Yonago Acta medica 2014;57:137–145

Original Article

Incidence and Risk Factors for Falling in Patients after Total Knee Arthroplasty
Compared to Healthy Elderly Individuals
Hiromi Matsumoto,* Makoto Okuno,† Tatsuhiko Nakamura,† Kichizo Yamamoto,† Mari Osaki* and Hiroshi Hagino*‡*Rehabilitation Division, Tottori University Hospital, Yonago 683-8504, Japan, †Clinical Department of Orthopedic Surgery, Hakuai
Hospital, Yonago 683-0853, Japan and ‡Department of Fundamental Nursing, School of Health Science, Tottori University Faculty of
Medicine, Yonago 683-8503, Japan

ABSTRACT

ter TKA, which was different from the results obtainedin the healthy elderly.

Background

It is possible that patients who have undergone total knee arthroplasty (TKA) are at a high riskof falling. However, there are insufficient data to confirm
the incidence and risk factors for falling in patients after
TKA compared with healthy elderly counterparts. The
purpose of this study was to elucidate the incidence andrisk factors for falling in patients after TKA comparedto the age- and gender-matched healthy elderly.
Methods Subjects who underwent TKA consistedof 252 patients over 60 years of age. Controls were 150
healthy elderly individuals over 60 years of age living
independently in the community. A self-administeredquestionnaire was mailed to patients after TKA and asimilar questionnaire was distributed to the controls by
investigators during the town-sponsored healthy aging
program. The questionnaire included questions for ambulatory ability, functional status in daily living, knee
pain, other joint pain and information on falls.
Results
Self-administered questionnares were returned by 192 of the 252 patients (76.1%) and 146 of
the 150 controls (97.3%). Age and gender matching was
performed for respondents between 70 and 80 years ofage. There were 81 patients and 80 controls who fulfilled
the inclusion criteria, and all of them agreed to participate. In the previous year, 34 of the 81 patients (38.2%)
fell. The incidence of falls was significantly higher inpatients than controls (23.8%, P = 0.041). In controls,
ability to stand up from a chair without using the arms
and restriction from joining social activities due to knee
pain showed the strongest association with recent falls.
In patients, self-reported kyphosis showed the strongest
association with recent falls.
Conclusion Patients after TKA are more likely to fall
than the general Japanese population. Kyphosis showed
the strongest association with recent falls in patients af-

Key words elderly; falling; fractures; risk factor; total
knee arthroplasty

Fragility fracture in the elderly has become a substantial
societal problem because fractures reduce physical function and the ability to perform activities of daily living(ADLs). In particular, hip fracture is usually regarded
as the most devastating fragility fracture with regards tomorbidity, mortality and cost. Approximately 20 to 40%
of individuals with a hip fracture who live independently
without a walking device prior to the fracture require a
walking device 1 year after fracture.1–3 Since most fragility fractures are associated with falls, it is necessary
to identify the elderly who have a high intrinsic fall risk
and prevent them from falling.
Osteoarthritis (OA) of the knee, in particular, causes
deformities of the joint and pain during walking. It has
been reported to increase the risk of falls and fractures:the annual falling rate among the patients with end-stage
knee OA was 48%.4 Patients diagnosed as with knee OA
have a greater risk of all non-vertebral and hip fractures
than patients with knee pain alone.5 Furthermore, 50%of patients with rheumatoid arthritis (RA) fall each year.
Their health assessment questionnaire (HAQ) disability scores, tender joint counts and balance impairment
scores are associated with an increased risk of falls.6-8
Thus, it is important to treat joint disease in order to prevent falls in this population.
Total knee arthroplasty (TKA) is a common surgery
for the management of severe pain in knee OA. TKA isa surgical intervention that eliminates pain and knee deformity and improves patient quality of life (QOL). Furthermore, TKA not only reduces pain in knee OA patients, but improves their gait performance and balance
function.9, 10 Thus, TKA may reduce falls, as well as fallrelated fractures. However, previous studies have foundthat patients undergoing TKA have a higher prevalenceof osteoporosis than the healthy elderly,11 and postoperative increases in bone resorption and decreases in patient
motor activity lead to a decrease in bone mineral density

Corresponding author: Hiromi Matsumoto, PT, PhD
h.matsumoto@med.tottori-u.ac.jp
Received 2014 September 16
Accepted 2014 November 4Abbreviations: ADL, activity of daily living; BMD, bone mineraldensity; BMI, body mass index; CI, confidence interval; HAQ,
health assessment questionnaire; OA, osteoarthritis; OR, odds ratio; RA, rheumatoid arthritis; TKA, total knee arthroplasty137

H. Matsumoto et al.
Table 1. Questions on ambulatory ability, functional status, knee pain and other joint pain
Domain

Questions

Ambulatory ability

Do you use a walking device? (without an assistive device, one cane or walker)
How much do you walk in a day? (1: almost no walking, 2: walking in only one room, 3: walking mainly in thehouse, 4: walking outside, 5: walking over 1 km)
Can you put on socks while standing?
Can you climb up and down stairs?
Can you stand up from a chair without using your arms?
Are you very worried about falling?
Do you have a regular exercise routine?
Do you have stiffness in your knees on a regular basis?
Do you have knee pain while walking?
Do you have knee pain while climbing up or down stairs?
Do you have knee pain while standing up from a chair?
Do you restrict from joining social activities due to knee pain in your daily life?
Can you bend your knees in a sitting position? (1: excellent, 2: good, 3: average, 4: poor, 5: bad)Do you have joint pain in any other joints besides the knees?

Functional status

Knee pain

Other joint pain

(BMD) around the implant.12 It is possible that elderly
patients who have undergone TKA are at a high risk ofperiprosthetic fracture associated with falling.
There are relatively few studies on falls and fractures after TKA. At 1 year after TKA, the number offalls was lower than at 3 months before surgery,13 andfear of falling had reduced 4 months after surgery.4 In
addition, a 6-month prospective study reported that
TKA may reduce the incidence of falls in patients with
OA or RA because the incidence of falling in patients
after TKA is lower than previously reported rates for
OA or RA patients.14 These previous studies suggested
that TKA reduces the incidence of falling in OA or RA
patients within 1 year of operation. However, there wereinsufficient data to confirm the difference in incidenceof falling and risk factors between patients after TKA
and the healthy elderly. The purpose of this study was
to elucidate the incidence and risk factors for fallingin patients after TKA by comparing with the age- andgender-matched healthy elderly controls.

A self-administered questionnaire was mailed to thepatients in August 2009. A similar questionnaire wasdistributed to the controls by investigators during thehealthy aging program between August and November
2009. The voluntary and confidential questionnaire included an informed consent form explaining the purposeof the study and instructions on how to complete andreturn the survey.

MATERIALS AND METHODS

Self-administered questionnaire

Patients and controls

Participants were 252 patients aged over 60 years withbilateral and unilateral TKA. All surgeries were performed by 3 orthopedists with the standard medial
parapatellar approach. The implants consisted of Scorpio(Stryker, Kalamazoo, MI) and LCS (DePuy, Warsaw,
IN). Early joint motion and weight bearing were encouraged after surgery. Patients underwent standard inpatient
rehabilitation. Controls consisted of 150 healthy elderly
individuals over 60 years of age who lived independently
in the community.

Study design and overview

The questionnaire included questions on personal characteristics, ambulatory ability, functional status in dailyliving, knee pain, other joint pain and fall assessment.
All data were self-reported and subjects were asked toindicate their responses by choosing Yes or No or using
a 5-point ordinal scale.

The present study was designed as a retrospective casecontrol study with matching by age and gender. We
gained approval from the Ethics Committees of Tottori
University Faculty of Medicine (Approval Number
1264) and the local ethics committees of Hakuai Hospital.
Cases consisted of patients who underwent TKA at
Hakuai Hospital between April 2002 and March 2008.
Data from the postoperative period and TKA laterality
were retrieved from medical records. Controls consistedof participants to a town-sponsored healthy aging program. They had not received services covered by nursing care insurance.

Personal characteristics of patients and controls

Both groups provided information on basic characteristics including age, sex, body height, body weight, total
number of prescribed medications taken on a regularbasis, use of hypnotic pills, hearing problems, eyeproblems, self-reporting kyphosis, self-reporting hallux
valgus, diagnosis of cardiac disease, respiratory disease,138

Falling after total knee arthroplasty

Patients

Controls

252 patients with TKA

150 healthy elderly

192 patients with TKA
returnedthe questionnaires(78.9 ± 5.4 years)

146 healthy elderly
returnedthe questionnaires(73.7 ± 7.2 years)

divided into 3 age categories

Fig. 1. Study flow chart.
TKA, total knee arthroplasty.

≤ 70 years of age(n = 9)> 70–80 years of age (n = 95)> 80 years of age(n = 88)≤ 70 years of age(n = 44)> 70–80 years of age (n = 83)> 80 years of age(n = 19)

95 patients after TKA

83 healthy elderlyage- and gender-matched possible only in > 70–80 years of age
81 patients after TKA
satisfiedthe inclusion criteria

80 healthy elderly
satisfiedthe inclusion criteria

diabetes, hypertension and other diseases. Patients werealso asked whether they had previously undergone hiparthroplasty.

grading scales between patients and controls or nonfallers and fallers from each group.
Both univariate and multivariate analyses were
performed. Variables with a significance level of
P < 0.10 in the univariate analysis were retained in themultivariate analysis. Multivariate logistic regression
was used to provide estimates of adjusted odds ratios(ORs) for associations with falls in the patients andcontrols. All data were analyzed using PASW statistical software (version 18 for Windows; SPSS, Tokyo,
Japan). For all the analyses, a P value < 0.05 was considered significant.

Ambulatory ability, functional status, knee pain and otherjoint pain

Questions on ambulatory ability, functional status, knee
pain and other joint pain are presented in Table 1. The
questionnaire was based on previous studies.15, 16 Daily
walking distance and range of motion with respect toflexion of the affected knee were assessed with a 5-point
ordinal scale. In addition, controls were asked whether
they had self-reported varus deformities of the knee andprior knee arthroplasty, and whether they had received
diagnosis or treatment of knee OA by a doctor at least
once in the past.

RESULTS
Response rate for the self-administered questionnaire

A flow chart of the study is presented in Fig.1. Selfadministered questionnaires were returned by 192
of the 252 patients after TKA (76.1%) and 146 of the
150 controls (97.3%). The mean age was significantly
higher in patients (78.9 ± 5.4 years) than controls (73.7± 7.2 years) (P < 0.001). Each group was divided into
3 age categories: ≤ 70 years, > 70–80 years and > 80
years. We analyzed only the data from the age category of > 70−80 years in each group, because the age
and gender distributions in other age categories weresignificantly different between patients and controls
with the non-paired t test and chi-squared test. In eachgroup, persons who met the following qualifications

Fall assessment

Both groups were asked about the number of falls, injuries due to falling and fracture due to falling in the 12months prior to the questionnaire. A fall was defined as
unintentionally coming down to the ground or lower,17
not as the result of a major intrinsic event such as a seizure, fainting or stroke.
Statistical analysis

All data were expressed as means ± SD. Differences
between groups were determined with Pearson’s chisquared test. The non-paired t-test was used to compare139

H. Matsumoto et al.
Table 2. Characteristics of the patients and controls
Patients (n = 81)

Controls (n = 80)

Personal characteristics			Age, mean ± SD (year)
75.9 ± 2.3
75.7 ± 3.0
Sex ratio (male/female)(7/74)(12/68)Height, mean ± SD (cm)151.1 ± 6.4
151.0 ± 7.4
Weight, mean ± SD (kg)57.4 ± 10.0
50.0 ± 8.4
25.3 ± 4.6
22.0 ± 2.9
BMI, mean ± SD (kg/m2)
Total number of prescription medications, mean ± SD
3.2 ± 2.5
2.5 ± 1.9
Use of hypnotic pills (%)
18.4
15.0
Time since surgery (year)
3.8–
Prior hip arthroplasty (%)
14.8–
TKA laterality (bilateral/right/left)(43/18/20)–
Physical problems
Hearing problems (%)
34.3
25.3
Eye problems (%)
56.8
58.8
Kyphosis (%)
34.4
65.6
Hallux valgus (%)
16.9
28.7
Complication
Cardiac disease (%)
11.1
15.0
Respiratory disease (%)
3.7
5.0
Diabetes (%)
18.5
7.5
Hypertension (%)
42.0
42.5
Ambulatory ability
Walking without assistive device (%)
44.2
85.0
One cane (%)
33.8
13.8
Walker (%)
22.0
1.2
Grading of walking distancei) Almost no walking (%)0.00.0ii) Walking in only one room (%)0.0
0.0iii) Walking mainly in the house (%)11.4
6.2iv) Walking outside (%)
53.2
45.0
v) Walking over 1 km per day (%)
35.4
48.8
Functional status
Putting on socks while standing (%)
32.1
66.3
Climbing up and down stairs (%)
67.5
86.3
Standing up from a chair without using the arms (%)
59.2
86.3
Fear of falling (%)
45.3
22.5
Regular exercise (%)
67.5
66.3

P value
0.622
0.211
0.494
< 0.001< 0.001
0.060
0.567
–
–
–
0.231
0.802
0.017
0.085
0.464
0.687
0.038
0.946
< 0.001

0.182< 0.001
0.005< 0.001
0.003
0.864

BMI, body mass index; TKA, total knee arthroplasty.

were excluded from the study: i) whether they received
services covered by nursing care insurance (because
they were suspected of having dementia or frailty); ii)
whether they were unable to walk and iii) whether they
had RA or Parkinson’s disease. Persons treated with
TKA were excluded from the control group. Ultimately, 81 patients (mean age, 75.9 ± 2.3 years; 7 males, 74
females) and 80 controls (mean age, 75.7 ± 3.0 years;
12 males, 68 females) satisfied the inclusion criteria.

The characteristics and knee pain and other joint
pain in patients and controls are presented in Tables 2
and 3. Comparison between both groups showed significantly higher levels for patients in weight (P < 0.001),
body mass index (BMI) (P < 0.001), the prevalenceof diabetes (P = 0.038), fear of falling (P = 0.003) andankle pain (P = 0.027).
Comparison between both groups showed significantly lower levels for patients in the percentageof kyphosis (P = 0.017), walking without assistive
device (P < 0.001), ability to put on socks while standing (P < 0.001), ability to climb up and down stairs(P = 0.005), ability to stand up from a chair without using the arms (P < 0.001), knee pain while climbing up or
down stairs (P = 0.046), and knee flexion range of motion (P < 0.001).

Characteristics of the patients and controls

Of the 80 (35.0%) controls, 28 reported that they had avarus knee deformity. Furthermore, 18 of the 80 controls(22.5%) have received diagnosis or treatment of knee
OA by a doctor at least once in the past.
140

Falling after total knee arthroplasty
Table 3. Knee pain, knee flexion range of motion and other joint pain
Patients (n = 81)

Controls (n = 80)

Knee pain			
Regular stiffness (%)
36.3
47.5
Pain while walking (%)
22.0
35.0
Pain while climbing up or down stairs (%)
22.0
40.0
Pain while standing (%)
19.7
26.2
Restriction from joining social activities due to knee pain (%)
25.0
19.0
Knee flexion range of motion			i) Excellent (%)
27.6
82.5
ii) Good (%)36.0
6.3iii) Average(%)
22.3
5.0iv) Poor (%)5.2
3.7v) Bad (%)
3.9
2.5
Other joint pain
Spine (%)
43.2
46.2
Hip (%)
4.9
2.5
Ankle (%)
13.5
3.7

P value
0.158
0.073
0.046
0.110
0.468
< 0.001

0.698
0.414
0.027

Table 4. Numbers of fallers and fractures in the patients and controls

Number of fallers (%)
Multiple falls (%)
Bruises and minor injuries due to falling (%)
Fracture due to falling (%)

Patients(n = 81)Controls(n = 80)

Chi-squaredDf

P value

38.2
19.8
11.1
6.2

23.8
13.8
7.5
3.8

4.189
1.039
0.621
0.500

1
1
1
1

0.041
0.308
0.431
0.479

Df, degree of freedom.

The rate of persons who had prescribed medications
on a regular basis was higher in patients than controls(P = 0.060). The percentage of hallux valgus and knee
pain while walking tended to be lower in patients thancontrols (P = 0.085 and P = 0.073, respectively). The
other variables showed no significant differences between both groups.

had fear of falling was significantly higher in fallers than
non-fallers (P = 0.041 and P = 0.016, respectively). The
ability to stand up from a chair without using the arms
and the knee flexion range of motion were significantly
worse in fallers (P = 0.001 and P = 0.043, respectively).
The comparison of fallers and non-fallers in bothgroups is presented in Tables 5 and 6. Personal characteristics and complications were not significantly different between fallers and non-fallers in both groups. In
patients, the percentage of kyphosis was significantly
higher in fallers than non-fallers (P = 0.030). Knee flexion range of motion was significantly lower in fallers
than non-fallers (P = 0.005). More fallers had a fear of
falling and regular stiffness of the knee than non-fallers(P = 0.082 and P = 0.069, respectively). The percentageof the ability to stand up from a chair without using thearms tended to be lower in fallers (P = 0.061). In controls, the percentage of restriction from joining social
activities due to knee pain was significantly higher infallers than non-fallers (P = 0.030). The percentage ofthe ability to stand up from a chair without using thearms was significantly lower in fallers than non-fallers(P = 0.011).

Numbers of falls and fractures

The numbers of falls and fractures during the previous
year observed in patients and controls are presented inTable 4. In the patients, 31 of 81 patients (38.2%) fell;
6 patients fell twice, and 10 patients fell 3 times. In thecontrols, 19 of 80 subjects (23.8%) fell; 7 subjects fell
twice, and 4 subjects fell 3 times. The incidence of falls
was significantly higher in patients than controls (P =0.041). Rates of multiple falls, injuries and fracturesdue to falling were not significantly different between
both groups. Those who sustained fall-related fractures
within the last year were 5 in patients and 3 in controls.
Non-fallers and fallers

In the overall analysis of the incidence of falling, thepercentage of persons who underwent TKA and who141

H. Matsumoto et al.
Table 5. Comparison of characteristics of fallers and non-fallers in the patients and controls
Patients			
Non-fallers
Fallers		
(n = 50)(n = 31)
P value

Controls
Non-fallers(n = 61)

Fallers(n = 19)

P value

Surgery information						Time after surgery (year)
3.7 ± 1.7
4.2 ± 2.1
0.226
–
–
–
Prior hip arthroplasty (%)
14.3
16.7
0.775
–
–
–
TKA laterality (bilateral/right/left)(27/10/13)(16/8/7)
0.830
–
–
–
Physical problems						Hearing problems (%)
33.3
37.0
0.753
36.8
21.7
0.185
Eye problems (%)
56.8
58.6
0.879
57.9
59.0
0.931
Kyphosis (%)
23.8
50.0
0.030
50.8
57.9
0.590
Hallux valgus (%)
15.2
20.8
0.554
31.1
21.1
0.396
Complications						Cardiac disease (%)
10.2
12.9
0.710
18.0
5.3
0.173
Respiratory disease (%)
0.0
6.1
0.160
6.6
0.0
0.252
Diabetes (%)
18.4
19.4
0.912
6.6
10.5
0.566
Hypertension (%)
42.9
38.7
0.714
44.3
36.8
0.568
Ambulatory ability						Walking without assistive device (%)
43.8
42.9
0.349
88.5
73.7
0.170
One cane (%)
39.6
25.0		
9.8
26.3
Walker (%)
16.6
32.1		
1.6
0.0
Grading of walking distance						i) Almost no walking (%)
0.0
0.0		
0.0
0.0
0.746
ii) Walking in only one room (%)
0.0
0.0		
0.0
0.0
iii) Walking mainly in the house (%)
14.3
6.9
0.284
6.6
5.3
iv) Walking outside (%)
57.1
48.3		
42.6
52.6v) Walking over 1 km per day (%)
28.6
44.8		
50.8
42.1
Functional status						Putting on socks while standing (%)
34.7
25.0
0.377
68.9
57.9
0.378
Climbing up and down stairs (%)
70.8
60.7
0.365
78.9
88.5
0.290
Standing up from a chairwithout using the arms (%)
66.7
44.4
0.061
91.8
68.4
0.011
Fear of falling (%)
38.3
59.3
0.082
19.7
31.6
0.278
Regular exercise (%)
68.8
64.3
0.689
68.9
57.9
0.378
TKA, total knee arthroplasty.

age- and gender-matched healthy controls. Compared
to controls, patients had significantly worse ambulatory
ability and physical function in all ADLs despite a lower
proportion of persons with knee pain while climbing
up or down stairs. Knee pain and functional status improved after TKA, but persons are often plagued withquadriceps muscle impairment and functional limitations compared to their healthy elderly counterparts.18
Additionally, patients after TKA were significantly
worse at 6 months after surgery in the timed up and go
test, stair climbing test, 6-min walk test and 1-leg standing test compared to the healthy elderly.9 Our assessment included questions about putting on socks while
standing, climbing up and down stairs and standing up
from a chair without using the arms. We speculate thatthe questions are associated with extremity muscle function and standing balance, which were assessed in theprevious studies.9 Thus, our study indicated that patients
who have undergone TKA have lower levels of physicalMultivariate logistic regression analysis

In the overall analysis of the incidence of falling, ability
to stand up from a chair without using the arms showed
the strongest association with recent falls [OR = 0.340,
95% confidence interval (CI) = 0.145–0.799, P = 0.013].
Multivariate logistic regression was analyzed with fallrisk factors as the dependent variable in both groups.
In patients, kyphosis showed the strongest association
with recent falls (OR = 3.909, 95% CI = 1.113–13.730,
P = 0.033). In controls, the ability to stand up from achair without using the arms (OR = 0.060, 95% CI =0.009–0.382, P = 0.003) and restriction from joining
social activities due to knee pain (OR = 8.277, 95% CI =1.527–44.880, P = 0.014) showed the strongest association with recent falls.
DISCUSSION
This is the first study to compare the incidence and risk
factors for falling between patients after TKA and the142

Falling after total knee arthroplasty
Table 6. Comparison of state of the knee and joint pain of fall and non-fall groups in the patients and controls
Patients			
Non-fallers
Fallers		
(n = 50)(n = 31)
P value

Controls
Non-fallers(n = 61)

Fallers(n = 19)

Knee pain						Regular stiffness (%)
29.2
50.0
0.069
47.7
47.4
Pain while walking (%)
22.9
21.4
0.881
34.4
36.8
Pain while climbing up or down stairs (%)
27.1
22.2
0.642
39.3
42.1
Pain while standing (%)
14.9
17.9
0.735
26.2
26.3
Restriction from joining social activities
due to knee pain (%)
25.0
25.9
0.929
13.6
41.7
Knee flexion range of motion						i) Excellent (%)
41.7
3.7
0.005
80.3
84.2
ii) Good (%)
37.5
48.1		
4.9
10.5iii) Average (%)
14.6
33.3		
6.6
0.0iv) Poor (%)
2.1
11.1		
4.9
0.0v) Bad (%)
4.2
3.7		
1.6
5.3
Other joint pain						Spine (%)
40.8
48.3
0.506
45.9
47.3
Hip (%)
8.1
0.0
0.103
3.2
0.0
Ankle (%)
12.1
16.1
0.623
4.9
0.0
Varus deformity of the knee (%)
–
–
–
31.7
47.4

functioning than healthy elderly controls, consistently
with the previous reports.9, 18
The fall incidence among the general Japanese
population aged 65 years and over is between 10% and20%.19 In comparison, the incidence of falls among thecontrols in the present study was considerably higher.
Among the present controls, 35% had a varus deformityand 22.5% of them had received diagnosis or treatmentof knee OA by a doctor at least once in the past. The
present controls showed a higher morbidity of knee OA
and musculoskeletal pain, which are risk factors for falling.5, 21 This fact may evidence higher prevalence of falling in them, but the prevalence of knee OA showed nosignificant difference between the present controls andJapanese general population.20 In contrast, 31 of 81 patients (38.2%) had falls during the previous 12 months.
The incidence of injuries and fractures due to falling inpatients were not significantly different from controls,
but the incidence of falling was significantly higher.
Previous prospective studies13, 14 reported that the annual postoperative fall rate was 24.2% to 32.9% among
patients after TKA. These rates of falling are lower thanthose previously reported for OA or RA patients. Thus,
although TKA may reduce the incidence of falls in OA
or RA patients, OA patients who undergo TKA are
considered more likely to fall than the age- and gendermatched general Japanese.
We compared the risk factors for falling between
patients after TKA and age- and gender-matchedhealthy controls. The overall analysis showed that TKA
was not an independent risk factor for falling. However,

P value
0.990
0.847
0.830
0.994
0.030
0.548

0.911
0.424
0.324
0.212

the percentage of patients after TKA was significantly
higher in fallers than non-fallers in univariate analysis.
It is possible that functional decline and lower extremity
muscle weakness after TKA are associated with falling.
In controls, standing up from a chair without using thearms and restriction from joining social activities due toknee pain showed the strongest association with recent
falls. These are common risk factors for falling among
the elderly in general.22, 23 Inability to stand up from achair without using the arms is statistically significantly
associated with poor physical function.22 As a result,pain and poor physical function leads to restricted fromjoining social activities.23
In contrast, kyphosis showed the strongest association with recent falls among elderly individuals who
underwent TKA. Previous studies4, 13, 14 reported several risk factors for falling in patients after TKA. It isinteresting that risk factors differed in healthy elderly
individuals. Postoperative falling in patients after TKA
was predicted by depression symptomatology and, knee
pain, stiffness, function scores in The Western Ontario
and McMaster Universities Osteoarthritis Index and balance confidence scores did not show the strongest correlation with recent falls.13 Besides this, the postoperative
limited range of knee flexion and ankle plantarflexion
were significant risk factors, and knee muscle strengthand the duration of 1-leg standing were similar between
fallers and non-fallers.14 We speculate that common risk
factors for falls may not be suitable to stratify the risk offalling in patients after TKA, because they have worse
motor function of lower extremity muscle strength and143

H. Matsumoto et al.

balance than the healthy elderly. The hyperkyphotic posture is an easily identifiable independent risk factor for
falls in the general population.24, 25 Despite the fact thatthe incidence of kyphosis in the controls was higher, thepresent study showed a relationship between falling andkyphosis in the patients. According to a previous study,26a meaningful increase was observed in the sacral slope
in patients after TKA who achieved an increase in therange of knee extension greater than 10˚. We speculated
that a change in sagittal spinal alignment after TKA
may lead to decreased awareness of kyphosis. In contrast, even if TKA eliminated knee pain, patients who
had a spinal problem after surgery may be likely to fall.
However, we are unable to determine the likely directionof the relationship between TKA and kyphosis from ourdata.
Our study had several limitations. First, there is thepossibility of selection bias. The response rate for thequestionnaire was low in patients. In the present study,
it was probable that patients, who were on the averagemuch older than controls, could not answer and send thequestionnaire, and so analysis was limited to respondents between 70 and 80 years of age. Second, physicalfunction in both groups was only assessed through theself-administered questionnaire, which lacks objectivity.
The present study could not assess cognitive impairment; however, we thought that our subjects had enoughcomprehension to answer our questions. Third, controls
in the present study may have had better physical function, and the incidence rates of falls reported here should
be compared to those in OA or RA patients who haveequivalent levels of physical function. However, we usedage- and gender-matched controls, and the incidence offalls in patients after TKA seemed to be substantiallyhigher than that in the general population. Fourth, we
could not objectively assess kyphosis and range of motion of the knee. Further prospective studies will needto assess the relationship between kyphosis and fallingwith objective methods. We should identify the period oftime after surgery when the tendency to fall and sustain
a fracture is elevated. The details of falls, the situation,
location and season, should be assessed, as well.
In conclusion, patients after TKA have worse motor
function, such as lower extremity muscle strength andbalance, than the healthy elderly. They are consideredmore likely to fall than the general Japanese population.
Kyphosis showed the strongest association with recent
falls in patients after TKA, which was different from thefindings in healthy elderly controls. For patients with kyphosis, improvement of physical function with exercise
and patient education on fall prevention is necessary.

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