Bone on bone is one of the most common culprits of knee pain. Well, at least it is one of the most blamed causes of knee pain. Research challenges the belief that osteoarthritis is guaranteed to cause pain.
It is tough to say when a joint reaches the stage of ‘bone on bone’ but it occurs as osteoarthritis progresses. Bone is normally protected by a barrier known as cartilage. Osteoarthritis is the condition in which cartilage wears down.
A 2020 study shows knee osteoarthritis is present in nearly 23% of all individuals over the age of 40, globally.
Osteoarthritis is a normal symptom of aging, but there are strategies to delay its progress. Exercise and dietary strategies can be used to treat and delay the progress of osteoarthritis. While this can help protect the bones, pain is often the primary driver of treatment.
The question I want to answer is whether osteoarthritis causes pain.
Intact cartilage itself does not have nociceptors — nerve fibers that contribute to some pain sensations. However, with osteoarthritis, the loss of cartilage reveals an opportunity to reach areas with those nerve fibers.
This study examined the relationship between cartilage loss and worsening knee pain. They wanted to know whether the association of cartilage loss with worsening pain was influenced by worsening synovitis — inflammation in the joint — or change in bone marrow lesions (BMLs) — fluid in the bone marrow which are early indicators of osteoarthritis.
The study found cartilage thickness loss was associated with worsening knee pain. However, the relation between cartilage loss and worsening pain was, at best, modest.
A 0.1mm cartilage loss was associated with <1 point worsening on a 0–20 WOMAC pain scale. This suggests that preventing cartilage loss may not reduce pain in a knee with OA. Worsening synovitis may be an indicator of progressing knee pain, but BMLs are not.
On the surface, these results can be surprising. Other research suggests that synovitis and BMLs are sources of pain in OA. However, perhaps pain is not mostly triggered by cartilage loss.
Cartilage thickness loss is weakly associated with knee pain. The weakness causes us to question if cartilage-saving treatments for knee pain should be the primary focus of patients and healthcare providers.
Like most things in health, a narrow focus is often misguided. Instead, taking a multimodal approach — assessing diet, exercise, and mental health — will likely lead to better outcomes, especially when approaching the complex phenomenon of pain.