Osteoarthritis is well established to be a whole joint disease, and previous studies have found degenerative changes in periarticular tendons around osteoarthritic joints. Thus, we aimed to assess whether potential periarticular adaptations (patellar tendon) are related to intraarticular changes (tibial cartilage) at material-level. As they are both connected to the tibia, we explored the relationships between patellar tendon and tibial cartilage viscoelastic properties obtained from eight osteoarthritic cadaver knees. Six patellar tendon regions and six to eight tibial cartilage samples per knee underwent tensile and indentation sinusoidal measurements, respectively, at 0.1, 0.5, and 1 Hz. Osteoarthritis Research Society International (OARSI) grades were obtained from tibial cartilage histological sections and tested for associations with patellar tendon properties. All knees were deemed osteoarthritic according to tibial cartilage OARSI grades. Comparing the two tissues, we found strong inverse correlations in the phase difference between stress and strain (r:​ −0.887 to −0.934). Patellar tendon phase difference was also strongly, inversely correlated with average tibial cartilage OARSI grade (r:​ −0.889 to −0.890). Patellar tendon dynamic modulus was moderately correlated with tibial cartilage dynamic modulus (r:​ −0.561 to −0.575) and OARSI grade (r:​ 0.631–0.646). For the first time, we show that the viscoelastic properties of the human patellar tendon are strongly, inversely related to tibial cartilage viscoelastic properties and OARSI grades in osteoarthritic knees, suggesting these two tissues may undergo diverging adaptations with osteoarthritis. These results provide a foundation for more detailed future investigations on patellar tendon-cartilage interactions in knee osteoarthritis.