Chronic musculoskeletal pain, phantom sensation, phantom and stump pain in veterans with unilateral below-knee amputation

1 Introduction

Chronic pain is defined by the International Association for the Study of Pain as pain persisting over the healing phase of an injury [1]. The prevalence of chronic pain in the general population is estimated to be 20% [2] but the prevalence of pain in veterans may be different due to their special physical and mental characteristics [3]. One study reported the incidence of pain in veterans to be the following; 27% non-traumatic and traumatic joint pain, 25% back pain, 21% arthritis and 18% severe pain [4].

Bukit et al. stated that 64.5% of traumatic amputees experience mild to severe pain (61% stump, 58% phantom pain) weekly [5]. Low back pain in lower limb amputations has been reported to be much higher than in the general population [6], [7]. Overall, pain prevalence has been reported to be 50–80% in all amputees [8], [9], [10]. Many patients may complain about a combination of pains, but often one type of pain is more severe and can exert a lasting and direct effect on quality of life [11], [12], [13], [14].

The American Pain Society estimates that the costs of chronic pain care in the USA are 635 billion dollars a year which is higher than the total cost of heart disease, cancer, and diabetes combined in 2012 [15]. However, most costs are incurred indirectly. One study has shown that only 7% of the burden of lumbar pain costs is spent on treatment in the Netherlands [16]. Chronic pain reduces mobility and activity levels and increases depression, anxiety and sleep disorders, and may lead to isolation, loneliness, and disability. As a result, it may reduce the person’s occupational capabilities, impair family communication and impose a high cost on them [17], [18], [19], [20]. Therefore, it is necessary to implement improved therapies that will result in an enhanced quality of life.

There are about 5,000 veterans with unilateral below-knee amputations listed by the Iranian Veterans and Martyrs Affairs Foundation (VMAF). Improving our knowledge of the factors that contribute to the experience of chronic musculoskeletal pain in veterans with a unilateral below-knee amputation can lead to improved therapies. This study was designed to investigate various pain complaints in this population (phantom sensation, phantom pain, stump pain, upper extremity pain, lower extremity pain, and low back pain), and to identify possible relationships among different variables.

2 Methods

3 Results

Two hundred and forty-seven unilateral below knee amputees were investigated comprehensively. The age range of the participants was 22–82 years with a mean of 52.42±7.35 years. Land mine explosion was the most frequent cause of amputation in 64.8% of the participants (n=160). The average time elapsed since amputation was 29.76±6.19 years. Details obtained from the participants’ records are listed in Table 1.

97.9% (n=242) of the amputees used prosthetic devices. More details are presented in Table 2. 43.7% of the amputees (n=108) used walking aides outdoors and/or indoors.

Prevalence of pain in an upper limb was 23.0% (n=57). χ² test showed a statistically significant association between upper limb pain and walking aids usage in this group (p<0.001). The prevalence of pain in the lower extremity (both intact and amputated limbs) was 63.6% (n=157) and knee pain had the highest prevalence at 54.7% (n=135). The prevalence of pain in the lower extremity is given in Table 3. Low soft tissue coverage of the stump at 15.4% (n=38) and symptomatic osteoarthritis in the non-amputated lower extremity at 40.1% (n=99) had the highest prevalence according to the physician’s clinical assessment. The types and prevalence of complications are given in Table 3.

The prevalence of stump pain, phantom sensation and phantom pain was 84.2%, 77.3% and 73.7%, respectively. Table 4 shows the descriptive results for the variables. 47.5% of subjects with stump pain had at least one stump complication. Low back pain with a prevalence of 78.1% (n=193) was the most common pain condition in the study population. At the time of the assessment, the mean severity of low-back pain was 3.4±2.9 with a mean severity of “worst pain” of 7.5±2.5 and the mean degree of “bothersomeness” was 6.8±2.4. Only 9.8% of the participants had a history of low back pain before the amputation (n=19) and 7.2% (n=14) had a history of hospitalization, surgery or both due to lumbar conditions. 83.4% (n=175) of the amputees suffered from low back pain during the 12 weeks prior to evaluation and 26.9% (n=67) of the patients with low back pain had neuropathic symptoms.

χ² test showed a statistically significant correlation between stump and phantom pain and phantom sensation (p<0.001). ANOVA test showed no correlation between pain severity in the stump and the different types of stump complications (p>0.05). The results of logistic regression showed that there was no significant association between age and BMI with contra lateral knee pain (p>0.05). The mean BMI was 29.21±10.38 kg/m². Results showed that in amputees with phantom pain, the odds ratio of pain in the stump was 2.22 times higher than those who did not experience phantom pain [OR=2.22 (CI: 1.19–4.17); p=0.012]. The odds ratio for stump pain was increased by 13% per unit of increase in the intensity of low back pain [OR=1.13 (CI: 1.04–1.23); p=0.003] (Table 5). Also, stump pain was associated with low back pain, and the odds of low back pain in amputees with stump pain was 3.06 times higher than those without back pain [OR=3.06 (CI: 1.50–6.21); p=0.002]. Stump pain was not associated with stump complications (p>0.05). Walking or standing with a prosthesis was associated with low back pain and the odds of low back pain were decreased by 9% for 1 h per day of walking or standing with a prosthesis [OR=0.91 (CI: 0.83–0.99); p=0.039] (Table 5).

4 Discussion

Our findings revealed that a considerable proportion of the subjects suffered from musculoskeletal pains. The prevalence of stump pain, phantom sensation, phantom pain, low back pain, and knee pain was 84.2%, 77.3%, 73.7%, 78.1%, and 54.7%, respectively. The odds of stump pain in amputees with phantom pain were higher than those who did not experience this pain and the odds of low back pain were higher in amputees with stump pain.

In line with previous work, we found that more than 90% of the amputees wore their prostheses [26], [27], [28]. A large majority of the participants wore their prostheses seven days a week. Standing and walking time with the prosthesis was about 4 h. In the literature, several measures such as the number of walking steps [29] or the wearing duration time [28], [30], [31] have been applied to the prosthesis use. For this reason, it is difficult to compare our data with other studies. In the present study, the amputees wore their prostheses at least 2 h a day, most of them for 14 h a day, and walked more than 2 km a day with their prostheses. Most of them received a completely new prosthesis approximately every 10 years and had the present prosthesis for six years, on average. Smith et al. indicated that below knee amputees in their study were fitted with a new prosthesis every year. During the first 3 years, the mean number of prostheses acquired per patient was 3.4 and over the first 5 years was 4.4 Smith et al. [32] while Pezzin et al. documented that about 20% of individuals with lower limb amputation were fitted with a new prosthesis at least once a year [33]. The frequency of new prosthetic fitting in our sample is much lower than in previous studies which requires further investigation. In the current study, about 40% of the participants were found to have used at least one type of walking aid. Reffar et al. reported that 83% of amputees required a walking aid [34]. Our results indicated that walking with aids was related to the prevalence of the upper limb pain in these subjects. This indicates that a regular and more detailed examination of upper limb pain is necessary with the aim of preventing and treating upper limb symptoms in this population.

More than half of the subjects suffered from various pains in the lower extremity (both sound and amputated limbs). Knee pain had the highest prevalence and there was no significant association between age and the contralateral knee pain nor with BMI. Symptomatic osteoarthritis was found in more than one third of the veterans in accordance with previous studies that show that a unilateral below knee amputation has an increased risk of developing osteoarthritis in the intact limb. Mussman et al. stated that knee pain in the intact limb was the chief complaint of 55% of veterans with a mean age of 51 years and an average of having a prosthesis of 24 years [35]. Hungerford and Cockin found that 41% of veterans with transtibial amputation suffered from patellofemoral osteoarthritic degeneration in the intact limb [36], while Norvell et al. found that 16% of the below-knee amputees had symptoms of knee osteoarthritis as compared to 11% of a control group [37]. Hurley et al. showed that compensating movements increase stress and degenerative arthritis in the contralateral limb which could be the result of a poor prosthetic fit [38]. Burke et al. attributed gait asymmetry and an increased load on the intact limb to the higher prevalence of osteoarthritis (27% of the intact side knee) in long-term users of prosthetic devices [7]. Lloyd et al. stated similar results that asymmetry in unilateral below knee amputees was moderately related to osteoarthritis risk [39]. Therefore, rehabilitation teams must pay close attention to the prevention and treatment of complications in the intact lower limb.

Nearly half of those with stump pain had at least one complication in the stump. As shown in Table 3, our study was consistent with previous reports on trauma-related amputations. Some studies differ, however. Harris et al. reported neuroma (0.7%) and bony prominence (0.7%) 24 months after amputation [40]. Tintle et al. reported that revision amputation surgery was performed in the symptomatic residual limbs due to symptomatic heterotopic ossification (24%), neuroma (11%), and/or scar revision (8%) in a 23-month follow–up [41]. These studies assessed stump complications a relatively short time following amputation while we examined stump complications after 30 years which could reflect the continuity of stump problems. Our results showed stump complications could lead to pain but stump pain severity was not correlated with types of stump complications. These results may indicate that the etiology of stump pain is multifactorial although further studies need to be conducted to confirm this assumption.

The prevalence of phantom pain was high and our findings showed a relationship between stump pain, phantom pain and phantom sensation. According to one study, 78% of 2,750 veterans with amputation experienced phantom pain [42]. Among the veterans with above knee amputation, another study reported that 77% had phantom pain and 36.1% had stump pain [43]. Based on the results of a study where 914 individuals with upper or lower limb amputation were interviewed, 95% of them experienced pain after amputation (80% phantom pain and 70% stump pain) [8]. Though Nikolajsen et al. stated that persistent phantom pain decreases with time [44], our study revealed that the point prevalence is similar for all durations from amputation which is an indication that phantom pain does not decrease with time. In our study, this could be due to the lack of treatment for complications and for stump and prosthesis problems.

More than 80% of this sample experienced low back pain in the 12 weeks before the assessment (higher than stump and phantom pain). Despite the fact that a history of hospitalization or lumbar surgery was low, the mean severity of “worst” low back pain (NRS) was >7 and classified as severe. Smith and Ehde examined pain in unilateral lower limb amputation and found that 71% had low back pain which was more annoying than stump and phantom pain [45]. This is similar to our results. Kušljugić et al. who investigated chronic pain in civilians and war-related veterans with lower limb amputation reported 90% with chronic low back pain [46]. In the present study, only fewer than 10% of the participants had a history of back pain before the amputation and around 1/4 of them with low back pain had neuropathic symptoms. Biomechanical factors are hypothetically considered as a potential factor in developing low back pain in lower limb amputees [47], [48]. Biomechanical changes such as movement and muscular work asymmetries due to the dominance of the intact limb and weakness/atrophy of muscles on the amputated side could be responsible for the high prevalence of low back pain [47], [48]. Low back pain in amputees is an important challenge that should not be overlooked and further research is needed.

Our results also showed that the odds ratio of stump pain was increased in amputees with phantom pain compared with other participants. Similarly, the risk of developing low back pain in amputees with stump pain was higher as compared to their counterparts. Conversely, standing and walking with a prosthesis was associated with a reduced odds ratio of having low back pain. In the past, amputees’ pain was considered to have a psychological basis but nowadays, central and peripheral neurological changes are known to cause these types of pain [49]. Smith et al. confirmed the importance of the multidimensional view on the pain issue [45]. This finding is consistent with the neuroimaging studies which have revealed numerous structural and functional changes in the brains of people with chronic musculoskeletal pain [50], [51]. Also, converging evidence from animal and human studies indicates that chronic pain induces a dramatic anatomical and functional reorganization of brain structures and networks [52]. There is growing opinion that these changes may contribute to the development and maintenance of chronic pain [50], [51]. Because of the high prevalence of pain and its impact on medical care and quality of life, pain reduction is an important issue [53]. Therefore the pain experienced following amputation should be more extensively evaluated clinically in order to improve the functionality of the amputees [45] and to possibly prevent chronic pain and related rehabilitation problems in the population. This should be considered as a research priority.

5 Conclusions

This research enhances our understanding of musculoskeletal problems in below-knee amputees which can help health providers to identify rehabilitation needs and emphasizes the need to do regular assessments. In the long term, this knowledge will help to improve the quality of life and wellbeing of amputees.

6 Implications

The major implication of the present study is that special attention should be paid to the different aspects of pain and rehabilitation in veterans with unilateral below-knee amputation.