Persistent Pain after knee replacement
A note about Persistent (or chronic) pain
Persistent pain refers not to how bad pain is, but to the length of time that someone has had pain (= longer than 3 months). If you have pain, you are not alone – pain is the world’s leading cause of disability (a loss of ability to perform activities). Pain causes more disability than heart disease, stroke and cancer which makes pain just as important to treat as these other conditions.
Even though your persistent pain can feel the same as it did in the early days when it started, we know from research that the longer pain persists after an initial injury or surgery, the less it remains directly related to the initial injury or surgery and the more it is related to other factors.
Most of the body’s tissues will completely heal within 6 to 12 weeks of any injury or surgery (broken bones heal within 6 weeks, sprained ankles in 3 weeks). Inflammation peaks at 18 days but is usually fully resolved by 4 to 6 weeks. Untreated cancer, infection and inflammatory diseases such as rheumatoid arthritis can be associated with inflammation that doesn’t settle.
Our pain system can fail us
Our pain system serves an important role in detecting danger in our body to enable us to protect ourselves.
However, our pain detection system can easily change (maladapt) and start overdetecting danger and become overprotective.
This does not mean that we are weak, that pain is “all in our head” or that persisting pain is not real – in fact, you can think of chronic pain as being uber real – a super real pain, that can be more intense and interfering than the pain of the original injury or surgery.
Some of the factors known to be involved in helping to make pain persist include changes to our body (known as bioplasticity – the ability of our body’s tissues to adapt) such as changes to how our nerves and muscles function, changes in the way that our central nervous system (our spinal cord and brain) functions and changes to how we think and feel about pain.
But my body has changed and that can’t be good!
Following an injury or surgery, your body’s shape and structure may change and look different (such as leaving a scar). On scans such as x-rays, Computerised Tomography (CT) scans and Magnetic Resonance Imaging (MRI) scans, we can easily detect structural changes to our body – these start to occur as early as the teenage years. But in research, these structural changes on scans do not correlate well to our experiences of pain and certainly don’t mean that we will have pain. They are like grey hairs and wrinkles – something that happens with time but we adapt to.
It’s not the structure and how it looks, but how it functions that is most important for persistent pain.
Other, more personal factors that influence the experience of pain include genetics (a twin is 50% likely to get the same persistent pain as their twin), stress (emotional, physical and environmental), mood, anxiety, thinking styles, poor sleep and trauma (at the time of the injury or surgery as well as trauma in the past).
But doesn’t pain mean there is something wrong?
Persistent pain often leads us to feel that ‘there must be something wrong’ with our body and that is true, it’s just that the ‘something wrong’ is the bioplastic changes that have occurred to keep pain persisting and not the body part. For example, our focus after a knee replacement will usually be on the painful knee – I have pain in my knee so there must be something wrong with my knee! But, your surgeon might say “your knee has healed/ it’s fine/ there’s nothing wrong with it”! The explanation is in the tissues surrounding the knee, the spinal cord and the brain.
Injuries, osteoarthritis or surgery, combined with personal, psychological and social factors, can quickly start a process of bioplastic change occurring in our body, spinal cord and brain. After knee replacement, these changes lead to an increased awareness of our knee and increased pain in order to protect the knee more. Unfortunately, more detection and more protection = more pain and more disability.
Knee osteoarthritis, is usually associated with low levels of joint inflammation that can increase suddenly before settling down again over 4 to 6 weeks. This inflammation though, over time, can sensitize the knee and surrounding tissues leading to the bioplastic changes mentioned above. So for many people, persistent knee pain may have been present for many years prior to their knee replacement with their body, spinal cord and brain already adapted and waiting for another opportunity to detect danger and increase pain.
So, the persistent pain story goes a little something like this:
- Once upon a time, osteoarthritis and knee surgery led to bioplastic changes
- And despite the surgery healing over 6 to 12 weeks
- The changes to the body and brain meant that pain persisted
- Making it easier to detect danger and experience more pain
- Leading to the brain becoming overprotective of the body
- Which leads to changes in the way we move
- And changes to the things we do and how we do them
- And changes to the way we think
- And changes to the way we function and live our life
But – these are only changes…
And, Kneed, your pain rehabilitation program is designed to help you change them back, so that you can take control of your pain story and live happily ever after.
