Joint pain: more to it than just structural damage?
Osteoarthritis is the most frequent musculoskeletal diagnosis in the elderly population and hence the most common cause of disability,67 with 40% of females and 25% of males aged 60 to 70 years diagnosed with OA.91 With the expected global growth in the elderly population and a concomitant rise in stationary lifestyle choices, the incidence of OA is predicted to increase in the coming years, and hence, this review will mainly focus on OA as being representative of joint pain.
For the individual patient with joint pain (particularly OA), there is little relationship between the amount of tissue damage and the associated pain intensity,28,39,62 whereas this discordance is less evident on a population basis.17,52 Further, 30% to 50% of patients with severe OA-related joint damage are asymptomatic, whereas approximately 10% of patients with knee OA have moderate to severe knee pain but have normal X-rays.25,39 Furthermore, 10% to 20% of individuals with a regional pain problem subsequently develop widespread pain,13,61,80 particularly in musculoskeletal pain conditions.
Given the disconnection between the intensity of chronic pain and the severity of tissue damage (eg, joint degeneration as assessed by Kellgren and Lawrence score), health care professionals tend to underestimate the intensity of musculoskeletal pain as compared to patient-reported perception of the intensity of pain.75 Understanding the obvious discordance between joint pathology and pain and explaining how pain progresses over time are substantial research challenges.
Chronic pain, in general, and joint pain, in particular, have a significant impact on mortality90 and quality of life, which urgently calls for better, safer, and more effective conservative, pharmacological, and surgical management options.
The end-stage treatment for joint degeneration is surgery, and total joint arthroplasty is considered to be an effective way to improve function and reduce pain.23 By 2030, the incidence of total hip arthroplasty is projected to increase by approximately 200% and that of knee arthroplasty by 700%.51 Although most patients experience pain relief after joint replacement, about 20% of knee replacement patients and 10% of hip replacement patients develop chronic postoperative pain.19 Therefore, understanding the fundamentals of joint pain applies to both patients with joint pain and patients with continued pain after joint replacement, and this review will address both of those issues.