Primary total knee arthroplasty (TKA) is effective in relieving pain and improving patient-reported physical function in patients with advanced knee osteoarthritis. Consequently, the demand for TKA, particularly among younger active adults, is growing significantly (1). Although improved postoperative function is well documented, little is known about whether the gain in functional ability translates into new physical activity habits that will support weight management. Moreover, the majority of preoperative TKA patients have a body mass index (BMI) in the obese range and report low levels of physical activity due to the combination of knee pain, obesity, and associated comorbidities (2, 3). Therefore, in this issue of Arthritis Care & Research, Riddle and colleagues (4) pose an important public health question: do TKA patients have improved ability to manage weight after successful surgery?
Riddle et al report weight change over a 5-year period following TKA among 917 patients from the Mayo Clinic knee registry database compared to weight change of an age- and sex-matched population-based random sample of 237 persons from the Rochester Epidemiology Project. Thirty percent of patients with a successful TKA gained 5% or more of baseline body weight at 5 years after surgery compared to 20% of the control group. Adjusted for age, sex, BMI, education, comorbidity, and presurgical weight change, multivariate analysis showed that patients undergoing TKA were at greater risk (odds ratio 1.6, 95% confidence interval 1.2–2.2) of a gain of 5% or more of body weight over a period of 5 years following surgery compared to the control group over the same time period. In addition, patients ages <70 years, those who had greater weight loss prior to surgery, or those undergoing additional arthroplasty surgeries were at higher risk of weight gain. Not surprisingly, younger patients who lost a large amount of weight prior to TKA regained more weight after surgery. Riddle et al note that preoperative patient weight loss may have been intentional in preparation for the surgery, and intentional weight loss is often difficult to maintain over time.
Patients choosing TKA report goals to relieve pain and improve daily activity, including standing without pain, climbing stairs, and walking longer distances. However, we previously reported that although TKA improves physical function in the majority of patients, there is a subgroup of patients who report limited or no gain in function (5). In addition, higher BMI is associated with significantly poorer self-reported function at 12 months post-TKA. The Framingham study and others have documented the direct association between BMI and knee and hip arthritis, and between BMI and total joint replacement use (6, 7). Therefore, it would be interesting to understand if the 30% of TKA patients who report weight gain overlap with the subset of patients who do not report improved physical function after surgery or have significant osteoarthritis in the contralateral knee or hips that can limit active lifestyles. Comparison of weight trajectories of osteoarthritis patients who undergo TKA and those who do not is difficult. However, it is conceptually possible that TKA tames the weight gain curve of many patients by facilitating activity, whereas patients with osteoarthritis who do not undergo surgery are expected to increasingly limit their activity and may have steeper increases in BMI over time.
Riddle et al contrast their TKA results with a total hip arthroplasty (THA) study showing weight loss after surgery in obese patients. The authors of the THA study note reports of increased activity levels after THA (8). However, THA patients are, on average, less obese at the time of surgery than TKA patients (Franklin PD: unpublished observations). Riddle et al did not report physical activity levels pre- or postsurgery in their TKA study. However, our preliminary research using accelerometry to objectively measure physical activity before and after TKA reported that greater BMI was associated with lower mean numbers of steps per day before TKA (9) and at 6 months post-TKA (Franklin PD et al: unpublished observations). In addition to greater BMI, poorer emotional health, coexisting chronic conditions, and arthritis pain in other weight-bearing joints were correlated with lower daily activity. Therefore, these variables are important to consider when evaluating activity levels in patients post-TKA.
Importantly, the authors call for interventions to support effective weight control strategies in overweight and obese patients, including in TKA patients. Others call for interventions to increase the public health value of TKA beyond pain relief by supporting more active lifestyles after surgery (10). To achieve these goals, behavioral interventions to support lifestyle changes in the perioperative period might be most effective by addressing weight management through both dietary changes as well as increased physical activity. We have just completed a randomized trial of a behavioral intervention in the post-TKA period (11). Patients were randomized to receive a 12-session, telephone-delivered motivational support program to increase physical activity and exercise following TKA or to usual care. Ninety-eight percent of the intervention patients completed the calls and valued the support. This suggests that TKA patients are receptive to complementary programs after surgery that may improve lifestyle habits. We are in the final phase of analyzing data from this trial. While improved physical activity was the primary outcome of this trial, not weight management, it will be important to evaluate the relationship between activity and weight in the postoperative period. Another important factor in weight management that this intervention did not address is dietary habits, which would be important to address in future studies in this generally obese population.
In summary, the US population is aging and becoming more obese at the same time that larger numbers of adults of all ages report painful knee osteoarthritis and choose TKA. Is the TKA surgical event an opportunity to support patients to reengage with daily physical activity that will support weight management? All TKA patients are referred to physical therapy after surgery to recover full knee range of motion and to rebuild quadriceps strength and leg function. Can the rehabilitation phase expand its goals beyond knee function to support daily physical activity and lifestyle changes? If so, how can best practices in behavior change be linked to post-TKA rehabilitation to optimize the number of TKA patients who adopt active lifestyles? Further research is needed to address these important questions.