Biomechanical Comparison of 3D-Printed Polylactic Acid Scaffold-Reinforced Hybrid Spacers and Conventional Polymethylmethacrylate Spacers for Advanced Femoral Bone Loss: An In Vitro Experimental Study

Abstract Background Two-stage exchange is widely regarded as the gold standard treatment for periprosthetic joint infection after total hip replacement [1]. When patients have massive femoral bone loss, conventionally peroperatively hand-made polymethylmethacrylate (PMMA) spacers are more susceptible to instability and structural failure [2, 3]. In this study, we compared 3D-printed polylactic acid scaffold-reinforced hybrid spacers with conventional PMMA spacers designed for advanced femoral bone defects. We evaluated whether hybrid spacers provide suitable biomechanical performance in this patient group. Methods Twelve cylindrical specimens were fabricated and divided equally into two groups (n = 6 per group). For the 3D group, cylindrical polylactic acid (PLA) scaffolds (outer diameter, 18 mm; inner diameter, 8 mm; height, 70 mm) were printed using an UltiMaker 3 Extended printer and coated with a 5-mm layer of polymethylmethacrylate (PMMA; Simplex P, Stryker Bone Cement), resulting in an outer diameter of 28 mm. The conventional group comprised PMMA cylinders (outer diameter, 28 mm; inner diameter, 8 mm; height, 70 mm) fabricated using 3D-printed molds. Both groups underwent axial compression testing (target load, 4500 N) and three-point bending testing (target load, 4800 N) on a servo-hydraulic universal testing machine (Autograph AG-IS 5 kN, Shimadzu, Kyoto, Japan) at a crosshead speed of 20 mm/min. Maximum load and displacement at the target load were recorded during testing. Group comparisons were performed using the Mann–Whitney U test in IBM SPSS Statistics, version 26. Statistical significance was set at p < 0.05. Results All specimens of both groups met the axial compression limit of 4500 N. For the 3D group, the mean displacement value was 1.00 ± 0.23 mm; for the conventional group, it was 1.06 ± 0.21 mm (p = 0.818). For the three-point bending test, all six specimens of the 3D group reached the required 4800 N force threshold, while only five out of six did so among the conventional specimens. One conventional specimen failed at 1558 N. The mean bending force in the 3D group was 4800 ± 0 N, compared to 4259.69 ± 1323.49 N in the conventional test group (p = 0.405). Conclusions Under the tested axial compression and bending conditions, hybrid 3D-printed PLA–PMMA spacers showed no significant performance difference from conventional PMMA spacers. All hybrid specimens reached the target load; one conventional specimen failed under bending (Table 1). The small sample size (n = 6 per group) limits the strength of these findings. These results support further evaluation of 3D-printed PLA–PMMA hybrid spacers in two-stage revision procedures for patients with advanced femoral bone defects.