“Doc, I Just Want My Life Back…”: Total Knee Arthroplasty and Its Effects on Chronic Bodily Pain

Commentary From my perspective, few patient statements can elicit quite the visceral and often shuddered response as that of “Doc, I just want my life back….” Like many of my colleagues, I frequently hear this at least once per day. Typically uttered at the closing moments of consultation (often while exiting the room), much of the enthusiasm I may have had for a predictable outcome can be abruptly drained by this seemingly innocuous, yet frequently unnerving, sentiment. I say this of course somewhat facetiously, but there is some truth in every statement, and almost certainly in this circumstance there is an authentic reason for hesitation and pause. Our orthopaedic training was designed to prepare us to repair, rebuild, and reconstruct; nowhere within this scope of practice do I recall being expected to seemingly “make anew.” By most objective standards, total knee arthroplasty (TKA) represents an extraordinarily successful operation, with high degrees of satisfaction and low complication rates1. However, the measurement of patient satisfaction is a highly complex variable that is often poorly defined and imperfectly measured2. The metrics used for patient-reported outcomes (PROs) are largely subjective, and, by design, are susceptible to bias and influenced by expectation. Although the shift toward PROs in reporting is essential, factors such as socioeconomic status and access to care, opioid-use disorders, pain catastrophizing, and several others have been shown to influence satisfaction3. As such, despite technological improvements, efforts toward patient optimization, and perioperative care pathway development, the rate of patient dissatisfaction after TKA as reported in the literature has remained substantial at 10% to 20%4. Riddle and Dumenci attempt to address one of the potential causes of patient dissatisfaction after TKA: chronic widespread bodily pain. More precisely, the authors evaluated preexisting pain in multiple areas of the body other than the surgical knee and determined how the outcome of ipsilateral total knee arthroplasty affected pain in these areas. The authors analyzed prospectively obtained data from 367 patients undergoing primary TKA at 5 U.S. institutions. They hypothesized that a reduction in knee pain would be associated with a reduction in pain in other regions (whole body, ipsilateral limb, contralateral limb, and lower back). The authors used a latent change statistical model, which has been shown to approximate causal inference regarding variables in observational studies. Their findings suggest that an improvement in knee WOMAC (Western Ontario and McMasters Universities Osteoarthritis Index) pain scores is positively associated with a reduction in whole body pain, ipsilateral limb pain (by the greatest factor), and contralateral limb pain. Lower back pain had the lowest overall reduction. The authors suggest that a causal link may exist between a reduction in knee pain and a reduction in pain in other bodily regions, and in fact they assert that the relationship may be directly physiological (in keeping with the findings of similar studies5), rather than predominantly compensatory or indirect. Several clinically relevant ideas and points may be gleaned from this interesting article. Nociplastic pain sources (pain centralization syndromes) are distinct from nociceptive or neurogenic pain sources and remain poorly elucidated phenomena (but ones that appear to be increasing in incidence)6. It should be of concern (but not likely a surprise) that 43% of patients included in this study reported chronic widespread pain. The postulation that a physiological relationship between joint pain (in this case) and heightened or even causative somatic pain elsewhere is a fascinating concept that has not been extensively investigated. Resilience and fragility are likely constitutional traits that may influence this phenomenon, although societal trends and “comfort creep” as described by the author Michael Easter appear to be symptomatic of a modernized civilization7. The results of this study provide encouragement that certain aspects of chronic bodily pain in patients may improve after TKA and offer some guidance for making these predictions. However, we should remain cautious and emphasize to our patients that improvement does not equate to cure and that persistent pain unfortunately remains common (as also demonstrated by this study). Finally, this study further emphasizes that metrics of performance and value after TKA should be evaluated through the lens of increasingly complex patients with evolving expectations.

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