Based on the results it can be concluded that preoperative neuropathic-like symptoms could serve as an additive predictor for CPSP. In the total group, patients with preoperative neuropathic-like symptoms had over twice-higher odds of experiencing CPSP one year after arthroplasty. Separate analyses revealed that only hip patients with preoperative neuropathic-like symptoms had statistically significantly higher odds of experiencing CPSP, so results for the total group were probably explained by the hip patients in the study group. To our knowledge, our findings are unique with respect to using neuropathic-like symptoms in a multivariate model, i.e. looking at the additional value while adjusting for relevant known predictors for CPSP. The impact and importance of adjusting is clearly visible in the results of the hip group. In line with previous research [12, 35], the basic multivariate model showed initially that higher preoperative pain intensity was a strong significant predictor for CPSP, although this effect became non-significant when adding neuropathic-like symptoms to the model. This suggests that neuropathic-like symptoms (pain quality) are a different concept and a better predictor for CPSP than pain intensity. This can be explained by the fact that neuropathic-like symptoms are likely an expression of a central sensitized state that could still be present after arthroplasty, even in a situation where the peripheral articular nerves that induce sensitization were removed [23].
Available literature describing the association between preoperative neuropathic-like symptoms and CPSP is scarce. Only three studies in knee patients were available for comparison [24, 25, 37], which was hampered by the limited number of preoperative patients with neuropathic-like symptoms in one study [24], a shorter postoperative time period in two others [25, 37], and one study using a different neuropathic pain-screening tool [25]. Two out of the three studies found no correlation between preoperative neuropathic-like symptoms and postoperative CPSP [24, 25]. The third study [37] found little if any correlation between preoperative neuropathic-like symptoms and postoperative pain (r = 0.397). These results are in line with our non-significant adjusted ORs found in the knee group, which suggests no association between neuropathic-like symptoms and CPSP. Comparisons were even harder to make for the hip group. There was only one study available, and it was aimed solely at the early postoperative period (two days after THA), thus not at CPSP [38]. Still, the study did share our finding that preoperative neuropathic-like symptoms are associated with higher postoperative pain scores. Hence experiencing preoperative neuropathic-like symptoms seems only predictive for CPSP in hip patients and not in knee patients.
With respect to dissatisfaction, only one knee study reported that preoperative neuropathic-like symptoms were not predictive for dissatisfaction [24]. To our knowledge, no such studies have been conducted among hip patients. The reported knee study results seem to be in line with ours, as we found that preoperative neuropathic-like symptoms were not associated with dissatisfaction in the total group. Given that our analysis was restricted to the total group, future joint-specific research seems warranted.
As the odds for experiencing CPSP one year after surgery are relatively high, it could be suggested that orthopedic surgeons should screen OA patients and especially hip OA patients, more frequently on their pain phenotype. Especially considering the association between neuropathic-like symptoms, lower joint-specific function and quality of life [39]. Customized treatment for their predominant and/or accompanying pain phenotype (nociceptive vs. neuropathic) could lengthen the conservative treatment phase, postponing or even aborting an arthroplasty. Furthermore, in case of an arthroplasty, treating neuropathic-like symptoms preoperatively could lower a patient’s odds of experiencing CPSP. Further research into the effectiveness of these treatments is warranted.
Strengths of this study include a generous sample size, a prospective longitudinal design up to one year postoperatively, and its aim to investigate whether neuropathic-like symptoms – next to known predictors – are an additive predictor for CPSP and dissatisfaction. As hip studies are lacking, this study is the first to elucidate an association between preoperative neuropathic-like symptoms and CPSP. Another strength is that we used the OKS/OHS, which next to the Western Ontario and McMaster Universities Arthritis Index (WOMAC) is the recommended multi-item questionnaire to capture CPSP [40]. Despite the sample size, there was a limited number of cases of moderate-to-severe pain on the OKS/OHS, especially for the hip group, which made it possible to adjust for only a few variables. The limited number of cases also hampered the joint-specific analyses to predict dissatisfaction. As a result, multivariate logistic regression modelling was only possible for the total group. Another limitation of our study could be that we did not include some important potential predictors, like comorbidities and psychological factors. For instance, pain catastrophizing seems to be a significant predictor for CPSP in knee patients [12]. Future studies with bigger sample sizes would be beneficial, as they can deal with more preoperative predictors. Larger studies will also help conduct the needed joint-specific analyses for dissatisfaction after arthroplasty.