Meniscal root repairs are susceptible to unrecoverable loosening that may displace the meniscus from the initial position reduced during surgery. Despite this, the effects of a loosened meniscal root repair on knee mechanics are unknown. We hypothesized that anatomic root repairs without loosening would restore knee mechanics to the intact condition better than loosened anatomic root repairs, but that loosened repairs would restore mechanics better than untreated meniscal root tears. Finite element knee models were used to evaluate changes in cartilage and meniscus mechanics due to repair loosening. The mechanical response from loosened anatomic root repairs was compared to anatomic repairs without loosening and untreated root tears. All conditions were evaluated at three flexion angles, 0 deg, 30 deg, and 60 deg, and a compressive force of 1000 N to simulate return-to-activity loading. The two-simple suture method was represented within the models to simulate posteromedial meniscal root repairs and the loosening of repairs was derived from previous biomechanical experimental data. Loosening decreased hoop stresses throughout the meniscus, increased posterior extrusion, and shifted loading through the meniscus-cartilage region to the cartilage-cartilage region compared to the anatomic root repair without loosening. Despite differences between repairs and loosened repairs, the changes from loosened repairs more closely resembled the anatomic repair without loosening than the untreated root repair condition. Therefore, meniscal root repairs are susceptible to loosening that will prevent a successful initial repair from remaining in the intended position and will alter cartilage and meniscus mechanics, although repairs that loosen appear better than leaving tears untreated.