Total knee arthroplasty (TKA) is an established modality to improve pain and functioning in patients with severe knee osteoarthritis (OA).12 Despite advances in surgical techniques, postoperative management strategies, and prostheses, a considerable number of patients still complain of discomfort after TKA; several studies found that up to 20% of patients report disappointing results after TKA although no major problems are present from the surgeon’s perspective.2345678

It is our anecdotal experience that a considerable proportion of patients have night pain and sleep disturbances after TKA. Several studies have shown an association between sleep deprivation and increased pain sensitivity.910111213 In one report, approximately 81% of patients with knee and hip OA experienced night pain.14 Gong et al.15 demonstrated that a good sleep quality group showed faster recovery than a control group in the early period after TKA. However, to the best of our knowledge, there are no studies on the prevalence of night pain and sleep disorders after TKA or on whether the presence of night pain affects outcomes even a year after TKA.

The nature of neuropathic pain in OA patients warranting TKA is another concern. The contribution of neuropathic natural pain in OA has been reported in previous studies.16171819 More than 20% of patients with knee or hip OA showed pain scores in the neuropathic range before total joint arthroplasty.2021 Whether the presence of neuropathic pain before surgery adversely affects the outcome after TKA surgery is controversial. A recent study reported that patients with high preoperative neuropathic pain scores had higher pain visual analogue scale (VAS) scores at 6 months postoperatively than those with low preoperative neuropathic pain scores.22 On the other hand, there are reports that preoperative neuropathic pain scores had no significant effect on postoperative pain VAS scores.2324

In addition, surgeons are concerned and anticipate poor postoperative outcomes for patients with depressive disorder or other psychiatric disorders. Whether depression adversely affects clinical outcomes after TKA is controversial. Some studies show that depression is one of the factors significantly related to negative outcomes.82526 Pérez-Prieto et al.27 revealed that patients with depression had poorer pain scores and clinical results before and after TKA than patients without depression. However, they showed that the net changes in clinical outcome scores were not significantly different and that patient satisfaction was similar.27 Rice et al.28 showed that depression was not a statistically significant variable of persistent postoperative pain predictors.

This prospective, longitudinal cohort study aimed to 1) document the prevalence of night pain, neuropathic pain, and depressive disorder in patients with advanced knee OA undergoing TKA and 2) determine whether the specific coexisting pain and/or disorder at the time of TKA adversely affected postoperative outcomes.

This study revealed a considerable prevalence of night pain, neuropathic pain, and depressive disorder in patients undergoing TKA and found that patients with these specific conditions reported poorer functional outcome scores and health-related quality of life (HRQOL) scores preoperatively. However, there was no difference in functional outcome scores and HRQOL scores after TKA between the groups with and without the preoperative coexisting conditions.

Night pain is the most common problem that patients complain of before and after TKA, and this problem has yet to be resolved. When night pain and the accompanying sleep disturbances improve after TKA is still unknown and controversial. In our study cohort, 71.6% of patients complained of night pain before TKA, which is well matched with the study of Sasaki et al.,31 in which 75% of patients with Kellgren-Lawrence grade 4 OA complained of night pain. Although sleep disturbances were not evaluated in our study, nearly half of the patients complained of night pain up to 3 months after surgery, and the results showed that most of these disturbances improved at 1 year after surgery. In addition, the severity of pain was reduced in patients who still had night pain after TKA. Previous studies did not directly assess night pain, but they reported that sleep disturbances were worse or not significantly different in the early postoperative period (4.7 ± 2.0 weeks or 6 weeks) but significantly improved in the late postoperative period (3, 6 or 10 months) compared with before surgery.323334 These results seem to be consistent with our results.

In a subgroup analysis, the preoperative functional outcome score was poorer in the night pain group than in the non-night pain group, but at 1 year after surgery, both the clinical outcome and quality of life score were not significantly different from those of the preoperative non-night pain group. These results are consistent with the report that TKA improves both pain and sleep quality.3435 Although there was also a paper that showed that poor sleep quality before surgery affects postoperative pain and functioning, it was shown that poor preoperative sleep quality had no significant correlation with the clinical outcome at 2 weeks or more after TKA surgery.36 Based on our results, we can inform patients who complain of night pain before and after surgery that night pain will decrease after 3 months and that such preoperative night pain will not worsen the long-term outcome. However, how to alleviate night pain after TKA has not yet been established. Gong et al.15 reported that postoperative administration of zolpidem reduced postoperative night pain and increased postoperative satisfaction; however, this study showed results only up to 2 weeks after surgery, so further studies are needed. Other studies have reported that gabapentin was effective in the treatment of insomnia in various medical conditions,3738 but further studies are needed to determine whether gabapentin is effective in relieving pain after orthopaedic surgery.

Neuropathic pain was seen in approximately 15% of patients before surgery, appeared in almost half of patients at 6 weeks and 3 months after surgery, and decreased to a level similar to that before surgery at 1 year after surgery. In our study cohort, all patients with preoperative neuropathic pain were female. A higher rate of neuropathic pain in women than in men has already been reported.20 In addition, it is thought that this result in our cohort was due to the proportion of men being significantly small. However, the percentage of patients with neuropathic pain is lower than that reported in a systematic review (by approximately 23%) that evaluated the prevalence of neuropathic pain in patients with knee and hip OA.212224 The cause of these results is the difference in the questionnaire used to evaluate neuropathic pain, and there may be demographic differences in the study group. In particular, our cohort was composed of patients who decided on TKA, and patients with severe pain of neuropathic nature may have been excluded from the decision-making process to undergo TKA. From 6 weeks to 3 months after surgery, it is thought that the number of patients with high DN4 scores increased due to symptoms such as tingling, pins and needles, surgical wound itching, and the numbness of the lateral side of the knee. When surgical wound recovery was complete, DN4 scores seemed to return to the previous level.

In one study, patients with neuropathic pain were reported to have worse postoperative results,22 but our study adds strength to the evidence that patients with preoperative neuropathic pain do not show poorer results after TKA.2324 Many studies have reported that preoperative central sensitization or widespread pain sensitization is associated with chronic pain or dissatisfaction after TKA.223940 However, it is thought that it is difficult to conclude that a person has sensitization to pain simply by showing pain of a neuropathic nature, especially when using DN4, which does not evaluate the severity of neuropathic nature pain.

The prevalence of depressive disorder before TKA was 16.9% and decreased to 9.5% at 1 year after TKA. The prevalence of depression before TKA surgery differs from study to study, ranging from 10% to 27.9%.262741424344 This difference is thought to be due to differences in the demographic characteristics of the study groups and in the tools used to evaluate depression. However, in several studies, similar to the results of our study, depression tended to improve after TKA surgery, although not completely.26414445 Therefore, it is thought that the pain and dysfunction caused by knee OA act as causes of depression. Therefore, in some patients with depression before surgery, knee pain and dysfunction as well as depression may be improved through TKA.

A number of papers have suggested that pre- and postoperative functional outcome scores and HRQOL scores are poorer in patients with preoperative depression than in those without depression.2527424647 However, some papers report that the net change in the outcome improvement itself is no different between the groups with and without depression274148 and that there is no difference in satisfaction.262743 In addition, some studies have reported that depression is not included as a predictor of persistent postoperative pain or poor outcome.2849 Among the results of our study, the poor preoperative functional outcome scores and HRQOL scores in the group with preoperative depression were consistent with those in previous reports. However, there was no significant difference in functional outcome scores and HRQOL scores in the groups with and without preoperative depression 1 year after TKA. This result differs from those of previous papers in that the net change in the outcome score was larger in the group with depression. These results may be due to drug administration, such as SNRIs, or active cooperative treatment with psychiatrists in patients with depression. However, in a recent study, there was no difference in postoperative outcomes between the treated group and the untreated group in patients with depression,42 so further studies are thought to be needed.

This study has several limitations. First, although the total sample size of our study was not small, the numbers of patients with preoperative neuropathic pain or depressive disorder were relatively small. However, the sample size was sufficient to reject the hypothesis that differences in clinical outcome scores at 1 year after TKA were maintained between subgroups. Second, the patient group was recruited from only a single institution in one country, and the proportion of women was overwhelmingly high. Third, DN4 was used as a tool to evaluate neuropathic pain, and central sensitization was not directly evaluated. In addition, the cut-off value for neuropathic pain was set at 3 points because only 8 patients had preoperative DN4 scores of 4 or more. Since there were few patients with very high DN4 scores in our cohort, additional studies on patients with neuropathic pain of various severities are needed. Fourth, because this study was not a randomized controlled trial, there is a limitation that all drugs taken by patients were not controlled equally. Appropriate medications were additionally administered according to the patient's complaint. Because this is what happens in real practice, full control over the drug was not considered necessary.

In conclusion, this study revealed a considerable prevalence of night pain, neuropathic pain, and depressive disorder in patients undergoing TKA and found that patients with these specific conditions reported poorer functional and quality of life scores preoperatively. However, such adverse effects disappeared at 1 year after TKA. The findings of our study suggest that TKA can provide satisfactory outcomes for patients with preoperative night pain, neuropathic pain, or depressive disorder, equivalent to those for patients without these conditions.