SAN FRANCISCO — Patients who gain range of motion and improved function after total knee replacement also increase their level of sports activity, a study of 417 patients found.
There have been little data on the relationship between changes in objective or functional outcomes after total knee arthroplasty and changes in activity level. The number of articles published on this topic grew from around 5 per year in 1996 to 20 or so in 2006, according to Dr. Michael A. Mont, director of joint preservation and reconstruction at Sinai Hospital, Baltimore.
He and his associates conducted a survey of 162 men and 255 women receiving total knee arthroplasty. All of the patients underwent the procedure to treat pain associated with osteoarthritis.
The survey asked about the hours and types of sports activity the patients had participated in during the year prior to surgery and up to a mean of 3 years after surgery. The researchers compared the survey results with evaluations of the knee using Knee Society objective and functional scores and a 10-point satisfaction scale.
They found a positive correlation between increases in Knee Society functional scores and increases in weighted activity scores. Every 10-point increase in Knee Society functional score predicted a 1.2-point increase in the weighted activity score, Dr. Mont said in a poster presentation at the annual meeting of the American Academy of Orthopaedic Surgeons.
The investigators used a new questionnaire to derive the weighted activity score, which accounted for the impact level of a sports activity and the amount of time a patient spent in that activity. The calculation begins by assigning 1 point to low-impact activities (including aerobics, bicycling, golf, dancing, gardening, or others), 2 points to moderate-impact activities (ice skating, skiing, or singles tennis, among others), or 3 points to higher-impact activities (including baseball, basketball, football, gymnastics, jogging, and other activities).
The investigators then multiplied the frequency of an activity (in days per week) by the duration (in hours per day) reported by a patient, and multiplied the product by the number of impact points. Calculations were done for each activity reported by a patient, and the sums added up to the weighted activity score.
A highly active patient might report cycling, golf, singles tennis, and basketball. Cycling 7 days per week for 1 hour per day, multiplied by 1 impact point, is 7 points. One 3-hour golf outing per week multiplied by 1 impact point totals 3 points. Singles tennis 1 day per week for 1 hour multiplied by 2 impact points totals 2 points. Basketball 1 day per week for a half-hour multiplied by 3 impact points totals 1.5 points. Summing up all the activity points (7 plus 3 plus 2 plus 1.5) gives a weighted activity score of 13.5 points.
A low-activity patient who reports speedwalking 1 hour per week (totaling 1 point) and gardening a half-hour per week (totaling 0.5 point) would have a weighted activity score of 1.5.
Overall, Knee Society functional scores increased by a mean of 48 points from the preoperative assessment to the final follow-up. The corresponding increase in weighted activity score was 2.5 points, with a mean weighted activity score of 6.2 points at the final follow-up, he said.
Weighted activity scores increased for 53% of patients, decreased for 19%, and did not change for 29%. Patients under 60 years old were significantly more likely to increase their activity scores after knee replacement than were older patients.
Dr. Mont is a consultant for Wright Medical Technology, and he and two coinvestigators are consultants for Stryker. Both companies market artificial knee implants.