More than nine million people in the United States have symptomatic knee osteoarthritis (OA) [1], with pain being the primary reason patients seek care and the leading cause of disability from the disease [2,3]. Patients who present with OA are usually asked to describe their level of pain, often by referencing a numeric rating scale. However, a discrepancy between patients’ reports of their pain level and OA disease severity as assessed by radiographic studies has often been observed [4–6]. Therefore, it has been suggested that demographic and psychosocial factors may influence pain reports.

Factors that have been assessed for their possible relation to reports of OA-associated pain include age, sex, body mass index (BMI), race/ethnicity, substance abuse, and psychological variables such as depression, hopelessness, overall well-being, and social stress [4,7–10]. The results of such correlation studies have varied, however, and some factors that may affect pain-level reports have not been examined. With the goal of increasing understanding of determinants of pain reports in patients with knee OA, we conducted a retrospective study of the possible correlation between pain score and several demographic, psychosocial, disease, and treatment characteristics, as well as between pain score and the severity of OA as assessed radiologically with use of the Kellgren-Lawrence (KL) classification system [11]. In addition, because little research has been done on a possible link between patients’ reported pain levels and clinical decision making, we examined whether pain scores were correlated with a recommendation by the surgeon that the patient undergo surgical rather than nonoperative treatment of OA. Our hypothesis was that demographic, psychosocial, and overall health-status variables would correlate with patients’ reported levels of pain.

In a univariate analysis of a large, diverse cohort of patients with knee OA, we found that several psychosocial, sociodemographic, disease, and treatment variables were each significantly associated with higher reported knee-pain scores. A subsequent multivariate analysis showed a significant association between higher pain scores and Hispanic or Native American ethnicity, opioid agent prescription, and depression. There was no relation between pain score and KL grade, a discordance also observed in several earlier studies [4–6]. Many of the factors analyzed have not, to our knowledge, previously been correlated with pain score: Hispanic or Native American ethnicity, age, opioid prescription, fibromyalgia, illicit drug use, antidepressant prescription, alcohol use (inverse relation), gabapentinoid prescription, health-insurance status, smoking, previous knee injection, and recommendation for surgical versus nonoperative treatment of knee OA. It is important to note that although the results yielded statistical significance across multiple factors analyzed in this study, the factors with clinical significance, according to our stated criteria of a difference in pain score of at least two, are opioid prescriptions and illicit drug use.

Other research has examined a possible link between knee OA-associated pain and race/ethnicity. A study by Creamer et al. [4] included only black and white patients and noted that the former reported higher pain scores than the latter. Additionally, one of the few studies to include Hispanic patients with rheumatic disease found significantly poorer global estimates of participant health, compared with those made by physicians [13]. The diversity of our study cohort provided an opportunity to compare pain scores among four different racial/ethnic groups. Both our univariate and multivariate analyses found that Native American or Hispanic patients had significantly higher pain scores than white patients.

Studies of arthritis-associated pain in Native Americans are scarce; however, in an investigation by Kramer et al. [14] in which face-to-face interviews were conducted with fifty-six Native Americans living in an urban area, most interviewees commented on their cultural practice of minimizing pain complaints and reported that American Indians do not readily discuss pain. The Native Americans studied by Kramer et al. lived in an urban area, whereas many of our Native American patients live in rural areas and are of different tribes. There may be cultural variations among tribes regarding the pain experience or the reporting of pain in a setting in which few, if any, of the clinicians are Native American. Nevertheless, these studies do show the importance of clinician awareness of possible ethnic-group differences in reporting OA-pain experience.

The association between current opioid agent prescription and higher pain scores possibly stems from neuromodulation of pain sensitivity resulting from chronic opioid use [15,16]. It is possible that some of our patients with an opioid prescription reported greater pain as a manifestation of drug-seeking behavior whereas other patients may simply have higher baseline pain levels. However, the differences in pharmacodynamics, opioid-receptor interactions, and bioavailability of a particular opioid dose likely play an important role in sufficient pain relief. The use of a pain-assessment instrument that evaluates patients’ functional abilities, such as the Western Ontario and McMaster Universities Osteoarthritis Index [17], might be useful when pain assessment is unclear.

Our multivariate analysis also found a significant relation between higher pain scores and depression. Previous studies found that depression affects reported pain in patients with rheumatoid arthritis [18], and an influence of depression on pain severity in patients with OA has been suggested [6,19]. The higher reported pain scores might reflect pain catastrophizing, which is a tendency to focus on negative pain sensations, thereby exaggerating the pain experience and enhancing feelings of helplessness [20]. It was previously shown that depression can lead to increased pain through pain catastrophizing in patients with musculoskeletal conditions [21], and pain catastrophizing has been linked to higher pain scores in patients with OA [22]. Cognitive behavioral therapy or psychotherapy aimed at reducing catastrophizing in these patients and similar patients with fibromyalgia may produce better outcomes than pharmacologic therapy [23].

In agreement with earlier findings [7,8], the sex of the patient was not correlated with pain scores. Interestingly, although the prevalence of knee OA increases with age, pain scores were significantly higher in our study’s younger patients. Psychological factors such as depression may have influenced pain reports in these patients. Indeed, younger adults with OA have been shown to have higher rates of depression and depressive symptoms than older adults with the disease [24,25]. In addition, life stress and hypochondriasis, which are associated with higher pain scores, are more prevalent in younger people [10].

Obesity, a known risk factor for development of OA, has been linked to an increased severity of OA-related pain, although Somers et al. [26] found that BMI was not correlated with pain scale scores. Our results show that patients with higher BMIs were significantly more likely to have higher knee-pain scores. Clinicians counseling obese patients with OA-related knee pain should consider suggesting weight loss as possible treatment.

The association between higher pain scores and uninsured status is probably related to socioeconomic status because OA pain and symptomatic knee OA have been correlated with lower income levels [7] and the poverty rate in a community [27], respectively. In addition, “feeling helpless” has been found to constitute an important determinant of higher pain scores [8], and patients without health insurance may have an increased tendency to experience this feeling, perhaps accompanied by a feeling of disenfranchisement.

Our study had the usual limitations of a retrospective, observational investigation. In addition, there may have been interactions among the variables assessed that our study design could not identify. Some factors not examined, such as whether the patient was currently involved in a workers’ compensation evaluation, might have influenced pain-score reports. Additionally, our study had a small number of black patients, with a large percentage of Hispanic and Native American patients. This unique ethnic distribution, however, is a reflection of our state’s composite population. Finally, the pain-evaluation method that was used was a simple numeric rating scale. This assessment can be administered quickly, but it may not sufficiently characterize a patient’s pain experience.

Despite these limitations, our results indicate that psychosocial and sociodemographic factors significantly affect patients’ reports of their level of OA-related knee pain and that patients with OA do not constitute a homogenous group for which the same management approaches will suffice. Management should be tailored to the individual and characterized by more extensive patient education regarding the specific factors contributing to their pain, as well as discussion of appropriate expectations for pain-level. The usefulness of a pain assessment based primarily on a numeric pain score is of variable utility. Extensive reliance on such an assessment in clinical decision-making may be inappropriate, especially when invasive procedures are contemplated. With the limitations that come with the visual analog scale, clinicians could consider employing various self-reported and physical measures recommended by the Osteoarthritis Research Society International (OARSI) such as the Dallas Pain Questionnaire or the WOMAC Questionnaire. Ultimately, pain-treatment decisions should not be based primarily on KL grade but the entire patient presentation.

Although clinicians cannot modify some of the factors associated with higher pain scores in our study, they can increase their insight into the possible causes of an observed discrepancy between a patient’s clinical appearance with respect to comfort and his or her pain score and perhaps mitigate the influence of factors that can be changed. Clinicians who are aware of the psychosocial and sociodemographic characteristics that affect their patients’ reports of OA-related knee pain will thereby be able to provide more effective, patient-centered care.