Abstract
[Purpose] We investigated the immediate effects of an ankle-assist device (AAD) on gait speed, stride length, and cadence at postoperative weeks 1 and 2 following total hip arthroplasty. [Participants and Methods] Participants undergoing unilateral total hip arthroplasty were assigned to an AAD-assisted rehabilitation group or a conventional physiotherapy group. Gait speed, stride length, and cadence were measured immediately before and after rehabilitation sessions at postoperative weeks 1 and 2. Immediate effects were calculated as post minus pre changes. [Results] At postoperative week 2, the AAD group showed a significantly greater improvement in gait speed than the control group. Small improvements in stride length and cadence were also observed in the AAD group. [Conclusion] AAD-assisted rehabilitation may enhance immediate gait performance at postoperative week 2 after total hip arthroplasty, however, these findings should be interpreted as preliminary.
Key words: Total hip arthroplasty, Gait speed, Ankle-assist device
INTRODUCTION
Total hip arthroplasty (THA) is one of the most successful orthopedic procedures for reducing pain and restoring joint function in patients with end-stage hip disease. Despite substantial postoperative improvements in pain and joint mechanics, gait deficits often persist during the early recovery period. Gait speed, a primary indicator of mobility, is particularly affected, with many patients showing reduced propulsion, shorter stride length, and irregular cadence for several weeks after surgery. Because gait speed is strongly associated with quality of life, independence in daily activities, and long-term survival, its early improvement is a key goal of postoperative rehabilitation.
Gait speed is more than a simple measure of walking ability. It is a well-established biomarker of global health1). Previous work has also suggested that small but measurable changes in gait speed represent clinically meaningful functional improvements in older adults2). A landmark pooled analysis by Studenski et al. showed that gait speed predicts mortality across multiple cohorts of older adults. Improvements as small as 0.1 m/s have been associated with clinically meaningful gains in function3). Therefore, interventions that enhance gait speed, even acutely, are of particular interest after THA. Previous studies have reported reference values and age-related characteristics of gait speed in adults and older populations4,5,6,7,8,9). A study has reported that gait speed and other spatiotemporal gait parameters remain impaired for weeks to months following THA despite improvements in pain and joint function10). One of the key biomechanical determinants of gait speed is ankle push-off power11, 12). Classic biomechanical work by Winter and subsequent studies showed that ankle plantarflexion provides the dominant propulsive force in late stance and contributes substantially to forward progression and stride length11). Reduced ankle plantarflexor power has been identified as a major biomechanical factor contributing to slower walking speeds and compensatory proximal joint mechanics2, 13). Following THA, proximal discomfort, altered neuromuscular coordination, and generalized deconditioning often reduce effective push-off, which limits gait recovery14, 15). Technologies that augment ankle propulsion may therefore accelerate the restoration of efficient gait mechanics during early rehabilitation.
Ankle-assist devices (AADs) have emerged as promising adjuncts in rehabilitation16,17,18). AADs provide mechanical or powered support to the ankle joint during plantarflexion and may enhance forward propulsion, increase stride length, and improve cadence. Studies in neurological and geriatric populations report that ankle assistance can acutely increase gait speed and reduce metabolic cost during walking. However, despite these theoretical advantages, few studies have examined AAD use in the immediate postoperative period following THA, a phase marked by dynamic improvements in pain, joint motion, and neuromuscular control.
The early postoperative period, particularly the first 2 weeks after THA, represents a critical window for gait intervention. By the second postoperative week, pain typically decreases, patients begin transitioning away from assistive devices, and gait patterns begin to stabilize. This window may therefore be optimal for interventions that enhance distal propulsion, such as AADs. However, the immediate within-session effects of AAD use during this period remain unclear. Determining whether AADs produce measurable improvements in gait speed, stride length, and cadence before long-term training effects occur is essential for evaluating their clinical utility.
Given this background, we hypothesized that AAD-assisted gait training would produce greater immediate improvements in spatiotemporal gait parameters than conventional therapy alone, especially at postoperative week 2. The present study aimed to evaluate the immediate effects of AAD on changes in gait speed, stride length, and cadence at weeks 1 and 2 after THA.
The CoCoroe ankle assist device was selected because it assists ankle plantarflexion during gait and may facilitate walking performance during early postoperative rehabilitation.
PARTICIPANTS AND METHODS
Participants were patients who underwent elective unilateral THA for osteoarthritis or osteonecrosis. Demographic data, including age, sex, height, and body weight, were collected for 57 participants in the ankle-assist device (AAD) group and 39 participants in the control group. Mean age was 69.9 ± 12.7 years in the AAD group and 62.8 ± 10.7 years in the control group. Mean height was 153.2 ± 8.5 cm and 157.2 ± 9.6 cm, and mean body weight was 55.2 ± 11.3 kg and 57.9 ± 11.9 kg, respectively. The AAD group included 12 men and 45 women, and the control group included 8 men and 31 women.
Participants were divided into an AAD group and a control group based on the period during which the gait assessments were conducted. During the earlier phase of the study, rehabilitation sessions using the ankle assist device were implemented (AAD group), whereas during the later phase conventional rehabilitation without the ankle assist device was performed (control group). All surgical procedures were performed using standard techniques, and postoperative rehabilitation followed institutional protocols. Inclusion criteria were: the ability to walk independently before surgery, with or without assistive devices; no neurological or cardiopulmonary disorders affecting gait; and the ability to participate in repeated gait assessments at postoperative weeks 1 and 2. Exclusion criteria were cognitive impairment affecting comprehension of instructions, postoperative complications limiting ambulation, or refusal to participate in the study. Written informed consent was obtained from all participants before enrollment.
This study was approved by the Ethics Committee of Teikyo University (approval number: Teirin 22-025). Participants were assigned to either the AAD group or the control group. In the AAD group, the CoCoroe AAD (Yaskawa Electric Corporation, Fukuoka, Japan) provided powered assistance during ankle plantarflexion on the operated side. Assistance timing was synchronized with the terminal stance phase to augment the push-off mechanics11, 12). Each session included a familiarization period, followed by 10–15 minutes of AAD-assisted gait training under the supervision of a physical therapist. The control group received standard gait training without powered assistance.
Spatiotemporal gait parameters, including gait speed, stride length, and cadence, were measured using a walkway system (WalkWay MW-100; Anima Corporation, Tokyo, Japan).
Gait assessments were performed immediately before and after rehabilitation sessions at postoperative weeks 1 and 2. Outcome measures included gait speed (m/s), stride length (cm), and cadence (steps/min). Immediate effects were calculated as change values (Δ), defined as post-intervention values minus pre-intervention values. The primary outcome was Δ gait speed at postoperative week 2. Secondary outcomes were Δ gait speed at postoperative week 1 and Δ stride length and Δ cadence at postoperative weeks 1 and 2.
Statistical analyses were performed using SPSS Statistics version 29 (IBM Corp., Armonk, NY, USA). Within-group comparisons used paired t-tests, and between-group comparisons of Δ values used Welch’s t-tests. Statistical significance was set at p<0.05.
Participants in the AAD group wore the ankle assist device once during each assessment session (approximately 10–15 minutes), and gait parameters were measured immediately before and after wearing the device.
RESULTS
At postoperative week 1, both groups showed modest within-session increases in gait speed, with no significant between-group difference in the change in gait speed. Changes in stride length and cadence also showed small improvements in both groups, with no significant between-group differences.
At postoperative week 2, improvements in gait parameters were more pronounced in the AAD group. The primary outcome, change in gait speed, was significantly greater in the AAD group than in the control group. Improvements in stride length and cadence were also observed in the AAD group compared with the control group.
Table 1 summarizes the spatiotemporal gait parameters and their corresponding change values.
Table 1. Spatiotemporal gait parameters and immediate changes at postoperative weeks 1 and 2.
| Parameter | Week | Group | Pre (mean ± SD) | Post (mean ± SD) | Δ (mean ± SD) |
| Gait speed (m/s) | 1 | AAD | 0.54 ± 0.20 | 0.58 ± 0.20 | 0.04 ± 0.08 |
| 1 | Control | 0.62 ± 0.19 | 0.66 ± 0.18 | 0.03 ± 0.07 | |
| 2 | AAD | 0.61 ± 0.20 | 0.64 ± 0.22 | 0.03 ± 0.08* | |
| 2 | Control | 0.75 ± 0.19 | 0.74 ± 0.19 | −0.01 ± 0.08 | |
| Stride length (cm) | 1 | AAD | 70.5 ± 20.8 | 74.1 ± 20.5 | 3.59 ± 8.42 |
| 1 | Control | 76.7 ± 23.3 | 79.5 ± 22.7 | 2.86 ± 8.67 | |
| 2 | AAD | 76.3 ± 22.3 | 78.0 ± 24.0 | 1.72 ± 6.93 | |
| 2 | Control | 83.6 ± 22.5 | 87.6 ± 20.5 | 4.00 ± 8.73 | |
| Cadence (steps/min) | 1 | AAD | 89.5 ± 20.4 | 90.3 ± 16.1 | 0.83 ± 12.5 |
| 1 | Control | 96.8 ± 19.6 | 97.2 ± 16.4 | 0.39 ± 9.51 | |
| 2 | AAD | 93.5 ± 17.0 | 94.6 ± 15.3 | 1.04 ± 10.6 | |
| 2 | Control | 102 ± 15.2 | 100.7 ± 15.4 | −1.27 ± 7.04 |
Values are presented as mean ± standard deviation (SD). Δ indicates within-session change (post – pre). *p<0.05 for between-group comparison of Δ values. AAD: ankle assist device.
DISCUSSION
Prior work has suggested that increases of approximately 0.1 m/s in gait speed are clinically meaningful and associated with improved survival and independence in older adults3). Although the immediate gain of 0.03–0.04 m/s observed in this study is smaller than this threshold, achieving a measurable improvement within a single session suggests a short-term effect of the intervention.
Gait speed reflects the integrated function of multiple factors, including stride length, cadence, ankle push-off power, pain, neuromuscular coordination, and confidence during ambulation11, 12). The greater increase in gait speed observed in the AAD group at postoperative week 2 suggests that participants were increasingly able to utilize augmented ankle plantarflexion as recovery progressed. At this stage, reduced pain, improved joint stability, and more organized neuromuscular control may have facilitated more efficient gait patterns.
Ankle push-off plays a critical role in forward progression during gait. After THA, proximal dysfunction and generalized deconditioning often reduce effective push-off, which limits stride length and gait speed. By providing supplemental plantarflexion assistance during terminal stance, the AAD may have partially compensated for reduced propulsive capacity in the early postoperative period11, 12). The concurrent improvements in stride length and cadence in the AAD group support the interpretation that AAD use enhanced overall gait efficiency rather than increasing walking speed alone.
The lack of significant differences at postoperative week 1 may reflect physiological constraints in the very early postoperative phase. Pain, protective guarding, and incomplete neuromuscular coordination commonly limit load acceptance and effective push-off shortly after surgery. Under these conditions, the benefits of ankle assistance may be limited. As recovery progressed to postoperative week 2, participants appeared better able to benefit from distal propulsion assistance. Both groups showed a tendency toward gait improvement over time, which may partly reflect the natural recovery process following total hip arthroplasty. The improved gait parameters observed at postoperative week 2 may therefore reflect both device-related effects and the natural recovery that occurs during the early postoperative period.
The outcome measures used in this study, namely, gait speed, stride length, and cadence, are widely accepted indicators of walking performance and can be reliably measured in clinical settings. Assessing immediate within-session changes allowed evaluation of short-term responsiveness to the intervention without the confounding effects of longer-term adaptation or training effects.
This study had several limitations. First, the study design was not blinded, which may have introduced performance bias. Second, the sample size was moderate, and outcomes were limited to immediate within-session effects, so the persistence of these improvements and their impact on longer-term function remain unclear. Third, participant characteristics may have been influenced by variations in patient recruitment during the study period. These factors should be considered when interpreting the results.
Despite these limitations, the findings support the hypothesis that AAD-assisted gait training enhances immediate gait performance during early postoperative rehabilitation after THA, particularly at postoperative week 2. AAD use may be a feasible adjunct to conventional physiotherapy when appropriately timed during the recovery process. Future studies should employ randomized controlled designs with larger samples, extended follow-up periods, and additional outcome measures, including balance, metabolic cost, and patient-reported function, to further clarify the clinical utility of AAD-based interventions.
AAD-assisted rehabilitation produced significantly greater immediate improvements in gait speed at postoperative week 2 following total hip arthroplasty, with supportive changes in stride length and cadence. These findings suggest that integrating ankle-assisted devices into early postoperative rehabilitation may enhance gait recovery. This study did not adjust for potential confounding factors such as sex, bone strength, or comorbidities due to the limited sample size. Future studies with larger cohorts should consider multivariate analyses.
Funding
This study received no specific grants from any funding agency.
Conflict of interest
The authors declare that there are no conflicts of interest related to this study.
REFERENCES
- 1.Studenski S, Perera S, Patel K, et al. : Gait speed and survival in older adults. JAMA, 2011, 305: 50–58. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Farris DJ, Sawicki GS: The mechanics and energetics of human walking and running: a joint level perspective. J R Soc Interface, 2012, 9: 110–118. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Perera S, Mody SH, Woodman RC, et al. : Meaningful change and responsiveness in common physical performance measures in older adults. J Am Geriatr Soc, 2006, 54: 743–749. [DOI] [PubMed] [Google Scholar]
- 4.Bohannon RW: Comfortable and maximum walking speed of adults aged 20–79 years: reference values and determinants. Age Ageing, 1997, 26: 15–19. [DOI] [PubMed] [Google Scholar]
- 5.McGibbon CA: Toward a better understanding of gait changes with age and disablement: neuromuscular adaptation. Exerc Sport Sci Rev, 2003, 31: 102–108. [DOI] [PubMed] [Google Scholar]
- 6.DeVita P, Hortobagyi T: Age increases the skeletal versus muscular component of lower extremity stiffness during stepping down. J Gerontol A Biol Sci Med Sci, 2000, 55: B593–B600. [DOI] [PubMed] [Google Scholar]
- 7.Mündermann A, Asay JL, Mündermann L, et al. : Implications of increased medio-lateral trunk sway for ambulatory mechanics. J Biomech, 2008, 41: 165–170. [DOI] [PubMed] [Google Scholar]
- 8.Ishii Y, Noguchi H, Sato J, et al. : Recovery of walking ability after total hip arthroplasty. J Arthroplasty, 2011, 26: 1003–1008. [Google Scholar]
- 9.Perry J, Burnfield JM: Gait analysis: normal and pathological function, 2nd ed. Thorofare: SLACK, 2010. [Google Scholar]
- 10.Bennett D, Humphreys L, O’Brien S, et al. : Temporospatial parameters of hip replacement patients walking on a pressure-sensitive walkway. Clin Biomech Bristol Avon, 2008, 23: 594–599. [Google Scholar]
- 11.Winter DA: The biomechanics and motor control of human gait: normal, elderly and pathological, 2nd ed. Waterloo: University of Waterloo Press, 1991. [Google Scholar]
- 12.Hsiao H, Knarr BA, Higginson JS, et al. : The relative contribution of ankle moment and trailing limb angle to propulsive force during gait. Hum Mov Sci, 2015, 39: 212–221. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Lipfert SW, Günther M, Renjewski D, et al. : Impulsive ankle push-off powers leg swing in human walking. J Exp Biol, 2014, 217: 1218–1228. [DOI] [PubMed] [Google Scholar]
- 14.Nankaku M, Tsuboyama T, Kakinoki R, et al. : Gait analysis of patients in early stages after total hip arthroplasty: effect of lateral trunk displacement on walking efficiency. J Orthop Sci, 2007, 12: 550–554. [DOI] [PubMed] [Google Scholar]
- 15.Kanzaki H, Nankaku M, Kawanabe K, et al. : The recovery of the walking ability of patients at early stages after total hip arthroplasty from the perspective of the displacement of the center of gravity. J Phys Ther Sci, 2008, 20: 225–231. [Google Scholar]
- 16.Sawicki GS, Ferris DP: Powered ankle exoskeletons reveal the metabolic cost of plantar flexor mechanical work during walking with longer steps at constant step frequency. J Exp Biol, 2009, 212: 21–31. [DOI] [PubMed] [Google Scholar]
- 17.Collins SH, Wiggin MB, Sawicki GS: Reducing the energy cost of human walking using an unpowered exoskeleton. Nature, 2015, 522: 212–215. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 18.Awad LN, Bae J, O’Donnell K, et al. : A soft robotic exosuit improves walking in patients after stroke. Sci Transl Med, 2017, 9: eaai9084. [DOI] [PubMed] [Google Scholar]