Improved levels of physical activity in patients over 75 years following total knee arthroplasty

Abstract

Purpose:

There is insufficient evidence regarding the precise levels of physical activity (PA) in older patients following total knee arthroplasty (TKA). The aims of this study were (1) to describe the changes in the amount and intensity of PA before and after TKA with an accelerometer in older patients, compared with age- and sex-matched healthy participants and (2) to assess the effect of TKA on PA depending on age.

Methods:

Sixty-six primary TKA patients aged 60 years or over (mean age, 73.3 years) wore an accelerometer (Lifecorder EX) for 10 consecutive days and completed the Oxford Knee Score (OKS) before and at 6 months after TKA. PA was evaluated by mean step count and time spent (min) engaged in PA per day. PA intensity was classified as light (1.5–3 metabolic equivalents (METs)), moderate to vigorous (≥3 METs), and total (≥1.5 METs). Sixty-four healthy participants completed a single assessment of PA.

Results:

Each of the PA measures and OKS increased significantly after TKA. Compared with healthy controls, light and total PA improved to 100% at 6 months after TKA in patients 75 years or older. By contrast, moderate-to-vigorous PA was 32% of that of the controls and rose to 78% after TKA. PA intensity in patients aged 60–74 years was 31–74% of the controls but did not reach the same level after TKA.

Conclusion:

TKA in older patients increases the amount of PA, with light and total PA suitable parameters for assessing PA.

Keywords

accelerometer arthroplasty older adults osteoarthritis knee physical activity prospective study

Introduction

In Asia, population aging is progressing rapidly, and the number of patients with end-stage osteoarthritis who require total knee arthroplasty (TKA) has concomitantly increased. In Japan, approximately 17 million people (13.8% of the total population) are 75 years or older,¹ and a total of 72,000 TKA surgeries are performed annually, including in those patients aged over 75 years,² a figure which is also expected to increase in the future. In terms of postoperative outcomes after TKA, older patients report improvements in pain, knee function, and quality of life to a similar degree as that in younger patients.^3,4 However, there is insufficient evidence regarding the actual levels of physical activity (PA) in older patients following TKA, particularly in patients 75 years or older.

Studies evaluating PA in TKA patients using an accelerometer showed that postoperative PA was lower than or equal to preoperative PA,⁵ and, if improved, it was considerably lower than that of the healthy control group.⁶ There is evidence that increased bone quality will improve prosthesis fixation and decrease the incidence of early loosening.⁷ Therefore, older patients who undergo TKA should be encouraged to remain active to maintain bone and muscle quality to sustain the long-term outcomes of TKA. Most studies measure PA using step counts and moderate- to vigorous-intensity PA (MVPA) levels after TKA. However, in recent years, cardiometabolic health and all-cause mortality have been reported to be improved in response to increased levels of light-intensity activity.⁸ Therefore, measures of PA in actual daily living should also include an estimation of light PA.

The aims of this study were (1) to describe the changes in the amount and intensity of PA before and after TKA with an accelerometer among older patients compared with age- and sex-matched healthy participants and (2) to assess the effect of TKA on PA with respect to patient age (60–74 years vs. ≥75 years).

Methods

Participants

This prospective study included 66 patients who were scheduled for primary TKA between March 2010 and November 2013 at our university hospital in the Kyusyu region. The inclusion criteria included patients who were (1) scheduled for primary TKA, (2) aged 60 years or over, and (3) were living independently. A sample size of 56 patients (including a 20% dropout) was required to have the power to detect a type II error (0.95), with an effect size of 0.5 and 0.05 significance (G*Power 3.1.9.2; Düsseldorf, Germany).⁹

An age- (±5 years of age) and sex-matched healthy control group was recruited from volunteer organizations around the Kyusyu region. The healthy control group consisted of 64 volunteers in community dwellings with no disorders or previous surgery to the lower extremity. The healthy control group had a lower mean body mass index (BMI) than the patient group (26.0 vs. and 22.5, p < 0.05).

Procedure

All eligible patients on the TKA waiting list were invited to participate in the study before surgery. TKA patients completed measures of PA using an accelerometer and a self-administered questionnaire twice: 1 month before TKA surgery and at 6 months after TKA. The controls completed a single assessment.

Ethical considerations

The present study was approved by the relevant ethics committee at our institution (approval number 26-69). The privacy of the research participants was protected, and the confidentiality of their personal information was ensured. Participants were informed that study participation was voluntary, it would not affect their treatment, they could withdraw from the study at any point, and only aggregated data would be reported. Subsequently, written informed consent was obtained from all participants.

Physical activity

PA was measured using an accelerometer (Lifecorder EX, Suzuken Co. Ltd, Nagoya, Japan; size, 72.0 × 42.0 × 29 mm³, 45 g) worn on the waist. The epoch length of the Lifecorder is 2 min. The mean step count and time spent engaged in PA (minutes per day) was evaluated. PA intensity was classified into light PA (1.5–3 metabolic equivalents (METs)), MVPA (≥3 METs), and total PA (≥1.5 METs).¹⁰ Participants were requested to wear the accelerometer throughout the day for 10 consecutive days, except during sleeping and bathing. Of these 10 days, data from the first 2 days and the last day were excluded from the analysis to account for patient noncompliance, leaving a total of 7 days for the analysis. We used a PA analysis software package (Liferiser Coach 05, Suzuken Co. Ltd) and Microsoft Excel (Microsoft Corp., Redmond, WA, USA) to analyze the activities measured via the accelerometer. Based on a previous study,¹¹ we adopted an actual wearing time of >10 h/day, and the mean duration of continuous activity measurement was 14.5 h (10.8–17.8 h).

Subjective knee function

We used the knee disease-specific scale of the Oxford Knee Score (OKS) self-administered questionnaire (Japanese version) for measures of subjective knee function.¹² The OKS comprises 12 items, measured using a 5-point Likert-type scale, to assess knee function and pain. Total scores range from 0 to 48, with higher scores indicating better conditions.

Patient characteristics

Patient characteristics, including age, sex, BMI, diagnosis, and type of TKA, were obtained from patient medical records.

Data analysis

PA measures and OKS total scores before and after TKA were compared using paired t-tests. PA after TKA was also compared with the healthy control group, stratified by age (60–74 years and ≥75 years),¹³ using a Student’s t-test. Relative recovery was used to compare PA parameters of TKA patients with those of healthy controls. Relative recovery was defined as the percentage of recovery of PA in TKA patients relative to 100% of that in the controls. The Mann–Whitney U test was used to compare the outcomes after TKA performed by surgical procedures or implants. All data were analyzed using SPSS, version 23, for Windows (SPSS, IBM Corp., Armonk, NY, USA). The values of p < 0.05 were considered statistically significant.

Results

The present study included TKA patients (mean age of 73.3 years, 46% aged ≥75 years; 83% female). Patients diagnosed with osteoarthritis accounted for 93.9%. In all, 56.1% had bilateral knee involvement and underwent bilateral knee arthroplasty. There were no significant differences in postoperative PA measures or OKS scores for patients with bilateral and unilateral TKA. All TKA patients received noncemented prostheses with either a Bi-Surface 5 implant (Kyocera, Japan; n = 19) or a Scorpio PS NRG implant (Stryker, Kalamazoo, MI, USA; n = 47). Both implants were of the posterior-stabilized type—hence, the posterior cruciate ligament was resected in all patients. There were no significant differences in PA measures or OKS scores between these two types of implant (Appendix 1).

PA measures and OKS scores after TKA were significantly higher in all patients compared with those taken before TKA (Table 1). When stratified by age, measures of MVPA, total PA, step counts, and OKS scores all increased significantly in the 60- to 74-year group, and all PA measures and OKS scores improved in the 75 years or older group. Compared with age-matched healthy controls, light PA, MVPA, total PA, and step counts were lower in patients aged 60–74 years; any improvement in PA intensity in this TKA group did not reach the same level as that of the healthy controls at 6 months after TKA (Table 1). By contrast, light and total PA improved to 100% for the TKA patients aged 75 years and older at 6 months after TKA as compared with the healthy controls (Figure 1), with no significant differences observed between the healthy and the TKA (75 years and over) groups.

Table 1.

PA and OKSs in patients before and after TKA compared with healthy controls.

Group	Patients (n = 66)			Healthy controls (n = 64)
	Before TKA	After TKA	p Value
	Mean ± SD		p Value	Mean ± SD	p Value
Light PA (min/day)
All	40.6 ± 25.7	46.9 ± 24.2	0.007^a
60–74 years	43.7 ± 22.5	48.2 ± 19.6	0.116^a	65.3 ± 25.3	0.002^b
≥75 years	36.5 ± 29.4	45.2 ± 29.5	0.025^a	44.4 ± 18.6	0.834^b
MVPA (min/day)
All	2.9 ± 4.3	6.0 ± 7.9	<0.001^a
60–74 years	3.1 ± 4.1	5.8 ± 7.3	0.006^a	18.5 ± 16.3	<0.001^b
≥75 years	2.7 ± 4.5	6.3 ± 8.9	0.003^a	8.1 ± 7.6	0.452^b
Total PA (min/day)
All	43.5 ± 29.0	52.9 ± 29.6	<0.001^a
60–74 years	46.8 ± 25.4	54.0 ± 25.2	0.034^a	83.8 ± 32.3	<0.001^b
≥75 years	39.2 ± 33.2	51.5 ± 35.3	0.004^a	52.2 ± 23.2	0.979^b
Steps (number/day)
All	3784 ± 2549	4750 ± 2712	<0.001^a
60–74 years	4059 ± 2266	4805 ± 2374	0.016^a	7813 ± 3105	<0.001^b
≥75 years	3430 ± 2845	4587 ± 3149	0.003^a	4730 ± 2060	0.851^b
OKS
All	23.4 ± 6.9	37.2 ± 8.1	<0.001^a
60–74 years	23.7 ± 6.8	37.7 ± 6.6	<0.001^a	—	—
≥75 years	23.0 ± 7.1	36.5 ± 9.9	<0.001^a	—	—

TKA: total knee arthroplasty; SD: standard deviation; PA: physical activity; MVPA: moderate- to vigorous-intensity PA; OKS: Oxford Knee Score.

^a p Values were determined using paired t-test (before and after TKA).

^b p Values were determined using Student’s t-test (6 months after TKA and in healthy controls).

Figure 1.

Relative recovery of PA parameters in TKA patients compared with healthy controls. Relative recovery was defined as the percentage of recovery of PA in TKA patients relative to 100% of that in the controls. TKA: total knee arthroplasty; PA: physical activity; MVPA: moderate- to vigorous-intensity PA.

Discussion

In this study, the amount and intensity of PA before and after TKA were evaluated with an accelerometer in older patients. Among patients scheduled for TKA surgery, we found significantly higher PA and OKS scores at 6 months after surgery as compared with presurgical scores. This was particularly the case for patients aged 75 years or older, who showed improvements in total PA and light PA at 6 months after TKA that equaled the activity levels of healthy, age- and sex-matched control participants. By contrast, MVPA was only 32% of that of the controls before TKA and rose to 78% after TKA. Therefore, overall we find that TKA increases the amount of PA in older patients and that measures of light PA and total PA, including light to MVPA, allowed insight into the effect of surgery in this population. An evaluation of PA in older patients undergoing TKA is recommended to show the beneficial effects of postoperative activity, including light PA, in this patient group.

In other studies of accelerometer-based PA in TKA patients, no significant change in postoperative PA was observed,^14,15 and, in another study, the measured PA after TKA was lower than that of age-matched control participants.⁶ We segregated PA by age group and activity intensity (light PA, MVPA, and total PA), and similarly found only a small improvement in PA after surgery among the younger patients (60–74 years) that did not reach the level of PA of healthy controls. Yet, among the older patients (75 years or over), all three PA measures (light PA, MVPA, and total PA) were improved compared with pre-TKA values, with no differences observed as compared with the healthy controls. The PA of the control group in this study was similar to that of the general Japanese population in terms of mean step counts and PA intensity.^10,16

According to PA guidelines,¹⁷ a minimum of 150 min of moderate-intensity exercise is recommended per week for both older and younger adults; among the cohort, only 16.5% of TKA patients reached these activity levels;⁶ this activity level is likely to be a burden for TKA patients aged 75 years and over. Generally, PA in healthy participants slowly decreases with aging, particularly the time spent in MVPA. These reductions in moderate activity coincide with a switch to low-intensity activity.⁹ Yet the significant health benefits of light PA on the heart and other vital organs are attracting attention.^8,18 Given the associated age-related changes in exercise habits, we suggest that light and total PA are suitable parameters to assess activity levels in older patients after TKA.

Postoperative knee function and pain were markedly improved, consistent with the results of previous studies,^19,20 indicating that knee functional improvements further increased the amount and intensity of activity in daily living. Not only improving knee function but the additional health benefits are also important for older patients receiving TKA.

This study has certain limitations. Our sample size was small, and the patients who refused to participate may have included those with low activity levels. The PA measures and OKS scores after TKA, along with the differences in surgical procedures or implants, were not significantly different, so this short-term assessment did not refer to their influence. Therefore, further studies are needed to evaluate PA and OKS after TKA in the medium to long term that includes these variables.

Conclusion

This study reports that TKA in older patients leads to an increase in the amount of PA, as compared with preoperative PA levels. This is particularly the case for patients aged 75 years or older, for which postoperative PA improved to attain the same activity levels as seen in the healthy controls. We recommend light and total PA as suitable PA parameters for older patients undergoing TKA.

Footnotes

Acknowledgements

We thank Edanz Group ) for editing a draft of this manuscript. We thank the TKA patients who participated in this study and the staff of Saga University Hospital for their support.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by JSPS KAKENHI Grant-in-Aid for Young Scientists (B) 24792561 and Grant-in-Aid for Scientific Research (C) 26463444.

ORCID iD

Yuriko Matsunaga-Myoji

Appendix 1.

PA and OKS after TKA with two types of implant.

	Scorpio PS NRG (Stryker, Kalamazoo, MI, USA)	Bi-surface 5 (Kyocera, Japan)
	n = 47	n = 19
	Mean ± SD		p Value^a
Light PA (min/day)	47.0 ± 25.7	46.6 ± 19.9	0.975
MVPA (min/day)	6.1 ± 8.2	5.4 ± 7.6	0.956
Total PA (min/day)	53.1 ± 31.1	52.0 ± 25.4	0.975
Steps (number/day)	4755 ± 2839	4585 ± 2376	0.962
OKS	37.5 ± 8.0	36.3 ± 8.9	0.596

TKA: total knee arthroplasty; SD: standard deviation; PA: physical activity; MVPA: moderate- to vigorous-intensity PA; OKS: Oxford Knee Score.

^a p Values were determined using the Mann–Whitney U test.

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