Spatiotemporal gait characteristics post-total hip arthroplasty and its impact on locomotive syndrome: a before-after comparative study in hip osteoarthritis patients

Primary outcome measures

Gait movements were measured using an optical motion capture (OMC) system (Vicon Nexus 2.12; Vicon Motion Systems, London, UK) equipped with 12 infrared cameras (Vantage 5 and Vantage 8; Vicon Motion Systems, London, UK) and six force plates (OR6-5 and BP400600; Advanced Mechanical Technology, Inc.,Watertown, MA, USA). The participants wore skin-tight clothing (Under Armour, Baltimore, MD, USA) with 35 reflective markers (14 mm diameter) attached according to the Plug-in-Gait model protocol (Kadaba, Ramakrishnan & Wootten, 1990). The sampling frequency was set at 100 Hz, and all the equipment took measurements synchronously. In this study, the OMC system was used to obtain spatiotemporal gait parameters. However, since this study does not use kinematic or kinetic data, any alternative systems capable of obtaining spatiotemporal gait parameters would be sufficient, and it is not necessary to use the OMC system.

Spatiotemporal gait parameter: The patient walked barefoot freely and was measured three times after practicing walking without discomfort. The data of the movement the patient was most satisfied with were adopted. An analysis software (Vicon Nexus 2.12) was used to calculate spatiotemporal gait parameters (cadence, stride time, step time, single support time, double support time, stride length, step length, and walking speed). First, the “Detect Events from a Bertec Force Plate Treadmill” program in Vicon Nexus was used to determine a gait cycle based on the timing of initial contact and toe-off. Then, the “Gait Cycle Parameters Calculator” program was used to calculate spatiotemporal gait parameters based on the coordinate data of the reflective markers. The instructions for quantifying the movements were: (1) walk freely; (2) rest for 20 s between movements.

Secondary outcome measures

LS was evaluated using the following three LS risk tests. The clinical decision limits and total clinical decision limits of each test were classified as stages 0–3. Measurement procedures and assessments were performed before and three months after THA according to the JOA guidelines. Data were collected as previously described in Miyazaki et al. (2021).

1. The stand-up test: The stand-up test evaluates leg strength by the height at which the participant subject can stand up from both legs or a single leg at four different heights: 40 cm, 30 cm, 20 cm, and 10 cm (Nakamura & Ogata, 2016). The test starts with sitting on a 40-cm platform and standing up with both legs. If it can be successfully done, the procedure is repeated with single-leg standing alternating between the left and right legs. If the participant subject cannot stand up on either leg on the 40-cm platform, the test is considered a failure and repeated on a 10-cm lower platform. The scoring system employed nine performance scores (Ogata et al., 2015): 0 (inability to stand); 1, 2, 3, or 4 (stand using both legs from a height of 40, 30, 20, and 10 cm, respectively); and 5, 6, 7, and 8 (stand using one leg from a height of 40, 30, 20, and 10 cm, respectively). Clinical decision limits stages refer to the following: stage 3-unable to stand on both legs from a height of 30 cm; stage 2-unable to stand on both legs from a height of 20 cm but able to stand from a height of 30 cm; and stage 1-unable to stand on either leg from a height of 40 cm but able to stand on both legs from a height of 20 cm. Scores <2, <3, and <5 were classified as clinical decision limits stages 3, 2, and 1, respectively. The instructions to quantify motion were given. (1) Fold arms in front of the chest at a sitting position. (2) Place feet shoulder-width apart. (3) Position lower legs at an angle of approximately 70° to the floor. (4) Stand up without gaining momentum. (5) Maintain the standing posture for 3 s.

2. The two-step test: The two-step test evaluates walking ability, including lower limb muscle strength, balance, and flexibility (Yoshimura et al., 2015), by using the maximum two stride lengths that can be taken from a stationary standing position without losing balance. The test score was calculated as the “2-step value” by dividing the maximum two stride lengths (cm) by the patient’s height (cm). The 2-step values <0.9, ≥1.1 to <1.3, and ≥0.9 to <1.1 were classified as clinical decision limits stages 3, 2, and 1, respectively. The instructions to quantify motion were given. (1) Align toes at the starting line with a stationary standing position. (2) Take two of the longest possible steps forward, then align toes together in a stationary standing position. (3) If the participant subject loses balance, start over. (4) Measure the stride length of the two steps. (5) Perform two times and adopt the better score.

3. GLFS-25 (Seichi et al., 2012): The GLFS-25 is an easy-to-use instrument for early diagnosis developed to screen the elderly with risk factors of motor dysfunction. The test is a self-administered questionnaire consisting of 25 questions: four questions on pain, 16 questions on ADL, three questions on social functions, and two questions on mental health in the past month. The 25 questions were graded on a 5-point scale from 0 (average) to 4 (most severe). The most severe was scored as 100 points, with higher scores indicating a decline in motor function. Clinical decision limits stage 3 scores ≥24 points, stage 2 scores ≥16 to <24 points, and stage 1 scores ≥7 to <16 points.

4. The total clinical decision limits: Total clinical decision limits stage is determined based on the results of the stand-up test, the two-step test, and the GLFS-25. Total clinical decision limits stage refers to the following: stage 3-progressive decline in mobility functions, which interferes with social participation; stage 2-progressive decline in mobility functions; and stage 1-beginning decline in mobility.

PC1: Overall walking ability

In PC1, among the 16 spatiotemporal gait parameters, the absolute factor loadings of 14 variables were between 0.2 and 0.3. The variables with positive factor loadings included eight parameters: cadence, stride length, step length, and walking speed on both the THA and non-THA sides, indicating that higher values represent greater walking ability. On the other hand, the variables with negative factor loadings included six parameters: stride time, step time, and double support time on both the THA and non-THA sides, indicating that lower values represent greater walking ability. Therefore, PC1 was interpreted as representing the overall walking ability of THA patients, and the term “overall walking ability” was used. Comparing before and three months after THA, PC1 showed a significant change toward positive, indicating improved overall walking ability three months after THA.

PC2: Stance phase

In PC2, the six variables with factor loadings of 0.3 or higher were single support time, stride length, and step length on both the THA and non-THA sides. A gait cycle is defined as “the period from the initial contact of one foot to the next initial contact of the same foot”. The gait cycle is divided into two phases: stance phase and swing phase. The stance phase refers to the period when the foot is in contact with the ground, and all six variables indicated the stance phase. Therefore, PC2 was interpreted as representing the stance phase of THA patients, and the term “stance phase” was used.

According to systematic reviews by Bahl et al. (2018), the evidence for improvements in pre-THA compared with three months after THA showed that the prolongation of single support time was strong, the increase in stride length was moderate, and the increase in step length was strong. Furthermore, Da Cunha et al. (2016) also reported significant improvements in the prolongation of single support time and increases in stride length and step length in post-THA. From these findings, the stance phase of the gait cycle is particularly characteristic of THA patients, and the change toward positive in PC2 indicates improvement in gait function.

PC3: Asymmetry of support time

In PC3, all variables with factor loadings of 0.3 or higher were related to support time. The double support time and single support time had opposite signs, indicating that higher values represent a shorter single support time on the THA side. The term “asymmetry of support time” was used to describe the differences between double support time and single support time on the THA side. In patients with limping, a shortened single support time on the THA side was observed compared to double support time on both the THA and non-THA sides, which can be inferred from the positive values of PC3.

Limping after THA is caused by pain, leg length inequality, nerve damage, and periprosthetic muscle dysfunction (Horstmann et al., 2013; Röder et al., 2012; Khan & Knowles, 2007). Additionally, limping is an adverse clinical outcome that affects patient satisfaction (Pongcharoen & Chaichubut, 2019). According to a large-scale cohort study that evaluated limping at the time of THA and five years after THA, the presence of limping after THA leads to patient dissatisfaction, and the strength of this association varies depending on the severity of the limping and the presence of associated pain (Bonnefoy-Mazure et al., 2022). PC3 is a component that evaluates the state of limping, and it is considered an important assessment indicator for improving patient satisfaction after THA.

Relationship between PC1, 2 and LS

PC1 demonstrated a strong influence on all three LS risk tests, particularly on GLFS-25. GLFS-25 is a self-administered questionnaire consisting of 25 questions designed as a screening tool for the elderly with mobility impairment, reflecting difficulties in ADL over the past month (Akai et al., 2016; Seichi et al., 2012). Regarding the relationship between motor function and GLFS-25, previous studies reported clinical outcomes and findings of hip muscle strength three months after THA using GLFS-25 (Maezawa et al., 2018). However, there are no previous studies that have investigated the relationship between gait function and GLFS-25. The findings of this study suggest that improvements in overall physical walking ability strongly influence improvements in the GLFS-25 score obtained from the self-administered questionnaire. This implies that THA and rehabilitation have a significant impact not only on the improvement of overall physical walking ability but also on the improvement in ADL and social participation.

PC2 reveals a lesser influence than PC1 on all three LS risk tests. However, interestingly, it demonstrated an impact on the two-step test, which is used to assess walking ability. In a previous study Kobayashi & Ogata (2018), PCA was used to examine the relationship between gait patterns during normal walking and the two-step scores. It was reported that elderly with lower two-step scores had a smaller range of motion in the sagittal plane of the hip, knee, and ankle joints during the stance phase. The correlation between the change in PC2 and the change in the two-step score suggests that the two-step score decreases as both stride length and step length decrease. This finding indicates that the change toward negative in PC2 signifies decreased movement of the lower limb in the sagittal plane during the stance phase, indicating that the stance phase is closely related to the two-step test.

Relationship between PC3 and LS

Unlike PC1 and 2, PC3 did not demonstrate any improvements in LS. The results indicated that PC3 showed changes toward the opposite direction of improvement in regard to total clinical decision limits stage and stand-up test. Standing up requires lower limb muscle strength, joint range of motion, flexibility, and balance (Nakamura & Ogata, 2016; Ogata et al., 2015). Particularly, the range of motion of the hip and knee joints and knee extension muscle strength in the quadriceps femoris muscle are important. The outcomes of the present study indicate that PC1 and 2 had significant influences, while PC3 had minimal impact. PC3 showed a change toward negative, which means an improvement in limping three months after THA. Unfortunately, the improvement in limping did not lead to an improvement in LS. This may be due to the fact that only a limited number of participants in this study had strong limping before THA.