Knee Flexion Characteristics Alter With the Onset of Knee OA
Knee Flexion Characteristics Alter With the Onset of Knee OA
There was no significant difference in gender distribution between patients with knee OA and healthy controls (λ = 2.12, p >0.1). A significant difference between patients with knee OA and healthy controls was found in BMI. Patients with knee OA had higher a BMI value compared to healthy controls (28.7 ± 3.74 and 25.5 ± 2.9, respectively, p = 0.004). There was no significant difference in BMI between females and males with knee OA as well as between healthy females and healthy males. In addition, there was no significant difference in age between healthy females and healthy males. There was, however a significant difference in age between females and males with knee OA. Males with knee OA were slightly younger than females with knee OA (60.0 ± 5.0 and 68.4 ± 7.4, respectively).
The knee profile was examined for the 21 healthy volunteers and 23 patients. An example is provided for one of each in Figure 3.
(Enlarge Image)
Figure 3.
Examples of a typical stride for a control subject and one with bilateral osteoarthritis. The blue trace is the left knee and the green trace is the right knee.
Data are summarised in Table 1. High correlation was found between left and right knees for both controls and patients with bilateral OA (r ~ 0.82), hence left and right data were averaged for these subjects. For patients with unilateral OA, data for the OA limb was included with the data for subjects with bilateral OA, and the data for the unaffected limb was analysed separately. Overall, 39 OA knees, 42 control knees and 9 non-OA knees were analysed. ANOVA showed statistically significant differences between the groups (controls, OA knees and non-OA knees in OA patients) for both swing and stance flexion ROM; post-hoc analysis confirmed differences between controls and OA knees (p < 0.001 for stance phase and p = 0.003 for swing phase), but no statistical difference between the non-OA knees and either the controls or OA knees. There was no statistically significant difference in stride duration between the control and OA subjects (p = 0.073), although patients with knee OA walked slower.
Gender analysis was carried in order to examine whether the aforementioned significant differences in knee angles are related to gender. Similar trends were found in both females and males with differences in knee flexion ROM during swing (P = 0.006 for females, P = 0.08 for males) and knee flexion ROM during stance (P = 0.001 for females, P = 0.02 for males). This suggests that gender was not a confounder to the results of this study.
Scatter plots of the knee flexion ROM data for the OA and control knees are shown in Figure 4; it can be seen that there is considerable overlap between the controls (group 1) and those with knee OA (group 2) for the knee flexion ROM in swing, whereas there is little overlap between the two groups for knee flexion ROM in stance.
(Enlarge Image)
Figure 4.
Scatter plot of ROM knee flexion in swing (°) and ROM knee flexion in stance (°) for typical stride: controls = Group 1; OA = Group2.
ROC analysis of the data is shown in Figure 5, with the area under the curve being 0.914 for stance knee flexion ROM, and 0.741 for swing knee flexion ROM. The ROC analysis indicated that a cut-off value of 13.6° of flexion ROM in stance could discriminate between controls and patients with OA with a specificity of 0.952 and a sensitivity of 0.783.
(Enlarge Image)
Figure 5.
ROC plots for knee flexion ROM in swing (left plot) and stance (right plot). The areas under the curves are 0.741 (swing) and 0.913 (stance).
ROC analysis was also preformed on females and males separately. For females, the area under the curve being 0.987 for stance knee flexion ROM, and 0.773 for swing knee flexion ROM. For males, the area under the curve being 0.889 for stance knee flexion ROM, and 0.722 for swing knee flexion ROM. This indicates that stance knee flexion ROM is a strong predictor of OA even when male and female data are analysed separately. We also examined the relationship between stance knee flexion ROM and BMI. Within each group, there was a very slight but non-significant decrease in knee stance flexion ROM with BMI (ROM = -0.277*BMI + 16.76 (OA); ROM = -0.248*BMI + 24.34 (control)). Although neither of these regressions are significant, the similarity of the regression coefficients and the difference in the intercepts suggests that difference in BMI is not a confounding factor.
Results
There was no significant difference in gender distribution between patients with knee OA and healthy controls (λ = 2.12, p >0.1). A significant difference between patients with knee OA and healthy controls was found in BMI. Patients with knee OA had higher a BMI value compared to healthy controls (28.7 ± 3.74 and 25.5 ± 2.9, respectively, p = 0.004). There was no significant difference in BMI between females and males with knee OA as well as between healthy females and healthy males. In addition, there was no significant difference in age between healthy females and healthy males. There was, however a significant difference in age between females and males with knee OA. Males with knee OA were slightly younger than females with knee OA (60.0 ± 5.0 and 68.4 ± 7.4, respectively).
The knee profile was examined for the 21 healthy volunteers and 23 patients. An example is provided for one of each in Figure 3.
(Enlarge Image)
Figure 3.
Examples of a typical stride for a control subject and one with bilateral osteoarthritis. The blue trace is the left knee and the green trace is the right knee.
Data are summarised in Table 1. High correlation was found between left and right knees for both controls and patients with bilateral OA (r ~ 0.82), hence left and right data were averaged for these subjects. For patients with unilateral OA, data for the OA limb was included with the data for subjects with bilateral OA, and the data for the unaffected limb was analysed separately. Overall, 39 OA knees, 42 control knees and 9 non-OA knees were analysed. ANOVA showed statistically significant differences between the groups (controls, OA knees and non-OA knees in OA patients) for both swing and stance flexion ROM; post-hoc analysis confirmed differences between controls and OA knees (p < 0.001 for stance phase and p = 0.003 for swing phase), but no statistical difference between the non-OA knees and either the controls or OA knees. There was no statistically significant difference in stride duration between the control and OA subjects (p = 0.073), although patients with knee OA walked slower.
Gender analysis was carried in order to examine whether the aforementioned significant differences in knee angles are related to gender. Similar trends were found in both females and males with differences in knee flexion ROM during swing (P = 0.006 for females, P = 0.08 for males) and knee flexion ROM during stance (P = 0.001 for females, P = 0.02 for males). This suggests that gender was not a confounder to the results of this study.
Scatter plots of the knee flexion ROM data for the OA and control knees are shown in Figure 4; it can be seen that there is considerable overlap between the controls (group 1) and those with knee OA (group 2) for the knee flexion ROM in swing, whereas there is little overlap between the two groups for knee flexion ROM in stance.
(Enlarge Image)
Figure 4.
Scatter plot of ROM knee flexion in swing (°) and ROM knee flexion in stance (°) for typical stride: controls = Group 1; OA = Group2.
ROC analysis of the data is shown in Figure 5, with the area under the curve being 0.914 for stance knee flexion ROM, and 0.741 for swing knee flexion ROM. The ROC analysis indicated that a cut-off value of 13.6° of flexion ROM in stance could discriminate between controls and patients with OA with a specificity of 0.952 and a sensitivity of 0.783.
(Enlarge Image)
Figure 5.
ROC plots for knee flexion ROM in swing (left plot) and stance (right plot). The areas under the curves are 0.741 (swing) and 0.913 (stance).
ROC analysis was also preformed on females and males separately. For females, the area under the curve being 0.987 for stance knee flexion ROM, and 0.773 for swing knee flexion ROM. For males, the area under the curve being 0.889 for stance knee flexion ROM, and 0.722 for swing knee flexion ROM. This indicates that stance knee flexion ROM is a strong predictor of OA even when male and female data are analysed separately. We also examined the relationship between stance knee flexion ROM and BMI. Within each group, there was a very slight but non-significant decrease in knee stance flexion ROM with BMI (ROM = -0.277*BMI + 16.76 (OA); ROM = -0.248*BMI + 24.34 (control)). Although neither of these regressions are significant, the similarity of the regression coefficients and the difference in the intercepts suggests that difference in BMI is not a confounding factor.