Patient factors are commonly more accurate predictors of outcomes of total joint arthroplasty than are a specific surgical technique or implant1-4. Older age1,5-8, female sex6,7,9-11, high body mass index6,12-17, limited education18, low income19-21, medical comorbidities8,22, and a minority race/ethnicity9,23 are all demographic patient factors that have been associated with poorer patient-perceived outcomes following total joint arthroplasty. With the rapidly increasing economic burden of total knee arthroplasty24, patient selection for this elective surgery has gained importance.
Independently, low socioeconomic status or psychopathological distress has been negatively associated with orthopaedic and non-orthopaedic patient outcomes25-31. A link between low socioeconomic status and psychopathology and general health has been established32-34. A low socioeconomic status, or perceived low social state, in combination with a negative psychological state can have a combined effect on general health and overall mortality34,35. A higher prevalence of psychopathology is also seen in the low socioeconomic class33,36. Whether psychological stress influences or is influenced by socioeconomic state is still debated37.
Little is known regarding the prevalence of psychopathology in the indigent population undergoing total knee arthroplasty and its effect on functional outcomes. The purposes of this study were to (1) identify patients with Axis-I psychological diagnoses (somatization, depression, anxiety, and panic) in an indigent population undergoing total knee arthroplasty and (2) analyze the effects of psychopathology on the functional outcome of the total knee arthroplasty. We aimed to determine whether patients with psychopathology who have undergone total knee arthroplasty improve at the same rate as patients without psychopathology. Our hypothesis was that there is a high prevalence of Axis-I psychopathology in the indigent population undergoing a total knee arthroplasty and that there is a significant difference in the rate of improvement at one year between patients with psychopathology and those without psychopathology.
Patient Cohort
Consecutive patients undergoing total knee arthroplasty from July 2006 to January 2010 who satisfied the inclusion/exclusion criteria and agreed to participate were recruited to enroll in this institutional review board-approved prospective cohort study. These participants were treated at a county public facility where all local county residents, regardless of income or health coverage, are eligible for full medical, including orthopaedic, care. Patients received identical treatment regardless of their socioeconomic status, psychopathology, or whether they chose to enroll in the study.
All patients with severe end-stage arthritis (osteoarthritis, rheumatoid arthritis, or posttraumatic arthritis), literacy in English or Spanish, and a self-reported household income of less than 25,000 U.S. dollars (indicating an indigent economic status) were included in the study. No patients were excluded on the basis of sex, previous nonoperative therapy, comorbidities, race/ethnicity, previous psychological diagnosis, or concurrent treatment with antidepressants or anxiolytics. Patients who had had a prior total knee arthroplasty or who were incapable of completing the study questionnaires were excluded.
The criterion for indigence was based on the definition of poverty provided by the 2008 U.S. Department of Health & Human Services Poverty Guidelines38. Although poverty is typically based on the number of persons in the household, this was not included in our criteria for indigence. An income level of less than 25,000 U.S. dollars was chosen as a reasonable definition of an individual with insufficient funds to support his or her own health care and in need of financial assistance. Proof of income in the form of a tax return or an income stub was not required for the purposes of this study. Participants were not defined as indigent on the basis of their medical insurance status. Most had either Medicare/Medicaid or the county HealthPlus program, a means-tested payment program for any local county resident who is treated at the county hospital. To be eligible for the HealthPlus program, a patient must provide unemployment documentation or proof of income.
Of five hundred and eighty patients who underwent a total knee arthroplasty during the study period at the county public facility, 187 met the study criteria and agreed to participate in the study. Forty-three patients had a household income of more than 25,000 U.S. dollars and were excluded. Twenty patients, who were originally included in the study, were removed because of invalid preoperative patient health questionnaires. The remaining 330 patients either chose not to participate in the study or were excluded because of language or literacy barriers.
Outcome Measures
Patients were asked to complete an outcome-measure packet preoperatively (within three weeks prior to their scheduled total knee arthroplasty) and at twelve months postoperatively. The outcome-measure packet included a demographics questionnaire, the Short Form-36 Health Inventory (SF-36)39,40, the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC)41, the Knee Society Score (KSS)42, the Pain Disability Questionnaire (PDQ)43,44, and the Patient Health Questionnaire (PHQ)45,46. No financial incentive was provided to the patients. The research coordinator was available to answer questions regarding the surveys. Assistance was not given for interpretation or completion of any portion of the questionnaires. Spanish versions of the questionnaires were either validated translations or translated by a certified translator.
Demographic data collected included age, sex, weight, height, medical comorbidities, ethnicity, primary language, insurance, income level, and highest level of education achieved. Body mass index was calculated on the basis of the weight and height data. Patients were also asked whether they were currently taking any psychotropic medications.
The standard SF-36 was administered to all patients. Norm-based values were used for the physical and mental component summary scores40. The raw data from the SF-36 were converted to a norm-based number with a range from 0 (low quality of life) to 100 (high quality of life). A norm-based conversion signifies that a score of 50 represents an average score for an American adult39.
The WOMAC was used as a validated disease-specific outcome measure for end-stage arthritis. The WOMAC specifically evaluates pain, stiffness, and function of the lower extremity. The KSS is both a subjective and an objective outcome measure that quantifies pain, function, and range of motion of the knee. The primary investigator or an experienced orthopaedic resident familiar with the KSS completed these surveys during the clinical evaluation of the patient preoperatively and at twelve months postoperatively.
The PDQ was used to measure each patient’s perceived level of disability. The PDQ is based on fifteen statements with an 11-point visual analog scale and is divided into functional and psychosocial components. The functional portion ranges from 0 to 90, while the psychosocial portion ranges from 0 to 60. Scores of 0 to 70 represent no or mild/moderate disability, those of 71 to 100 represent severe disability, and those of 101 to 150 represent extreme disability.
The PHQ was designed to complement the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) (SCID) diagnosis. The PHQ is a validated shortened assessment that identifies the presence of Axis-I clinical disorders without the need for an interview46. The questionnaire identifies specific psychological diagnoses, including somatization disorder, major depressive syndrome, other depressive syndrome, panic syndrome, and anxiety syndrome. It provides a more specific and accurate diagnosis than the mental component summary score of the SF-36. Axis-I disorders are defined as major psychopathological conditions.
Surgical Techniques
All patients underwent a standard total knee arthroplasty with cement. The senior surgeon (R.B.) performed all procedures. A standard midline medial parapatellar approach was used with the patient under general anesthesia. Either cruciate-retaining or cruciate-stabilizing components were used at the discretion of the surgeon. All patients were given intravenous antibiotics for twenty-four hours as well as chemical and mechanical prophylaxis against deep venous thrombosis. Patients began physical therapy on the first day following the procedure and then subsequently received therapy for two to four weeks at an inpatient or outpatient therapy center or at home. Once they were discharged from the hospital, each patient was evaluated at standard regular follow-up appointments. All medical and surgical complications were recorded.
Data Analysis
Univariate analyses, controlled for age and sex, were used to compare the patients identified as having psychopathology with those without psychopathology. Differences in quality of life, pain, function, and perceived disability were assessed with use of Pearson chi-square tests for categorical variables and analysis of covariance (ANCOVA) for continuous variables. The alpha level was set at 0.05, and a Holm-Bonferroni step-down method was utilized to correct for any potential Type-I errors. On the basis of the moderate effect size and an alpha of 0.05, a power analysis was conducted to determine adequate sample size. The achieved power for this study was calculated to be 0.84.
Source of Funding
There was no external source of funding for this study.
Of the 187 indigent patients enrolled in this study, 154 (82%) were available for the follow-up assessment at one year. Four patients dropped out of the study, and two moved out of the country and were not available for follow-up. The remaining twenty-seven patients were lost to follow-up. There was no difference in demographic or psychosocial data between those who were available for follow-up and those who were not. At the initial preoperative assessment, fifty-four patients (35%) had a psychological Axis-I disorder, including somatization disorder, major depressive disorder, other depressive disorder, panic disorder, or anxiety disorder (Table I). Nineteen patients (12%) had two or more Axis-I diagnoses. A chi-square analysis demonstrated that the indigent patients were 9.3 times more likely to have an Axis-I diagnosis than the non-indigent patients (chi-square = 12.861, p < 0.0001, 95% confidence interval [CI] = 2.1, 40.0).
The demographic data are presented in Table II. There were no significant differences between the patients with and those without psychopathology with regard to age, sex, ethnicity, education, or income level. More patients in the psychopathology group had Medicaid medical coverage (20% versus 5%), whereas more patients in the no-psychopathology group had Medicare medical coverage (35% versus 22%). Patients with psychopathology were 2.4 times more likely to be currently taking a prescription medication treating depression or anxiety preoperatively than were patients without psychopathology (chi-square = 5.321, p = 0.21, 95% CI = 1.1, 5.0).
The results of the analyses of the baseline, one-year, and change scores for the physical measures are shown in Table III. The psychopathology group differed significantly from the no-psychopathology group with regard to the baseline WOMAC pain, stiffness, and function subscale scores (p = 0.014, p = 0.005, p = 0.008, respectively). They also differed significantly with regard to the one-year pain subscale score (p = 0.004). No differences were found in the change scores for any of the WOMAC subscales or the total score. This indicates that patients in the psychopathology group improved at the same rate as those in the no-psychopathology group.
The KSS assessment did not show significant differences between groups with regard to the results of the physician’s evaluation or the self-report function scores at baseline. However, a difference was noted in the change scores for the self-report KSS functional assessment between baseline and the one-year follow-up visit (p = 0.005), indicating that the patients in the psychopathology group did not improve at the same rate as those in the no-psychopathology group.
The results of the evaluations of psychosocial measures are presented in Table IV. The SF-36 scores demonstrated no difference between the psychopathology and no-psychopathology groups with regard to the baseline, twelve-month, or change physical component summary scores. Both groups showed expected improvement in their physical component summary score, with a similar amount of improvement. The psychopathology group had significantly lower baseline and one-year mental component summary scores (38.5 and 44.1, respectively) as compared with the no-psychopathology group (51.1 and 52.2, respectively; p < 0.001).
The PDQ, which measures perceived psychosocial and functional disability, showed significant differences between the psychopathology and no-psychopathology groups with regard to the psychosocial subscale at both baseline and one year, with the psychopathology group reporting greater levels of perceived psychosocial disability. For the functional component of the PDQ, the change scores indicate that the two groups improved at the same rate. Interestingly, the psychopathology group actually showed more improvement in the psychosocial component of the PDQ compared with the no-psychopathology group. However, as a result of the nature of this assessment, there may have been “ceiling effects” with the one-year follow-up scores in the no-psychopathology group.
Three patients had deep vein thrombosis, and three patients had pulmonary embolism. In the psychopathology group, only one patient had a deep vein thrombus and none had a pulmonary embolism. Two patients without psychopathology returned to the operating room for knee manipulation under anesthesia to treat arthrofibrosis. While the rate of complications was very low, the sample size of this study does not allow proper comparisons between groups.
The results of this study parallel those in other studies in which self-report or non-validated psychological tests were used, as they show significant differences in patient-perceived outcomes following total knee arthroplasty between patients with psychological distress and those without it6,47-49. Numerous studies have shown that a lower socioeconomic status and psychopathology are both independently associated with poorer patient-perceived outcomes after elective surgery26-29,50-53, including hip or knee replacement surgery8,19,21,54. The reasons for poor outcomes following total joint arthroplasty in the indigent population are unclear. Some studies have suggested a disparity in access to health care55-57 or a lack of appropriate expectations58,59.
The indigent population has a high prevalence of psychopathology, typically anxiety or depression60,61. In the present study, 35% of the patients had at least one diagnosis of Axis-I psychopathology, and 26% had a depressive disorder. This contrasts with a reported annual prevalence of depression of 6.6% in the American adult population62. Depression and anxiety have both been associated with poor outcomes following a total hip or a total knee arthroplasty47-49,63-66. Authors of previous studies have used the mental component summary score of the SF-3647,48,67 or a self-report diagnosis of depression or anxiety to distinguish patients when evaluating outcomes following total joint arthroplasty6. Brander et al.65 used both the Beck Depression Index and the State Trait Anxiety Index to evaluate the effects of anxiety and depression on the results following total knee arthroplasty and found that preoperative pain and anxiety were associated with worse pain outcomes at one year postoperatively. These authors only assessed the degree of depression and anxiety symptoms rather than identifying an accurate diagnosis of Axis-I psychopathology. The PHQ allowed us to make such an assessment in our study.
Although the participants with psychopathology tended to have worse baseline and one-year postoperative scores for the physical measures according to the WOMAC, their change score or overall improvement was similar quantitatively to those in the group without psychopathology. This trend was also seen in the KSS, the PDQ, and the mental component summary score of the SF-36 (Fig. 1) as well as in a study by Lingard and Riddle47. The pain score of the WOMAC revealed the same improvement in both groups over a one-year period although the baseline and one-year scores indicated more pain in the psychopathology group. Increased pain following joint arthroplasty has been closely linked to psychopathology65,66,68,69.
Although previous authors47,48 have used either a mental health subscale or a mental component summary score of <50 to indicate psychological distress, in our study the mean mental component summary score for patients without psychopathology was 51 at baseline and 52 at one year postoperatively. These findings suggest that using the SF-36 mental component summary score may overestimate the number of patients with psychological distress or psychopathology in a given cohort. To our knowledge, this is the first study to use a validated tool to identify psychopathology in a cohort of participants undergoing a total joint arthroplasty.
Regardless of the patient’s socioeconomic background or evidence of psychopathology, a knee arthroplasty should ideally improve his or her health-related quality of life70,71. According to a study by Escobar et al., the minimal clinically important difference in the WOMAC score after a total knee arthroplasty in the general population are improvements of 22.87, 19.01, and 14.53 for pain, function, and stiffness, respectively, on a 0 to 100-point scale72. The data from our study showed the mean improvement to be 32.50, 34.40, and 36.25 in the cohort with psychopathology and 33.0, 32.06, and 26.25 in the cohort without psychopathology with regard to pain, function, and stiffness, respectively, when converted to a 0 to 100-point scale. This indicates that an indigent patient, with or without psychopathology, who has end-stage arthritis may expect to have a clinically important improvement after a total knee arthroplasty, assuming that the minimal clinically important difference in the indigent population is equal to that in the general population.
This study has limitations. Because the cohort included only patients with a lower socioeconomic status, non-indigent patient controls were not evaluated. Another limitation is the lack of long-term follow-up. Previous studies have demonstrated maximum improvements in the first six to twelve months after the procedure with a plateau of the SF-36 and WOMAC scores after one year47,67,73. Patient fatigue is another concern given the number of questionnaires administered at each study period. Another limitation is the use of the KSS as it introduces interobserver error for the objective portion of the questionnaire74,75. This error was minimized by ensuring that experienced surgeons collected these data. Finally, while all patients were evaluated for Axis-I psychopathological diagnoses at baseline, there was no analysis stratifying those being treated for depression or anxiety and those who were not. Additional studies should be performed to evaluate the effects of psychotropic medications on outcomes following total knee arthroplasty.
We affirmed our first hypothesis that there is a high prevalence of psychopathology in the indigent population. Overall, our second hypothesis was not affirmed as, in a majority of the outcome measures, there were no differences in improvement between patients with and those without psychopathology in the indigent population. While it appears that patients with psychopathology have a perception of worse functional level, greater pain, more stiffness, lesser quality of life, and more disability prior to arthroplasty and at one year postoperatively, their rates of improvement did not differ from those of patients with no psychopathology. We recommend that patients undergoing knee arthroplasty be routinely assessed for psychological distress prior to surgery and that the impact of any psychopathology on perceived outcome be discussed with the patient preoperatively.
Note: The authors thank Dr. Robert Gatchel for his advice and guidance during the design of this study. They also thank Rosa Ayala and the orthopaedic residents at the University of Texas Southwestern for participating in patient enrollment.