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The incidence of acute Achilles tendon rupture (ATR)
in the general population is 7 to 40 per 100,000 people
per year.1-6) As a result of growing participation in recre-
ational and competitive sports, the incidence of ATR has
increased rapidly in recent decades.2-4,7) Along with this
trend, the number of patients who suffer a contralateral
ATR after unilateral ATR, called nonconcurrent bilateral
ATR, is also increasing because the risk of contralateral
ATR in patients with unilateral ATR is significantly higher
than that of the general population owing to genetic pre-
disposition, degenerative changes, and atrophy of the con-
tralateral tendon.8-11) Accordingly, interest in the prognosis
of nonconcurrent bilateral ATR is gradually increasing.
Although there may be individual differences, de-
pending on the severity and location of the injuries, bilat-
eral injuries in musculotendinous structures are generally
known to have a poor prognosis, compared to unilateral
Prognosis of Nonconcurrent Bilateral Achilles
Tendon Rupture Is Worse Than Unilateral Achilles
Tendon Rupture: Patient-Reported Outcomes at
Minimum 2-Year Follow-up
Young Hwan Park, MD, Young Bin Lee, MD, Sang Roc Han, MD, Hak Jun Kim, MD
Department of Orthopedic Surgery, Korea University Guro Hospital, Seoul, Korea
Background: Approximately 5%–7% of patients who have had Achilles tendon rupture (ATR) suffer from contralateral ATR. How-
ever, no studies have evaluated the clinical outcomes of contralateral ATR in patients with an existing ATR. Therefore, in this study,
we aimed to investigate patient-reported ankle function and activity levels in patients with nonconcurrent bilateral ATR.
Methods: We retrospectively reviewed the data of 222 patients with an acute ATR who presented at our 2 institutions between
2005 and 2017. All patients had a minimum 2-year follow-up period, with no other major injuries to the ankle joint. Of these pa-
tients, 17 patients had nonconcurrent bilateral ATR. Patient-reported outcomes were assessed by telephone interview, using the
Achilles tendon Total Rupture Score (ATRS), the ankle activity score, and a patient satisfaction questionnaire. Telephonic interviews
were conducted by 2 authors, using a prepared script to minimize bias owing to individual interviewers.
Results: The mean age of the patients was 45.1 ± 9.8 years, and 89% were men. Patients with nonconcurrent bilateral ATR had
significantly lower values in terms of ATRS, ankle activity score, and satisfaction with current activity level, compared to patients
who had unilateral ATR (
p
< 0.001,
p
= 0.027, and
p
= 0.012, respectively).
Conclusions: Patients with nonconcurrent bilateral ATR had poorer ankle function, activity levels, and satisfaction than those with
unilateral ATR in terms of patient-reported outcome measures with an intermediate-term result and a 2-year minimum follow-up
period. These results emphasize the importance of the impact of contralateral injury on the prognosis of patients with ATR and the
need for efforts to prevent contralateral rupture.
Keywords:
Ankle, Recovery of function, Outcome assessment, Tendon injuries
Original Article Clinics in Orthopedic Surgery 2024;16:800-806 • https://doi.org/10.4055/cios23126
© 2024 by The Korean Orthopaedic Association
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0)
which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Clinics in Orthopedic Surgery • pISSN 2005-291X eISSN 2005-4408
Received April 25, 2023; Revised May 15, 2024;
Accepted May 15, 2024
Correspondence to: Hak Jun Kim, MD
Department of Orthopedic Surgery, Korea University Guro Hospital, 148
Gurodong-ro, Guro-gu, Seoul 08308, Korea
Tel: +82-2-2626-3090, Fax: +82-2-2626-1163
E-mail: hjunkimos@gmail.com
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Park et al. Prognosis of Bilateral Achilles Tendon Rupture
Clinics in Orthopedic Surgery • Vol. 16, No. 5, 2024 • www.ecios.org
injuries. Faltstrom et al.12) reported that in cases of ante-
rior cruciate ligament (ACL) injury, patients with bilateral
injuries reported poorer knee function and quality of life
compared to those who had unilateral injury. Chang et
al.13) found that the clinical outcomes of patients with bi-
lateral quadriceps tendon ruptures were lower than those
of patients with similar, but unilateral, injuries. In addi-
tion, Nove-Josserand et al.14) reported that patients with
bilateral rotator cuff tears seem to have worse occupational
outcomes in private sector employed patients.
Having a contralateral ATR in addition to an exist-
ing ATR is considerably traumatic for the patient, and this
subsequent injury can have a significant impact on the
patient’s return to preinjury activities. However, to date,
no studies have evaluated the clinical outcomes of contra-
lateral ATR in patients with an existing ATR. Therefore,
this study aimed to investigate the patient-reported ankle
function and activity level of nonconcurrent bilateral ATR
and to compare them with those of patients with unilateral
ATR. We hypothesized that patients with nonconcurrent
bilateral ATR would report lower values on these param-
eters, compared with patients with unilateral ATR.
METHODS
This study was approved by the Ethics Committee of Ko-
rea University Guro Hospital (IRB No. 2019GR0380), and
informed consent was obtained from all enrolled patients
via telephone interviews.
Study Design and Patients
The study had a cross-sectional design. All patients who
underwent surgical treatment for their first acute ATR at
our 2 institutions (Korea University Guro Hospital, Ko-
rea University Ansan Hospital) between 2005 and 2017
were reviewed. This study included the patients from our
previous study,8) which investigated the risk factor of non-
concurrent bilateral ATR. Patients were excluded if they
had a history of previous surgery of the Achilles tendon,
Achilles tendon re-rupture, open rupture, avulsion frac-
ture, skeletal deformities around the ankle joint (varus
and valgus deformity of the distal tibia and cavovarus
deformity of the calcaneus), or a significant medical co-
morbidity that would potentially affect the Achilles tendon
(hypercholesterolemia with xanthoma, generalized laxity,
and uncontrolled diabetes combined with diabetic foot).
The occurrence of contralateral ATR in addition to an
existing ATR was identified via patient medical records
of the emergency department and outpatient clinic. For
the cases of contralateral ATR that occurred after the end
of the follow-up for the first injury and treated at other
institutions, the occurrence of contralateral ATR was also
surveyed during telephone interviews. During the 12-year
period, 338 patients presented with an acute ATR and 306
patients met the inclusion criteria. Telephone interviews
were conducted for this group. Among 306 patients, 205
of 287 patients with unilateral ATR (71.4%) and 17 of 19
patients with nonconcurrent bilateral ATR (89.5%) par-
ticipated and responded to the questionnaires. Finally, 222
patients were enrolled for the analysis (Fig. 1).
Data Collection
The data for patient demographics and pre-injury activity
level were collected from medical records. To assess pre-
injury activity level, the ankle activity score (categorizing
sports activity from 0 to 10) was used.15) A higher score
indicates more intense physical activity. The score was
originally developed to indicate sports-related ankle func-
17 Nonconcurrent
bilateral ATR205 Unilateral ATR
n=222
n=306
338 Patients with an ATR
(2005 2017) Exclusion I
3 History of previous Achilles tendon surgery
14 Re-rupture
6 Open rupture
4 Skeletal deformity involving the ankle joint
5 Significant medical comorbidity potentially
affecting the soft-tissue condition
Exclusion II
5 Refuse to participate
79 Lost to follow-up due to contact change
Fig. 1. Flowchart of patient enrollment.
ATR: Achilles tendon rupture.
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Clinics in Orthopedic Surgery • Vol. 16, No. 5, 2024 • www.ecios.org
tion, but it has also been used to assess the level of sports
activity in patients with acute ATR.16) Sports not included
in the original ankle activity score were also graded, based
on the consensus of 2 authors who were in charge of the
telephone interviews (YHP and YBL). Any discrepancies
between the 2 authors were resolved by consensus discus-
sion with a third author (HJK).
The Achilles tendon Total Rupture Score (ATRS)17)
was used as a primary outcome measurement to evaluate
the patient-reported Achilles tendon function, and the
questionnaires were completed via a telephone interview.
The patients were asked to respond to the 10 items of the
ATRS using a 0–10 scale; a score of 0 is equivalent to hav-
ing major limitations, and a score of 10 is equivalent to
having no limitations. The sum of these scales represented
the final ATRS value (range, 0–100).
As a second outcome measurement, the current
ankle activity level and patient satisfaction with activity
were surveyed. As with the pre-injury activity level, the
current activity level was scored by the ankle activity score.
Patient satisfaction was measured using a 7-point Likert
scale with the following question: “If you had to live with
your current ankle function for the rest of your life, would
you feel…?” with the following choices: delighted, pleased,
mostly satisfied, mixed, mostly dissatisfied, unhappy, and
terrible.12,18)
The patients were randomly assigned to the 2 tele-
phone interviewers. To minimize bias due to the individu-
al interviewer, the interviews were conducted based on the
scripts prepared in advance, and other conversations that
could affect the answers were restricted.
Surgical Treatment and Postoperative Rehabilitation
All the ATRs, including nonconcurrent bilateral ATRs,
Table 1. Characteristics of Patients
Variable Bilateral ATR (n = 17)* Unilateral ATR (n = 205)
p
-value
Age (yr)
At injury 36.4 ± 10.0 (19–61) 39.3 ± 9.9 (19–66) 0.296
Current 46.7 ± 8.7 (32–68) 44.6 ± 9.9 (24–72) 0.429
Sex 0.702
Male 16 (94.1) 182 (88.8)
Female 1 (5.9) 23 (11.2)
BMI (kg/m2) 23.0 ± 2.8 (18.8–25.5)†25.2 ± 3.1 (17.7–36.3) 0.154
Diabetes 1 (5.9) 8 (3.9) 0.519
Activity performed at injury 0.476
Football 6 (35.3) 66 (32.2)
Foot volleyball 3 (17.6) 23 (11.2)
Basketball 4 (23.5) 21 (10.2)
Badminton 0 19 (9.3)
Jogging 2 (11.8) 16 (7.8)
Volleyball 0 11 (5.4)
Tennis 0 8 (3.9)
Jump rope 1 (5.9) 6 (2.9)
Other sports (baseball, ballet, skiing, etc.) 0 20 (9.8)
Daily living activities 1 (5.9) 15 (7.3)
Values are presented as mean ± standard deviation (range) or number (%).
ATR: Achilles tendon rupture, BMI: body mass index.
*Data at the time of the first Achilles tendon rupture. †n = 12 (5 missing) as 5 patients were treated elsewhere.
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were surgically repaired using the Krackow suture tech-
nique within 1 week after injury. After surgery, a non-
weight-bearing short leg splint in 20° plantarflexion was
maintained for 2 weeks. Patients were transitioned to
tolerable weight-bearing activity with a controlled ankle
motion (CAM) boot 2 weeks postoperatively, which was
initially set at 20° plantarflexion and gradually increased
to neutral at 4–5 weeks following surgery. Patients were
weaned from the CAM boot beginning on postoperative
week 9 and instructed to start an exercise program. These
protocols were identically applied to contralateral ATR pa-
tients except for 5 patients who underwent surgical treat-
ment elsewhere.
Statistical Analysis
The normality of the data was determined using the
Shapiro-Wilk test. Variables with a normal distribution
(age, body mass index, and ATRS) were presented as mean
and standard deviation and were analyzed using Student
t-test. Variables with non-normal distribution (ankle ac-
tivity score and time between injury and follow-up) were
presented as median and interquartile range and were ana-
lyzed using the Mann-Whitney test. Categorical variables
such as sex and patient satisfaction were compared using
the chi-square test and the diabetes and activity performed
at injury were compared using the Fisher exact test. Sta-
tistical significance was accepted when p < 0.05. Statistical
analyses were performed with IBM SPSS version 23.0 (IBM
Corp.). A post-hoc power analysis was performed with
G*Power software, version 3.01 (Franz Faul, Christian-
Albrechts-Universität Kiel).19)
RESULTS
Patient Characteristics
A summary of the patient characteristics is in Table 1.
There was no significant difference in patient characteris-
tics between those having unilateral ATR and those having
the first injury of bilateral ATR. The preinjury activity level
in 13 patients was not determined because their preferred
sports were not categorized on the ankle activity score. Of
these, 9 were graded by consensus of the 2 interviewers
(kappa coefficient, 0.55), and 4 were graded by the third
author. In the bilateral ATR group, the mean age was 36.4
± 10.0 years (range, 19–61 years) at the first injury and
43.0 ± 8.5 years (range, 30–66 years) at the second injury.
The mean time between the first injury and the second
injury was 61.3 ± 42.3 months (range, 13–155 months).
Table 2. Results of the Questionnaires for Patient-Reported Outcomes
Variable Bilateral ATR (n = 17) Unilateral ATR (n = 205)
p
-value
ATRS
First injured ankle 81.2 ± 11.2 (61–100) 86.8 ± 11.8 (31–100) 0.056
Second injured ankle 75.7 ± 10.7 (57–92) - < 0.001*
Ankle activity score
Before the first injury 8 (4–8, 6–8) 7 (3–9, 5–8) 0.103
Before the second injury 6 (3–8, 5–7) - 0.390†
At follow-up 5 (2–7, 4–6) 6 (3–8, 5–7) 0.027
Satisfaction with current activity level 0.012
Delighted to pleased 1 (5.9) 86 (42.0)
Unhappy to terrible 5 (29.4) 35 (17.1)
Time between injury and follow-up (mo)
From the first injury 122 (42–293, 69–162) 69 (24–174, 39–97) < 0.001
From the second injury 58 (24–138, 28–77) - 0.135‡
Values are presented as mean ± standard deviation (range), median (range, interquartile range), or number (%).
ATR: Achilles tendon rupture, ATRS: Achilles tendon Total Rupture Score.
*ATRS of the second injured ankle compared to that of unilateral ATR patients. †Ankle activity score before the second injury compared to that of
unilateral ATR patients at follow-up. ‡Time between the second injury and follow-up compared to time between the first injury and follow-up for
unilateral ATR patients.
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Achilles Tendon Function and Activity Level
Results of the questionnaires for patient-reported out-
comes are summarized in Table 2. The ATRS of the second
injured ankle of the bilateral ATR group was significantly
lower than that of the unilateral ATR group, but the ATRS
of the first injured ankle of the bilateral ATR group did not
show significance, despite its trend of having a lower score
than the unilateral ATR group.
The ankle activity scores of the bilateral ATR group
(before the first injury) were similar to those of the unilat-
eral ATR group. Before their second injury, the ankle ac-
tivity scores in the bilateral ATR group recovered after the
first injury but showed no significant difference compared
to follow-up ankle activity scores in the unilateral ATR
group. However, after the second injury, the follow-up
ankle activity score of the bilateral ATR group was signifi-
cantly lower than that of the unilateral ATR group. When
the patients were asked about their satisfaction with their
current activity level, those in the bilateral ATR group
were less satisfied than those in the unilateral ATR group.
Post-Hoc Power Analysis
A post-hoc power analysis indicated that this study had
0.99 power to detect an effect size of 1.49 in ATRS between
the bilateral ATR and unilateral ATR groups, with a type I
error probability of 0.05.
DISCUSSION
The primary finding of this study is that the patients with
nonconcurrent bilateral ATR showed poorer self-reported
Achilles function than the patients with unilateral ATR at
a minimum 2-year follow-up after their second injury. The
reduced Achilles tendon function significantly affected
their prognosis; at follow-up, the return to the pre-injury
activity and activity level in patients who had nonconcur-
rent bilateral ATR was lower compared to patients who
had unilateral ATR. Satisfaction with the current activity
level was also lower in nonconcurrent bilateral ATR, re-
flecting functional outcomes.
Generally, assessment of patient-reported outcomes
is performed by the patients filling out questionnaires
themselves, following instructions provided by investiga-
tors. Therefore, there may be concerns about the use of
telephone interviews to fill out the questionnaires in our
study. However, assessment of patient-reported outcomes
by telephone interview has often been used in previous
studies, not only ATRS,20) but also other questionnaires for
the Achilles tendon,21-24) either alone or in combination
with email surveys. In the study of ATR, the long-term
follow-up visit for clinical evaluation is difficult because
the majority of ATR patients have returned to their daily
activities and recreational sports satisfactorily, although
their function has been somewhat reduced. Therefore,
considering the incidence of nonconcurrent bilateral ATR,
the authors thought that a telephone interview technique,
which could involve a large number of patients, was the
best option.
The ATRS, which is a primary outcome measure
of this study, is derived from a validated questionnaire; it
is widely used to evaluate the outcome of ATR. Nilsson-
Helander et al.25) reported a mean of 88 points at 1-year
follow-up after surgery, and Olsson et al.26) reported a
mean of 90 points at their 2-year follow-up. In a long-term
follow-up, Rosso et al.27) reported a mean score of 91 at 8
years after surgery. In our study, the ATRS in the unilateral
ATR group showed a mean score of 87 points, which was
considered comparable to the scores in previous studies
because a 10-point difference was reported to have clinical
relevance.17) However, the second injured side, in the cases
of bilateral ATR, showed a mean ATRS score of 76 points,
indicating that these patients reported impaired Achilles
tendon function, compared to previous studies and our
control group.
In this study, the ankle activity score after the first
injury was not different between bilateral ATR and unilat-
eral ATR cases, but the final ankle activity score of the cas-
es of bilateral ATR after the second injury was significantly
lower than that of the cases of unilateral ATR. Compared
to the first injury, the impact of contralateral injury on the
prognosis of the patients with ATR was substantial. As the
clinical outcomes in nonconcurrent bilateral ATR were
worse than those in unilateral ATR, the authors thought
that the strength and flexibility of the second ruptured
Achilles tendon may have played a role in the poor clini-
cal symptoms of these patients, although the psychologi-
cal factors of these patients related to additional rupture
may also have played a role.28) Therefore, knowledge of the
risk factors of bilateral ATR is important to help prevent
contralateral injury. However, in contrast to bilateral ACL
injury, for which many risk factors (being female, adoles-
cent, high activity level, etc.) have been found to be related
to contralateral injury,29-31) there was only 1 study investi-
gating the risk factors of bilateral ATR, which found that
patients who suffered ATR in their 30s had an increased
risk of contralateral injury.8) The authors thought the lack
of study on the risk factors for bilateral ATR was due to
the relatively small number of patients with bilateral ATR
at each institution. Studies involving a large number of
patients may reveal factors other than age, so further mul-
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Park et al. Prognosis of Bilateral Achilles Tendon Rupture
Clinics in Orthopedic Surgery • Vol. 16, No. 5, 2024 • www.ecios.org
ticenter studies are needed.
This study has 3 limitations. First, we only evaluated
patients’ subjective outcomes related to their perception
of health status, activity level, and satisfaction, without
objective assessments for ankle function, such as muscle
strength or stiffness of the Achilles tendon. Additionally,
we relied solely on telephone interviews, which have not
been commonly used in the literature. This was inevitable
because of the small number of patients who visited for
an objective assessment. Therefore, the purpose of the
study was confined to the investigation of patient-reported
outcomes. Thus, readers should be mindful of this limita-
tion when accepting our findings, as patient’s subjective
outcomes do not always correspond to their objective out-
comes. Second, this study has a possibility of interviewer
bias. Since the answers to the questionnaire could have
been affected by what the interviewers “wanted to hear,”
outcome assessment over the telephone is inherently vul-
nerable to interviewer bias. Although the interviews were
performed based on the scripts prepared in advance (to
minimize the influence from the interviewer), the possi-
bility of bias cannot be completely excluded. Third, the pa-
tients in this study underwent surgical treatment by differ-
ent orthopedic surgeons. Thus, according to the surgeons,
an initial concern regarding bias in the results existed.
However, except for 5 surgeries performed elsewhere, all
surgeries were performed in our 2 chosen institutions with
similar surgical timing, surgical method, and rehabilita-
tion protocols. Additionally, there was no difference in the
overall outcomes between the surgeons and institutions in
the preliminary result comparison conducted before the
start of the study. Therefore, it is unlikely that the surgeon’s
identity significantly affected the results of this study.
In conclusion, patients with nonconcurrent bilat-
eral ATR reported poorer ankle function, activity level,
and satisfaction than those with unilateral ATR having an
intermediate-term result with a 2-year minimum follow-
up. They had a similar activity level to patients with uni-
lateral ATR after their first injury, but showed an impaired
activity level after their contralateral injury. These results
emphasize the importance of the impact of contralateral
injury on the prognosis of patients with ATR and the need
of efforts to prevent contralateral rupture.
CONFLICT OF INTEREST
No potential conflict of interest relevant to this article was
reported.
ORCID
Young Hwan Park https://orcid.org/0000-0002-1732-5405
Young Bin Lee https://orcid.org/0009-0007-2361-1559
Sang Roc Han https://orcid.org/0009-0006-5631-7631
Hak Jun Kim https://orcid.org/0000-0003-3633-6174
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