3. The relationship between the ability to perform the sit-to-stand movement and the pelvic angles in patients with stroke

The sacral sitting posture, which involves a high degree of trunk flexion and neck extension, is frequently observed in stroke patients. This sitting posture is not the ideal posture for smoothly performing the sit-to-stand movement. Maintaining the sitting position with pelvic retroversion may be necessary to increase the sitting stability of stroke patients. However, the ability to achieve anteversion of the pelvis is necessary to perform the sit-to-stand movement.

The second section investigates the relationship between the pelvic anteversion and retroversion angles and the ability to perform the sit-to-stand movement [45]. The hypothesis of this study was that stroke patients who are able to stand from sitting in a chair have a larger maximum pelvic anteversion angle than patients who are unable to stand from a chair.

Thirty-two hemiparetic subjects (female, n = 15; male, n = 17; age, 66.7 7.6 years) and 50 agematched healthy control subjects (female, n = 40; male, n = 10; age, 64.2 8.2 years) participated in this study. The inclusion criteria were predetermined as follows: (1) a poststroke period of more than 3 months and (2) the ability to maintain the sitting position without the use of aids. The hemiparetic subjects were classified into two groups according to their performance in the sit-to-stand movement test (described later): a group with the ability to stand up (the stand-able group; n = 18 persons) and the group that was unable to stand up (the standunable group; n = 14 persons). Patients with a history of low back pain or surgery, hemispatial neglect, bilateral stroke, visual deficit, comprehension impairment, cognitive and/or communication deficits that precluded cooperation, as well as neurological or musculoskeletal disorders that were not related to the current stroke, were excluded. The exclusion criteria for healthy subjects included known vestibular dysfunction, a history of neurological disease, or orthopedic conditions that had the potential to interfere with the experiment.

The participants sat on the chair, with the front edge of the seat aligned with the point corresponding to 66% of their thigh length from the greater trochanter. The subjects sat with their feet in the parallel position with both arms crossed on their chest and with no support for the trunk or upper extremities. The chair seat height was adjusted to 100% of the subject's lower leg length (the distance from the lateral femoral condyle to the ground); the knee flexion angle was 90.

The pelvic angles were measured according to the sacral inclination angle (Figure 3). Pelvic anteversion was reported as a positive angle and pelvic retroversion was reported as a negative angle. The subjects were instructed to maintain the initial acromion anteroposterior position during the movements to avoid trunk anteroposterior movement. The stroke patients (barefoot) were then asked to stand up at a self-selected speed while keeping the arms folded across the chest. Three trials were performed with no restrictions on the position of the feet. Stroke patients who could independently perform all three trials were classified into the standable group. The remaining patients were classified into the stand-unable group.

The maximum pelvic anteversion angle in the stand-able, stand-unable, and control groups ranged from 5 to 4, 5 to 22, and 10 to 13, respectively (Figure 4). In the stand-able

Figure 3. A schematic illustration of the procedure for measuring the pelvic inclination angle: (A) the pelvic retroversion angle, (B) the pelvic anteversion angle [45].

Figure 4. The distribution of the pelvic angles in the stand-able, stand-unable, and control groups.

healthy subjects included known vestibular dysfunction, a history of neurological disease, or

The participants sat on the chair, with the front edge of the seat aligned with the point corresponding to 66% of their thigh length from the greater trochanter. The subjects sat with their feet in the parallel position with both arms crossed on their chest and with no support for the trunk or upper extremities. The chair seat height was adjusted to 100% of the subject's lower leg length (the distance from the lateral femoral condyle to the ground); the knee flexion

The pelvic angles were measured according to the sacral inclination angle (Figure 3). Pelvic anteversion was reported as a positive angle and pelvic retroversion was reported as a negative angle. The subjects were instructed to maintain the initial acromion anteroposterior position during the movements to avoid trunk anteroposterior movement. The stroke patients (barefoot) were then asked to stand up at a self-selected speed while keeping the arms folded across the chest. Three trials were performed with no restrictions on the position of the feet. Stroke patients who could independently perform all three trials were classified into the stand-

The maximum pelvic anteversion angle in the stand-able, stand-unable, and control groups ranged from 5 to 4, 5 to 22, and 10 to 13, respectively (Figure 4). In the stand-able

Figure 3. A schematic illustration of the procedure for measuring the pelvic inclination angle: (A) the pelvic retroversion

angle, (B) the pelvic anteversion angle [45].

orthopedic conditions that had the potential to interfere with the experiment.

able group. The remaining patients were classified into the stand-unable group.

angle was 90.

48 Clinical Physical Therapy

group, the maximum pelvic anteversion angles were all above 5; in contrast, to the angles in the stand-unable group were all below 5 (Figure 4). The mean and standard deviation of the maximum pelvic anteversion angles in the stand-able, the stand-unable, and control groups were 1.2 2.8, 12.4 6.1, and 1.6 5.0, respectively. The group was found to have a significant main effect (p < 0.001). The maximum pelvic anteversion angle in the stand-unable group was significantly smaller than that in the stand-able and control groups (Table 2). Thus, it became clear that the maximum pelvic anteversion angle and the range of pelvic motion in the stand-able group were significantly larger in comparison to the stand-unable group.

The maximum pelvic retroversion angles in the stand-able, stand-unable, and control groups ranged from 10 to 30, 10 to 27, and 10 to 46, respectively (Table 2). The mean and standard deviation of the maximum pelvic retroversion angles in the stand-able, standunable, and control groups were 18.5 5.6, 19.6 4.6, and 27.6 8.1, respectively (Table 2). The group was found to have a significant main effect. Significant differences were found between the control group and the stand-able group, and between the control group and the stand-unable group (Table 2). The maximum pelvic retroversion angle in the control group was significantly larger than that in both groups of stroke patients (Table 2). The maximum pelvic retroversion angles of the stand-able and stand-unable groups did not differ to a statistically significant extent (Table 2).

The range of pelvic motion in the in the stand-able, stand-unable, and control groups ranged from 10 to 28, 0 to 15, and 9 to 49, respectively (Table 2). The mean and standard deviation of the range of pelvic motion in the stand-able, stand-unable, and control groups was 19.7 5.1,


<sup>a</sup> Significant difference from the stand-able group.

<sup>b</sup> Significant difference from control group.

Table 2. The mean and standard deviation of the pelvic in the stand-able, stand-unable, and control groups [45].

7.2 5.1, and 25.9 7.6, respectively (Table 2). The range of pelvic motion in the stand-unable group was significantly smaller in comparison to the stand-able and control groups (Table 2).

The hypotheses that the maximum pelvic anteversion angle and the range of pelvic motion in the stand-able group would be significantly larger in comparison to the stand-unable group were confirmed. It is noteworthy that there was a cut-off value maximum pelvic anteversion angle that could divide stroke patients into the stand-able and stand-unable groups. The data suggest that, in order for stroke patients to perform the sit-to-stand movement, the maximum pelvic anteversion angle should be greater than 5.

To smoothly execute the sit-to-stand movement, the pelvis is anteverted to flex the hip joint and the trunk to perform the hip extension moment, reduce the knee extension moment, and project the center of gravity into the base of support [38–43]. The sitting position stability of stroke patients has been shown to be worse than that in age-matched healthy subjects [5, 11, 12]. It has been shown that stroke patients cannot sufficiently flex the hip joint when it is necessary to activate the trunk extensor muscles during sitting [33]. Stroke patients usually sit with kyphosis and pelvic retroversion to avoid falling backward due to insufficient function of the abdominal muscles. Thus, when performing the sit-to-stand movement, stroke patients may need to lean the trunk further forward to shift the center of gravity into the base of support using their feet due to the increased kyphosis and pelvic retroversion. Lecours et al. observed that, when performing the sit-to-stand movement, the trunk angle during forward leaning in stroke patients was larger than that in healthy subjects [35]. Hesse et al. reported that the average center of gravity projection in the base of support in stroke patients was 3 cm behind that of healthy subjects during the seat off phase in the sit-to-stand movement [49]. In addition, when the trunk is flexed, the hip extension moment becomes insufficient due to the lack of pelvic anteversion; thus, stroke patients may depend primarily on the knee extension movement to stand up.

Some studies have reported a high correlation between pelvic inclination in the sitting position and the degree of lumbar lordosis [5] and a strong relationship between the sacral angle of inclination and the degree of lumbar lordosis [46, 47]. Hence, pelvic inclination (anteversion and retroversion) reflects lumbar movement (lordosis and kyphosis). The range of pelvic motion in the stand-unable group was extremely limited, reaching merely 28% of the control group and 36% of the stand-able group. Accordingly, in the stand-unable group, the lumbar spine movement in the sagittal plane (lordosis and kyphosis) was probably limited in comparison to the control group and the stand-able group.

The pelvic angle measurements were conducted in the sitting position while the subject maintained 90 of knee flexion with their feet in contact with the ground. In the sitting position, the hip joints work as pivotal axes in pelvic anteversion and retroversion. One factor that should influence the range of motion of the hip is the extensibility of the hamstrings, which drive the hip and knee as biarticular muscles. Hamstring stretching was shown to improve the pelvic anteversion angle [17] and the mobility of the hip in elderly individuals [16]. The sitting position in this study fixed the knee flexion angle at 90, which should have increased hamstring tension during the measurement. Thus, it is likely that pelvic anteversion was restrained by the increased tension of the hamstrings.

Cheng et al. reported the following three characteristics of the sit-to-stand movement of stroke fallers, the stroke nonfallers, and healthy subjects: stroke patients, especially fallers, required a significantly longer time to perform the sit-to-stand movement; the rate of increase in vertical force (%BW/sec) in stroke fallers was significantly lower in comparison with nonfallers and healthy subjects; and the overshoot of vertical force (%BW) in stroke fallers was significantly lower than that in nonfallers and healthy subjects [50]. These characteristics of stroke fallers may be associated with their limited pelvic anteversion during the sit-to-stand movement. Messier et al. suggested that, to execute the trunk flexion task, stroke patients used a compensatory strategy that consisted in using mainly the upper trunk flexion because they were unable to tilt their pelvis anteriorly [37]. Thus, our data, which showed that the maximum pelvic anteversion angle of the stand-unable group was significantly smaller than that of the stand-able and control groups, were supported by these reports. Another point of view that should be mentioned is that Prudente et al. suggested that neuromuscular coordination abnormalities occurred in both of the lower limbs of stroke patients during the sit-to-stand movement [51].

On the other hand, since there was no significant difference in the maximum pelvic retroversion angle of the two stroke groups, it becomes clear that this angle does not affect the patient's ability to perform the sit-to-stand movement. However, it was also demonstrated that the range of pelvic motion in stroke patients was markedly restricted in comparison to healthy subjects. In stroke patients, pelvic anteversion appears to be an important factor for regaining the ability to perform the sit-to-stand movement.
