al-4V) to treat CSDs of the foot and ankle between June 1, 2014, and September 30, 2019. All patients had failed previous nonoperative or operative management before proceeding with treatment with a custom 3D-printed implant. Univariate and multivariate odds ratios (ORs) of a secondary surgery and implant removal were calculated for perioperative variables. Results: There were 39 cases of patients who received a custom 3D-printed implant with at least 1 year of follow-up. The mean follow-up time was 27.0 (12-74) months. Thirteen of 39 cases (33.3%) required a secondary surgery and 10 of 39 (25.6%) required removal of the implant because of septic nonunion (6/10) or aseptic nonunion (4/10). The mean time to secondary surgery was 10 months (1-22). Multivariate logistic regression revealed that patients with neuropathy were more likely to require a secondary surgery with an OR of 5.76 ( P = .03). Conclusion: This study demonstrated that 74% of patients who received a custom 3D-printed implant for CSDs did not require as subsequent surgery (minimum of 1-year follow-up). Neuropathy was significantly associated with the need for a secondary surgery. This is the largest series to date demonstrating the efficacy of 3D-printed custom titanium implants. As the number of cases using patient-specific 3D-printed titanium implant increases, larger cohorts of patients should be studied to identify other high-risk groups and possible interventions to improve surgical outcomes. Level of Evidence: Level IV, case series.

Purpose The purpose of this study is to understand how printing parameters and subsequent annealing impacts porosity and crystallinity of 3D printed polylactic acid (PLA) and how these structural characteristics impact the printed material’s tensile strength in various build directions. Design/methodology/approach Two experimental studies were used, and samples with a flat vs upright print orientation were compared. The first experiment investigates a scan of printing parameters and annealing times and temperatures above the cold crystallization temperature (Tcc) for PLA. The second experiment investigates annealing above and below Tcc at multiple points over 12 h. Findings Annealing above Tcc does not significantly impact the porosity but it does increase crystallinity. The increase in crystallinity does not contribute to an increase in strength, suggesting that co-crystallization across the weld does not occur. Atomic force microscopy (AFM) images show that weld interfaces between printed fibers are still visible after annealing above Tcc, confirming the lack of co-crystallization. Annealing below Tcc does not significantly impact porosity or crystallinity. However, there is an increase in tensile strength. AFM images show that annealing below Tcc reduces thermal stresses that form at the interfaces during printing and slightly “heals” the as-printed interface resulting in an increase in tensile strength. Originality/value While annealing has been explored in the literature, it is unclear how it affects porosity, crystallinity and thermal stresses in fused filament fabrication PLA and how those factors contribute to mechanical properties. This study explains how co-crystallization across weld interfaces is necessary for crystallinity to increase strength and uses AFM as a technique to observe morphology at the weld.

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