Traumatic injuries are common in the United States. In 2004, about 29.6 million people were treated for an injury in US hospital emergency departments and nearly 2 million injuries were severe enough to require hospitalization.1 Individuals who have suffered traumatic injury experience pain associated with the injury. The likelihood that patients with this acute injury-related pain will suffer chronic pain is relatively unknown in the trauma population.2–6 Chronic pain is often a common and persistent problem in the general population with relatively high incidence and low recovery rates.7 More specifically, chronic pain is being increasingly reported in patients who have suffered traumatic injuries. The risk for the development of chronic pain can potentially affect 30 million trauma victims each year.8 Chronic pain after physical trauma is a public health concern that affects patients far beyond the expected recovery period. The prevalence of chronic pain after a traumatic injury has been reported as low as 8% to 10% and as high as 64%.2–5 The variable rates of chronic pain make it unclear how prevalent chronic pain truly is among traumatically injured patients. One of the methodologic concerns is the variable time point after injury used for determination of chronic pain, defined as pain that lasts for more than 3 months. According to Holmes et al,9 75% of patients report pain 12 months after serious injury, and 1 in 6 will fulfill the criteria for chronic pain at 12 months. Given the definition of chronic pain, it is important to determine the incidence at a time period prior to 12 months after injury to develop interventions to address this significant problem for the trauma population.
Many of the previous studies investigating chronic pain after traumatic injury have had methodologic flaws that make it difficult to generalize the results. Much of the past research regarding chronic pain has been retrospective.10–14 Retrospective studies have difficulty controlling confounding variables and other bias that may affect the results. In addition, looking retrospectively at the history of a trauma is not a reliable way to determine the incidence of chronic pain. One major fault of retrospective studies is that they rely profoundly on the memory of the research participants rather than scientifically recorded data. Historically, it has been recognized that a person's recall memory about a traumatic incident is typically very poor.15–17 This potential bias brings into question the validity of retrospective studies in chronic pain research.
Moreover, Rivara et al5 started their data collection at 3 months posttrauma and Holmes et al9 limited chronic pain to pain above a severity level of 5. On the basis of the definition of chronic pain, an accurate recording of the incidence of chronic pain cannot be achieved by studies that use an alternate description for chronic pain.18 Both the group of researchers identified chronic pain only if the pain severity was 5 or greater.5,9 The definition of chronic pain does not include a severity score in its determination of what constitutes chronic pain. Thus, the mere existence of pain that has persisted for 3 months or more, regardless of the severity, is classified as chronic pain.18 These inconsistent definitions do not accurately reflect the incidence of chronic pain.
People from different backgrounds and life experiences can be affected by physical trauma. Chronic pain is an important problem faced by health care providers because it affects the patients not only physically but also mentally. Chronic pain patients report decreased physical and social functioning, increased bodily pain, low vitality, low mental and general health status, and physical and emotional problems that affect quality of life.19Therefore, the entirety of the pain experience must be evaluated.
Most of the research regarding chronic pain in trauma patients is based on specific populations, such as single locations/body parts and single types of trauma. However, this limitation does not accurately portray the diversity that exists in traumatic injuries. Chronic pain has been found to occur following many types of trauma including neck sprains after motor vehicle crashes, unintentional falls, and spinal cord injury.20–22 Recent evidence suggests that the prevalence of pain after major trauma may be as high as 62% 1 year later and 44% 3 years later.4–5 Rivara et al5 also found that 62.7% of the trauma patients they evaluated had severe pain 12 months posttrauma and that having pain at 3 months posttrauma was predictive of both the presence and higher severity of pain at 12 months. Persistent pain has been recognized as a direct consequence of traumatic injury and chronic pain is either the result of or triggered by trauma.23–26
This study was a prospective longitudinal evaluation of chronic pain at 4 months, just beyond the time intervals established by the definition of chronic pain, to capture established chronic pain. This study began collecting data at the time of hospitalization for the traumatic injury and again at 4 months. In our study, chronic pain is defined as pain that persists more than 3 months.18 This study used the time interval of more than 3 months to classify pain as chronic pain and used the pain severity score greater than zero, rather than use the numerical pain score (NPS) limit of 5 to determine chronic pain. This study also included a heterogeneous sample of community trauma patients who received care at a level 1 trauma center.
Therefore, the purpose of this study was to (1) report the incidence of chronic pain at 4 months in trauma patients and (2) investigate the affect that chronic pain has on a trauma patients' life interference. We hypothesized that there would be a high incidence of chronic pain, more than 60%, and that higher chronic pain severity leads to higher life interference.
The incidence of chronic pain at 4 months posttraumatic injury was evaluated in this study within a population of injured hospitalized trauma patients. Participants were screened from the trauma registry and recruited from the Trauma Surgery Inpatient Service upon their admission to a 500-bed Midwestern level 1 trauma center. The sample of patients consisted of all patients admitted during a 6-month period in 2010. Subjects were evaluated to determine their eligibility for this study. Criteria for inclusion in this study were admission to the Trauma Surgery Inpatient Service for at least 48 hours. Those who were alert were invited to participate in the study. Exclusion criteria were admission of less than 48 hours, Glasgow coma score of less than 15 by 48 hours after admission, age less than 18 years, and a current diagnosis of chronic pain that was present at the time of the interview as determined by the participant. From the trauma registry 1138 patients were evaluated at this level 1 trauma center and out of those patients, 235 met inclusion and exclusion criteria. Of those who were screened, 225 participants consented to the study. Only 10 patients who were approached for participation refused to consent. No reasons were solicited for their refusal to participate.
Of the 225 participants who participated in the initial phase of the study, 101 completed the follow-up questionnaire at 4 months, for a participation rate of 44.9%. Reasons for nonparticipation included participants who were unreachable by phone or mail and those who did not mail back the questionnaire. Two participants who were reached by telephone declined to complete further interviews after completing the initial one. Only 1 researcher completed all of the interviews.
Informed consent was obtained from participants during their stay in the hospital. Each participant was interviewed with the same process using a questionnaire. At the initial interview during hospitalization, the participants were given patient identifiers and their personal information was added to a confidential list that was kept separate from the interview documentation. The interview questions were read to the participant and the answers were recorded by the researcher. A copy of the interview questions was offered to the participants during the interview for them to read along. Once the interview was complete, the remainder of the information was gathered from the chart review. If the interview was interrupted, it was resumed at a later time within 2 days that was convenient to both the participant and the researcher. At 4 months posthospitalization, participants were contacted via telephone, and if the participant was available, the questionnaire was completed at this time. If the participant was unavailable, a message was left, if possible, and the questionnaire was mailed out to the participant's home. Contact began within 1 week before or after 4 months from the date of initial injury.
A yes or no question, “Do you have pain now that is related to your traumatic injury 4 months ago” was posed to determine the incidence of chronic pain. If the participants answered yes to the question, they completed the Brief Pain Inventory (BPI-SF). The BPI-SF is an instrument that measures pain's intensity and its interference with daily life using an 11-point scale. The NPS with a range of 0 (no pain) to 10 (pain as bad as you can imagine) was used in this study to measure chronic pain. First, if participants reported a score of 1 or more at the 4-month follow-up, they were recorded as having chronic pain. Therefore, the presence of pain, regardless of the pain severity, was used to determine the incidence of chronic pain in our trauma patients at 4 months. Chronic pain is usually defined as lasting 3 months or more.27 The pain score was further broken down into 3 categories: mild, moderate, and severe. Pain scores falling between 0 and 3 were categorized as mild pain, scores in the range of 4 to 6 were categorized as moderate, and scores in the range of 7 to 10 were categorized as severe.28 The BPI-SF was used to analyze the extent to which chronic pain interferes with life. The BPI-SF is a chronic pain assessment tool used in research. The BPI-SF was originally developed to obtain data about the prevalence and severity of pain in the general population and has been used to evaluate chronic pain management as well as to determine the severity of pain by its interference with mood, sleep, and activities of cancer patients.29–31 In the questionnaire, the question, “Fill in the circle that describes how, during the past 24 hours, pain has interfered with your:” covering 7 areas—general activity, mood, walking ability, normal work, relations with other people, sleep, and enjoyment of life—was posed to determine the extent to which pain interfered with life. The 7 areas were independently scored on a scale of 0, does not interfere, to 10, completely interferes.
Descriptive Statistics of Study Participants
Demographic variables were analyzed to determine whether there were significant differences between several groups. First, the entire population of trauma patients that was evaluated at the trauma center between May 4, 2010, and November 5, 2010, and the sample population of the subjects that participated in the study during that same time were compared. The groups were compared on the basis of age, gender, ethnicity/race, insurance status, and mechanism of injury. Age was entered as a continuous variable in this analysis and a t test statistic was used. The rest of the variables are categorical and are reported as a χ2 statistic. The groups were statistically different in respect to all of the demographics analyzed except ethnicity/race. The study participants were younger (mean age, 43.50 vs 47.71 years), and more likely to be male (75.4% vs 69.2%), to be black (26.8% vs 22.3%), to be involved in motor vehicle collisions (27.3% vs 18.1%), to have sustained gunshot wounds (12.3% vs 9.5%), to have been stabbed (10% vs 4.9%), and to be involved in a motorcycle collisions (19.1% vs 11.9%) than the trauma registry population. The study participants were less likely to be white (65.2% vs 69.3%), to be insured (72.9% vs 78.7%), and to have sustained a fall (17.3% vs 32.4%) than the trauma registry population (Table 1).
Next, the study participants initially enrolled and those who completed the 4-month evaluation were compared to determine whether those who participated at 4 months were representative of the initial group. There was a 55% dropout rate between the initial interview and the 4-month interview. Each of these groups was compared on the basis of age, gender, ethnicity/race, insurance status, and mechanism of injury, using χ2 analysis. Age was entered as a continuous variable in this analysis and the statistic used was a t test not χ2. The rest of the variables are categorical and are reported as a χ2 statistic. The groups were statistically different in respect to ethnicity/race and insurance status. However, there was no significant difference between the 2 groups with respect to age, gender, and mechanism of injury. The group that responded at 4 months was more likely to be older (mean age, 49.19 vs 38.69 years), white (79% vs 54%), and insured (80.2% vs 66.9%). The 4-month group was less likely to be black (17.8% vs 33.9%) or “other” ethnicities (3% vs 12.1%) as compared with the initial interviewees (Table 2).
Descriptive statistics were used to assess the incidence of chronic pain in trauma patients at 4 months. A 1-way between-groups analysis of variance was conducted to explore the impact of the severity of chronic pain on life interference. The relationship between severity of chronic pain and life interference was analyzed by using Pearson correlation to evaluate the strength of relationship between chronic pain and life interference.
Of the 225 initial participants, 101 responded at 4 months. The incidence of chronic pain was 79.2%. Of the 80 participants reporting chronic pain, 46 (57%) had mild pain, 19 (23%) had moderate pain, and 15 (20%) had severe pain. An important note is that 6 participants reported an average pain score of 0. These participants were categorized as mild pain because chronic pain is not defined by pain severity score and it can be intermittent.
Of those who had chronic pain at 4 months, life interference was evaluated by the BPI-SF. Seven aspects of life interference were measured on a 0 to 10 scale similar to the NPS. Those scores were averaged to get a life interference score. Sixty-six participants had some life interference because of their pain.
A 1-way between-groups analysis of variance was conducted to explore the impact of the severity of chronic pain on life interference, as measured by the BPI-SF on life interference scores. Pain category was the independent variable and participants were divided into 3 categories according to their pain severity score (mild: 0–2; moderate: 4–6; severe: 7–10). Life interference was the dependent variable and was divided into 4 categories similar to the pain severity score categories (mild: 0–2; moderate: 4–6; severe: 7–10) (Table 3).
There was a statistically significance difference in interference scores for the 3 severity groups: F(3,73) = 35.7, P < .001. The actual difference in mean scores between groups was quite large. The effect size, calculated using η2, was 0.3. Post hoc comparisons using the Scheffe test indicated that the mean score for life interference was lower for those with mild pain severity (mean = 2.28, SD = 2.38) compared with those with moderate (mean = 4.16, SD = 2.21) and severe pain severity and lower for those with moderate pain as compared with severe pain. The relationship between severity of chronic pain and life interference was analyzed using Pearson correlation to evaluate the strength of relationship between chronic pain and life interference which showed a strong significant positive correlation (n = 80, r = 0.79, P < .001). Of note, those who had chronic pain, 50.9% of participants were using narcotic pain medication.
The goal of this study was to prospectively determine the incidence of chronic pain in trauma patients at 4 months, and to determine the effect that chronic pain has on life interference.18 Using a definition of chronic pain that includes length of pain experience and absolute existence of pain, this study found that the incidence of chronic pain was present in 79.2% of trauma patients 4 months after their trauma. This finding was higher than the findings of other studies, which reported incidence rates for traumatically injured patients varying as low as 8% to 10% to as high as 44% to 64%.2–5 An explanation for the difference between this study and past research could be explained through the types of assessments implemented, participant selection, and the definition of chronic pain used. This information could be useful for health care providers in all areas of trauma care. This opens up the discussion for possible solutions to help reduce the incidence of chronic pain. Possible solutions could be more aggressive pain management and/or different treatment programs. Knowing the incidence of chronic pain can lead to implementing changes in nursing policy to include chronic pain screening in follow-up assessments. Policy changes could include not just measuring the presence or absence of pain but rather the severity of pain reported by a patient. All patients with persistent pain need to be continually evaluated.
This study also found that a strong positive correlation existed between chronic pain severity and the effect it has on quality of life after traumatic injury. The correlation suggests that the more severe the chronic pain one has, the more that it interferes with one's life. This interference can be either physical limitations or perceived limitations. Although this study does not prove causation for life interference, it does provide insight into some common problems that trauma patients experience posttrauma and provide areas where more aggressive pain management can be emphasized.
The portion of the questionnaire used during the interview to measure life interference consisted of a variety of daily life activities. The construct measured by life interference included the physical activities of general activity, walking ability, normal work, and sleep and the nonphysical activities of mood, relations with other people, and enjoyment of life. These activities encompassed the different aspects of a person's life that many people take for granted and, ultimately, activities that are commonly affected by chronic pain. Yet, collectively these factors constitute a person's quality of life. Another related construct is external locus of control. People who suffer from a higher severity of chronic pain believe that the pain is out of their control after months of possible ineffective treatment. This could result in a decrease in a person's physical activity level. This would show in our study as increase in perceived life interference caused by chronic pain. Further research needs to be done to investigate the affect that an external locus of control has on the life interference experience by people with a high severity of chronic pain.
This study is limited by the number of participants who completed the study. Because of the low number of participants and differently represented groups, the results of this study cannot be generalized to the broad trauma population. Another limitation is the number of participants who dropped out during the course of the study. These subjects could have self-selected either because they had pain or because they did not have chronic pain. There was no way to identify the reasons for those who did not participate at 4 months. A third limitation is that both of the variables, incidence of chronic pain and life interference, were based on a participant self-report mechanism. On the basis of this there is no method to verify whether or not the participants' answers were fully accurate. However, there were no benefits for the participants to record inaccurate answers either way, so their answers were not influenced by the researchers. The participants' self-reported answers can be safely assumed to be valid on the basis of our analysis.
The incidence of chronic pain 4 months posttrauma was quite high among the respondents in this study and there was a strong positive correlation between pain severity and life interference. Awareness of the high incidence of chronic pain reported 4 months after a traumatic injury may help practitioners identify the development of chronic pain in trauma patients. This study also brings to light the need for better practices by all health care providers involved with a trauma patient's rehabilitation program to reduce the amount of life interference that patients experience posttrauma. This study opens up the discussion and emphasizes the need for future investigation into the effect that chronic pain has on life interference and how this life interference can be reduced.
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