www.nature.com/scientificreports

OPEN

Three‑dimensional foot trajectoryin female patients with end‑stage
hip osteoarthritis during walking
Yu Kiko1*, Taiki Ogata2, Hirotaka Uchitomi2, Masaaki Matsubara3, Yoshihiro Miyake2 &Yoshiaki Wada1
Osteoarthritis (OA) is a risk factor for falls. To decrease the fall risk, it is important to evaluate thedetailed features of the gait of patients with OA. This study aimed to investigate the spatio-temporalparameters of gait in patients with end-stage hip OA, especially foot trajectory. We measured normal
speed gait in patients with hip OA and in healthy controls (HCs) using inertial measurement units
attached to shanks. The stride lengths in the affected and unaffected sides in the patients with hip OA
were shorter than those in the HCs, but the position of maximum foot clearance was not significantly
different between the two groups. The patients with hip OA compensated the position of maximum
foot clearance to avoid fall risk. The horizontal plane foot trajectory in patients with hip OA suggeststhat the lateral bending of the trunk during walking, which is frequently seen in them, was a result of
the lateral distance at swing down being located significantly more medially on the unaffected sidethan on the affected side. Herein, a new gait parameter of lateral distance at swing was discovered bya detailed evaluation of three-dimensional foot trajectory of female patients with end-stage hip OA.
Hip osteoarthritis(OA) is common in f­ emales1 and is a chronic progressive disease characterised by the degeneration and wear of articular cartilage, resulting in joint destruction and reactive bone growth (osteochondria
and osteophytes). Limited range of motion (ROM), inguinal pain and limping are ­characteristic2–5, and theireffects cause activity ­limitation6. The patients with hip OA have a higher risk of death than healthy individuals,
and the history of diabetes, cancer, or cardiovascular disease and gait disorders are listed as major risk ­factors7.
In addition, OA is also known to be a risk factor for f­ alls8. However, it is not well understood what kind of walking problem the OA patients have. The association between fall risk and pain and dysfunction has been modest
and not associated with radiographic O­ A9. In addition, female patients with end-stage hip OA have a higher
incidence of falls within 1 year, and an association between fall risk and limping and knee extensor strength has
been reported, but detailed gait evaluation has not been ­performed10. To decrease the fall risk during walking, it
is important to understand how hip OA affects gait features in detail. In addition, recently, it has been reported
that abnormal hip joint loading is involved in the progression of hip ­OA11. The hip joint loading is potentiallymodifiable with interventions using gait ­training12,13, which requires appropriate gait instruction and adjustmentof gait volume. For the appropriate instruction, it is also important to evaluate the gait of the patients with hip
OA accurately and in detail.
Regarding gait characteristics of patients with hip OA, it is well-known that walking speed decreases due
to short stride length and short affected limb ­step14–17. When walking on the treadmill at constant speed, thestep length on the affected side is longer than that on the unaffected side.18–20. Many researchers reports on thewalking speed of patients with hip O­ A14–17,21,22; however, reports comparing the stride speed of the affected andunaffected limbs are rare. There are various phases in the gait cycle such as swing and stance; the gait is generated by the rhythmic combination of these phases. Patients with hip OA have an asymmetry in step and swing
duration between affected and unaffected limbs caused by short s­ tep19,21,22 and stance d­ urations18,23 in the affected
limb. The increase in step length asymmetry is associated with a decrease in mechanical energy ­exchange20.
In addition, the external hip flexion, extension, and adduction moments during walking are lower in patietns
with hip ­OA24, and extension angles of the hip and knee in the latter half of the stance phase are smaller thanthose in healthy controls(HCs), but there is no difference in the ankle joint ­angle25. The peaks of hip flexion andextension angles decrease in the affected limb relative to those in the unaffected ­limb26. In patients with hip OA,
the variability of walking on the treadmill was higher on the affected side than in the HCs, but the variability
1

Department of Rehabilitation, Nissan Tamagawa Hospital, Tokyo 158‑0095, Japan. 2Department of Computer
Science, Tokyo Institute of Technology, Kanagawa 226‑8503, Japan. 3Department of Orthopedic Surgery, Nissan
Tamagawa Hospital, Tokyo 158‑0095, Japan. *email: reha@tamagawa-hosp.jp

Scientific Reports |(2022) 12:9843| https://doi.org/10.1038/s41598-022-14070-8

1Vol.:(0123456789)

www.nature.com/scientificreports/

Mean (SD)
Variables

HC (N = 25)

LOA (N = 25)

ROA (N = 25)

p-valueAge (years)

60.9 (7.0)

63.4 (7.3)

65.5 (7.6)

0.090

Height (cm)155.7 (6.2)

154.4 (4.5)

154.3 (6.5)

0.618

Weight (kg)53.3 (8.9)

53.9 (8.4)

54.2 (8.9)

0.865

BMI

22.0 (3.3)

22.6 (3.2)

22.6 (2.5)

0.544

Table 1.  Participant demographics. The means and standard deviations of age, height, weight and BMI for
each group.

was lowest when the gait speed was close to the self-selected walking ­speed27. The variability of stride duration
decreased significantly 1 year after total hip arthroplasty (THA) compared with that preoperatively and wascomparable to that of the ­HCs28.
As seen in these previous studies, various gait characteristics of hip OA have been reported. However, to thebest of our knowledge, there is no report that investigates the gait characteristics of patients with hip OA in detailusing three-dimensional foot trajectory. Since the gait parameters of patients with hip OA are asymmetric thefoot trajectory is likely also asymmetric. The three-dimensional foot trajectory shows features in the sagittal,
frontal, and horizontal planes, but gait features in the horizontal plane were not almost reported. Patients withhip OA frequently show an exaggerated lateral bending of the trunk during gait. The lateral bending of the trunk
may be characteristic of the foot trajectory, especially during the swing phase.
This study aimed to evaluate the three-dimensional foot trajectory of female patients with end-stage hip
OA on the affected and unaffected limbs and to clarify the gait characteristics in comparison with HC. The
average prevalence of hip OA in Japan is 1.0%, but is higher in females (2.0%) than males (0%)1. Male patientswere excluded in this study to avoid possible confounding due to unbalanced sex distribution. The evaluationof three-dimensional foot trajectory provides multiple gait features such as the sagittal, horizontal, and frontal
planes of the spatio-temporal parameters. In recent years, there has been an increase in gait analysis with wearable inertial measurement unit (IMU) sensors that have provided an accessible and affordable alternative to
traditional optical gait analysis s­ ystems29. Mao et al. proposed a system to estimate the foot trajectory in three
dimensions during walking by attaching the IMUs on shanks just above both a­ nkles30. The gait indices such as
the stride length, the position of maximum foot clearance (maximum foot clearance), and speed estimated bythis system strongly correlate with those measured by the optical motion-capture system. This system can also
evaluate stride duration, stance duration and swing duration for the right and left lower limbs. In this study, we
use this wearable system to evaluate the gait characteristics of patients with hip OA.

Methods

Participants. The participants were 50 outpatients with unilateral end-stage hip OA at the Department ofOrthopedic Surgery, Nissan Koseikai Tamagawa Hospital, (25 LOA ; 25 ROA ; all females) in 2018-2019. We
calculated that with a sample of 75 participants, the study would have 80% power to detect a 0.17 effect size,with a type I error rate of 5%. The patients had a minimal joint space (MJS) of less than 2 mm and a low Japan
Orthopaedic Association (JOA) hip score, and were considered severe enough to require THA. We defined thesepatients as end-stage. The HC consisted of 25 age-matched females who were independent in their daily activities and able to walk on their own. We excluded the patients if they had neurological, vascular, and other lower
extremity musculoskeletal conditions or psychiatric disorders that affected gait or functional performance. We
also excluded patients with self-reported lack of sensation in the foot or lower limb and those who were unable
to walk short distances (30 m) without an assistive device and patients with pain in the hip on the unaffectedside. This study was approved by the Institutional Review Board of Nissan Tamagawa Hospital and the Tokyo
Institute of Technology for research ethics committee. All participants provided written informed consent before
participation. All methods were performed in accordance with the Helsinki Declaration and relevant guidelines
and regulations. There were no differences in age, height, weight, or BMI between patients with hip OA and HCs(Table 1). The hip flexion, extension, abduction, adduction, external rotation, and internal rotation ROM angles,
hip abduction muscle strength, knee extension muscle strength, MJS, and JOA Hip score were significantly different between the affected and unaffected sides for the patients with hip OA (Supplementary Table S3). There
was no significant difference of affected sides between the patients with LOA and ROA except for hip abduction (Supplementary Table S4). In addition, there was no significant difference in unaffected sides between thepatients with LOA and ROA. There was no significant difference in the stage of hip OA between the affected andunaffected sides of patients with LOA and ROA (Supplementary Table S5).
The hip joint ROM angles were determined by passively moving the patients’ legs and measuring the maximum angles using a goniometer. The pelvis was stabilised to prevent rotation or t­ ilting31 when passive ROM wasmeasured by an experienced physical therapist. The measuring was conducted with the patients in the supine
position except for measuring the external and internal rotation angles. The external and internal rotation angles
were measured in the prone position at 90◦ flexion knee joint. The hip abductor strength was measured using ahand-held dynamometer (µTAS F-1, Anima Co., Ltd.) in the supine position. The sensor pad was fixed to the
distal thigh. The maximum isometric contraction for 5 seconds was performed three times on each side, and the
maximum value was determined as the weight ratio (kgf/kg). The knee extension strength was also measured
using the hand-held dynamometer. The sensor pad was fixed at the distal leg in a seated lower leg droop position,
Scientific Reports |Vol:.(1234567890)(2022) 12:9843 |https://doi.org/10.1038/s41598-022-14070-8

2

www.nature.com/scientificreports/

Figure 1.  Configuration of the IMUs. (a) The IMU with the accelerometer and gyroscope. (b) The special bandfor wearing the IMU on the shank. (c) The position and coordination of the IMU. Two IMUs are attached to theshank just above the malleolus at a distance of r. IMUs are attached to the shank in the position 0.03 m above
the malleolus. The axes x, y, and z are the coordinate system of the IMU, where the z-axis is perpendicular to thesagittal plane formed by the y and z-axes.

and the maximum isometric contraction for 5 seconds was performed three times on each side. The maximum
value was measured as the ratio of body weight (kgf/kg). MJS was measured by an orthopaedic surgeon using asimple radiograph. In addition, the severity of the patients with hip OA were measured by the JOA hip score, aphysician-completed disease-specific scale consisting of four items: pain (40 points), ROM (20 points), ability
to walk (20 points), and activities of daily living (20 points). The JOA hip score was used because the JOA scoreis designed in term of the Japanese life style. In addition, it was reported that there was no significant difference
in total score between the Harris hip score and the JOA hip score, and there was a strong correlation between­them32. Hip pain during walking was measured using the visual analogue scale. The stage of hip OA was classified by orthopaedic surgeons based on the Japanese Orthopedic Association’s osteoarthritis staging system.

Apparatus and gait measurement.

The IMUs (TSND121, ATR-Promotions) that were used for measured gait are shown in Fig. 1a. Using this IMU, we measured the acceleration and angular velocity to estimate
the gait parameters. The two IMUs were attached on the shanks on both sides just above the malleolus using a
special band (Fig. 1b). The attachment position and coordinate system of the IMUs are shown in Fig. 1c. The
x , y , and z axes represented inferior/superior, posterior/anterior, and medial/lateral directions, respectively.
The measurement ranges of acceleration and angular velocity were ±8 G and ±1000 dps, respectively, and thesampling frequency was set to 100 Hz. The size of the TSND121 is 37 mm × 46 mm × 12 mm and the weight isapproximately 22 g.
We estimated spatio-temporal gait parameters using the method proposed by Mao et al30. Spatio-temporalparameters were estimated via the double integration of the linear acceleration transformed by the IMU orientation information. To reduce the integral drift error, an inverted pendulum model, applied with a linear error
model, was introduced at the mid-stance to estimate the update v­ elocity30. The motion of the IMU at the midstance can be modelled as a rotational motion in a three-dimensional space. The position vector r and angularvelocity in the laboratory coordinate frame were computed from the estimated orientation of ­IMU30. By thismethod, we estimated the maximum foot clearance, stride length, stride speed, stride duration, stance durationand swing duration for left and right lower limbs.

Task and procedure. For the measurements, participants walked about 30 m down a straight and flat corridor at their self-selected speed. The measurement was carried out with participants familiar shoes with flat soles.
The number of left and right strides were measured; at least 30 for each stride. All measurements were taken once
for each participant. All participants walked without any assistive devices.
Statistical analysis. We used the fourth to the 13th stride of each leg to calculate means for each gaitparameter. We aggregated each parameter for the left and right legs instead of affected and unaffected sides
to simply compare the results of the LOA and ROA patients with the HCs. The mean of each spatio-temporalparameter and lateral distance at swing phase were analysed using two-way mixed ANOVA. The factors for the
ANOVA were three groups (the LOA patients, ROA patients, and HCs) and two legs (left and right legs). For
multiple comparisons, we used Shaffer’s method. We used the Student’s T-test and the Mann-Whitney U test
for the participant demographics, affected/unaffected physical functions and JOA hip score with and without

Scientific Reports |(2022) 12:9843 |https://doi.org/10.1038/s41598-022-14070-8

3Vol.:(0123456789)

www.nature.com/scientificreports/

Figure 2.  An example of the three-dimensions estimated foot trajectory obtained from shank during walking.
(a) Three-dimensional foot trajectory of healthy control (HC) left leg, (b) left hip osteoarthritis (LOA) left
leg, (c) right hip osteoarthritis (ROA) left leg. An example of (d) sagittal plane, (e) horizontal, and (f) coronalplane of the three-dimensional estimated foot trajectory obtained from shank during gait. An example of foottrajectory in the sagittal (g), horizontal (h), and frontal planes (i) for the left and right legs of HC. The black
dots indicate the positions of toe off, maximum foot clearance, and swing down during the swing phase ofwalking (g–i). In the horizontal and frontal planes, the midline was set as 0, and the lateral distance (LD) fromthe midline was examined with the swing leg side as (+) and the stance leg side as (−) (h,i). The LD farthestfrom the midline to the swing legs side was defined as the maximum, and the LD closest to the stance legs side
was defined as the minimum (h). From left to right and top to bottom: HC, LOA, ROA. Anterior-Posterior: AP,
Cranio-caudal: CC, Left-right: LR.

normal distribution, respectively. In addition, the stage of hip OA was analysed using the chi-square test. All
statistical analyses were performed using R with the significance level set at p < 0.05.

Results

Foot trajectory. An example of each group in the three-dimensional foot trajectory of the left leg during
walking is shown in Fig. 2a–c. An example of each group of the three-dimensional estimated foot trajectory inthe sagittal, horizontal, and frontal planes during walking are shown in Fig. 2d–f. An example of foot trajectoryin the sagittal (Fig. 2g), horizontal (Fig. 2h), and frontal planes (Fig. 2i) for the left and right legs of HC. The
black dots indicate the positions of toe off, maximum foot clearance, and swing down during the swing phase ofwalking (Fig. 2g–i). In the horizontal and frontal planes, the midline was set as 0, and the lateral distance (LD)Scientific Reports |Vol:.(1234567890)(2022) 12:9843 |https://doi.org/10.1038/s41598-022-14070-8

4

www.nature.com/scientificreports/

Figure 3.  All gait parameters of (a) maximum foot clearance, (b) stride length, (c) speed, (d) stride duration,(e) stance duration, (f) swing duration. Blue is the left leg, orange is the right leg, and error bars indicate the SD.
From left to right: healthy control (HC), left hip osteoarthritis (LOA), right hip osteoarthritis (ROA). * indicatessignificance at p < 0.05 and ** indicates significance at p < 0.01.
from the midline was examined with the swing leg side as (+) and the stance leg side as (-) (Fig. 2h,i). The LD
farthest from the midline to the swing legs side was defined as the maximum, and the LD closest to the stancelegs side was defined as the minimum (Fig. 2h). In the sagittal plane, the stride length of the patient with hip
OA is shorter than that of the HC, but the maximum foot clearance does not seem to be significantly different(Fig. 2d). Therefore, the foot trajectory of the patient with hip OA shrinks only in the direction of walking. The
foot trajectory in the horizontal and frontal planes of the HC and the patient with hip OA appears to be very different (Fig. 2e,f). The foot trajectory in the horizontal and frontal planes are in approximate symmetry in the HC,
but in asymmetry and varied in the patient with hip OA, and the foot trajectory of the unaffected side is more
medial than that of the affected side(Fig. 2e,f). In addition, the foot trajectory of the affected side of the patientsof hip OA did not go medially, but spread laterally in some patients. However, the variation could be caused byindividual differences(Fig. 2e,f). Therefore, the three-dimensional foot trajectory also appears to have a larger
variation for the unaffected side limb of the ROA than the affected side limb of the LOA(Fig. 2b,c).
Due to space limitation, we show only important statistical results. All results of the statistical test are shownin the supplementary information.
Spatial gait parameters. The spatial gait parameters of the left and right lower limbs for HC, LOA, and ROA,
i.e., maximum foot clearance and stride length are shown in Fig. 3a,b. Mixed ANOVA was performed for themean of each gait parameter of HC, LOA, and ROA (Supplementary Table S1). Because significant interactions were found in the maximum foot clearance ( F(2, 72) = 3.94, p = 0.024, ηp2 = 0.099)and stride length( F(2, 72) = 11.82, p < 0.001, ηp2 = 0.247), we conducted the post hoc test for these gait parameters. When thesimple effect of the group was found, we conducted a multiple comparison using Shaffer’s method. The results
are shown in Table 2. For maximum foot clearance (Fig. 3a), there was no significant different between HC,
LOA, and ROA. The stride lengths (Fig. 3b) in patients with LOA and ROA were significantly shorter in both theaffected and unaffected sides than those in the HC. The stride length was significantly shorter in the affected sidethan in the unaffected side for both the patients with LOA and ROA.
For the LD at swing phase of spatial gait parameters, the mean, maximum and minimum LDs of the left
and right lower limbs of the HC, and the patients with LOA and ROA from the horizontal plane during toe off,
Scientific Reports |(2022) 12:9843 |https://doi.org/10.1038/s41598-022-14070-8

5Vol.:(0123456789)

www.nature.com/scientificreports/

Gait

Left/

Mean (SD)

Parameters

Right

HC

p-value
LOA

ROA

HCvsLOA

Maximum footLeft

0.11 (0.01)

0.11 (0.02)

0.12 (0.01)

No significant simple effect

Clearance (m)Right

0.11 (0.02)

0.11 (0.01)

0.11 (0.02)

No significant simple effect

HCvsROA

LOAvsROA

ηp2

StrideLeft

1.26 (0.12)

1.06 (0.13)

1.05 (0.11)< 0.001< 0.001

0.600

0.389

length (m)Right

1.26 (0.12)

1.09 (0.14)

1.02 (0.10)< 0.001< 0.001

0.048

0.394

Speed (m/s)

Left

1.33 (0.16)

1.01 (0.16)

0.98 (0.16)< 0.001< 0.001

0.441

0.513

Right

1.33(0.16)

1.04(0.17)

0.96(0.15)< 0.001< 0.001

0.066

0.512

StrideLeft

0.95 (0.07)

1.07 (0.10)

1.08 (0.10)

No significant main effectDuration (s)Right

0.95 (0.07)

1.07 (0.10)

1.08 (0.10)

No significant main effectStanceLeft

0.51 (0.05)

0.56 (0.08)

0.62(0.08)

0.025< 0.001

0.013

0.245

Duration (s)Right

0.51 (0.05)

0.60 (0.08)

0.58 (0.07)< 0.001< 0.001

0.454

0.239

Swing

Left

0.43 (0.03)

0.50 (0.05)

0.47 (0.03)< 0.001

0.004< 0.001

0.385

Duration (s)Right

0.44 (0.03)

0.47 (0.04)

0.50 (0.05)

0.008< 0.001

0.007

0.299

Table 2.  The result of multiple comparison tests for the group. For the gait parameters other than the
maximum foot clearance and the stride duration, the significant interactions and simple effect of group were
found. Thus, the multiple comparison was conducted for the groups for the left and right legs separately. In
the maximum foot clearance, a significant interaction was found but the simple effect was no significant. Thus,
the result of the multiple comparison for the main effect is shown. Means and (standard deviations) of gaitparameters. Healthy control (HC), left hip osteoarthritis (LOA), right hip osteoarthritis (ROA).

maximum foot clearance, and swing down are shown in Fig. 4. Mixed ANOVA was also performed for the mean,
maximum and minimum of each swing phase of LDs of the HC and the patients with LOA and ROA (Supplementary Table S2). Because significant interactions were found in the LD at toe off maximum ( F(2, 72) = 3.70,
p = 0.029, ηp2 = 0.093), toe off minimum ( F(2, 72) = 3.59, p = 0.033, ηp2 = 0.091), and swing down minimum( F(2, 72) = 7.20, p = 0.001, ηp2 = 0.167), we conducted the post post hoc test for these LDs of each swing phase.
The results are shown in Table 3. The LD at maximum foot clearance maximum (Fig. 4e) was significantly narrower on the affected side of the patient with ROA. The LD at toe off minimum (Fig. 4g) was significantly medialin the unaffected lower limb of the patient with ROA. The LD at swing down minimum (Fig. 4i) was significantly
more medial on the unaffected side than on the affected side for both patients with LOA and ROA.
Temporal gait parameters. The temporal gait parameters of the left and right lower limbs for the HC, patientswith LOA and ROA, speed, stride duration, stance duration, and swing duration, are shown in Fig. 3. Mixed
ANOVA was performed for the mean of each gait parameter of the HC and patients with LOA and ROA (Supplementary Table S2). Because significant interactions were found in the speed (F(2, 72) = 10.74, p =< 0.001,
ηp2 = 0.230), stance duration ( F(2, 72) = 25.80, p =< 0.001, ηp2 = 0.418), and swing duration(F(2, 72) = 27.44,
p =< 0.001, ηp2 = 0.433), we conducted the post hoc test for these gait parameters. When the simple effect of thegroup was found, we conducted a multiple comparison using Shaffer’s method. The results are shown in Table 2.
For the stride duration, only the main effect of the group was found in mixed ANOVA ( F(2, 72) = 16.84,
p =< 0.001, ηp2 = 0.319); therefore, we conducted the multiple comparison for the groups (Table 2). The speed(Fig. 3c) of the patients with LOA and ROA was significantly slower in both the affected and unaffected sides
than that of the HC, but there was no significant difference between the LOA and ROA. The speed was significantly slower in the affected side than in the unaffected side for both the patients with LOA and ROA. The stride
duration (Fig. 3d) was significantly longer in the left and right legs of the patients with LOA and ROA than thoseof the HC, but there was no significant difference in the stride duration between the patients with LOA and ROA.
In addition, there was no significant difference between the left and right legs in both the patients with LOA and
ROA. The stance duration (Fig. 3e) was significantly longer in both left and right legs of the patients with LOA
and ROA than those in the HC, but there was no significant difference between the patients with LOA and ROA.
In addition, the stance duration of the patients with LOA and ROA was significantly shorter in the affected sidethan that in the unaffected one. The swing duration (Fig. 3f) was significantly longer in both left and right legsof the patients with LOA and ROA than that in the HC, but there was no significant difference between thepatients with LOA and ROA. The swing duration of the patients with LOA and ROA was significantly longer in
the affected side than that in the unaffected side.

Discussion

This study investigated in detail the spatio-temporal parameters in three-dimensional foot trajectory featuresof female patients with end-stage hip OA using the IMUs attached to the shanks on the affected and unaffected
limbs. The results were summarised and the speed of each stride, maximum foot clearance, and the minimum
LDs of the foot during swing phase were especially highlighted either for their differences from previous studies
or for their novel perspectives.
In the summary of spatial gait parameters, there was no difference in the maximum foot clearance between
the patients with hip OA and the HCs while the stride length was significantly shorter in the patients with OA.
In addition, in patients with hip OA, the stride length was significantly shorter in the affected side compared to
Scientific Reports |Vol:.(1234567890)(2022) 12:9843 |https://doi.org/10.1038/s41598-022-14070-8

6

www.nature.com/scientificreports/

Figure 4.  All swing phase of (a) lateral distance (LD) at toe off, (b) LD at maximum foot clearance, (c) LD atswing down, (d) LD at toe off maximum, (e) LD at maximum foot clearance maximum, (f) LD at swing down
maximum, (g) LD at toe off minimum, (h) LD at maximum foot clearance minimum, (i) LD at swing downminimum. Blue is the left leg, orange is the right leg, and error bars indicate the participant’s SD. From left toright: healthy control (HC), left hip osteoarthritis (LOA), right hip osteoarthritis (ROA). * indicates significanceat p < 0.05 and ** indicates significance at p < 0.01.
those in the unaffected side. There was no difference in the mean, maximum and minimum LDs of the foot during
the swing phase between patients with hip OA and HCs in toe off and maximum foot clearance and swing down.
However, the unaffected sides were located more medially than the affected sides at the swing down minimum.
For the temporal gait parameters, the speed of patients with hip OA was significantly slower, and their stride
duration, stance duration, and swing duration were significantly longer in the patients with hip OA than thosein the HCs. In addition, in patients with hip OA, the speed, and stance duration were significantly decreasedon the affected side compared to those on the unaffected side; and the swing duration was significantly longer
on affected side than that on the unaffected side. However, there was no significant difference in stride duration
between the affected and unaffected sides.
Some of the results basically supported previous studies. The results for stride length, speed, stance duration,and swing duration were consistent with gait characteristics of individuals with hip OA in the previous ­study33.
On the other hand, the results for the speed of each stride and the maximum foot clearance differed form thosein some previous studies. In measuring the speed of each stride in the left and right lower limbs, there was asignificant difference in the stride speed between the affected and unaffected side in the patients with LOA and
ROA. This lower speed in the affected side would be caused by a decrease in hip ­moment24 and pain, resulting in
Scientific Reports |(2022) 12:9843 |https://doi.org/10.1038/s41598-022-14070-8

7Vol.:(0123456789)

www.nature.com/scientificreports/

Left/

Mean (SD)LDs at swing phase

Right

HC

p-value

LD at

Left

0.03 (0.02)

0.02 (0.01)

0.02 (0.01)

No significant simple effecttoe off (m)Right

0.02 (0.02)

0.02 (0.01)

0.02 (0.01)

No significant simple effect

LD at maximum

Left0.03 (0.03)

0.03 (0.02)

0.04 (0.02)

No significant simple effectfoot clearance(m)Right

0.03 (0.03)

0.03 (0.02)

0.03 (0.02)

No significant simple effect

LD at

Left

0.01 (0.02)

0.01 (0.01)

0.01 (0.01)

No significant simple effectswing down(m)Right

0.01(0.02)

0.01(0.01)

0.01(0.01)

No significant simple effect

LD at Toe off

Left

0.06 (0.02)

0.05 (0.03)

0.06 (0.03)

No significant simple effectmaximum (m)Right

0.05 (0.02)

0.06 (0.03)

0.05 (0.03)

No significant simple effect

LD at maximum footLeft

0.08 (0.04)

0.08 (0.05)

0.09 (0.05)

No significant simple effectclearance maximum (m)Right

0.08 (0.04)

0.09 (0.04)

0.07 (0.04)

No significant simple effect

LD at swing down

Left

0.04 (0.02)

0.04 (0.02)

0.04 (0.02)

No significant simple effectmaximum (m)Right

0.03 (0.02)

0.04 (0.02)

0.03 (0.02)

No significant simple effect

LD at Toe off

Left− 0.01 (0.02)− 0.01 (0.02)− 0.01(0.03)

No significant simple effectminimum (m)Right− 0.01 (0.02)− 0.01 (0.03)

0.00 (0.01)

No significant simple effect

LD at maximum footLeft

− 0.03 (0.04)− 0.01 (0.03)− 0.02 (0.05)

No significant simple effectclearance minimum (m)Right− 0.02 (0.04)− 0.02 (0.04)− 0.01 (0.03)

No significant simple effect

LD at swing down

Left

− 0.02 (0.02)− 0.01 (0.02)− 0.02 (0.02)

No significant simple effectminimum (m)Right− 0.01 (0.02)− 0.02 (0.03)− 0.01 (0.02)

No significant simple effect

LOA

ROA

HCvsLOAHCvsROA

LOAvsROA

Table 3.  The result of multiple comparison tests for the group. For the lateral distance (LD) at swing phaseother than the toe off maximum, toe off minimum and swing down minimum, significant interactions were
found. Means and (standard deviations) of LDs at swing phase. Healthy control (HC), left hip osteoarthritis(LOA), right hip osteoarthritis (ROA).

a decrease in affected stride length. However, a previous study showed no significant difference in speed between
the affected and unaffected ­sides34. This difference between that study and ours is likely caused by the higher
radiographic severity of the patients in our study than that in the previous one. Thus, the slower stride speed in
the affected side compared with the unaffected side would be associated with heavy radiographic severity. In fact,
the hip moment loading asymmetry is associated with OA radiographic severity. Foucher et al. demonstrated
that with increasing Kellgren-Lawrence grade, subjects exhibited a greater degree of gait abnormalities known
as motion ­discontinuity35.
In the patients with hip OA, the hip extension-flexion angle during gait ­decreases36. From this perspective, wemight expect a decrease in the maximum foot clearance. However, the results of this study revealed no significant difference in the maximum foot clearance between the patients with hip OA and HCs, though their stride
lengths were shorter than the HCs. Thus, regardless of the small hip extension-flexion angle, the patients withhip OA could raise their foot as high as HCs. In the future, the hip extension-flexion angle and foot trajectoryof patients with hip OA during gait should be measured at the same time.
One possible explanation for patients keeping the max foot clearance is as follows. The sagittal view of thepelvis during push-off of hip OA showed 2.5 times more pelvic upward tilt than that of the nonclinical ­subjects17.
This large pelvic tilt could guarantee the maximum foot clearance as high as in healthy individuals. In addition,knee joint angle during walking increases in patients with hip OA compared with the H­ C25, which could also
guarantee the maximum foot clearance. Another possibility for maintaining the maximum foot clearance could
be increased strength of foot muscles. Although the degree of the ankle joint movement was not different in thepatients with hip OA compared with that in the ­HCs25, the ankle dorsiflexion increased in both the affected andunaffected sides of the patients with hip OA compared with the HCs. In addition, the electromyogram of thetibialis anterior muscle in the unaffected side also increased in the patients with hip ­OA37. These possibilities
should be investigated by measuring more indices relating to gait, including the foot trajectory.
Moreover, the trajectory analysis for the lateral direction importantly suggested a new perspective. LD at theswing down minimum in patients with hip OA was located significantly more medially on the unaffected sidethan on the affected one. In the frontal plane, there was no significant difference between affected and unaffectedsides with respect to hip adduction angle. Thus, the medial LD at swing down minimum would not relate to
the ROM of the angle. The medial LD could relate to an exaggerated lateral bending of the pelvic and trunk toaffected side during gait in hip OA patients, which is called a Duchenne limp. The Duchenne limp is a movement performed in order to compensate for weakened hip abductor muscles in the affected side to maintain astance on the affected l­eg26,38. However, this compensation causes the centre of gravity to move to the affectedside. Thus, this shift of the centre of gravity is one possible reason for medial LD at swing down minimum inpatients with hip OA.
However, the present experiment specifically showed that there was no significant difference in the LD atmean and maximum, but LD at swing down minimum for patients with hip OA was located significantly more
medially in the unaffected limb than that in the affected limb. When the unaffected limb swings down in theswing phase, the affected limb is at the terminal stance phase. In patients with hip OA, the anterior femoral head

Scientific Reports |Vol:.(1234567890)(2022) 12:9843 |https://doi.org/10.1038/s41598-022-14070-8

8

www.nature.com/scientificreports/­coverage39 and peak hip extension angle of the affected limb d­ ecrease26. Thus, the hip external rotation (femoral
external rotation relative to the pelvis) movement could also decrease the anterior coverage of the femoral head
during terminal stance, and could be compensated by pelvic rotation, which may lead to a medial trajectory of
the swing phase.
The incidence of falls within 1 year is high in female patients with end-stage hip OA, and the main causesof falls are tripping (43.5%) and loss of balance (37.0%)10. The causes of tripping have been discussed from theviewpoints of the foot trajectory. For example, the minimum foot clearance (MFC) and minimum toe clearance(MTC) have been reported as risk factors for ­falls40,41. On the contrary, the causes of loss of balance have not been
considered within the context of the foot trajectory. The gait features in LD are potentially related to the loss ofbalance due to the increased sway of the centre of gravity to the left and right. It could be important to instruct
the patient to walk with the swing of the unaffected side limb slightly outward to avoid falling. In the future, it isnecessary to investigate whether this gait instruction is effective in preventing falls in patients with hip OA andwhether this affects the function of the affected side limb.

Conclusions

This study aimed to investigate the spatio-temporal features, especially, the foot trajectory, in gait parameters ofpatients with end-stage hip OA using IMUs attached on both shanks. The stride length of the patients with hip
OA was significantly shorter on both the affected and unaffected sides than that of the HCs; but maximum footclearance was not significantly different between the patients with hip OA and HCs. Thus, the foot trajectoryof the patient with hip OA was less than the HC only in the forward direction. This result suggests that hip OA
compensates the maximum foot clearance in gait as much as healthy people to decrease fall risk. The horizontal
and frontal planes foot trajectories are almost symmetrical in HCs, but appear asymmetrical in patients with hip
OA. In the horizontal plane foot trajectory of patients with hip OA, the mean LD from the midline of toe off,
maximum foot clearance, and swing down during the swing phase were not significantly different from those ofHCs, but the swing down minimum of the swing phase in patients with hip OA was located significantly more
medially on the unaffected side than on the affected one. The stride length and speed were significantly decreased
in both affected and unaffected sides compared with the HC. The stride length and speed were significantly lower
in the affected side than in the unaffected side. The stride duration was significantly longer in the hip OA thanthose of the HC. The stance and swing durations were shorter and longer in the affected side than in the unaffected side. These temporal gait parameters were consistent with gait characteristics of individuals with hip OA
in a previous study. In this study, a new gait feature was discovered by detailed evaluation of three-dimensionalfoot trajectory of female patients end-stage hip OA. In the future, it is necessary to clarify the relationship between
these gait characteristics, clinical symptoms, and physical functions.

Date availability

The data that support the findings of this study are available from the corresponding author upon reasonable
request.
Received: 2 December 2021; Accepted: 31 May 2022

References

1. Yoshimura, N. et al. Acetabular dysplasia and hip osteoarthritis in Britain and Japan. Br. J. Rheumatol. 37, 1193–1197. https://​doi.​
org/​10.​1093/​rheum​atolo​gy/​37.​11.​1193 (1998).
2. Birrell, F. et al. Predicting radiographic hip osteoarthritis from range of movement. Rheumatology 40, 506–512. https://​doi.​org/​
10.​1093/​rheum​atolo​gy/​40.5.​506 (2001).
3. Arokoski, M. H., Haara, M., Helminen, H. J. & Arokoski, J. P. Physical function in men with and without hip osteoarthritis. Arch.
Phys. Med. Rehabilitat. 85, 574–581. https://​doi.​org/​10.​1016/j.​apmr.​2003.​07.​011 (2004).
4. Bierma-Zeinstra, S. M. et al. Joint space narrowing and relationship with symptoms and signs in adults consulting for hip pain inprimary care. J. Rheumatol. 29, 1713–1718 (2002).
5. Brown, M. D., Gomez-Marin, O., Brookfield, K. F. & Li, P. S. Differential diagnosis of hip disease versus spine disease. Clin. Orthop.
Relat. Res. 1976–2007(419), 280–284. https://​doi.​org/​10.​1097/​00003​086-​20040​2000-​00044 (2004).
6. Hirata, S. et al. Ambulatory physical activity, disease severity, and employment status in adult women with osteoarthritis of thehip. J. Rheumatol. 33, 939–945 (2006).
7. Nüesch, E. et al. All cause and disease specific mortality in patients with knee or hip osteoarthritis: Population based cohort study.
BMJ 342, d1165. https://​doi.​org/​10.​1136/​bmj.​d1165 (2011).
8. Nevitt, M. C., Cummings, S. R., Kidd, S. & Black, D. Risk factors for recurrent nonsyncopal falls: A prospective study. JAMA 261,
2663–2668 (1989).
9. Foley, S., Lord, S. R., Srikanth, V., Cooley, H. & Jones, G. Falls risk is associated with pain and dysfunction but not radiographic
osteoarthritis in older adults: Tasmanian older adult cohort study. Osteoarthritis Cartilage 14, 533–539. https://​doi.​org/​10.​1016/j.​
joca.​2005.​12.​007 (2006).
10. Ikutomo, H. et al. Incidence and risk factors for falls in women with end-stage hip osteoarthritis. J. Geriatr. Phys. Therapy 42,
161–166. https://​doi.​org/​10.​1519/​JPT.​00000​00000​000156 (2019).
11. Tateuchi, H. et al. Daily cumulative hip moment is associated with radiographic progression of secondary hip osteoarthritis.
Osteoarthritis Cartilage 25, 1291–1298. https://​doi.​org/​10.​1016/j.​joca.​2017.​02.​796 (2017).
12. Schröter, J., Güth, V., Overbeck, M., Rosenbaum, D. & Winkelmann, W. The ‘entlastungsgang’. a hip unloading gait as a new conservative therapy for hip pain in the adult. Gait Posture 9, 151–157. https://​doi.​org/​10.​1016/​s0966-​6362(99)​00007-7 (1999).
13. Solomonow-Avnon, D. et al. Positive outcomes following gait therapy intervention for hip osteoarthritis: A longitudinal study. J.
Orthopaedic Res. 35, 2222–2232. https://​doi.​org/​10.​1002/​jor.​23511 (2017).
14. Aminian, K. et al. Evaluation of an ambulatory system for gait analysis in hip osteoarthritis and after total hip replacement. Gait
Posture 20, 102–107. https://​doi.​org/​10.​1016/​s0966-​6362(03)​00093-6 (2004).
15. Fang, M. A. et al. Clinical and spatiotemporal gait effects of canes in hip osteoarthritis. PM R 4, 30–36. https://​doi.​org/​10.​1016/j.​
pmrj.​2011.​08.​534 (2012).

Scientific Reports |(2022) 12:9843 |https://doi.org/10.1038/s41598-022-14070-8

9Vol.:(0123456789)

www.nature.com/scientificreports/
16. Tanaka, R., Shigematsu, M., Motooka, T., Mawatari, M. & Hotokebuchi, T. Factors influencing the improvement of gait ability after
total hip arthroplasty. J. Arthroplasty 25, 982–985. https://​doi.​org/​10.​1016/j.​arth.​2009.​06.​009 (2010).
17. Watelain, E., Dujardin, F., Babier, F., Dubois, D. & Allard, P. Pelvic and lower limb compensatory actions of subjects in an earlystage of hip osteoarthritis. Arch. Phys. Med. Rehabilit. 82, 1705–1711. https://​doi.​org/​10.​1053/​apmr.​2001.​26812 (2001).
18. Vogt, L., Banzer, W., Bayer, I., Schmidtbleicher, D. & Kerschbaumer, F. Overground and walkway ambulation with unilateral hip
osteoarthritis: Comparison of step length asymmetries and reproducibility of treadmill mounted force plate readings. Physiother
Theory Practice 22, 73–82. https://​doi.​org/​10.​1080/​09593​98050​02130​35 (2006).
19. Verlinden, V. J. et al. Asymptomatic radiographic hip osteoarthritis is associated with gait differences, especially in women: A
population-based study. Gait Posture 54, 248–254. https://​doi.​org/​10.​1016/j.​gaitp​ost.​2017.​03.​009 (2017).
20. Huang, C.-H., Aydemir, B., Jalasutram, A., Kabir, I. & Foucher, K. C. Impact of step length asymmetry on walking energetics inwomen with hip osteoarthritis: A pilot study. J. Biomech.https://​doi.​org/​10.​1016/j.​jbiom​ech.​2021.​110862 (2021).
21. Kyriazis, V. Pre-and postoperative temporal gait analysis of female hip monoarthritic patients operated with cementless hip
replacement: A 3-year study. Computing 37, 686–691 (1999).
22. Kyriazis, V. & Rigas, C. Temporal gait analysis of hip osteoarthritic patients operated with cementless hip replacement. Clin.
Biomech. 17, 318–321. https://​doi.​org/​10.​1016/​s0268-​0033(02)​00024-4 (2002).
23. Isobe, Y., Okuno, M., Otsuki, T. & Yamamoto, K. Clinical study on arthroplasties for osteoarthritic hip by quantitative gait analysis.
Bio-med. Mater. Eng. 8, 167–175 (1998).
24. Diamond, L., Allison, K., Dobson, F. & Hall, M. Hip joint moments during walking in people with hip osteoarthritis: A systematic
review and meta-analysis. Osteoarthritis Cartilage 26, 1415–1424. https://​doi.​org/​10.​1016/j.​joca.​2018.​03.​011 (2018).
25. Eitzen, I., Fernandes, L., Nordsletten, L. & Risberg, M. A. Sagittal plane gait characteristics in hip osteoarthritis patients with mild
to moderate symptoms compared to healthy controls: A cross-sectional study. BMC Musculoskelet. Disord. 13, 1–13. https://​doi.​
org/​10.​1186/​1471-​2474-​13-​258 (2012).
26. Zeni, J. Jr., Pozzi, F., Abujaber, S. & Miller, L. Relationship between physical impairments and movement patterns during gait inpatients with end-stage hip osteoarthritis. J. Orthop. Res. 33, 382–389. https://​doi.​org/​10.​1002/​jor.​22772 (2015).
27. Kiss, R. M. Effect of walking speed and severity of hip osteoarthritis on gait variability. J. Electromyogr. Kinesiol. 20, 1044–1051.
https://​doi.​org/​10.​1016/j.​jelek​in.​2010.​08.​005 (2010).
28. Wada, O., Asai, T., Hiyama, Y., Nitta, S. & Mizuno, K. Gait variability in women with hip osteoarthritis before and after total hip
replacement: A prospective cohort study. Am. J. Phys. Med. Rehabilit. 98, 866–871. https://d​ oi.o​ rg/1​ 0.1​ 097/p​ hm.0​ 00000​ 00000​ 01206(2019).
29. Kobsar, D. et al. Wearable inertial sensors for gait analysis in adults with osteoarthritis—A scoping review. Sensors 20, 7143. https://​doi.​org/​10.​3390/​s2024​7143 (2020).
30. Mao, Y., Ogata, T., Ora, H., Tanaka, N. & Miyake, Y. Estimation of stride-by-stride spatial gait parameters using inertial measurement unit attached to the shank with inverted pendulum model. Sci. Rep. 11, 1–10. https://​doi.​org/​10.​1038/​s41598-​021-​81009-w(2021).
31. Holm, I. et al. Reliability of goniometric measurements and visual estimates of hip rom in patients with osteoarthrosis. Physiother.
Res. Int. 5, 241–248. https://​doi.​org/​10.​1002/​pri.​204 (2000).
32. Fujisawa, M., Naito, M. & Asayama, I. A comparative study of hip joint functional scoring systems between Japanese orthopaedic
association hip score and Harris hip score. Seikeigeka 52, 628–633 (2001).
33. Constantinou, M., Barrett, R., Brown, M. & Mills, P. Spatial-temporal gait characteristics in individuals with hip osteoarthritis: A
systematic literature review and meta-analysis. J. Orthopaedic Sports Phys. Ther. 44, 291-B7. https://​doi.​org/​10.​2519/​jospt.​2014.​
4634 (2014).
34. Farkas, G. J. et al. Gait asymmetries in unilateral symptomatic hip osteoarthritis and their association with radiographic severity
and pain. Hip International 29, 209–214. https://​doi.​org/​10.​1177/​11207​00018​773433 (2019).
35. Foucher, K. C., Schlink, B. R., Shakoor, N. & Wimmer, M. A. Sagittal plane hip motion reversals during walking are associatedwith disease severity and poorer function in subjects with hip osteoarthritis. J. Biomech. 45, 1360–1365. https://​doi.​org/​10.​1016/j.​
jbiom​ech.​2012.​03.​008 (2012).
36. Zügner, R., Tranberg, R., Lisovskaja, V. & Kärrholm, J. Different reliability of instrumented gait analysis between patients withunilateral hip osteoarthritis, unilateral hip prosthesis and healthy controls. BMC Musculoskelet. Disord. 19, 1–9. https://​doi.​org/​
10.​1186/​s12891-​018-​2145-0 (2018).
37. Schmidt, A. et al. Unilateral hip osteoarthritis: Its effects on preoperative lower limb muscle activation and intramuscular coordination patterns. Gait Posture 45, 187–192. https://​doi.​org/​10.​1016/j.​gaitp​ost.​2016.​01.​028 (2016).
38. Reisman, D. S., Block, H. J. & Bastian, A. J. Interlimb coordination during locomotion: What can be adapted and stored?. J. Neurophysiol. 94, 2403–2415. https://​doi.​org/​10.​1152/​jn.​00089.​2005 (2005).
39. Uemura, K., Atkins, P. R., Maas, S. A., Peters, C. L. & Anderson, A. E. Three-dimensional femoral head coverage in the standing
position represents that measured in vivo during gait. Clin. Anatomy 31, 1177–1183. https://​doi.​org/​10.​1002/​ca.​23262 (2018).
40. Barrett, R., Mills, P. & Begg, R. A systematic review of the effect of ageing and falls history on minimum foot clearance characteristics during level walking. Gait Posture 32, 429–435. https://​doi.​org/​10.​1016/j.​gaitp​ost.​2010.​07.​010 (2010).
41. Nagano, H., Begg, R. K., Sparrow, W. A. & Taylor, S. Ageing and limb dominance effects on foot-ground clearance during treadmill
and overground walking. Clin. Biomech. 26, 962–968. https://​doi.​org/​10.​1016/j.​clinb​iomech.​2011.​05.​013 (2011).

Acknowledgements

This work was supported by JST, CREST Grant Number JPMJCR21C5, Japan.

Author contributions

Y.K., T.O., H.U., M.M., and Y.W. designed this study. Y.K. conducted the experiment and analysed the data. Y.K.,
T.O., M.M., Y.M., and Y.W. discussed and interpreted the results. Y.K., T.O., and H.U. drafted the manuscript,
and all authors reviewed the manuscript and approve the final version of the paper for publication.

Competing interests

The authors declare no competing interests.

Additional information

Supplementary Information The online version contains supplementary material available at https://​doi.​org/​
10.​1038/​s41598-​022-​14070-8.
Correspondence and requests for materials should be addressed to Y.K.
Reprints and permissions information is available at www.nature.com/reprints.

Scientific Reports |Vol:.(1234567890)(2022) 12:9843 |https://doi.org/10.1038/s41598-022-14070-8

10

www.nature.com/scientificreports/
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps andinstitutional affiliations.
Open Access This article is licensed under a Creative Commons Attribution 4.0 International
License, which permits use, sharing, adaptation, distribution and reproduction in any medium or
format, as long as you give appropriate credit to the original author(s) and the source, provide a link to theCreative Commons licence, and indicate if changes were made. The images or other third party material in thisarticle are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to thematerial. If material is not included in the article’s Creative Commons licence and your intended use is not
permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly fromthe copyright holder. To view a copy of this licence, visit http://​creat​iveco​mmons.​org/​licen​ses/​by/4.​0/.
© The Author(s) 2022

Scientific Reports |(2022) 12:9843 |https://doi.org/10.1038/s41598-022-14070-8

11Vol.:(0123456789)