Patients should now expect a better range of motion, function and survivorship of their knee replacement. A combination of better implants, improved surgical technique and optimised pain management and rehabilitation have resulted in these better outcomes.
The current treatment aim is a forgotten joint, with minimal discomfort and full function. More patients are achieving this.
Knee replacements were always said to last 10 years. This is no longer the case. The Australian Orthopaedic Association National Joint Replacement Registry monitors the survivorship of all knee replacement surgery performed in Australia over the past 20 years.
It can demonstrate the better and poorer performing implants, allowing surgeons to choose a well-performing knee replacement. Currently over 90% of knee replacements would be expected to survive for more than 20 years. Caution still needs to be exercised in younger and larger patients who have been shown to have higher revision rates.
Multi-modal analgesia has become the norm in knee replacement surgery. This most commonly involves a spinal anaesthetic, sedation or GA, peripheral nerve blocks, local anaesthetic infiltration, simple analgesia, pregabalin, NSAIDs and judicious use of narcotics.
This enables quicker rehabilitation with earlier hospital discharge. Current hospital stays average between two to four days, with only those lacking social support or multiple co-morbidities requiring a stint in the rehabilitation unit prior to discharge home.
Improved techniques
Improvements to instrumentation and technology have optimised surgical technique. The most recent advance is the introduction of surgical robots. These vary from the robots used for prostatic surgery. These ‘soft tissue’ robots enable the surgeons to improve their dexterity and surgical precision.
Orthopaedic or ‘hard tissue’ robots build a three-dimensional model of the limb and allow surgery to be planned virtually. Soft tissue balance can be considered in this model intra-operatively and the plan individualised. The robotic arm assists the surgeon by executing the required bone cuts. Robotic knee replacement has been shown to decrease soft tissue damage during the procedure, decreasing pain and opioid requirements. This technology is now being used in over 20% of all knee replacements in Australia.
Individualised alignment in knee replacement is an area of intense clinical research. Previously, all patients received a knee replacement positioned in the same alignment. Now, it is commonly accepted that there is wide variation in the native alignment of patient’s legs.
Tools and techniques exist to enable individual plans for alignment. The challenge is to identify the ideal alignment for each patient. Advanced technologies such as computer navigation and robotics are assisting assessment of individual alignment and allowing data collection to further optimise this process in the near future.
Decreased complications
Infection control plays a vital part in decreasing post-operative complications. Skin decolonisation together with optimisation of co-morbidities such as diabetes has decreased infection rates, but joint infection remains a major complication in just under 1% of patients.
A combination of early mobilisation, surgical technique and prophylaxis has seen a decrease in the rates of thromboembolic disease post-surgery. The major complication of knee replacement remains pain and stiffness. Optimising pain control and early rehabilitation remains key to preventing this. Early referral back to the surgeon if any concern regarding possible complications is always the safest management.
Functional outcomes after knee replacement have improved dramatically over the past 20 years, largely due to improved range of motion achieved. Although directly related to pre-operative range, the average patient should expect full extension and over 120 degrees of flexion allowing all ADLs to be achieved.
Over 50% of patients should be able to kneel. Return to social sport should be expected in those fit enough to do so and patients should be able to walk for over 60 minutes without discomfort. Return to work should occur between six and 12 weeks, depending on occupation.
Future improvements?
Unfortunately, knee osteoarthritis (OA) is not likely to have a cure in the medium term and knee replacement will remain the mainstay of treatment for end stage knee OA.
We will see continued improvement in surgical technique and optimised individualisation of that technique. Knee OA is also likely to be one of the first areas where big data and machine learning will assist, with treatment algorithms helping guide both doctors and patients on the optimal treatment at different stages of the disease, as well as the optimal surgical management when the time for knee replacement occurs.
Key messages
- Knee replacement surgery remains the best treatment for end stage knee osteoarthritis
- Outcomes from total knee replacement have improved markedly
- Technology is enhancing individualised treatment.
Author competing interests – the author is a research and development consultant for the manufacturer of Mako robot.