joint pain - Knees
The knee is a complex joint and pain can arise from many structures. Understanding this greatly aids in accurate diagnoses and effective treatment, and also explains why arthroscopy has limited utility
Is it really a surprise that arthroscopes don’t work for knee osteoarthritis?
In short, yes and no. Yes, because this really isn’t consistent with my experience of the procedure. As I am sure many of you have done, I have referred patients for knee scopes who have had good, even great, outcomes. Thus the BMJ’s recent review of arthroscopic surgery for knee pain doesn’t really ring true. On the other hand, no it really isn’t a surprise knee arthroscopes aren’t as effective as we thought for those with knee osteoarthritis. The reasons for this are to do with both anatomy and the multi-faceted nature of the pain experience (See Dan’s Approach to Pain).
Knee osteoarthritis is a whole joint disease, and as cartilage is aneural it is unlikely the primary pain driver. Surrounding synovium, ligaments, subchondral bone, periosteum and capsule are all richly innervated and likely sources of pain in osteoarthritis. Additionally, neural mechanisms driving peripheral and central sensitisation have been implicated in osteoarthritis, and clearly pain can also be modulated by social and psychological factors. To add to the complexity, an interesting study by of patients with osteoarthritis found that 32% had pain arising from an extraarticular or extra-synovial source.
These patients tended to have more diffuse pain, and be older, with higher grades of disease. A cross-sectional study3 , supported these findings, suggesting that 36% of patients with knee osteoarthritis had at least one “non-articular” source of pain. So if these studies are correct, and about 30% of patients with osteoarthritis have extra-articular sources of pain, this may go some way to explaining why knee arthroscopy on average is unsuccessful, and why 13% to 38% of patients still have pain 12 months post joint replacement. Clearly, knee pain in osteoarthritis is not simple, and we should stop thinking simply about it.
Anatomical position of the infrapatellar branch of the saphenous nerve