Weight-shifting-based robot control system improves the weight-bearing rate and balance ability of the static standing position in hip osteoarthritis patients: a randomized controlled trial focusing on outcomes after total hip arthroplasty

Introduction

Hip osteoarthritis (OA) is a degenerative joint disease that is characterized by clinical symptoms such as, limited joint range of motion, swelling, and pain. Total hip arthroplasty (THA) is a surgical procedure performed on patients with hip OA to alleviate pain, improve function, and enhance activities of daily living (ADL). THA is useful for improving quality of life (QOL), such as gait function (Laupacis et al., 1993), sports activities (Huch et al., 2005), and cardiopulmonary function (Ries et al., 1997). Patients who have received this treatment can return to their social lives early. Studies have reported that the implant survival rate for cemented THA ranges from 80%–91% at 10–15 years, 77%–84% at 20–25 years, and 73%–78% at 30–35 years (Callaghan et al., 2009; Hernández-Vaquero, Suárez-Vazquez & Fernandez-Lombardia, 2008; Mullins et al., 2007). Furthermore, in uncemented THA, the implant survival rate was 58%–96.4% at 10–14 years and 60%–77% at 15–23 years on the acetabular si+de (Tezuka et al., 2014; Emms et al., 2010; Civinini, D’Arienzo & Innocenti 2nd, 2008) and 92%–100% at 11–15 years, 85%–100% at 15–20 years, and 95% at ≥20 years on the femoral side (Ateschrang et al., 2014; Tezuka et al., 2014; Schuh, Schraml & Hohenberger, 2009; Lombardi Jr, Berend & Mallory, 2006). Both cemented and cementless procedures have been found to be effective in achieving long-term functional durability as demonstrated in previous studies.

Rehabilitation after THA has been shown to significantly improve muscle strength, hip range of motion, and gait ability (Heiberg et al., 2012; Gilbey et al., 2003; Wang, Gilbey & Ackland, 2002). Previous studies have also reported the effectiveness of incorporating resistance training, hydrotherapy, and bicycle ergometers into the rehabilitation program after THA to improve muscle strength and physical function, and reduce pain (Giaquinto et al., 2010; Liebs et al., 2010; Suetta et al., 2004). Furthermore, accelerated perioperative care and rehabilitation intervention can significantly shorten hospital stays and improved QOL three months after surgery (Larsen et al., 2008). In particular, performing early rehabilitation following THA is crucial for enhancing the weight-bearing amount (WBA) on the operated side, improving balance and gait (Miyazaki et al., 2022; Matheis & Stöggl, 2018; Hol et al., 2010). Nonetheless, conventional treatment methods may not always yield in satisfactory results in improving balance and gait by enhancing WBA (operated side) and weight-bearing ratio (WBR). To overcome this issue, we introduced a novel weight shifting–based robot control system (LOCOBOT), which is capable of controlling a spherical robot on a floor by changing the center of pressure (COP) on a force–sensing board (Yamako et al., 2023). The LOCOBOT is an exercise robot designed to be enjoyable and motivate patients when performing balance exercise.

The purpose of the present study was to elucidate the effect of rehabilitation using the LOCOBOT on WBR and balance ability in a static standing position in patients with unilateral hip OA who underwent primary uncemented THA.

Materials & Methods

Patient selection

Inclusion criteria were (1) patients who were diagnosed with Kellgren–Lawrence (K–L) grade 3 or 4 hip OA on the operated side and who underwent primary uncemented THA during the period from May 2021 to June 2022, (2) patients with K–L grade 0 normal hip on the non-operated side, and (3) patients who consented to participate in all evaluations prior to THA and the day prior to discharge from our institutions (post-THA day 12: 11.9 ± 1.6 days) after THA. Exclusion Criteria were (1) patients with rheumatoid arthritis, trauma, femoral head necrosis, and those who received bilateral THA or revision THA, (2) patients who were unable to participate in the evaluation 12 days after THA, (3) patients requiring load restriction of the lower extremity on the operated side after THA, and (4) patients with a post-THA rehabilitation length (days) of less than 7 days.

Following an assessment for eligibility, 26 patients were selected. All the patients underwent THA via the anterior minimally invasive surgery (AMIS) or transgluteal approach performed by four experienced orthopedic surgeons at the hospital with which the authors are affiliated. We used the minimization method for allocation, with patients randomly allocated to either the LOCOBOT treatment group (LOCOBOT group) or the control group. Allocation adjustment factors included the following: (1) gender (male/female), (2) age (≥40 years and <68 years/ ≥68 years and ≤100 years), (3) operated side (right side/left side), (4) operated side disease classification (K–L grade 3/grade 4), (5) THA approach (AMIS approach/transgluteal approach), (6) Berg Balance Scale (BBS) (≥0 points and <21 points/ ≥21 points and ≤56 points), (7) 3-m timed up & go (3-m TUG) test (≥0.01 s and <10.00 s/ ≥10.00 s and ≤119.99 s). The numerical values for (6) and (7) were used as pre-THA data. For random allocation, we used the University Hospital Medical Information Network (UMIM) Internet Data and Information System for Clinical and Epidemiological Research, Cloud version (INDICE Cloud, UMIM, Tokyo, Japan). As a result, 13 individuals were each randomly allocated to the LOCOBOT and control groups (Fig. 1). In the LOCOBOT group, one patient who required load restriction of the lower extremity on the operated side after THA did not receive the allocated intervention. Two patients who were in poor physical health discontinued intervention. In the control group, one patient discontinued intervention due to poor physical health. Two patients were excluded from analysis. One patient had missing data of primary outcome measures. The other patient was excluded because the rehabilitation length after THA was 6 days. After careful selection and strict screening, 20 patients were included in the present study (Table 1) (Fig. 1). An expert orthopedic surgeon screened the patients and an expert physical therapist guided the patients throughout the rehabilitation program.

Table 1:

Subjects’ characteristics.

Characteristic	LOCOBOT group (n = 10)	Control group (n = 10)
Age (y)	65.3 ± 5.9	63.8 ± 6.5
Sex (male)	2	1
Height (cm)	155.0 ± 8.3	150.8 ± 8.4
Weight (kg)	55.2 ± 8.2	51.8 ± 10.9
BMI (kg/m2)	22.9 ± 2.5	22.6 ± 2.9
Length of hospitalization (day)	14.5 ± 1.4	14.6 ± 1.2
Length of rehabilitation (day)	8.6 ± 0.7	8.4 ± 1.1
Day of evaluation at discharge	11.5 ± 1.6	12.2 ± 1.6
Operated side (right)	6	5
Kellgren-Lawrence grade 4 (operated side)	7	8
THA approach (AMIS approach)	7	7

DOI: 10.7717/peerj.15397/table-1

Notes:

BMI

body mass index

THA

total hip arthroplasty

AMIS

anterior minimally invasive surgery

Age, height, weight, BMI, length of hospitalization, length of rehabilitation and day of evaluation at discharge values are means ± standard deviation.

Weight shifting–based robot control system

LOCOBOT^® (LOCOBOT Inc., Miyazaki, Japan) controls a spherical robot (Sprk+, Sphero Inc., Boulder, CO, USA) based on weight-shifting board (Fig. 2). Patients can move the robot on a floor in the direction of COP based on the force board (50 × 32 cm) which has four loadcells at each corner of the board. A laptop PC is connected to the board, the vector of COP is calculated from the loads, and the moving direction is wirelessly sent to the robot. The robot stops still while the COP is within the center circle (diameter of six cm) of the board. Patients need active COP control by postural changes on the board to freely move the robot and enjoy various synchronized games, such as track races, bowling, and tag in real space, together with other users. Our previous study showed that this robot system can efficiently train the ankle joint muscles, which would improve ankle joint stability for preventing falls (Yamako et al., 2023).

Results

Table 2 presents the difference in each parameter between the LOCOBOT and control groups before THA. For all parameters, there was no significant difference observed between the two groups. The mean WBR was 0.85 ± 0.21 in the LOCOBOT group and 0.77 ± 0.14 in the control group. The mean WBA (operated side) was 4.45 ± 0.53 N/kg in the LOCOBOT group and 4.28 ± 0.49 N/kg in the control group. Both groups had lower mean WBA on the operative side, and there was no significant difference between the two groups (mean WBR, p = 0.481; mean WBA on the operated side, p = 0.445).

Table 3 presents the difference in each parameter between the LOCOBOT and control groups 12 days after THA. The mean WBR was 1.07 ± 0.13 in the LOCOBOT group and 0.85 ± 0.25 in the control group. The mean WBA (operated side) was 5.04 ± 0.31 N/kg in the LOCOBOT group and 4.41 ± 0.67 N/kg in the control group. The LOCOBOT group showed significantly higher mean WBR and mean WBA (operated side) than the control group, indicating improvement (mean WBR, p = 0.024; mean WBA on the operated side, p = 0.019). The mean WBA (non-operated side) was 4.75 ± 0.31 N/kg for the LOCOBOT group and 5.38 ± 0.69 N/kg for the control group. ODA was 25.2 ± 7.0 mm ² in the LOCOBOT group and 62.2 ± 45.5 mm ² in the control group. The LOCOBOT group showed significantly lower mean WBA (non-operated side) and ODA than the control group, indicating improvement (mean WBA on the non-operated side, p = 0.022; ODA, p = 0.031).

Table 4 presents the change in each parameter between measurements taken before THA and 12 days after THA in the LOCOBOT group and control group, respectively. In the LOCOBOT group, the mean WBR (0.85 ± 0.21 to 1.07 ± 0.13, p = 0.013) and mean WBA (operated side) (4.45 ± 0.53 to 5.04 ± 0.31, p = 0.004) increased significantly from before THA until 12 days after THA, indicating improvement. The mean WBA (non-operated side) (5.33 ± 0.52 to 4.75 ± 0.31, p = 0.004) and ODA (50.9 ± 33.2 mm ² to 25.2 ± 7.0 mm ², p = 0.041) decreased significantly from before THA till 12 days after THA, indicating improvement. In the control group, TTL (57.1 ± 7.3 mm to 80.8 ± 25.6 mm, p = 0.010) and ODA (29.5 ± 18.6 mm ² to 62.2 ± 45.5 mm ², p = 0.028) increased significantly from before THA till 12 days after THA, indicating deterioration.

Discussion

In the present study, we included patients with unilateral hip OA who underwent primary uncemented THA. We evaluated WBR, WBA, TTL, and ODA in the static standing position as well as the OLS test, 3-m TUG test, BBS, and FR test before and 12 days after THA, to examine the specific effect of rehabilitation using the LOCOBOT. According to our search of the literature, there are currently no studies on the use of LOCOBOT in patients with hip OA who underwent THA. The present study is the first to examine the effect of treatment using the LOCOBOT on improving balance ability in the static standing posture, with a focus on WBR. The most important findings obtained in the present study are that the LOCOBOT can be operated from day 2 after THA and that of the mean length of rehabilitation of 8.6 days in the LOCOBOT group, the mean length of LOCOBOT usage was 7.2 days; in this short time, a significant improvement was obtained in terms of WBR and ODA. This result revealed that the LOCOBOT is a useful system that effectively improves WBR and balance ability in a short period after THA.

As a result of weight-bearing pain, patients with unilateral hip OA adopt a posture strategy of shifting the COG to the non-operated side (Fearon et al., 2017; Dekker, van Dijk & Veenhof, 2009). This postural strategy decreases the balancing ability during the standing posture (Truszczyńska et al., 2016). Reduced weight-bearing on the operated side occurs before THA and persists after THA. Consequently, an asymmetry of the trunk caused by unequal load of the legs should be corrected in the process of posture re-education after THA (Truszczyńska et al., 2014). The static standing posture WBR before THA was 0.85 in the LOCOBOT group and 0.77 in the control group, which indicates that the WBA was lower on the operated side before THA in both groups. In hip OA, movement, walking, and weight-bearing pain exacerbate as the disease progresses and becomes persistent. In the present study, all the participants had weight-bearing pain, and reduced WBA on the operated side was observed. Compared to the control group, the LOCOBOT group showed a significant higher in WBR and WBA on the operated side 12 days after THA. Furthermore, the LOCOBOT group showed a significant increase in WBR from 0.85 before THA to 1.07 twelve days after THA. In other words, WBA was greater on the non-operated side before THA, and 12 days after THA, the WBR of the operated and non-operated sides became equal, indicating that WBA increased on the operated side. Matheis & Stöggl (2018) reported that the additional mobilization and strength training targeting the muscles of the hip joint with full weight-bearing commencing from day 3 after THA resulted in improved hip range of motion and gait ability within 1 week when compared to standard physiotherapy. These results demonstrated the effectiveness of rehabilitation with full weight-bearing early after THA. Therefore, we found that treatment using the LOCOBOT improved WBR more effectively compared to standard treatment.

Several reports have examined the effectiveness and safety of early full weight-bearing after uncemented THA. Tian et al. (2017) conducted a meta-analysis and reported that early full weight-bearing in patients who received uncemented THA is safe and does not increase the onset of postoperative complications. Furthermore, Hol et al. (2010) conducted a systematic review and reported that early rehabilitation following primary uncemented THA should enable patients to promptly support their body weight within a tolerable range. The participants of the present study were allowed to support their body weight within a tolerable range from the first day after THA. Therefore, because the LOCOBOT could be used from day 2 following surgery and LOCOBOT operation was simple and safe, the treatment was effective, and a significant improvement was observed even in a short time with 7.2 days of LOCOBOT usage. Furthermore, LOCOBOT operation can be “enjoyable” because the robot feels like one’s own body, resulting in patients experiencing little subjective fatigue and a psychologically positive effect.

In the COG shift test, the balance ability is evaluated by analyzing parameters such as the distance, area, and speed of body shifts obtained by measuring the center of foot pressure in the static standing posture (Scoppa et al., 2013). The present results revealed no significant difference between the LOCOBOT and control groups before THA; however, 12 days after THA, the LOCOBOT group showed a significant improvement in ODA compared to the control group. The fact that COG shift in static standing posture improves after THA has been previously reported (Rasch, Dalén & Berg, 2010; Wykman & Goldie, 1989). Furthermore, Di Laura Frattura et al. (2022) conducted a systematic review and reported that for up to 2 weeks after THA, the balance deteriorated more than before THA. In the present study, treatment using LOCOBOT improved balancing ability in a short period, within 12 days after THA. This is the first report of a treatment that has improved balancing ability in such a short period, and is therefore clinically significant. Reinforcing symmetry, one of the components of balance, is important in improving balancing ability (Nichols, 1997). Anker et al. (2008) reported that increased weight-bearing asymmetry reduces the efficiency of hip load/unload mechanisms and increases ankle movements, thereby increasing postural instability. Based on these reports, we consider that this is attributed to an improvement in balance ability as a result of the WBA of the operated side and the non-operated side becoming equal through the treatment program using the LOCOBOT. Furthermore, changes from before THA to 12 days after THA included a significant increase in TTL and ODA in the control group but a significant decrease in ODA in the LOCOBOT group. Balance ability temporarily decreased soon after THA and then recovered normally; however, with treatment using the LOCOBOT, we found that an improvement could be obtained without a decline in balance ability after THA (Di Laura Frattura et al., 2022).

We found that treatment with the LOCOBOT effectively improved WBR and balance ability in just 12 days after THA. This is an important finding for patients who wish to resume work as soon as possible and for those who wish to return to their home as soon as possible. Furthermore, for elderly individuals, it may reduce the risk of falls and complications such as deep vein thrombosis. A topic for future study is whether treatment with the LOCOBOT can improve gait motion. To address this question, we plan to implement treatment with the LOCOBOT for 6 weeks after THA and elucidate changes in temporo-spatial parameters as well as shifts in the COG. If LOCOBOT therapy is found to be effective for improving walking ability in the early post-THA period, it will significantly shorten the time required to gain walking independence, which currently takes about 3 months after THA (Miyazaki et al., 2022). This will promote the acquisition of independence in ADL early after THA and help optimize the efficiency of medical care, both of which are clinically significant.

One limitation of the present study is that the ongoing effect of treatment with the LOCOBOT is not thoroughly examined. Evaluations in the present study were performed before THA and 12 days after THA. To obtain an accurate conclusion regarding the ongoing effect of treatment with the LOCOBOT, a larger sample size from 12 days after THA to 3 months after THA is needed. The blinding process was not observed in the study, so the device’s effect on THA may have been overestimated.

Conclusions

Patients with unilateral hip OA who underwent primary uncemented THA showed a significant improvement in the WBR, WBA on the operated side, and ODA 12 days after THA when using LOCOBOT, compared to the control group. Furthermore, in the LOCOBOT group, the WBA on the operated side, WBR, and ODA significantly improved from before THA to 12 days after THA. These findings indicate that the LOCOBOT is an effective tool for improving WBR and balance ability in the early postoperative period following THA. The use of LOCOBOT during rehabilitation early after THA can facilitate the acquisition of independence in ADL early after THA and help to optimize the efficiency of medical care.

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