One in Three Hip and Knee Replacement Patients Had Obesity, Audit Finds

Around one in three patients who underwent hip or knee replacement surgery over the past decade had obesity, with a body mass index (BMI) above 30, according to the latest National Orthopaedic Register national report covering 2015-2024.

The audit examined 43,291 hip and knee joint replacements carried out across 17 public and private hospitals, making it the most comprehensive analysis of such surgeries to date. It found that 33% of patients who underwent knee replacement surgery had a BMI over 30, compared with 27% of hip replacement patients.

Osteoarthritis was the main reason for these surgeries, linked to 94% of hip replacement patients and 97% of knee replacements.

The report also noted that the number of patients with a BMI over 40 increased slightly in 2024, and future reports will examine these trends in more detail.

Understanding BMI and Joint Replacement Surgery

Body mass index (BMI) is a measure used to assess whether a person has a healthy weight for their height. A BMI of 30 or above is classified as obesity. While being overweight or obese is determined by BMI, research indicates that patients in every BMI category, including those with class two (BMI 35–39.9) and class three (BMI ≥ 40) obesity, can achieve meaningful improvements in joint function and pain relief following joint replacement surgery.

Clinical lead John Quinlan stated: “Joint replacement surgery is often performed when osteoarthritis has caused severe pain and significantly limits a person’s mobility and quality of life.”

Implications for Patient Care

The findings highlight the growing complexity of care for joint replacement procedures in patients with obesity. Healthcare providers are increasingly called upon to optimize surgical outcomes while managing comorbid conditions associated with higher BMI.

Efforts to reassess BMI-based access to joint replacement surgery emphasize that patients across all weight categories benefit from these procedures, supporting inclusive access to care based on individual clinical need rather than weight alone.

Looking Ahead

As obesity rates continue to rise globally, orthopaedic services must adapt to meet the needs of an increasingly diverse patient population. Ongoing audits and research will be essential in refining surgical protocols, rehabilitation strategies, and long-term follow-up care for joint replacement patients across the BMI spectrum.