In this 3-part series we’ll get to the bottom of what osteoarthritis is, what it may mean for you, and how it can be managed. We’ll also unpick and dispel some of the common myths related to this condition as well as frequently asked questions that we hear in clinic. This blog is part 1 in the series where we’ll learn what osteoarthritis is. Keep an eye out for part 2 and 3 that will delve into management, myths and FAQs!
If you are reading this blog and you think you may have osteoarthritis or you may have already been told you have by a healthcare professional and aren’t sure what to do, then do come in and see one of our specialist musculoskeletal physiotherapists who will be able to help you understand your problem, how to manage it and help you work towards your goals.
Let’s begin.
What is osteoarthritis?
Is it bone on bone? Wear and tear? Degeneration? A part of aging? Damage? Joints wearing down? To some of you these descriptions may be how you view osteoarthritis and if so, it is understandable that it might sound a bit scary, but I’m hoping by the end of this blog you might feel differently about it.
So, what actually is it?
Osteoarthritis or OA as it is commonly known, is a joint condition that can sometimes result in pain, disability and loss of function and is highly prevalent worldwide [1]. OA is estimated to affect 7% of the world’s population which amounts to around 500 million people [1] [2]. In the UK approximately 10 million people are affected by OA, 5.4 million of those with knee OA and 3.2 million with hip OA [3]. As the knee is the most affected joint by OA both worldwide and within the UK, this series will be focussing on knee OA [1] [4].
To understand knee OA better we firstly need to understand the anatomy of the knee and how it functions. Bear with me whilst we take a whistlestop anatomy tour.
Anatomy of the knee
The knee is a strong weight bearing structure that bends and straightens as we move. There are two joints within the knee, the larger of the two joints is the tibiofemoral joint, which is where the femur (thigh bone) meets the tibia (shin bone), and secondly the patellofemoral joint, where the patella (kneecap) meets the femur (thigh bone). As we move and put weight through the knee, these bones come into contact with each other. This could be described as “bone on bone” and is a normal part of how the knee functions. You may have previously heard OA be described as “bone on bone” but now knowing that this is actually a normal occurrence in any knee joint when it is moving is hopefully reassuring that this phrase is nothing to fear.
The surfaces of the bones in these two knee joints are covered in something called hyaline cartilage. This cartilage is smooth and resilient, and distributes mechanical forces as we move, in order to promote frictionless movement [5]. Within our tibiofemoral joint (the larger of the two knee joints) we also have another structure made from a different type of cartilage known as the meniscus. The role of the meniscus is to withstand shear, tension and compressive forces and also plays a role in weight-bearing, load transmission and shock absorption [6].
As well as cartilage and bones we also have other important structures that make up a joint. Ligaments provide stability by connecting bones at a joint, while the synovial fluid that is within a joint lubricates and nourishes the joint and its structures [5]. Synovial fluid is able to nourish the cartilage of the knee joint via something called dynamic load, which is basically any weight bearing physical activity, for example walking, squatting etc., which is really important for our cartilage and joint health. Muscles are found throughout the body and are attached to bones via tendons at a joint, their main function is to produce movement [7]. Tendons attach muscles to bones and are strong structures that can efficiently transmit forces produced by muscles to the bones, minimising energy loss and maximising efficiency of movement [8]. Together, all these components work together to allow for seamless motion and weight-bearing activities.
Phew that was a lot of anatomy, but now we hopefully understand the function of our knee joint a bit more.
Ok, so what happens to the knee when there is OA?
Well, in a joint our cartilage goes through a continuous balanced cycle of what is described as degeneration and regeneration during dynamic loading (weight bearing physical activity). We could also describe this as breaking down and removing older tissue and replacing it with new and stronger tissue. This is a normal process. In OA an imbalance occurs during this cycle, the cartilage becomes unable to keep up with the loading demands and can result in more degeneration (breaking down) compared to regeneration (creating and replacing). Now this can sound worrying and maybe even painful, but it shouldn’t be. Hyaline cartilage does not have a nerve supply, this means it cannot be a source of pain, so despite this process occurring it will not result in causing us pain. This process also happens very slowly over time and what this is more likely to result in is possibly less smooth movement than we previously had and a reduced tolerance to continuous loading. So, we may need to consider more recovery time between periods of loading [9].
But knee OA can be painful sometimes, so where does that pain come from? Well, this cycle imbalance doesn’t only affect the cartilage, other structures in the joint will be affected too. Before a joint has undergone OA changes, some of the structures within and around that joint could be described generally as thick and smooth and the composition of the synovial fluid is such that it can easily lubricate and nourish the joint. Over time, with OA, these structures can undergo some changes and this may result in them becoming a bit thinner, a bit rougher and the synovial fluid may be less lubricating and have more inflammatory properties which can sometimes lead to a feeling of stiffness. Sometimes this can also lead to pain as a lot of the structures within and around our knee joint have a rich nerve supply [10].
You may be wondering if it would be helpful to know the extent of these changes using an X-ray? The short answer is no. If someone was to have an X-ray of their knee joint and we were to see some of these OA changes, that does not mean that this person is going to be experiencing pain. In fact, research has shown that knee pain itself is an inaccurate measure of the extent or severity of OA changes that can be seen on an X-ray [11]. So just because these changes have taken place, does not mean they will be painful, and just because someone is experiencing pain, does not mean they will have severe OA changes within their joint [11].
So, it turns out X-ray images aren’t always the most helpful when it comes to OA, but we’ll delve deeper into the role of imaging and OA in part 2 and 3 of this blog series.
Loading the knee joint: should we or shouldn’t we?
Earlier I mentioned that our cartilage goes through a continuous cycle and when a joint has OA this cycle becomes imbalanced and the cartilage is unable to keep up with the loading demands. This may lead you to thinking that in order to protect our cartilage from degenerating further surely we should stop all loading right?
Wrong! We know that loading is so important for our cartilage and joint health so we definitely should continue, and furthermore, too much loading is not always to blame for this imbalance occurring, not loading our knee joint enough is a risk factor as well [5]. So how much is enough load? According to researchers, to be in what can be described as the “goldilocks zone” we need to be loading our knee joints with approximately 0.25 to 8 times our body weight, depending on our physical activity levels and abilities [5]. To put that into perspective take a look at the examples below that demonstrate the amount of loading that goes through our knee joints during certain activities.
- Walking: On average 1.8 to 2.8 times our body weight goes through our knee joint [12].
- Running: Anywhere from 3 to 8 times our body weight goes through our knee joint during running, depending on factors such as speed, stride length and terrain [13][14][15].
- Squatting: Approximately 0.8 to 3.2 times our body weight will go through the knee joint during a bodyweight squat [16].
Well this is really positive to hear that keeping active and continuing to load our knee is actually good for our joints, we just may need to factor in more time in between loading to allow for sufficient recovery time [9].
In summary
We hopefully now have more of an understanding of what osteoarthritis is. Next step is what do we do! Stay tuned for part 2 and 3 of this series where we will discuss management, common myths and misconceptions, and frequently asked questions.
References
1 Long H, Liu Q, Yin H, et al. Prevalence Trends of Site-Specific Osteoarthritis From 1990 to 2019: Findings From the Global Burden of Disease Study 2019. Arthritis & Rheumatology. 2022;74:1172–83. doi: 10.1002/art.42089
2 Hunter DJ, March L, Chew M. Osteoarthritis in 2020 and beyond: a Lancet Commission. The Lancet. 2020;396:1711–2. doi: 10.1016/S0140-6736(20)32230-3
3 The State of Musculoskeletal Health. Versus Arthritis. https://versusarthritis.org/about-arthritis/data-and-statistics/the-state-of-musculoskeletal-health/ (accessed 14 August 2025)
4 Prevalence | Background information | Osteoarthritis | CKS | NICE. https://cks.nice.org.uk/topics/osteoarthritis/background-information/prevalence/ (accessed 14 August 2025)
5 Finding the Goldilocks Zone of Mechanical Loading: A Comprehensive Review of Mechanical Loading in the Prevention and Treatment of Knee Osteoarthritis. https://www.mdpi.com/2306-5354/11/2/110 (accessed 29 August 2025)
6 Makris EA, Hadidi P, Athanasiou KA. The knee meniscus: structure-function, pathophysiology, current repair techniques, and prospects for regeneration. Biomaterials. 2011;32:7411–31. doi: 10.1016/j.biomaterials.2011.06.037
7 McCuller C, Jessu R, Callahan AL. Physiology, Skeletal Muscle. StatPearls. Treasure Island (FL): StatPearls Publishing 2025.
8 Bordoni B, Black AC, Varacallo MA. Anatomy, Tendons. StatPearls. Treasure Island (FL): StatPearls Publishing 2025.
9 Infographic. Running Myth: recreational running causes knee osteoarthritis | British Journal of Sports Medicine. https://bjsm.bmj.com/content/56/6/357 (accessed 18 September 2025)
10 Scuderi GR, Tria AJ. The Knee: A Comprehensive Review. World Scientific 2010.
11 Bedson J, Croft PR. The discordance between clinical and radiographic knee osteoarthritis: A systematic search and summary of the literature. BMC Musculoskelet Disord. 2008;9:116. doi: 10.1186/1471-2474-9-116
12 Bergmann G, Bender A, Graichen F, et al. Standardized Loads Acting in Knee Implants. PLOS ONE. 2014;9:e86035. doi: 10.1371/journal.pone.0086035
13 Kutzner I, Heinlein B, Graichen F, et al. Loading of the knee joint during activities of daily living measured in vivo in five subjects. Journal of Biomechanics. 2010;43:2164–73. doi: 10.1016/j.jbiomech.2010.03.046
14 Heinlein B, Kutzner I, Graichen F, et al. ESB Clinical Biomechanics Award 2008: Complete data of total knee replacement loading for level walking and stair climbing measured in vivo with a follow-up of 6-10 months. Clin Biomech (Bristol). 2009;24:315–26. doi: 10.1016/j.clinbiomech.2009.01.011
15 Tibiofemoral contact forces during walking, running and sidestepping | Request PDF. ResearchGate. doi: 10.1016/j.gaitpost.2016.06.014
16 Schellenberg F, Taylor WR, Trepczynski A, et al. Evaluation of the accuracy of musculoskeletal simulation during squats by means of instrumented knee prostheses. Medical Engineering & Physics. 2018;61:95–9. doi: 10.1016/j.medengphy.2018.09.004
