Total Knee Replacement

Dr Yeo Seng Jin, Senior Consultant, Dept of Orthopaedic Surgery, Singapore General Hospital

Chronic knee pain is most commonly caused by osteoarthritis. Many non-surgical options are available to people with chronic knee, such as medications, self management programs and physiotherapy. However, these interventions have been shown to have only small effect sizes on knee pain. When these conservative treatments fail, patients may be offered surgical options such as osteotomy and arthroscopy, although these procedures have limited success in pain reduction. The only intervention that has a large effect size on relieving chronic knee pain is total knee replacement.

Total Knee Replacement (Figure 1 on the left) is widely considered as an effective treatment and successful end-stage surgical procedure for relieving chronic knee pain and functional disability. There appears to be rapid and substantial improvement in the patient’s pain, functional status, and overall health-related quality of life in 90% of patients. Data suggests that these improvements in patient reported outcomes persist in both the short- and long-term studies. With improvements in surgical techniques, instrumentation and prosthetic design, the survivorship of the Total Knee Replacements have improved over the past 30 years since the surgery was introduced (Figure 2 below). 90% survivorship is expected at 15 years. Technical factors in performing surgery still influence the shortand  long-tem success rates. Proper alignment of the prosthesis appears to be critical in minimising long-term wear and loosening of the prosthesis. Revision Total Knee Replacement is possible but the results are inferior to primary Total Knee Replacement and every effort is made for initial successful and long lasting primary Total Knee Replacement.

In the past, patients between 60 and 75 years of age were considered to be the best candidates for Total Knee Replacement. Over the past two decades, however the age range has been broadened to include, on the one hand, more elderly patients (e.g. octogenarians and beyond), many of whom have a higher number of comorbid conditions, and, on the other hand, younger patients who may have higher levels of physical activity. Advanced age alone is not a contraindication for Total Knee Replacement; over time (Courtesy Swedish Knee Arthroplasty Registry) however, perioperative complications are higher in patients who are older at surgery as well as in those with more comorbid conditions. There are few absolute contraindications for Total Knee Replacement other than active local or systemic infections and other medical conditions that substantially increase the risk of serious perioperative complications or death. Complications following Total Knee Replacement include wound healing problems; wound and deep tissue infection; deep vein thrombosis and pulmonary embolism; pneumonia; myocardial infection; joint instability, stiffness, and/or malalignment; nerve and vascular injuries. One of the most important factors leading to successful Total Knee Replacement is proper surgical technique.

Because of these successful outcomes, Total Knee Replacement is now the most common surgical procedure performed by the Department of Orthopaedic Surgery at the Singapore General Hospital (SGH). 1400 Total Knee Replacements are performed in SGH annually accounting for half the total number performed in Singapore. There is a direct association between hospital and surgeon procedure volume and the outcomes of Total Knee Replacement. For example surgical site infection risk is reduced with increasing hospital and surgeon volume and the deep infection risk in SGH is 0.6%. Other outcome results are available on the SGH website.

New improvements in perioperative pain management, less invasive surgical approaches, clinical care pathways and accelerated rehabilitation programs have reduced the recovery period and hospital stay which averages 4 days. Patients are now encouraged to start ambulation the following day after surgery and are able to climb stairs before discharge.

At present, there is no consensus regarding activity limitation following successful Total Knee Replacement. In general, patients are advised to avoid activities that involve high impact repetitive loading on the implant such as jogging or skipping. Most surgeons would set the limit of activity at the level achieved during doubles tennis.

Normal occurrences that patients notice during the recovery period include; intermittent clicking inside the knee; area of skin numbness on the lateral aspect of the wound; swelling after exercise and at end of the day; warmth around the knee; ankle swelling that resolves overnight; bruising; and difficulty with sleeping.

Abnormal symptoms and signs include increased redness around the wound, fever, any drainage around the wound and calf pain and swelling, and require early referral to the specialist. 

The challenge now is for the younger patients i.e. less than 60 years of age, who present with degenerative arthritis that require Total Knee Replacement. These patients are more active and are expected to have more than 20 years of life remaining and thus more likely to outlive their prosthesis. New technologies have been introduced to try to address this problem and increase the lifespan of the Total Knee Replacement. These include newer materials for the bearing surfaces in Total Knee Replacement and Computer Assisted Surgery (Figure 3) which increases the precision of implantation of Total Knee Replacement. Both have the potential to reduce wear in Total Knee Replacement and hence increase the longevity of the prosthesis. Another novel approach is to perform partial knee replacements (Figure 4) where only the damaged parts are addressed. The advantages are preservation of the cruciate ligaments and bone stock such that should revision be required in the future, it will be an easy conversion with a standard Total Knee Replacement as opposed to a complex revision surgery.