Our study illustrates a high prevalence of sarcopenia among patients with end-stage OA of the knee. There were 58 patients entered at baseline, of which 19 (32.8%) had sarcopenia and 39 (67.2%) were not. The prevalence of sarcopenia in Asia ranged from 6.7–18.6% in older men and 0.1–23.6% in older women according to various reports from Japan, Taiwan, Hong Kong and Korean[31–34]. However, it has also been found that the prevalence of sarcopenia among community-dwelling elderly with OA is near three times that of those without OA and this possibly explains the relatively high prevalence of sarcopenia among our OA subjects[35].
This study demonstrated that total knee arthroplasties can benefit patients with severe knee OA with or without co-existing sarcopenia by improving knee function and symptoms, in turn enhancing their gait speed and potentially lean muscle mass. It is the deficit in gait speed and lean muscle mass which are the core components that defined sarcopenia. According to the latest review in Lancet on sarcopenia, physical activity is regarded as the primary treatment of sarcopenia while there is currently no specific drugs approved for the treatment of sarcopenia [36]. Our study illustrates the importance of identifying sarcopenic patients with concomitant joint disease and managed accordingly to facilitate them having physical activity as the treatment of sarcopenia. At the end of this study, five sarcopenic patients at baseline turned non-sarcopenic, leading to a total of 44 patients without sarcopenia (75.9%). However, our results also showed that knee arthroplasty alone cannot allow sarcopenic subjects to pick up the overall difference in average lean muscle mass compared to non-sarcopenic subjects. This highlights the importance of managing sarcopenia through a multimodal approach, for example, a combination of high protein diet, knee arthroplasties, and followed by supervised exercise program which by then should be more effective as the physical limitation by knee osteoarthritis has been alleviated.
Having a supervised exercise program is especially important for these groups of patients as they are adapted towards a sedentary lifestyle to cater the pain and weakness induced by osteoarthritis and/or sarcopenia and they tend to continue the same comfortable, sedentary lifestyle if without proper encouragement and training[36]. In our study, the patients would only receive standard physiotherapy designed for rehabilitation of knee arthroplasty surgery. The physiotherapy aims at regaining the knee range and walking ability of patients after surgery but does not target building skeletal muscle strength and mass as in those resistance exercise program for sarcopenia. This allowed us to observe the isolated effect of knee arthroplasty on muscle mass and function. However, further studies are warranted to investigate any additive effect of supervised resistance exercise program after knee arthroplasty on sarcopenia. Having said that, some of these OA patients were elderly with low motivation and possibly content with a pain-free knee without further interest to participate in subsequent endurance muscle training. As such some passive physical intervention or “exercise mimetics” like neuromuscular electrical stimulation or whole-body vibration can be considered for those elderly who are unwilling or unable to do physical exercise given their frailty.[37] [38] In fact, whole-body vibration has been shown to increase knee extensor strength and decrease lower leg swelling after TKA and thus worth further investigation on their combined effect on sarcopenia[39].
Previous studies have reported on the negative impact of sarcopenia on surgical outcome. For example, sarcopenia has been identified as risk factors for morbidity and mortality in colorectal surgery and gastric cancer surgery, and also a risk factor for prosthetic infection after joint arthroplasty [40–42]. In our study, no increase in infection rate nor other complications were found, nevertheless, the occurrence of late infection and late complications are beyond our study period. One important difference between the current study and the previous researches on sarcopenia with surgery is that those surgeries mainly induce a catabolic status in the patients while knee arthroplasty induces catabolism in early phase followed by anabolism due to patient regaining their mobility and ability to exercise. This phenomenon could also be a possible explanation of the significant improvement of lean mass in overweight or obese sarcopenic female in our study as they lost fat and weight during the initial catabolism after arthroplasty and built up muscle, made possible by better walking ability and less bodyweight hindering movement, during their subsequent rehabilitation[20, 35, 43]. In essence, knee arthroplasty helps break the vicious cycle of immobility, obesity and sarcopenia by returning these individuals to normal lower limb function.
There are certain limitations to our study. As mentioned previously, all patients receive standard physiotherapy in the early phase for post-op rehabilitation. Afterwards, we did not restrict or prescribe further exercise to patients and each of them may engage in variable degrees of exercise. This could contribute to variable improvement in muscle mass among our patients. Similarly, although we encourage our patients to have high protein intake according to dietitian advice, we could not control the exact patients’ diets at home and those having a relatively higher protein diet may have better muscle mass building than their counterpart[36].