Total joint arthroplasty remains the most effective treatment to relieve pain and restore function in damaged and diseased joints; however, less invasive, more functional solutions are necessary for young, active patients who have chondral defects and are at the early stages of disease. Unfortunately, attempts at providing such a method have provided variable and often unsatisfactory outcomes. Unicondylar knee replacement, for example, is associated with a markedly higher rate of revision when compared with total knee arthroplasty, and there is a distinct probability of disease progression in the remaining joint compartments. Small metallic caps intended for filling the cartilage defects are commercially available, but the clinical follow-up of patients who have undergone this treatment is short. Although not yet in clinical use, synthetic polymeric implant scaffolds, with and without cell-seeding, are also under development. The biomechanical requirements for treating chondral lesions, like those of total knee arthroplasty, are wear and fixation. A lesion-filling implant must carry large joint loads without damaging the opposing tissue. Integration with surrounding cartilage and subchondral bone would enhance load-sharing and load transfer. The challenge of meeting these requirements is difficult, but new forms of computational models and in vitro tests can aid in establishing performance and in rapidly screening possible solutions.