Knee replacement surgery is a common procedure performed to alleviate chronic pain and improve mobility for individuals with damaged knee joints, often due to arthritis. While the surgery aims to restore function, many patients experience an unexpected outcome: weight gain. This is a recognized concern, prompting a closer look at contributing factors. Understanding these reasons can help individuals better prepare for and navigate the post-operative period.
Reduced Physical Activity
Immediately following knee replacement surgery, significant reduction in physical activity is an expected part of the recovery process. Pain, swelling, and the need for tissues to heal limit movement, leading to fewer calories burned. Patients are typically advised to rest and avoid strenuous activities to protect the new joint and facilitate healing. This period of reduced activity means the body expends less energy than before surgery.
The discomfort associated with post-operative pain and the body’s inflammatory response can make routine movements challenging. Swelling, a common occurrence after knee surgery, restricts range of motion and makes movement uncomfortable. Many patients also experience a fear of movement, kinesiophobia, due to concerns about re-injury or exacerbating pain in their newly replaced knee. This apprehension can lead to further inactivity, contributing to a lower energy expenditure.
While physical therapy is an important component of recovery, early exercises are often gentle and do not immediately compensate for the decrease in activity. Patients may struggle to meet recommended activity levels, even months after surgery. Research indicates that physical activity levels often remain at or below pre-surgical levels, despite improved mobility. This sustained lower activity means the body’s energy balance shifts towards storage rather than burning.
Medication and Fluid Retention
Post-surgical weight gain can stem from physiological responses to the body’s trauma and the medications used during recovery. The body’s inflammatory response to surgery involves sending fluid to the affected area to aid healing, resulting in temporary fluid retention, or edema. This fluid accumulation can cause the number on the scale to increase, particularly in the days and weeks immediately following the procedure.
Certain pain medications, especially opioids, are prescribed after knee replacement surgery to manage discomfort. These medications can have side effects that contribute to weight gain, including fluid retention and slowed metabolism. Opioids can also cause constipation, leading to a feeling of bloating and discomfort that might be perceived as weight gain.
Non-steroidal anti-inflammatory drugs (NSAIDs), also used for post-operative pain and swelling, can contribute to fluid retention. The combined effect of the body’s healing processes and medication side effects can lead to an increase in body mass. While much of this fluid weight is temporary, it can concern patients.
Dietary and Metabolic Shifts
Changes in eating habits and the body’s metabolic response to reduced activity play a significant role in post-knee replacement weight gain. Reduced physical activity means the body requires fewer calories to maintain its weight, yet dietary intake may not decrease. Patients might continue eating the same amount of food as before surgery, or even increase their caloric intake.
Comfort eating can become prevalent during recovery, as individuals may use food to cope with pain, boredom, stress, or the emotional challenges of limited mobility. The ability to prepare healthy meals might be hindered due to post-surgical limitations, leading to increased reliance on convenience foods, often higher in calories and less nutritious. This combination of unchanged or increased intake with decreased energy expenditure creates a caloric surplus, promoting fat storage.
The body’s metabolism can adapt to prolonged inactivity, becoming less efficient at burning calories. While the body needs increased calories for healing after surgery, prolonged low activity can shift metabolic processes. Studies show a significant percentage of patients, sometimes as high as 66%, gain weight in the two years following total knee arthroplasty, with an average gain of about 14 pounds. This weight gain is clinically important, as it can increase the risk of other health issues, even if it does not directly affect the knee implant’s outcome.