Parkinson's disease is one of the most common neurological disorders in a medical era of increasing life expectancy and an aging population, and TKA is one of the most common procedures for older people. TKA is a safe and effective surgical procedure that can relieve pain and improve the function of the affected limb. The improvement of QOL in the patient of KOA after TKA has been extensively and positively described in the literature[12–17]. However, there is no such study been conducted in KOA patients with PD. We conducted a controlled study to demonstrate that TKA can improve QOL in these particular patients. Our results demonstrated that EQ-5D, PDQ, and PHQ-9 were significantly improved in the control group, while PD patients only showed slightly improvement in QOL assessed by PDQ. Although preoperative QOL were similar, PD patients had significantly worse QOL on all three measures at LFU than the control group.
QOL in PD patients
Studies have described the effect of symptoms of PD on QOL. Kuopio et al.  used the 36-item Health Survey Summary Scale (SF-36) in a community-based sample to investigate the relationship between non-motor symptoms of PD and QOL, and concluded that depression was most closely related to QOL. Barone et al. subsequently conducted a large multicentric study to investigate the incidence of non-motor symptoms and their impact on QOL in patients with PD. Based on 39-item Parkinson's Disease Questionnaire (PDQ-39), apathy, fatigue, attention, memory and mental symptoms are all detrimental to QOL. Motor symptoms have also been shown to be detrimental to QOL in people with PD. Floden et al.  suggested that non-motor symptoms (such as depression) prior to DBS treatment of PD significantly affected the QOL outcomes measured by PDQ-39. There was no correlation between preoperative motor symptoms and QOL as measured by the Unified Parkinson's disease Rating Scale, Part III. Finally, Soh et al.  conducted a systematic review of health-related QOL in PD patients and determined that depression, disease severity, and disability were the most detrimental to the improvement of QOL.
QOL in PD patients after TKA
TKA has been recognized to improve QOL in patients with KOA. TKA can relieve pain and make patients feel satisfied, and even improve the quality of life of octogenarian patients to the level of septuagenarian patients. Szmyd J et al. also proved that TKA significantly reduced the pain intensity of patients and significantly improved the patient's ability to live daily. In a 2-year follow-up after TKA, DT Wei et al.  found that improvements in knee specific outcomes (KSS and OKS) were closely associated with improvements in health-related quality of life (SF-36). Although the number of PD patients with TKA is relatively small, favorable surgical outcomes with TKA in these patients have occasionally been reported. For example, Sun QC et al. used KSS score to illustrate that for PD patients, both knee function and range of motion were greatly improved after TKA, especially in pain. However, no studies have reported the improvement of QOL in PD patients after TKA. Montiel et al. questioned the improvement of QOL in PD patients after TKA, but did not draw a conclusion on whether QOL was improved or not. Therefore, we tried to further explain the improvement of QOL in PD patients with TKA.
In this study, the preoperative QOL of PD patients was similar to that of non-PD patients, and there were no significant differences between EQ-5D, PDQ, and PHQ-9 (Table 2). Postoperatively, the control group showed significant improvement in all indicators, while the PD patients only showed slight improvement in PDQ. In addition, compared with the control group, postoperative QOL was significantly worse in PD patients as assessed by EQ-5D (0.531 vs.0.717, P < 0.01) and PDQ (81.4vs.52.3, P < 0.01), with only a small number of PD patients achieving EQ-5D MCID (25%vs.56%, P = 0.04). These results indicate that patients with PD have a poorer improvement in QOL after TKA compared to patients with KOA alone, but still relieve symptoms or pain related disability. The results are not entirely consistent with the view that TKA can significantly improve pain in PD patients [40, 41].More importantly, all of these results indicate that there was no significant improvement in overall QOL after TKA in the PD patient. The reason why the QOL of PD patients cannot be significantly improved after TKA is not clear. It is possible that the disease burden associated with Parkinson's disease limits improvement in QOL, even if KOA symptoms are alleviated. And another explanation may be that postoperative physical therapy is ineffective in PD patients. The difficulty of diagnosing both PD and KOA at the same time also needs to be considered, as the clinician may not be able to distinguish the degree of influence of KOA and PD on gait changes from symptoms. Therefore, it is possible that the specific gait changes and postural stability of PD in patients make TKA treatment less effective than expected.
Multivariate regression was used to analyze the confounding factors between the control groups. The independent impact of PD on absolute changes in QOL and the improvement in QOL exceeding the MCID (Table 3, 4). In both models, after adjustment for demographics, comorbidities, surgical characteristics, preoperative QOL, and follow-up time, PD significantly and independently predicted a decrease in EQ-5D improvement (β=-0.09, P < 0.01), and failed to reach the EQ-5D MCID (OR:0.07, 95%[CI]: < 0.01–0.49, P < 0.01). Moreover, PD was not associated with improvement in either PDQ or PHQ-9.
QOL measurements are a more global assessment of health. While a poorer surgical outcome may be associated with a poorer QOL, patient satisfaction may relate to relief of pain and improved function of the operated knee. In fact, when asked, most patients prioritize relief of pain. The finding that there is in statistically significant difference in PDQ between the two groups is then especially important. Furthermore, it is not surprising either that patients with PD report a poorer overall QOL as they still are affected by their PD.