Relative risk of different operations for medial compartment osteoarthritis of the knee.

The relative risk of total knee arthroplasty (TKA), high tibial osteotomy (HTO), and medial unicompartment (UKA) replacement for medial compartment arthritis is presented. Risk is defined as the product of the probability of an event occurring and its consequence. To define consequence, 2 related scales of impact (1 systemic and 1 local) are suggested. The probability of a complication is derived from the incidence as found in the published literature and expressed as a decimal of 1. The cumulative risk is expressed as the sum of the risks of all individual complications. The overall impact of specific comorbidities has been calculated when their influence on the incidence of a particular complication is known. Of the 3 operations, TKA has the highest cumulative risk of systemic complications and HTO is the most likely to produce local technical problems. UKA is the safest of the procedures. The relative risk of TKA:HTO:UKA is 1.00:1.01:0.31. For TKA, the greatest additional risk is morbid obesity, which increases overall risk by 31% by virtue of a 7.8-fold increase in infection rate. Cardiorespiratory disease, diabetes mellitus, smoking, and cirrhosis of the liver increase cumulative risk by 20%, 17%, and 17%, respectively.The authors conclude that a quantitative assessment of operative risk is possible and useful. However, it depends on the availability of reliable complication incidence data.