(1) Background: Metal-on-metal (MoM) total hip arthroplasty (THA) and hip resurfacing arthroplasty (HRA) was presumed to provide superior functional outcomes compared to metal-on-polyethylene (MoP) THA. (2) Methods: We compared muscle mass, power, step test asymmetry, and patient-reported outcomes between MoM THA/HRA and MoP THA. A total of 51 MoM THA/HRAs and 23 MoP THAs participated in the cross-sectional study at a mean of 6.5 (2.4–12.5) years postoperatively. Muscle mass was measured by Dual energy X-ray Absorption (DXA) scans and muscle power in a Leg Extensor Power Rig. Step test asymmetry was obtained with an Inertial Measurement Unit (IMU). The patients completed the Harris Hip Score (HHS) and the Copenhagen Hip and Groin Outcome Score (HAGOS). (3) Results: The MoM THA/HRA group had a greater inter-limb difference in hip muscle mass compared to the MoP THA group (p = 0.02). Other inter-limb differences in muscle mass and power were similar (p > 0.05). Muscle mass of the thigh and calf area and muscle power in both legs were higher in MoM THA/HRA compared to MoP THA (p < 0.009). Step test time asymmetry when ascending was lower in MoM THA/HRA compared to MoP THA (p = 0.03). HHS and HAGOS scores were similar between groups (p > 0.05). (4) Conclusion: Overall, we could not verify the hypothesis that MoM THA/HRA contributes to superior functional outcomes compared to MoP THA.

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