## 4 Discussion
Results from trials with closed eyes are also worse in the women patients compared to the reference data, but with results showing a trend to statistical significance only for the contralateral limb (\(p\) = 0.05), and without significant changes in Autonomy. This result was quite unexpected. Based on the premise that Stability on a single limb eliminating visual control should enlighten the quote of proprioception control, data provided from the present study support this assumption, and only in the female patients. Also, no between-limb differences were found. Considering that patients included in the study were scheduled for a unilateral knee prosthesis, a possible explanation of this symmetry is that knee OA usually affects both knees [34]. Another possible explanation of this result, is represented by the low scores of the Stability Index and the Autonomy of healthy subjects. It is likely to think that performing a single-limb stance task with eyes-closed leads to the recording of low scores for postural stability for patients with knee OA, but also for healthy adults and elderly, in particular if they are sedentary and not involved in balance exercise programs [35; 36]. This means that adults/elderly individuals mostly rely on other afferent sensitive information, such as tactile information, more than sensitive information arising from other proprioceptors, when asked to maintain postural stability on a single limb and with eyes closed. Findings in the male patients also need careful interpretation. Although values reported by these patients were always below the reference values both for SI and Autonomy, and both in the OE and CE trials, evidence from statistical analysis did not demonstrate differences. Some explanation should be hypothesized, such as greater muscle strength in the lower limb, which allows a good compensation to the lack of postural stability in single support, as discussed below. In general, clinical-functional scores of patients in the present study are not different from values available in other studies on knee OA patients for KSS [37; 38; 39] and for SPPB [40; 41; 42]. Also, knee OA as radiologically measured by means of the Kellgren-Lawrence score resulted in correlation to the average Stability Index in the open eyes trial, suggesting that a worse functional performance is present in more severe radiological OA. This finding confirms previous evidence of impaired postural stability in patients with osteoarthritis of the knee, especially those diagnosed with grade III or IV degeneration [6; 17; 20]. The worst performance of women in the clinical-functional scores, namely the KSS-F and SPPB scores, confirm a strong relationship between clinical and instrumental tests, in accordance with previous literature reporting higher levels of disability in females compared to males with knee OA [43]. It has also been reported that females usually have a more severe pathology than males and higher levels of pain [44; 45], but, in our findings, females did not show significant differences with men in the radiological level of knee OA, and in the KSS-C, which includes pain assessment. Other factors, such as muscle strength, or previous and current physical activity level, might give important information for the interpretation of this result. In particular, quadriceps strength, one of the main features of knee OA [46] which has been shown to be more reduced in women than in men with knee OA [47; 48], has a significant correlation with static and dynamic balance [23; 49]. In light of the impairments in postural stability and proprioception found in this study, it is essential to address clinical practice towards ongoing assessments of postural stability and proprioception in patients with knee OA, in particular in those patients who chose a conservative treatment rather than the surgical intervention for TKA, and in particular in female patients. The observation that the measures of postural stability and proprioception are related to clinical and functional scores further support these observations.