Enhancing structural integrity of PMMA hip spacers for two-stage revision surgery through titanium reinforcement

PMMA hip spacers used in two-stage revision surgery are prone to brittle fracture due to their low fracture toughness and the presence of defects that can initiate crack growth, motivating the need to assess the effectiveness of metallic reinforcement under quasi-static loading conditions. This study evaluates the fracture behavior of reinforced and unreinforced hip spacers using a validated explicit finite element model combined with a sub-modeling approach, in which a spacer embedded in a femoral cavity is simulated and a quarter-elliptical corner crack is introduced in the most highly stressed region to compute stress intensity factors for Modes I, II, and III across varying crack sizes and reinforcement thicknesses. The numerical predictions showed good agreement with experimental load-displacement results, confirming the validity of the model. For unreinforced spacers, Mode I stress intensity factors exceeded the fracture toughness of PMMA for all crack sizes, indicating a high risk of crack propagation and fracture, with Mode I identified as the dominant failure mechanism while Modes II and III contributed minimally. The incorporation of titanium reinforcement significantly reduced stress intensity factors, achieving reductions exceeding 85% for 6 mm reinforcement and further improvement for 8 mm reinforcement, while increasing thickness to 10 mm produced only limited additional benefit. Overall, reinforcement enabled the spacer to withstand loads representative of daily activities, demonstrating that unreinforced spacers are highly susceptible to fracture whereas reinforced designs substantially improve structural integrity, with an 8 mm titanium reinforcement providing an optimal balance between mechanical strength and efficiency.