Subjective evaluations often are used after knee arthroplasty to quantify function; however, these scores may be influenced by pain and/or function of the nonoperated limb. Multiple influences increase variability of these scores, which in turn may result in a greater change in score required to be considered clinically important. We determined the relationships among the Knee Society pain and function scores, range of motion (ROM), and functional force measures of the surgically treated and nonoperated limbs. Before and 3 months after total or unicompartmental knee arthroplasty, 36 patients answered questions necessary to calculate the Knee Society pain and function scores. A dual-force platform was used to record the lift-up force of each limb during a stepping task. Function scores were correlated to pain scores, lift-up force of the nonoperated limb, and ROM before surgery. After surgery, function scores correlated with pain scores but not with objective functional measures or ROM. As patient-reported function scores and functional force measures of the surgically treated limb seem to provide distinctly different information, both measures may need to be collected after knee arthroplasty to fully understand a patient's functional recovery.