The outcomes that we reviewed included maintenance of the achieved correction , progression of osteoarthritis ( based on the Kellgren and Lawrence classification ) , severity of pain ( as assessed on a visual analog scale [ VAS ] ) , knee function ( as measured with the Hospital for Special Surgery [ HSS ] score and Knee injury and Osteoarthritis Outcome Score [ KOOS ] ) , walking distance , complications , and survival with conversion to a total knee arthroplasty as the end point .