Demographics

All patients screened for inclusion were included in the study. In total, 203 patients were included in this study, with a median age of 66 years [13] – 100 patients in Center A and 103 patients in Center B. The study group consisted of 106 female patients and 97 male patients with a median BMI of 28.10 [6.53] kg/m2; see Table 1. As for the OKS-related demographic data, 92.1% of patients had stairs at home, 71.4% were still driving a car, 26.6% were using walking aids, 33.5% were still working, and 62.6% underwent previous knee surgery (Table 1).

Table 1 Patient demographics for the general cohort separated by center; p-value for testing for difference between both centers

For demographic data, there were differences between both centers in age (p < 0.001), the use of walking aids (p = 0.036), and previous surgeries (p = 0.031; Table 1).

Oxford Knee Score and scored weight

The highest average score in the OKS was found for pain, with 3.61 points, and for kneeling, with 3.29 points (Table 2). The lowest average scores were found for washing, with 1.56 points, and walking for a longer distance, with 1.90 points (Table 2). The most important questions for the patients were the questions for pain, washing, night pain, stability, and walking stairs, with a median of 5. The scores for the OKS and the Likert scale on importance are given in Table 2.

Table 2 Mean and median values for the questions of the OKS and their importance according to the 5-point Likert scalePredictive analysisQuestion 1: Pain

In the regression models for the weight of each of the questions, pain was associated with older age (p = 0.009; B = −0.013) and gender (p = 0.015, B = 0.301; Table 4).

Question 2: Washing

Washing was associated with older age (p = 0.013, B = −0.010) and gender (p < 0.001, B = 0.387) in the regression model (Table 4).

Question 3: Transport

The question on transport was associated with the patients’ self-use of a car (p < 0.001; B = 0.707) in the regression model (Table 4).

Question 4: Walking for a longer distance

The question on walking was associated with older age (p = 0.041, B = −0.013), gender (p = 0.046, B = 0.347), height (p = 0.015, B = 0.022), and self-use of a car (p = 0.002, B = 0.496) in the regression model (Table 4).

Question 5: Standing up after eating

Getting up after eating was associated with older age (p = 0.009, B = −0.013) and self-use of a car (p = 0.031, B = 0.285) in the regression model (Table 4).

Question 6: Limping

Limping was associated with older age (p = 0.011, B = −0.016), gender (p = 0.031, B = 0.385), and self-use of a car (p = 0.037, B = 0.334) in the regression model (Table 4).

Question 7: Kneeling

In the regression model, kneeling was associated with the self-use of a car (p = 0.027, B = 0.394; Table 4). A significant negative correlation between the recorded OKS score and recorded OKS weight was found for the question on kneeling (r = −0.158, p = 0.024; Table 3).

Table 3 Predictive analysis between the recorded OKS score and recorded OKS weight (significant values in bold letters)Question 8: Night pain

A significant positive correlation between the recorded OKS score and recorded OKS weight was found for the question on night pain (r = 0.143, p = 0.043) (Table 3). In the regression model, night pain was associated with older age (p = 0.037, B = −0.009) (Table 4).

Table 4 Regression coefficient B and p-values for the regression models for each question of the OKS and age, gender, height, weight, BMI, stairs, driving, use of walking aids, working status, and previous knee surgeriesQuestion 9: Working

In the regression model, the weight of the question on work was associated with gender (p = 0.004, B = 0.345), height (p = 0.041, B = 0.013), and self-use of a car (p = 0.014, B = 0.269; Table 4=). A significant positive correlation between the recorded OKS score and recorded OKS weight was found for the question on working (r = 0.174, p = 0.014; Table 3).

Question 10: Stability

In the regression model, instability was associated with older age (p < 0.001, B = −0.015), self-use of a car (p = 0.007, B = 0.301), and previous surgery (p = 0.040, B = 0.192; Table 4). A significant positive correlation between the recorded OKS score and recorded OKS weight was found for the question on stability (r = 0.166, p = 0.018; Table 3).

Question 11: Shopping

Household shopping was again influenced by gender (p = 0.019, B = 0.304) and previous surgery (p = 0.028, B = 0.217; Table 4).

Question 12: Walking stairs

Walking down a flight of stairs was associated with older age (p = 0.025, B = −0.010), having a set of stairs at home (p = 0.008, B = 0.470), self-use of a car (p = 0.038, B = 0.248), and previous surgery (p = 0.021, B = 0.224; Table 4).