Exercise is Medicine

Why exercise before a knee replacement leads to a better outcome

Knee osteoarthritis is an increasing problem in New Zealand. Currently, the chance of developing symptomatic knee osteoarthritis is over 40%, and this will increase as the population ages. By the late 2030s, one-quarter of the NZ population will be over 65.

Total knee replacement has become the treatment of choice for end-stage osteoarthritis, relieving pain and restoring function so that most patients can now expect to remain active well into their retirement. The success of the procedure is reflected in its popularity: the lifetime risk of knee replacement in the NZ population is currently 18%.1

However knee replacement is far from perfect, and up to 20% of patients report dissatisfaction with their result. Evidence suggests that better pre-operative health status (greater physical function and strength) is a strong predictor of good postoperative outcome. Additionally, there is clear evidence that health-related quality of life deteriorates during the pre-operative period - especially relevant in NZ with often long waitlists in the public system. This period may represent an opportunity, as patient education and exercise prior to surgery (prehabilitation) can benefits mobility, improve function, and optimise the outcome of the surgery.

A recent systematic review looked at the value of prehabilitation prior to joint replacement. It reviewed the results of 35 randomised controlled trials, including almost 3,000 patients.2 Significant improvements were observed in function, quadriceps strength, and length of stay in patients who underwent a structured prehabilitation program prior to both hip and knee replacement surgery. There was also a trend to reduced anxiety around the surgery, as a key fear of many patients is how they will cope with the post-operative rehabilitation, and pre-operative exercise improved their confidence.

How much exercise is enough?

Most of the included studies involved a 6-8 week program, exercising 3-5 days per week. One of the challenges is that pain may limit the type and intensity of exercise a patient with osteoarthritis can do. An exercycle is particularly effective, and turning the resistance down and raising the seat can help patients tolerate it initially. Other exercises that work well in osteoarthritic patients include cross-trainers and water-walking.

If a longer lead-in time is available, pre-operative exercise is also useful as part of a weight reduction program prior to the operation. An elevated body mass index (BMI>40) at the time of surgery confers a 6-times higher risk of deep infection – a devastating complication following knee replacement. Deep infection almost always requires further surgery and prolonged antibiotic treatment, and elevated BMI is the most important modifiable risk factor.3

A good pre-operative exercise program continues into the post-operative phase – aiding recovery and return to function. Modern ‘Enhanced recovery after surgery’ (ERAS) protocols focus on better anaesthesia, pain management, and early mobilisation.  While still a major operation, the average length of hospital stay has dropped from 7-10 days in 2000 to 2-3 days today, with earlier mobilisation reducing the risk of complications such as blood clots. The stronger a patient is leading into surgery, the easier they will find such rehabilitation afterwards: encourage your patients to get ready to get going.

  1. Henzell IS, Zhou L, Frampton C, Hooper G, Ackerman I, Young SW. Lifetime risk of primary total knee replacement surgery in New Zealand from 2000 to 2015. N Z Med J. 2019;132(1489):48-56.
  2. Moyer R, Ikert K, Long K, Marsh J. The Value of Preoperative Exercise and Education for Patients Undergoing Total Hip and Knee Arthroplasty: A Systematic Review and Meta-Analysis. JBJS Rev. 2017;5(12):e2. doi:10.2106/JBJS.RVW.17.00015.
  3. Jung P, Morris AJ, Zhu M, Roberts SA, Frampton C, Young SW. BMI is a key risk factor for early periprosthetic joint infection following total hip and knee arthroplasty. N Z Med J. 2017;130(1461):24-34.