Preoperative Posterior Pelvic Tilt Angle is Associated with Decreased Gait Speed and Hip Function in Older Patients with Hip Osteoarthritis

ABSTRACT

Objectives: This study examined the relationships between preoperative posterior pelvic tilt with muscle strength, gait speed, hip function, and quality of life in older patients with hip osteoarthritis.

Methods: This cross-sectional study included 65 patients with hip osteoarthritis (75.0 ± 10.4 years; 83.1% female). Pelvic tilt angle was calculated from the frontal view of the hip joint in the standing position using radiographic images. The patients were divided into anterior (n=13) and posterior (n=52) groups based on a standard pelvic tilt angle of 27.9°. Clinical outcomes included preoperative isometric hip flexion and knee extension muscle strength, a five-time sit-to-stand test, gait speed, the Harris Hip Score (HHS), and the Japanese Orthopedic Association Hip-Disease Evaluation Questionnaire score. Multiple regression analysis was performed to clarify the relationships between the posterior pelvic tilt and clinical outcomes.

Results: The posterior pelvic tilt group had significantly lower isometric knee extension muscle strength (P=0.032), HHS (P=0.020), and gait speed (P=0.006) than the anterior pelvic tilt group. Multiple regression analysis showed that the posterior pelvic tilt was significantly associated with lower gait speed (β=−0.271, P=0.046) and HHS (β=−0.272, P=0.045).

Conclusions: Preoperative posterior pelvic tilt is associated with decreased gait speed and hip function in patients with hip osteoarthritis. Given that a posterior pelvic tilt may compromise stability during gait, restrict daily activities, and increase the risk of falls, physical therapy interventions targeting these factors are essential, even before total hip arthroplasty.

INTRODUCTION

Hip osteoarthritis is a common chronic joint disease that imposes a growing medical and economic burden worldwide.¹⁾ The prevalence rate of hip osteoarthritis is 8.55% worldwide and 4.26% in Asia.²⁾ The prevalence of hip osteoarthritis increases with age,^2,3) causing joint space narrowing and osteophyte formation.⁴⁾ The progression of hip osteoarthritis causes inactivity because of increased pain and stiffness, leading to muscle weakness and decreased gait speed.⁴⁾ Therefore, there is significant need to maintain physical function in patients with hip osteoarthritis.

In recent years, the population of older adults has increased, and the number of older patients with hip osteoarthritis has been increasing.³⁾ These patients are reported to have decreased muscle strength, gait speed, hip function, and quality of life (QOL) compared with healthy individuals and younger patients with hip osteoarthritis.^5,6,7,8,9) In addition, in younger patients with hip osteoarthritis, lumbar lordosis and pelvic anteversion are enhanced by decreased femoral head coverage and hip flexion contracture.^10,11) However, older patients with hip osteoarthritis are reported to have a posterior pelvic tilt that results in lumbar kyphosis.³⁾ Posterior pelvic tilt is reported to be associated with locomotive syndrome and decreased grip strength, which indicates lower limb muscle strength, in healthy older patients.^12,13) However, the relationships between posterior pelvic tilt and muscle strength, gait speed, hip function, and QOL, which are common in older patients with hip osteoarthritis, have not been clarified to date.

Clarifying the relationships between posterior pelvic tilt angle and muscle strength, gait speed, hip function, and QOL may lead to modification and implementation of a physical therapy program according to changes in pelvic tilt. This work may also help in understanding the need for preoperative physical therapy in older patients with osteoarthritis before total hip arthroplasty (THA). This study aimed to determine the relationships between the preoperative pelvic tilt angle and muscle strength, gait speed, hip function, and QOL in older patients with osteoarthritis of the hip before THA.

MATERIALS AND METHODS

Study Design

This single-center, cross-sectional, observational study included preoperative candidates for progressive and terminal-stage hip osteoarthritis who were admitted to the Department of Orthopedic Surgery at the Odawara Municipal Hospital (417 beds) in Odawara, Kanagawa Prefecture, between April 2018 and June 2022. Exclusion criteria for THA included femoral head necrosis, femoral neck fracture, hip dislocation, and rheumatoid arthritis. Patients with challenges in obtaining a standing frontal view of the hip joint or those who had not undergone a pre-THA assessment were also excluded from the analysis. This study was conducted in accordance with the principles of the Declaration of Helsinki. This study was reviewed and approved by the Odawara Municipal Hospital Review Board (Approval No. 2021–14). The patients were fully informed of the study, and written consent was obtained.

Pelvic Tilt Angle

The pelvic tilt angle before THA was calculated using radiographic images and a frontal view of the hip joint in the standing position. The distance from the midpoint of the line connecting the lower edges of the bilateral sacroiliac joints to the upper edge of the pubic symphysis was defined as the vertical diameter. This measurement was divided by 165 for female patients and 157 for male patients, and the resulting quotient was transformed by inverse trigonometric function to give the pelvic tilt angle (Fig. 1).¹⁴⁾ This measurement method allowed pelvic tilt to be calculated from the frontal hip joint image using a trigonometric function without the need to evaluate the lateral hip joint image. The intra- and inter-rater reliabilities were reported to be high, with an intra-rater correlation coefficient greater than 0.9.¹⁴⁾

Fig. 1.

Calculation of pelvic tilt angle. The pelvic tilt angle was calculated from the vertical diameter, which was defined as the distance from the midpoint of the line connecting the lower edges of the bilateral sacroiliac joints to the upper edge of the pubic symphysis (dotted line). Pelvic tilt angle was calculated as: for women, Pelvic tilt angle = arcsin (vertical diameter / 165); for men, Pelvic tilt angle = arcsin (vertical diameter / 157).

Clinical Outcomes

Clinical outcomes were preoperative isometric hip flexion muscle strength, isometric knee extension muscle strength, five-times sit-to-stand test, gait speed, Harris Hip Score (HHS), Japanese Orthopaedic Association Hip-Disease Evaluation Questionnaire (JHEQ) score, and visual analog scale (VAS) of pain assessment. Isometric hip flexion and knee extension muscle strength were measured using a handheld dynamometer ergo FIT (Nihon Medix, Kashiwa, Japan). Isometric hip flexion muscle strength was measured using the hip and knee joints both at 90° in a seated position. The force arm was defined as the distance from the palpation area of the femoral artery to the HHD sensor, which was placed on the proximal anterior surface of the second transverse finger just above the patella. Isometric knee extension muscle strength was measured in the sitting position with the knee joint at 90°. The HHD sensor was located on the proximal anterior surface of the second lateral finger of the lateral malleolus, and the force arm was defined as the distance from the center of the knee joint to the HHD sensor.¹⁵⁾ The maximum isometric muscle strength was measured. The patients were instructed to exert maximum force for 5 s. For our analysis, the greater of the two measurements was recorded and divided by the body weight. The five-times sit-to-stand test is widely used as a physical function test in older adults. Patients were instructed to rise and sit on a chair as fast as possible five times and to place both upper limbs in front of their trunk.¹⁶⁾ Gait speed was measured at a comfortable walking speed using a stopwatch on a 10-m section of walking path with 3-m acceleration and deceleration paths. The HHS is an index used to evaluate joint function before and after hip arthroplasty.¹⁷⁾ HHS was evaluated using eight items: pain, sitting position, range of motion, walking ability, walking aids, claudication, sock fitting, stairs, and public transportation.¹⁸⁾ The JHEQ is an index used to evaluate health-related QOL, hip joint condition, pain, movement, and mental health, and a higher total score (maximum 84 points) indicates a higher QOL.¹⁹⁾ The VAS pain score is self-evaluated by the patient on a 10-cm analog scale. VAS data were extracted from the JHEQ pain item.

Other Variables

Information on age, body mass index (BMI), knee disease, spine disease, and THA on the nonoperative side were extracted from medical records. Given that this study evaluated older patients with hip osteoarthritis, the proportion of patients aged over 65 years was also recorded.

Statistical Analysis

Continuous variables were tested using the Shapiro–Wilk test and are presented as mean ± standard deviation for normally distributed variables and median [interquartile range] for non-normally distributed variables. Categorical variables are presented as frequencies and percentages.

Patients were classified into anterior and posterior pelvic tilt groups based on the standard pelvic tilt angle of 27.9° set by Kitajima et al.¹⁴⁾ Comparisons of each variable between the anterior and posterior pelvic tilt groups were performed using the Student’s t-test or the Mann–Whitney U-test, depending on normality. Categorical variables were tested using the Chi-squared test.

Multiple regression analysis for isometric hip flexion strength, isometric knee extension strength, five-times sit-to-stand test, gait speed, HHS, and JHEQ was conducted to determine the association between pelvic tilt angle and each clinical outcome. Age, VAS score, THA on the nonoperative side, spinal disease, and knee disease were adjusted as potential confounders in the multiple regression model. Statistical analyses were performed using SPSS software version 28.0 (IBM, Armonk, NY, USA), and statistical significance was set at P < 0.05.

RESULTS

Of 108 patients who underwent standby THA, 21 had femoral head osteonecrosis, 1 had femoral neck fracture, 3 had hip dislocations, 3 had rheumatoid arthritis, 9 had difficulty taking a standing frontal view of the hip joint, and 6 lacked data; therefore, these 43 patients were excluded. A total of 65 patients (mean age, 75.0 ± 10.4 years; mean BMI, 23.0 ± 3.47 kg/m²) were included in the analysis (Fig. 2).

Fig. 2.

Flowchart of patient recruitment.

Based on the standard pelvic tilt angle of 27.9°, patients were classified into the anterior pelvic tilt group (n = 13) or the posterior pelvic tilt group (n = 52). Patient characteristics according to pelvic tilt angle are shown in Table 1. Age (anterior pelvic tilt group: 68.0 years; posterior pelvic tilt group: 76.0 years, P = 0.006) was significantly older in the posterior pelvic tilt group than in the anterior pelvic tilt group. Sex, BMI, and medical history did not significantly differ between the anterior and posterior pelvic tilt groups.

Table 1. Patient characteristics according to pelvic tilt angle

Characteristic	Anterior group	Posterior group	P value
	(n=13)	(n=52)
Age, years	68.0 ± 6.12	76.0 ± 10.4	0.006
≥65 years	9 (69.2)	26 (50.0)
Sex (female)	12 (92.3)	42 (80.8)	0.239
BMI, kg/m2	23.5 ± 3.57	23.4 ± 3.13	0.886
>25 kg/m2	4 (30.8)	21 (40.4)
Spine disease	3 (23.1)	5 (9.62)	0.192
Lumber spinal stenosis	2 (15.4)	2 (3.84)
Spondylosis deformans	1 (7.70)	1 (1.92)
Spondylolisthesis	0 (0.0)	1 (1.92)
Lumbar compression fracture	0 (0.0)	1 (1.92)
Knee disease	0 (0.00)	8 (15.4)	0.149
Knee osteoarthritis	0 (0.00)	5 (9.62)
Tibial meniscus injury	0 (0.00)	2 (3.84)
Tibial plateau fracture	0 (0.00)	1 (1.92)
Staging			0.800
Terminal	13 (100.0)	51 (98.1)
Progressive	0 (0.0)	1 (1.92)
THA on the nonoperative side	3 (23.1)	7 (13.5)	0.317

Data given as mean ± standard deviation or number (percentage).

Clinical outcomes according to pelvic tilt angle are shown in Table 2. Knee extension muscle strength (anterior pelvic tilt group, 0.96 Nm/kg; posterior pelvic tilt group, 0.76 Nm/kg, P=0.032) and HHS (anterior pelvic tilt group, 66.4; posterior pelvic tilt group, 55.8, P=0.020) were significantly lower in the posterior pelvic tilt group than in the anterior pelvic tilt group. Gait speed (anterior pelvic tilt group, 0.94 ± 0.23 m/s; posterior pelvic tilt group, 0.70 ± 0.27 m/s, P=0.006) was significantly slower in the posterior pelvic tilt group than in the anterior pelvic tilt group. The VAS score (anterior pelvic tilt group, 52.3 ± 31.9 mm; posterior pelvic tilt group, 90.0 ± 133.5 mm; P=0.006) was significantly higher in the posterior pelvic tilt group than in the anterior pelvic tilt group.

Table 2. Clinical outcomes according to pelvic tilt angle

Outcome	Anterior group (n=13)	Posterior group (n=52)	P value
Hip flexion muscle strength, Nm/kg	0.61 ± 0.25	0.59 ± 0.23	0.808
Knee extension muscle strength, Nm/kg	0.96 [0.85, 1.11]	0.76 [0.65, 0.93]	0.032
Five-times sit-to-stand test, s	11.3 [8.23, 14.1]	13.4 [10.5, 15.8]	0.126
Gait speed, m/s	0.94 ± 0.23	0.70 ± 0.27	0.006
HHS	66.4 ± 12.7	55.8 ± 14.7	0.020
JHEQ	21.1 ± 14.1	23.6 ± 13.2	0.061
VAS, mm	54.0 [34.0, 80.0]	80.0 [63.0, 93.0]	0.030

Data given as mean ± standard deviation or median [interquartile range].

The results of the multiple regression analysis of the pelvic tilt angle are shown in Table 3. Pelvic tilt angle was significantly associated with gait speed (posterior pelvic tilt group, β=−0.271; P=0.046) and HHS (posterior pelvic tilt group, β=−0.272; P=0.045). In contrast, pelvic tilt angle was not significantly associated with hip flexion muscle strength (posterior pelvic tilt group, β=0.022; P=0.859), knee extension muscle strength (posterior pelvic tilt group, β=−0.237; P=0.082), five-times sit-to-stand test (posterior pelvic tilt group, β=0.188; P=0.201), or the JHEQ (posterior pelvic tilt group, β=−0.253; P=0.051). Th potential confounders of spinal diseases and knee disease showed no association with clinical outcomes.

Table 3. Multiple regression analysis for pelvic tilt angle

Factor	Clinical outcomes
	Hip flexion muscle strength		Knee extension muscle strength		Five-times sit-to-stand test		Gait speed		HHS		JHEQ
	β	95% CI	β	95% CI	β	95% CI	β	95% CI	β	95% CI	β	95% CI
Age (>65 years)	−0.516	−0.545 to −0.197*	−0.300	−0.504 to −0.036*	−1.123	−6.348 to 2.500	−0.162	−0.378 to 0.089	−0.071	−15.436 to 8.796	−0.228	−20.996 to 0.782
VAS (>5 mm)	−0.122	−0.200 to 0.067	0.042	−0.151 to 0.208	0.252	−0.650 to 7.026	0.078	−0.126 to 0.232	0.006	−9.123 to 9.564	−0.165	−13.977 to 0.037
THA on the nonoperative side	0.143	−0.060 to 0.245	0.024	−0.180 to 0.218	−0.338	−8.802 to −0.736	0.096	−0.124 to 0.272	0.264	0.275 to 21.772*	0.279	1.142 to 18.793*
Spine disease	−0.036	−0.189 to 0.140	−0.059	−0.272 to 0.171	0.024	−4.157 to 4.919	0.106	−0.132 to 0.310	0.028	−10.267 to 12.699	−0.041	−11.719 to 8.474
Knee disease	0.271	0.021 to 0.346*	0.019	−0.203 to 0.234	−0.025	−5.188 to 4.279	0.038	−0.186 to 0.251	0.179	−3.705 to 20.329	0.246	−0.063 to 20.465
Pelvic tilt	0.022	−0.140 to 0.168	−0.237	−0.376 to 0.023	0.188	−1.357 to 6.263	−0.271	−0.384 to −0.004*	−0.272	−20.073 to −0.221*	−0.253	−18.154 to 0.037

Pelvic tilt is defined as 1 for posterior pelvic tilt.

CI, confidence interval.

* P < 0.05;** P < 0.01.

DISCUSSION

This study aimed to determine the association between pelvic tilt angle and muscle strength, gait speed, hip function, and QOL before THA in older patients with hip osteoarthritis. Posterior pelvic tilt was significantly associated with decreased gait speed and hip function.

A previous study indicated that anterior pelvic tilt increases the activation of muscles connected to the pelvis, such as the gluteus maximus and vastus medialis, and tends to increase the anterior pelvic tilt to sustain gait speed.²⁰⁾ Conversely, backward pelvic tilt during gait in healthy adults is associated with decreased gait speed.²¹⁾ It has been reported that the gluteus maximus and gluteus medius act to control hip flexion and stabilize the pelvis during gait.^22,23) Posterior pelvic tilt while standing has also been shown to be associated with lower mobility of the pelvis and adjacent joints during gait than anterior pelvic tilt.²⁴⁾ Moreover, diminished stride length resulting from a restricted range of motion in each joint contributes to a decreased stability during gait.²⁵⁾ In contrast to anterior pelvic tilt, posterior pelvic tilt may lead to diminished muscle activity in the gluteus maximus and gluteus medius, coupled with a constrained range of motion in adjacent joints, resulting in reduced stability during gait. Previous studies have reported that hip pain increases as hip osteoarthritis progresses,²⁶⁾ which is a factor affecting gait speed. In the early stages of hip osteoarthritis, the hip range of motion is restricted to escape hip pain.²⁷⁾ This leads to muscle weakness as a result of changes in hip alignment, which contributes to instability during walking. In this study, because hip osteoarthritis was in its terminal stage, it is possible that muscle weakness caused by pelvic tilt was more related to gait speed than the degree of pain.

Posterior pelvic tilt is significantly associated with decreased hip function. A study involving patients after acetabular osteotomy revealed that patients with postoperative posterior pelvic tilt experienced progressive hip osteoarthritis and lower HHS,²⁰⁾ wherein HHS included items for gait and activities of daily living.¹⁸⁾ Studies have indicated that healthy older adults with spinal deformities face limitations in both activities of daily living and outdoor gait when compared with healthy older adults.²²⁾ These limitations may be attributed to a decline in walking ability, characterized by reduced balance and stride length.²⁵⁾ Furthermore, additional studies have suggested a positive correlation between forward trunk tilting and increased posterior pelvic tilt.²³⁾ It has been observed that a shift towards posterior pelvic tilt not only elevates the risk of falling but also hinders the ability to stand up.²⁸⁾ In the patients considered in this study, posterior pelvic tilt may have contributed to limitations in daily activities, diminished gait ability, and potentially decreased hip function.

Posterior pelvic tilt was not significantly associated with muscle strength, the five-times sit-to-stand test, or QOL. With regard to muscle strength, the iliopsoas muscle follows a course near the articular surface and articular capsule, deviating from a straight line because of its interaction with the bone and soft tissue.²⁸⁾ Consequently, the strength of the iliopsoas muscle may not be readily influenced solely by posterior pelvic tilt. In addition, posterior pelvic tilt was not significantly associated with the five-times sit-to-stand test. In healthy adults, knee extension muscle strength is the most pertinent factor in the five-times sit-to-stand test.¹⁶⁾ It is possible that knee extension muscle strength was also strongly related to the five-times sit-to-stand test in this study of patients with hip osteoarthritis. Although posterior pelvic tilt was not significantly associated with lower QOL in this study, patients with spinal disease and healthy individuals show an association between posterior pelvic tilt, sagittal vertical axis, and health-related QOL.^29,30) It has also been suggested that changes in pelvic and spinal column alignment may alter the alignment of adjacent joints and contribute to a lower health-related QOL.³⁰⁾ In the present study on hip osteoarthritis, changes in the alignment of adjacent joints may have had a greater effect than posterior pelvic tilt. The hip-spine syndrome proposed by Offierski and MacNab³¹⁾ is closely related to the spine and hip joints and may alter their mutual alignment. Hip-spine syndrome may affect not only the hip joint but also the spine in some patients. Further studies are required to evaluate this aspect of the spine.

This study has several limitations. First, this was a cross-sectional study, and the causal relationship between posterior pelvic tilt and each outcome was unclear. Future longitudinal studies are needed to investigate the effects of the pelvic tilt angle on muscle strength, gait speed, hip function, and QOL before THA. Second, this was a single-center study. A multicenter study is required to generalize these results. Third, the sample size was small (65 patients), which may have resulted in type II errors because of insufficient statistical power. Furthermore, the sample size of 65 patients, especially when divided into the anterior and posterior tilt groups (n=13 for anterior and, n=52 for posterior), may have been too small to draw robust conclusions. Future studies need to be conducted with a larger number of participants in a multicenter approach. Fourth, this study evaluated only the static pelvic tilt angle and not the dynamic pelvic tilt angle or the adjacent joints. To demonstrate the relationship between pelvic tilt angle and gait speed, it is necessary to evaluate the alignment of adjacent joints, muscle strength, and range of motion, in addition to evaluating the pelvic tilt angle during movement. Additionally, the pelvic tilt angle is frequently evaluated with lateral radiographs; however, the current study was conducted with frontal radiographs, which may have influenced the results. Fifth, this study did not consider potential confounders, such as hip osteoarthritis status on the nonoperative side, history of THA on the nonoperative side, and medication status. Because these factors may have influenced the results, future studies should increase the sample size and consider potential confounders.

CONCLUSION

This study aimed to clarify the relationships between pelvic tilt angle and muscle strength, gait speed, hip function, and QOL before THA in older patients with hip osteoarthritis. The results of the study suggest that posterior pelvic tilt is significantly associated with decreased gait speed and hip function in older patients with hip osteoarthritis. Given that posterior pelvic tilt may compromise stability during gait, restrict daily activities, and elevate the risk of falls, physical therapy interventions targeting these factors are essential, even before THA.

ACKNOWLEDGMENTS

The authors thank the staff of Odawara City Hospital for their cooperation and thank Editage (www.editage.com) for English language editing.

CONFLICTS OF INTEREST

The authors declare no conflict of interest.

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