Pain doesn’t always behave the way we think it will. An intervention that relieves pain in the majority of patients might not provide relief for a significant minority. But that might mean we need to change the way we think about pain.
Many patients with knee osteoarthritis (OA) choose to undergo total knee arthroplasty (TKA) because they believe it will succeed where more conservative methods of pain management have failed. But the medical literature suggests that up to 25% of patients end up dissatisfied with the results of their TKA procedure. And multiple recent studies suggest that patients whose knee degeneration on x-rays (Kellgren-Lawrence, or KL score) is mild to moderate are up to three times as likely to be dissatisfied as those with greater radiographic severity—even when preoperative pain levels are similar.
That means something unrelated to the knee joint itself must be influencing pain in patients with less-severe KL scores before and after TKA. A new study, epublished in February by the Journal of Arthroplasty, suggests the prevalence of chronic nonorthopedic conditions might play a significant role. In that study, less severe KL scores were associated with higher levels of dissatisfaction than severe KL scores, and chronic nonorthopedic conditions—including depression and anxiety, fibromyalgia, low back pain, and traumatic brain injury and stroke—were more prevalent in the less severe group.
These findings are consistent with the concept of central sensitization, in which a patient’s sensitivity to pain is elevated even when there is no local explanation for it. Patellofemoral pain (PFP) researchers have been starting to explore this concept, which generated a great deal of discussion at their last research retreat (see “Conference coverage: 3rd PFP research retreat,” November 2013, page 19). More recently, investigators from the University of Kentucky in Lexington reported at the American Physical Therapy Association Combined Sections Meeting in February that individuals with PFP demonstrate lower pressure-pain thresholds than controls—not just at the knee, but also at the elbow.
What all of this means is that, if a patient’s lower extremity pain is not responding as expected to local interventions, it’s worth asking whether his or her local lower extremity pain might also have a central component, possibly related to one of the nonorthopedic conditions listed earlier. If so, the most effective intervention for that patient’s lower extremity pain might turn out to involve multiple clinical disciplines, and it might not involve the lower extremity at all. Better management of fibromyalgia symptoms, for example, might have a positive effect on knee OA symptoms in a patient who is struggling with both conditions.
There are still a lot of unknowns regarding the most effective methods of treating patients with central sensitization. But correctly identifying the problem brings practitioners one step closer to finding a solution. And finding a solution to the central sensitization aspects of a patient’s pain, particularly patients whose KL scores don’t match their knee OA symptoms, will go a long way toward improving clinical outcomes and patient satisfaction.