Moderate evidence supports that an eight month delay to total knee arthroplasty (TKA) does not worsen outcomes.

There was one high quality study (Tuominen, U., 2010) that addressed the question of worsening of outcomes or an increase in complications on delayed cases of KA among adult patients with osteoarthritis, compared to cases without delay after having failed non-surgical management.
This study evaluated the effects of waiting time on health related quality of life, knee pain and physical function. The study also addressed the use and costs of medication of patients awaiting TKA. The mean waiting time was 94 days among those patients short waiting times versus 239 days (mean of 8 months) among those with non-fixed waiting times groups, respectively. Those in the short waiting time group had higher weekly costs of medication at admission, and reached better quality of life 3 months earlier than those in the other group, but the latter had better quality of life after operation. 
  1. Tuominen,U., Sintonen,H., Hirvonen,J., Seitsalo,S., Paavolainen,P., Lehto,M., Hietaniemi,K., Blom,M. Is longer waiting time for total knee replacement associated with health outcomes and medication costs? Randomized clinical trial. Value Health 2010/12; 8: 998-1004