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Knee Surgery, Sports Traumatology, Arthroscopy
https://doi.org/10.1007/s00167-022-07142-9
ANKLE
Achilles tendon resting angle isable todetect deficits afteranAchilles
tendon rupture, butit isnotasurrogate fordirect measurements
oftendon elongation, function orsymptoms
ElinLarsson1· KatarinaNilssonHelander1· LottaFalkhedenHenning2,3· MerviHeiskanen1· MichaelR.Carmont2,4·
KarinGrävareSilbernagel5· AnnelieBrorsson2,6
Received: 4 May 2022 / Accepted: 23 August 2022
© The Author(s) 2022
Abstract
Purpose The aim of this study was to investigate how the Achilles tendon resting angle (ATRA), an indirect measurement
of tendon elongation, correlates with ultrasonography (US) measurements of the Achilles tendon length 6 and 12months
after an acute ATR and relates to other clinical outcome measurements such as heel-rise height, jumping ability and patient-
reported outcome measurements (PROMs).
Methods Patients were included following acute Achilles tendon rupture (ATR). Achilles tendon length, ATRA, heel-rise
height (HRH), drop countermovement jump (Drop CMJ) and PROMs (Achilles tendon total rupture score (ATRS) and
physical activity scale (PAS)) were evaluated 6 and 12months after injury. Achilles tendon length was evaluated using US,
while the ATRA was measured with a goniometer.
Results Sixty patients (13 women, 47 men), mean (SD) age 43 (9) years, with an acute ATR undergoing either surgical (35%)
or non-surgical (65%) treatment were evaluated. A negative correlation (r = − 0.356, p = 0.010) between relative ATRA and
tendon elongation was seen at 12months after ATR. There were also significant positive correlations at 6 and 12months
between relative ATRA and HRH (r = 0.330, p = 0.011 and r = 0.379, p = 0.004). There were no correlations between ATRA
and ATRS or ATRA and Drop CMJ, at either 6 or 12months after the injury.
Conclusion In combination with other clinical evaluations such as HRH and US, ATRA could be a clinical tool for indirect
measurements of tendon elongation. However, ATRA cannot be recommended as a direct surrogate for US for determining
Achilles tendon length.
Level of evidence III.
Keywords Achilles tendon rupture· Achilles tendon resting angle· ATRA · Tendon elongation· Tendon length·
Ultrasound· Functional tests
Abbreviations
ATR Achilles tendon rupture
DVT Deep vein thrombosis
MRI Magnetic resonance imaging
US Ultrasonographic
ATRA Achilles tendon resting angle
PROMs Patient-reported outcome measures
HRH Heel-rise height
Drop CMJ Drop countermovement jump
ATRS Achilles tendon total rupture score
* Elin Larsson
elin.ma.larsson@vgregion.se
1 The Department ofOrthopaedics, Sahlgrenska University
Hospital Mölndal, Institute ofClinical Sciences
atSahlgrenska Academy, Gothenburg University,
Göteborgsvägen 31, 43180Mölndal, Sweden
2 Department ofOrthopaedics, Institute ofClinical Sciences
atSahlgrenska Academy, Gothenburg University,
Gothenburg, Sweden
3 Aktiva Rehab Team, Gothenburg, Sweden
4 The Department ofTrauma andOrthopaedic Surgery,
Princess Royal Hospital, Shrewsbury andTelford Hospital
NHS Trust, Shropshire, UK
5 Department ofPhysical Therapy, University ofDelaware,
Newark, DE, USA
6 IFK Kliniken Rehab, Gothenburg, Sweden
Knee Surgery, Sports Traumatology, Arthroscopy
1 3
SU/Mölndal Sahlgrenska University Hospital/Mölndal
IQR Interquartile range
Introduction
The question of how best to treat an acute Achilles ten-
don rupture (ATR), surgically or non-surgically, has been
addressed in numerous studies, but there is still no consen-
sus [13, 16, 17, 19]. The aim of treatment is to optimise the
functional outcome and minimise the complications of the
injury and treatment. Meta-analyses have concluded that the
re-rupture rate is lower when ATR is treated surgically com-
pared with non-surgical treatment [9, 20]. The risk of other
complications, such as wound infection and iatrogenic nerve
injury, is reported to be higher with surgical treatment, while
the incidence of deep vein thrombosis (DVT) is similar in
both treatment regimens [9, 20].
Tendon elongation is a complication after an ATR, lead-
ing to reduced plantar flexion strength and poor outcome
[10]. Regardless of surgical or non-surgical treatment, the
injured tendon elongates during the healing process [10].
Reduced tendon elongation correlates with superior clini-
cal outcome [12]. There are several methods for assessing
tendon length and elongation. Radiography with intra-tendi-
nous markers and magnetic resonance imaging (MRI) have
been used, but these methods are expensive and may not
be accessible for monitoring during recovery [12, 15]. The
ultrasonographic (US) measurement of tendon length has
been validated and found to be a reliable and useful tool, but
requires expertise and suitable ultrasound machines may not
be readily available in clinics [26].
The Achilles tendon resting angle (ATRA) is a simple,
readily available, less expensive means of determining the
resting position of the ankle following ATR, with a low
measurement error [27]. The ATRA is defined as “the angle
between the long axis of the fibula and the line from the
tip of the fibula to the head of the fifth metatarsal” [4]. The
ATRA has been validated for assessing tendon elongation
against US [28]. According to Carmont etal. [3], the abso-
lute ATRA increases following injury, reduces as a result of
surgery and increases again during the first phase of reha-
bilitation by 3 months. In previous studies, the ATRA has
been reported to correlate with patient-reported outcome
measurements (PROMs) at three and 6months after surgi-
cal treatment [3]. In overall terms, the ATRA is a frequently
used evaluation of tendon length in studies focusing on reha-
bilitation after ATR, as it has been considered to be more
accessible at an earlier stage in the clinical practice than US
[3–5, 7, 8, 28].
Like the ATRA, the heel-rise test is an easily performed
evaluation of ankle plantar flexion function during reha-
bilitation. Studies evaluating recovery at 6 and 12months
often include measurements of both heel-rise endurance
(repetitions or total work performed) and maximum heel-
rise height [1–3, 21, 25]. The deficit in maximum heel-rise
height (HRH), as compared with the uninjured side, has
been found to correlate to the degree of tendon elongation.
The evaluation of tendon elongation and associated out-
comes needs to be further explored to improve our clinical
tools in order to optimise the rehabilitation and outcome
after an ATR. It is important to find a clinical evaluation
method that is valid and responsive to changes over time and
correlates with tendon elongation (14). The aim of this study
is therefore to determine how the ATRA correlates with the
length of the Achilles tendon measured with US, HRH, drop
countermovement jump (Drop CMJ) and the Achilles tendon
total rupture score (ATRS) 6 and 12months after an acute
ATR.
Materials andmethods
The research protocol was approved by the Swedish Ethical
Review Authority (Dnr 803–15).
All the subjects gave their written consent for enrolment
after having been provided with oral and written information
about the study.
The patients were recruited within 6months following an
acute ATR between 2016 and 2020 by physiotherapists at
five different clinics in Gothenburg, Sweden. The inclusion
criteria for the study were age 18–65years and treatment
commenced within 4 days of injury. The exclusion criteria
included previous injury to the Achilles tendon on either leg,
neurological disease or lack of comprehension of written
and oral Swedish.
The patients were evaluated at 6 and 12months following
rupture and the same experienced physiotherapist performed
all the evaluations.
Achilles tendon resting angle (ATRA)
For measurements of the ATRA, patients were positioned
prone with their knee flexed to 90 degrees and encouraged
to relax their ankle joints. The non-injured leg was exam-
ined first. The patients were encouraged to relax their ankle
joints. The axis of the goniometer (1˚increments) was posi-
tioned at the tip of the fibula. One arm of the goniometer was
aimed towards the head of the fibula and the other arm of
the goniometer was positioned to bisect the head of the fifth
metatarsal (Fig.1). The ATRA has been reliability tested by
Carmont etal. [4] and the reported ICC value of the ATRA
is 0.91–0.92 [4].
The ATRA was reported as either the absolute ATRA of
the injured foot or the relative ATRA referring to differen-
tiation between the resting angle of the injured foot and the
Knee Surgery, Sports Traumatology, Arthroscopy
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non-injured foot respectively. Increased dorsiflexion is con-
sidered to be a negative relative ATRA value and increased
plantar flexion a positive ATRA value compared with the
non-injured side [3].
Ultrasonographic (US) measurement
Achilles tendon length was measured using a US extended
field-of-view feature. The patients lay prone on the examina-
tion table with both feet hanging over the edge of the exami-
nation table. This enabled both feet to be equally relaxed
during measurement. The length of the tendon was measured
between the calcaneal notch, the most proximal attachment
of the Achilles tendon on the calcaneum, and the gastroc-
nemius musculotendinous junction, with extended field-of-
view US (Logiq E or Logiq P9 Ultrasound; GE Healthcare X
AB), using a wideband array linear probe (5.0–13.0MHz).
The B-mode at 10MHz and a depth of 3cm were used to
record the images. This has been found to be a valid and reli-
able method with an ICC value of 0.90 [26]. All the images
were measured by a second experienced physiotherapist.
The mean value of two to three images for each foot and
patient was used for calculations. The tendon elongation was
calculated as the value on the injured limb minus the value
on the healthy limb and expressed in centimetres.
Achilles tendon total rupture score (ATRS)
The evaluation of patient-reported symptoms and function
was assessed using the Achilles tendon total rupture score
(ATRS). The ATRS is a ten-item injury-specific and self-
administered score with a maximum score of 100. The maxi-
mum score implies no limitations and a full recovery. The
ATRS has been found to be a valid and reliable instrument
for measuring the outcome related to symptoms and physical
activity after ATR [18].
Functional evaluations
Functional evaluations were made with a test battery that
included the standing heel-rise work test to evaluate mus-
cular endurance (Joule) and the height of the heel rise (cm)
[23]. The single-leg heel rise, which is used in this study, is
a reliable and valid clinical test for evaluating patients with
ATR [24]. The Muscle Lab® measurement system (Ergot-
est Technology, Oslo, Norway) was used for functional
evaluations.
Before the evaluation, patients performed a 5-min warm-
up on a stationary bike and performed three sets of ten two-
legged heel rises. Standardised shoes (Bagheera Omega)
were worn and the non-injured side was evaluated first.
In the single-leg heel-rise test, the patient stood on one
foot on a box with a 10° incline and a linear encoder was
attached to the shoe on the tested leg. The patients were
instructed to lift as high as possible during the heel rise
and keep their knee straight. The test continued for as long
as patients were able to perform a heel rise of at least 2cm
height and maintain the tempo indicated by a metronome
at a tempo of 30 heel rises a minute. For heel-rise height,
the maximum height was used for calculations. Deficits in
heel-rise height were defined as the difference between the
injured and the non-injured side expressed in cm.
A further functional evaluation was performed using
a Drop CMJ test [23]. This is a one-legged jump from a
20cm high box down to the floor, followed by an immedi-
ate maximum vertical countermovement jump. A light mat,
consisting of infrared light beams placed in front of the box,
determined the height of the jump. Three to five jumps were
performed using each leg and the highest value for both the
injured and healthy limb was used.
Statistical analysis
The sample size was calculated based on the results of the
tendon length of the injured limb at 6 and 12months after
injury [25]. It was estimated that a sample of 57 patients
Fig. 1 The Achilles tendon resting angle (ATRA) measured with a
goniometer
Knee Surgery, Sports Traumatology, Arthroscopy
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was needed to detect a statistically significant difference
(p < 0.05, power 95%) for the elongation of the Achil-
les tendon length between 6 and 12months after injury.
Descriptive data are reported as the mean, standard devia-
tion (SD), median and interquartile range (IQR). A com-
parison between the ATRA, tendon length, HRH and Drop
CMJ between the injured and non-injured limb at 6 and
12months after injury was made using a paired t test. The
primary outcome for this study is the correlation between
tendon elongation, evaluated with US (cm), and the rela-
tive ATRA (°) 6 and 12months after the injury.
The correlations between two continuous variables
(relative ATRA, HRH, Drop CMJ, ATRS) were estimated
using Spearman’s rho correlation coefficient for non-nor-
mally distributed data and Pearson’s correlation for nor-
mally distributed data. The distribution was determined by
a visual inspection of a histogram and by the finding of a
statistically significant p value in the Shapiro–Wilk test.
As an effect size, r2 was calculated. The strength of the
correlation was determined by the correlation coefficient.
A correlation coefficient of > 0.8 was considered very
strong, 0.8–0.6 moderately strong, 0.5–0.3 fair and < 3
poor [6]. The level of significance was set at p < 0.05. All
the data were analysed using IBM SPSS Statistics Ver-
sion 28.
Results
Sixty-six subjects were included in this study. 6 patients
were excluded; 1 patient declined due to fear of COVID-
19, another suffered excessive elongation and was unable to
perform the evaluations, 1 patient was incorrectly included
(older than the upper age limit) and 3 subjects withdrew
from the study after the 6-month evaluation for unknown
reasons. The demographics of the study subjects are pre-
sented in Table1.
There was a significant difference between the injured
side compared with the non-injured side at 6months and
12months regarding the ATRA, tendon length, HRH and
Drop CMJ. The data are presented in Table2.
The correlations between the relative ATRA at 6 and
12months and tendon length, ATRA, HRH, Drop CMJ and
ATRS are presented in Figs.2, 3, 4, 5. A negative correla-
tion (r = − 0.356, p = 0.010) between the relative ATRA and
tendon elongation was seen at 12months but not at 6months
after ATR (Fig.2). There was also a positive correlation at
both 6 and 12months between the relative ATRA and HRH
(r = 0.330, p = 0.011; r = 0.379, p = 0.004) (Fig. 3). There
was no correlation between Drop CMJ and the relative
ATRA or ATRS and the relative ATRA, at 6 or 12months
after the injury (Figs.4 and 5).
Discussion
The most important finding in this study is that, in all out-
come measurements (ATRA, HRH, Drop CMJ and tendon
length), the injured side had significant deficits compared
with the uninjured side at both 6 and 12months. There
was a significant fair negative correlation between the rela-
tive ATRA and tendon elongation at 12months, but not at
6months after an ATR. Furthermore, there were fair posi-
tive correlations between the relative ATRA and deficits in
HRH at 6 and 12months, such as a resting angle in more
dorsiflexion related to a greater deficit in HRH.
The results demonstrate that clinical evaluations includ-
ing HRH, Drop CMJ and tendon length measured by US
provide a better full picture of the functional outcome after
an ATR, but that the ATRA follows a similar trend, indicat-
ing its value to indirect measurements of the presence of
tendon elongation. However, the ATRA could not be recom-
mended as a direct surrogate for US for determining Achilles
tendon length.
A correlation between the ATRA and tendon length was
also reported by Zellers etal. [28], who found a moderate
correlation (r = 0.491, p = 0.001) between the relative ATRA
and tendon elongation evaluated with US 12months after
an ATR. However, Zeller etal. [28] used an inclinometer
compared with the manual measurement by a goniometer
that was used in the present study, so the results may not be
completely comparable. Previously, Carmont etal. [3] found
a correlation with the absolute ATRA and the HRH limb
symmetry index (LSI) at 12months, but this was not found
to be the case at 9 months following injury. These results
are in line with ours. It is worth mentioning that we used
the deficits in heel-rise height and not the LSI values. Nor
did we use the absolute ATRA. In support of our results, Sil-
bernagel etal. [25] found statistically significant differences
Table 1 Patient demographics presented by the mean (SD) and per-
centage (n)
n number of patients
Variable Total
n = 60
Women
n = 13
Men
n = 47
Age, years 43 (9) 42 (8) 44
Height, cm 178 (8) 169 (5) 181 (6)
Weight, kg 82 (13) 68 (5) 86 (11)
BMI 25.7 (3.0) 24.0 (2.0) 26.1 (3.1)
Injured side
Right (n) 53% (32) 54% (7) 53% (25)
Left (n) 47% (28) 46% (6) 47% (22)
Treatment
Surgery 35% (21) 38% (5) 34% (16)
Non-surgery 65% (39) 62% (8) 66% (31)
Knee Surgery, Sports Traumatology, Arthroscopy
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between the injured and uninjured side after an ATR at 6 and
12months after injury (mean (SD) at 6/12months) in both
HRH (− 6.1cm (1.7)/ − 4.1cm (1.8)) and tendon length
measured by US (3.0 (1.2)/2.6cm (1.4)).
Mortensen etal. [15] and Kangas etal. [12] found that the
injured tendon elongates during the healing process during
the first months after an ATR, which is in line with Car-
mont etal.’s [3] finding that the ATRA also increases up
to 3 months after the same injury. However, Eliasson etal.
[11] reported elongation up to 6 months following a rupture.
Tendons have been noted subsequently to shorten a couple
of millimetres, a statistically non-significant amount, up to
12months following injury [12].
There was no significant correlation between Drop CMJ
and the ATRA at either 6 or 12months. This may require
further investigation if it is assumed that a greater relative
ATRA contributes to poorer plantar flexion power. It has
been shown that a vertical jump test may be less applicable
Table 2 Comparison between
the injured and non-injured side
at 6 and 12months presented by
the mean (SD)
a Achilles tendon resting angle
b Heel-rise height
c Drop countermovement jump
Variable 6months 12months
Non-injured side Injured side p value Non-injured side Injured side p value
ATRA
a (°) 47.1 (5.7) 52.9 (6.4) < 0.001 46.6 (6.2) 51.6 (5.6) < 0.001
Tendon length (cm) 21.4 (2.7) 23.4 (3.1) < 0.001 21.5 (2.2) 23.1 (2.9) < 0.001
HRHb (cm) 14.0 (2.4) 10.1 (3.1) < 0.001 13.9 (2.1) 11.6 (2.1) < 0.001
Drop CMJc (cm) 15.6 (4.8) 12.1 (4.6) < 0.001 15.8 (3.8) 13.1 (3.9) < 0.001
Fig. 2 Correlation between tendon elongation (cm) and relative Achilles tendon resting angle (degrees) at 6months and at 12 months after
Achilles tendon rupture. The line represents linear regression model
Fig. 3 Correlation between deficits in heel-rise height (cm) and relative Achilles tendon resting angle (degrees) at 6months and at 12 months
after Achilles tendon rupture. The line represents the linear regression model
Knee Surgery, Sports Traumatology, Arthroscopy
1 3
in the evaluation of lower limb strength and tendon elonga-
tion [14]. Jumping is a complex movement including multi-
ple muscle groups rather than the calf muscles in isolation.
Jumping additionally involves other aspects such as balance
and co-ordination [14]. It has also been shown that, dur-
ing jumping, the decrease in work performed at the ankle
can be compensated for by increased work performed at the
knee and the hip, resulting in no noticeable deficits in jump
heights [29].
In this study, there was no significant correlation between
the ATRA and patient-reported outcome (ATRS) at 6 or
12months after ATR. It is important to highlight the fact
that it is not uncommonly noticed that patients adapt their
everyday life to their limitations [1, 22]. However, Carmont
etal. [3] found a positive association with the ATRA and
ATRS at 3 and 6 months but not at 9 months following
surgery.
All the patients were evaluated by one experienced
physiotherapist with a standardised test battery, which is an
important strength. One limitation of this study is that the
study design did not include a standardised rehabilitation
protocol. Another aspect that could be taken into account
is the non-random inclusion of patients, which could be a
bias, since the patient population might not represent the
common population.
The measurement of the ATRA in patients with an ATR
is widely used among orthopaedic surgeons and physio-
therapists. The great advantages of the ATRA are that only
a goniometer is required and the measurement is easy to
perform. The findings in this study confirm that, together
with other clinical evaluations, the ATRA could be useful
in detecting and evaluating tendon elongation in the clinical
setting.
Conclusion
In combination with other clinical measurements, such as
HRH and US, the ATRA is a useful clinical tool for indirect
measurements of the presence of tendon elongation through-
out recovery. However, the ATRA cannot be regarded as a
direct surrogate for US.
Fig. 4 Correlation between deficits in drop countermovement jump (cm) and relative Achilles tendon resting angle (degrees) at 6months and at
12months after Achilles tendon rupture. The line represents the linear regression model
Fig. 5 Correlation between Achilles tendon total rupture score and relative Achilles tendon resting angle (degrees) at 6months and at 12months
after Achilles tendon rupture. The line represents linear regression model
Knee Surgery, Sports Traumatology, Arthroscopy
1 3
As a result, tendon elongation after an ATR is not pos-
sible to either detect or reject using only one clinical assess-
ment, such as the ATRA.
Authors contributions KGS, AB, LFH, MC and KNH participated in
the design of the study. LFH and AB performed all clinical evaluations
including the ultrasound measurement. EL, MH and AB performed
the data processing and statistical analysis. All of the authors have
contributed to the manuscript.
Funding Open access funding provided by University of Gothen-
burg. Funding was provided by the Local Research and Develop-
ment Board for Gothenburg and Södra Bohuslän, Sweden Dnr:
VGFOUGSB-904421 and Swedish Research Council for Sports Sci-
ence (CIF) nr: P2019-0156.
Declarations
Conflict of interest None of the authors have any conflicts of interest.
Ethical approval The research protocol was approved by the Swedish
Ethical Review Authority (Dnr 803–15).
Open Access This article is licensed under a Creative Commons Attri-
bution 4.0 International License, which permits use, sharing, adapta-
tion, distribution and reproduction in any medium or format, as long
as you give appropriate credit to the original author(s) and the source,
provide a link to the Creative Commons licence, and indicate if changes
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permitted by statutory regulation or exceeds the permitted use, you will
need to obtain permission directly from the copyright holder. To view a
copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/.
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