Walking related performance fatigability in patients with knee osteoarthritis as compared to healthy controls

1 Introduction

Osteoarthritis (OA) is a chronic degenerative joint disease primarily affecting the articular cartilage of the synovial joint, with knee being the most commonly involved joint and ranked as the 11^th leading contributor to world-wide disability [1, 2], with 1 : 3 male to female ratio [3]. Increase in age, decreased mobility, muscle weakness, impaired balance, and altered patterns of muscle activation are associated with reduced quality of life and mortality in persons with knee OA [4] with 1.6 times higher mortality as compared to people without OA [5]. The abnormal gait mechanics and impaired muscle performance leads to an increase in energy expenditure and impaired energy recovery [6, 7], causing increase in perceived fatigue resulting in functional decline and disability in mobility related activities [8, 9].

In OA, over 40% of people aged 65 years and above have reported clinically significant walking-related fatigue [10]. Fatigue is reported as a subjective experience rather than objective [11], which does not provide a clear understanding of how fatigue works and its effect on activity limitations [1]. For this reason the concept of fatigability was introduced [12] which is defined as a measure of change in individual performance [13], and performance fatigability is an objective measure which is quantified by performing different physical activities [11]. However, despite the association of performance fatigability with negative health outcomes and walking related disability, it is still not well understood in patients with knee OA as it is mostly perceived as a subjective outcome [12]. Furthermore, most of the treatment strategies have been focused on reducing the level of pain rather than understanding the role of performance fatigue and fatigability in walking disability and functional decline in persons with knee OA [1, 9, 12]. Therefore, the purpose of this study was to determine the difference in walking-related performance fatigability in persons with knee OA as compared to their healthy counterparts.

2 Methodology

3 Results

Male to female ratio of the participants was 1 : 4 with 16 females and 4 males in both groups. No significant differences (p > 0.05) were observed between healthy controls and participants with knee OA in terms of age, weight, height and body mass index (BMI) as shown in Table 1. However significant differences (p < 0.05) were observed in total distance covered in 6 minutes as well as distance covered in each minute between the two groups, with healthy controls covering greater distance as compared to individuals with knee OA (Table 2), which can also be visualized via the linear trend lines in Fig. 1. Furthermore, a significant difference (p < 0.05) was observed in gait velocity and walking related performance fatigability between the two groups, with persons with knee OA exhibiting greater fatigability (Table 2).

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Fig. 1

Linear trend of distance covered throughout the 6MWT.

This is the first study of its kind to compare walking-related performance fatigability in individuals with knee osteoarthritis and healthy controls, revealing a significantly higher level of walking-related performance fatigability in those with knee OA. This is an important finding as walking related disability is one of the most important and commonly reported functional limitations associated with knee OA [1, 6], and this study highlights the importance of fatigability in terms of walking related disability, suggesting that pain is perhaps not the only factor that contributes to walking related disability and functional decline in persons with knee osteoarthritis. Furthermore, in accordance with the findings of the current study, existing literature shows that biomechanical changes due to knee osteoarthritis such as decreased gait velocity, stride length, cadence, knee range of motion, increased base of support and impaired muscle performance [16] result in increased energy expenditure and impaired energy recovery [7], eventually causing increased fatigue in persons with knee OA as compared to healthy controls for the same amount of distance covered [8, 12]. Moreover, the findings of the current study also showed that persons with knee OA possessed significantly lower gait velocity as compared to their healthy counterparts, which is in accordance with the findings of Hafer JF et al showing higher gait velocity for asymptomatic older adults as compared to older adults with knee OA [16]. It is worth noting, however, that the average gait velocity was lower in both groups compared to the study conducted by Hafer JF et al’s stdy, with a velocity of 0.956±0.156 m/s for healthy controls in the current study and 1.33-1.35 m/s in Hafer JF et al’s study, and a velocity of 0.77±0.236 m/s for persons with knee OA in current study and 1.18-1.21 m/s in Hafer JF et al’s study [16], even though the average age of participants was higher in Hafer JF et al’s sample. These results suggest that the Pakistani population may be at a higher risk of functional decline and walking-related disability due to ethnographic and lifestyle differences, and thus more importance should be given in this regard. These findings are consistent with previous research indicating significant differences in the normative values of the 6-minute walk test between Pakistani and Western community-dwelling older adults, with 363±76.89 m for females and 425.18±73.98 m for males aged 56-65 years in the Pakistani population [17], and on the other hand 538±92 m for females and 572±92 m for males aged 60-69 in the Western population [18].

In addition to comparing the total distance covered during 6MWT between the two groups, the present study also examined the linear trend of distance covered during each minute and found that individuals with knee OA had significantly lower scores compared to the healthy controls. Additionally, persons with knee OA demonstrated a fluctuation in the distance covered during each minute, with a decrease from the 1st to 2nd minute, an increase from the 2nd to 4th minute, and a subsequent decrease from the 4th to 6th minute. In contrast, the healthy controls maintained a relatively stable mean walking distance throughout all six minutes. Furthermore, the linear trend lines show a linear decrease in distance covered from 1^st to 6^th minute in persons with knee OA, whereas healthy controls exhibit a comparatively more horizontal linear trend line. Based on the results of the current study, it can be concluded that individuals with knee OA exhibit greater decline in walking-related functional ability compared to healthy controls. This is reflected by greater fatigability, as well as lower gait velocity and covered distance.

5 Conclusion

Persons with knee osteoarthritis demonstrate greater walking related performance fatigability and lower gait velocity and distance covered during 6MWT, as compared to their healthy counterparts.