Rehabilitation of Achilles tendon ruptures: is early functional rehabilitation daily routine?

Abstract

Introduction:
Ruptures of the Achilles tendon are the most common tendon injuries of the lower extremities. Besides the initial operative or non-operative treatment, rehabilitation of patients plays a crucial role for tendon healing and long-term outcome. As only limited evidence is available for optimized rehabilitation regimen and guidelines for the initial (e.g., first 6 weeks) rehabilitation are limited, this study investigated the current rehabilitation concepts after Achilles tendon rupture.

Materials and methods:
We analyzed 213 written rehabilitation protocols that are provided by orthopedic and trauma surgery institutions throughout Germany in terms of recommendations for weight-bearing, range of motion (ROM), physiotherapy, and choice of orthosis. All protocols for operatively and non-operatively treated Achilles tendon ruptures were included. Descriptive analysis was carried out and statistical analysis applied where appropriate.

Results:
Of 213 institutions, 204 offered rehabilitation protocols for Achilles tendon rupture and, therefore, 243 protocols for operative and non-operative treatment could be analyzed. While the majority of protocols allowed increased weight-bearing over time, significant differences were found for durations of fixed plantar flexion between operative (o) and non-operative (n) treatments [fixed 30° (or 20)° to 15° (or 10)°: 3.6 weeks (±0.1; o) vs 4.7 weeks (±0.3; n) (p ≤ 0.0001) and fixed 15° (or 10)° to 0°: 5.8 weeks (±0.1; o) vs 6.6 weeks (±0.2; n) (p ≤ 0.001)]. The mean time of the recommended start of physiotherapy is at 2.9 weeks (±0.2; o) vs 3.3 weeks (±0.4; n), respectively.

Conclusion:
Our study shows that a huge variability in rehabilitation after Achilles tendon rupture exists. This study shows different strategies in rehabilitation of Achilles tendon ruptures using a convertible vacuum brace system. To improve patient care, further clinical as well as biomechanical studies need to be conducted. This study might serve as basis for prospective randomized controlled trials to optimize rehabilitation for Achilles tendon ruptures.

Full text

Vol.:(0123456789)
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Knee Surgery, Sports Traumatology, Arthroscopy
https://doi.org/10.1007/s00167-017-4791-4
ANKLE
Achilles tendon elastic properties remain decreased inlong term
afterrupture
B.Frankewycz1,3· A.Penz1· J.Weber1· N.P.daSilva2· F.Freimoser1· R.Bell3· M.Nerlich1· E.M.Jung2· D.Docheva1·
C.G.Pfeifer1
Received: 9 May 2017 / Accepted: 6 November 2017
© European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2017
Abstract
Purpose Rupture of the Achilles tendon results in inferior scar tissue formation. Elastography allows a feasible invivo
investigation of biomechanical properties of the Achilles tendon. The purpose of this study is to investigate the biomechani-
cal properties of healed Achilles tendons in the long term.
Materials and methods Patients who suffered from Achilles tendon rupture were recruited foran elastographic evaluation.
Unilateral Achilles tendon ruptures were included and scanned in the mid-substance and calcaneal insertion at least 2 years
after rupture using shear wave elastography. Results were compared to patients’ contralateral non-injured Achilles tendons
and additionally to a healthy population. Descriptive statistics, reliability analysis, and correlation analysis with clinical
scores were performed.
Results Forty-one patients were included in the study with a mean follow-up-time of 74 ± 30; [26–138] months after rupture.
Significant differences were identified in shear wave elastography in the mid-substance of healed tendons (shear wave veloc-
ity1.2 ±1.5 m/s) compared to both control groups [2.5 ±1.5 m/s (p < 0.01) and 2.8 ±1.6 m/s (p < 0.0001) contralateral and
healthy population, respectively]. There was no correlation between the measurements and the clinical outcome.
Conclusions This study shows that the healed Achilles tendon after rupture has inferior elastic properties even after a long-
term healing phase. Differences in elastic properties after rupture mainly originate from the mid-substance of the Achilles
tendon, in which most of the ruptures occur. Elastographic results do not correspond with subjective perception. Clinically,
sonoelastographical measurements of biomechanical properties can be useful to provide objective insights in tendon recovery.
Keywords Achilles tendon· Achilles tendon rupture· Shear wave elastography· Elasticproperties· Biomechanical
properties· Tendon biomechanics
* B. Frankewycz
borys.frankewycz@ukr.de
A. Penz
andrea.penz@stud.uni-regensburg.de
J. Weber
johannes1.weber@ukr.de
N. P. da Silva
natascha.platz-batista-da-silva@ukr.de
F. Freimoser
florian.freimoser@ukr.de
R. Bell
rb622@cornell.edu
M. Nerlich
michael.nerlich@ukr.de
E. M. Jung
ernst-michael.jung@ukr.de
D. Docheva
denitsa.docheva@ukr.de
C. G. Pfeifer
christian.pfeifer@ukr.de
1 Department ofTrauma Surgery andLaboratory
ofExperimental Trauma Surgery, Regensburg
University Medical Center, Franz-Josef-Strauß-Allee 11,
93053Regensburg, Germany
2 Department ofRadiology, Regensburg University Medical
Center, Franz-Josef-Strauß-Allee 11, 93053Regensburg,
Germany
3 Sibley School ofMechanical andAerospace Engineering,
Cornell University, 341 Upson Hall, Ithaca, NY14853, USA

Knee Surgery, Sports Traumatology, Arthroscopy
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Introduction
The Achilles tendon (AT) is one of the most frequently rup-
tured tendons in the human body with an increasing inci-
dence [1]. Ruptured tendons heal if the tendon stumps have
a significant amount of contact, but the healing results in
scar tissue formation [2]. During the healing process, bio-
mechanical properties are weakened and loading too early,
especially in younger and active patients [3], can lead to
re-rupture. Inferior properties of healed tendons most likely
result from mechanical adhesions, changes in structural
components, and scar tissue [4]. Information about biome-
chanical properties and the correlation with the clinical and
subjective outcomes of healed tendons invivo is lacking.
While biomechanical tests with excised tendon samples
allow for more precise description of tendon elasticproper-
ties, the feasibility is limited to exvivo research or animal
models. A combination of utilization of dynamometers and
strain mapping with B-mode ultrasound allows the calcula-
tion of biomechanical parameters of ATs invivo (stiffness,
Young’s modulus and hysteresis) [5]. However, settings in
these methods are dependent on muscle force of both gas-
trocnemius and soleus muscles, so the calculated values can
be biased as they refer to the muscle–tendon complex and
not the tendon only [5, 6].
Ultrasound elastography allows visualization of elastic
properties invivo. With the use of Acoustic Radiation Force
Impulses (ARFI), shear waves can be created perpendicu-
lar to the ARF impulse and their velocity can be measured
by the same transducer. Shear wave velocity (SWV) is pro-
portional to Young’s modulus of the scanned tissue, and
therefore, it can be utilized for quantification of the elastic
properties of the tissue of interest [7, 8]. While well estab-
lished in other fields, especially in liver diagnostics [9, 10],
Shear Wave Elastography (SWE) has begun to gain accept-
ance for musculoskeletal diagnostics. With this technique,
several studies investigated the AT and its biomechanical
properties in dependence of the ankle position [11, 12], dif-
ferences in anatomical regions of the tendon [12] and in
a fresh rupture situation [13]. However, no data exist on
long-term biomechanical changes of formerly ruptured ATs
as evaluated by SWE.
The purpose of this study was to investigate long-term
elastic properties of healed tendons in patients who suffered
from AT rupture (ATR). In particular, the goal was to iden-
tify any biomechanical changes in the restored tendon after
the healing process was fully completed. It was hypothesized
that (i) ruptured ATs, which have completed therapy with a
successful union of the stumps, have persistently decreased
elastic properties due to scar tissue healing. Furthermore,
the goal of this study was to evaluate the diagnostic value
of elastography, and the following hypothesis has been
proposed (ii): the elastographically measured values cor-
relate with the clinical outcome.
Materials andmethods
The database of University Hospital Regensburg was ret-
rospectively searched for patients who underwent therapy
for ATR between 2004 and 2014. Inclusion criteria were
operative or non-operative treatment, at least 18years of
age at the time of injury and regular follow-up visits dur-
ing treatment. To focus on comparable long-term results,
only patients with a minimum period of 24months between
injury and examination were included. Exclusion criteria
were arthrodesis of one of the upper ankle joints, contralat-
eral Achilles tendon rupture in the history, neuropathic or
malignant diseases, diseases or circumstances that prohib-
ited full weight bearing or mobilization 6 weeks after trauma
and incomplete documentation during the first 3months
of treatment. After image acquisition, ARFI images were
evaluated by a second independent reviewer for validity
of the measurements. Measurements were endorsed when
the boarders of the tendon were clearly visible throughout
the whole length of the tendon and the region of interest
(ROI) was explicitly placed within these visible boarders.
Whenever the ROI overlapped with tissue outside the ten-
don, the measurement was defined as invalid and excluded.
In addition, all patients were excluded from the study when
the corresponding contralateral side showed invalid meas-
urement series. 41 Patients could be included in the study
(34 male and 7 female, see Fig.1). For hypothesis (i), the
formerly ruptured ATs (group R) were compared to the con-
tralateral (non-ruptured) tendon (group C). Mean age of the
patients at time of examination was 53.2 ± 11.1; (31–77)
years, and mean follow-up-time after injury was 74 ± 30;
(26–138) months. An additional population of healthy par-
ticipants (group H, n = 36), who had no AT in their history,
was also investigated (n = 36; 14 male, 22 female; mean
age was 23.1 ± 3.5; (20–33)]. Prior to inclusion, both their
ATs were evaluated in B-Mode and Doppler ultrasound for
abnormalities. All participants provided written, informed
consent prior to voluntary participation. For evaluation of
the clinical outcome, patients completed two validated AT
scores (VISA-A and FAOS) [14, 15] at time of examination.
Data acquisition
Ultrasound scans were performed using an Acuson S2000
machine (Siemens Healthcare GmbH, Erlangen, Germany)
with a 4–9MHz linear transducer (type 9L4). Tendon elas-
tic properties were determined using VTTQ mode (SWV in
[m/s]). Patients were scanned in prone position with over-
hanging foot and a fully extended knee. Since ATR tendon

Knee Surgery, Sports Traumatology, Arthroscopy
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length may change (shortening or lengthening) due to indi-
vidual treatment variations, the ankle joint was kept in a
neutral, relaxed position to avoid pre-load-bias. Both ATs
of all patients were scanned in the distal and mid-substance
portions of the tendon (subgroups dist/mid). The distal por-
tion was defined as the area very adjacent to the calcaneal
bone, and the mid-portion was defined by measuring the
distal one-sixth of the distance between the palpable tuber
calcanei and popliteal fossa. In both areas, tendon diam-
eter and fiber alignment were evaluated in B-mode. In the
formerly ruptured tendons, scar tissue was also identified
in B-mode. Cross-sectional area (CSA) was measured in
the mid-substance of the tendon. For evaluation of tendon
elastic properties, five VTTQ measurements were acquired
of every area. The predefined ROI was virtually positioned
on the middle height of the AT (see Fig.2). The study was
performed after approval of the university’s ethical review
committee (University of Regensburg, AZ 15-101-0019).
Statistical analysis
Results of the data are noted as mean ± SD; (range). The
Wilcoxon and Mann-Whitney tests were used for the com-
parison of the three groups for paired and unpaired groups
and subgroups, respectively. Kendall’s τ-b rank correlation
coefficient was used to correlate values of distal and mid-
substance images to both the VISA-A and FAOS scores.
Values of p < 0.05 were considered significant. Reliability
(internal consistency) was measured very high (Cronbach’s
∝ > 0.94 for both distal and medial portion in all groups).
Based on pilot data, an a priori power analysis showed
that 34 specimens would provide 80% power to detect a
significant difference between two matched groups with an
effect size of 0.5 and alpha level set to 0.05.
Results
ARFI elastography using VTTQ
All of the examined tendons presented a solid continuity in
B-mode ultrasound, showing a healed union of the tendon
stumps. Of 41 patients, 21 had been treated operatively (o)
and 20 non-operatively (no). There were no differences in
elastographic stiffness when comparing o vs. no, neither in
the distal, nor in the mid-substance areas [n.s.]; therefore, in
further calculations, the two treatment groups were pooled.
Mean SWV of all groups are shown in Table1c. SWV of
formerly ruptured tendons (R) were significantly lower com-
pared to both the contralateral non-injured (C) and those of
the healthy population (H) (Figs.2, 3). CSA was signifi-
cantly increased (p < 0.0001) between both R vs. C, R vs.
H and also C vs. H (Table1a, b). A negative correlation
was found between SWV and CSA of the formerly ruptured
tendons in the mid-substance (τ-b = − 0.22, p = 0.05), but
this was not resembled in the healthy population (τ-b = 0.45
[n.s.]). In addition, a highly significant positive correla-
tion was found between the distal and the mid-substance
diameters of the ruptured tendons, resembling a permanent
structural deformation of the whole tendon after rupture
(τ-b = 0.35, p = 0.001). Scar tissue was identified in 25 ten-
dons (R), of which 2 were located in the distal part and
23 in the mid-substance of the AT. In numerous cases, the
shear wave velocity was incalculable, which was indicated
Fig. 1 Prisma diagram of
patient inclusion Database
Achilles tendon ruptures
2004 –2014
(n=208)
Eligible paents
(n=154)
113 Ineligible paents
5 deceased
45 not able to contact
54 declined to parcipate
9excluded by second reviewer
Included paents
(n=41)
54 Excluded Paents
16 ≤ 24 months aer injury
7 no follow-up within first
within 3 months
6 contralateral injury in the past
4avulsion fracture
3 malignant diseases
18 other exclusion criteria

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Fig. 2 Representative pictures of Achilles tendon ARFI measure-
ments, shear wave velocity (SWV) of ROI given in m/s (green). a, b
Uninjured tendon shows parallel alignment of collagen fibers in the
distal portion(a) and the mid-substance (b), with SWV values of typ-
ically more than 3m/s. c–f Formerly ruptured tendons. c, d 55-year-
old patient, 74months after rupture: SWV is within normal range at
the calcaneal insertion (c) with thickening of the tendon more proxi-
mal (yellow arrow), whereas the rupture site expresses low SWV (d).
e In contrast, in this thinned out calcaneal insertion of an 83-year-old
patient, the fiber structure is almost dissolved and the combination
with a very low SWV suggests a weakening of the whole tendon. f
58-year-old patient, 108 months after rupture: elastography shows
typically thickened diameter, scar tissue formation (hyperechoic con-
trast), inhomogeneous alignment, and irregular tendon borders (yel-
low arrows) as a sign of state after reparation with decreased SWV.
CB calcaneal bone, respectively
Table 1 Tendon diameter,
cross-sectional area, and shear
wave velocity
Tendon diameter (a), cross-sectional area (b), and shear wave velocity measured in Virtual Touch Quan-
tification mode (c) of all three groups (formerly ruptured tendons (R), contralateral non-injured (C), and
healthy population (H) and subgroups (distal and mid-substance)
mid mid-substance, dist distal portion of the AT, respectively
† p < 0.0001 for all three groups, compared to each other respectively
# Significance levels of SWV shown in Fig.3
R C H
a) D (mm)
Dist 7 ± 2; [4–12]†6 ± 1; [4–9]†5 ± 1; [3–6]†
Mid 11 ± 2; [4-16]†7 ± 2; [4–13]†5 ± 1; [3–7]†
b) CSA (mm2)
Mid 159 ± 69; [32–311]†80 ± 32; [42–175]†46 ± 10;
[23–72]†
c) SWV (m/s)
Dist 2.7 ± 2.1; [0.5–7.8]#3.1 ± 1.9; [0.5–7.2] 3.5 ± 2.0;
[0.5–7.5]#
Mid 1.2 ± 1.5; [0.5–7.2]#2.5 ± 1.5; [0.5–6.6] #2.8 ± 1.6;
[0.7–7.3]#

Knee Surgery, Sports Traumatology, Arthroscopy
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by “Vs = X.XX m/s” in the display. However, in most cases,
more gel and placing the probe stationary without any move-
ments resolved the problem. Yet still, in 33 out of 820 meas-
urements, data acquisition was not successful, in most cases
due to the very superficial position of the AT. Cronbach’s
∝ was 0.97/0.99 for R, 0.97/0.94 for C, and 0.99/0.95 for H
(dist/mid, respectively).
No differences were found between genders, or smokers
vs. non-smokers, or between age groups (data not shown).
When comparing the two areas of the Achilles tendon,
highly significant differences were found between R and C,
and R and H in the mid-substance of the tendon (Fig.3b).
No significant differences were found between the contralat-
eral healthy side (C) and the healthy individual group (H).
VISA-A score was 83 ± 20; (3–100), and FAOS was 89 ± 13;
(56–100) for the ruptured tendons of the patients. Correlat-
ing SWE results (group R) to the clinical scores, no cor-
relation was found [VISA score:τ-b= 0.19 [n.s.]− 0.10
[n.s.]; FAOS score:τ-b = − 0.17 [n.s.]− 0.11 [n.s.] (dist/
mid, respectively)].
Discussion
This study shows that formerly ruptured Achilles tendons
have long-term diminished elastic properties, compared to
their contralateral side. Calculating stiffness with the aid of
dynamometers, Bressel etal. found no differences in stiff-
ness between the formerly ruptured and the contralateral
non-ruptured tendons in the long-term results (1–5years
after rupture) [6]. Since stiffness does not take into account
the tendon thickness, this finding could be consistent with
our finding of increased thickness for ruptured tendons.
Since SWV is evaluated in one designated section (ROI), it
is not influenced by the tendons’ thickness. SWV is propor-
tional to the shear modulus, which can be calculated to the
Young’s modulus under the assumption of a linear isotropic
model [16]. In addition, SWV serves as an indicator of stiff-
ness, independently from CSA. To discuss this correlation
hereinafter, the measured SWV will be referred to as “elas-
tographic stiffness”.
The results showed a highly significant decrease of elasto-
graphic stiffness even after a long period of healing. Earlier
elastographic studies of ruptured ATs have shown an imme-
diate decrease of elastographic stiffness after injury. Chen
etal. examined 14 AT sonoelastographically, 12 of them
within 24h after rupture [13]. They have found significantly
lower SWE values compared to healthy tendons (p = 0.006).
The immediate loss of stiffness after rupture is not surpris-
ing due to loss of anatomic continuity of the tendon and
sonographic measurements of the posttraumatic hematoma.
At later timepoints, the AT is reported to regain its elas-
tographic stiffness. Zhang etal. have examined ruptured
ATs 12, 24 and 48 weeks after rupture and found a gradual
increase of the elastographically measured Young´s modulus
[17]. This increase can be explained with the physiological
healing process of tendon tissue which occurs in consecu-
tive phases [18]. However, these studies did not address the
long-term outcome compared to uninjured tendons.
Since tendon healing is a long process, that is accom-
panied by long-term structural and metabolic changes and
can last for more than 1 year [18, 19], we included patients
who suffered Achilles tendon ruptures from a minimum
of 24months prior to investigation. Recently, a similar
approach was presented with the utilization of dynamom-
eters. Geremia etal. examined 18 patients 2 years after
surgical AT repair (electro)physiologically in combination
with B-mode ultrasound [20]. They found a significant loss
of force, stiffness, stress, and Young’s modulus of formerly
ruptured ATs compared to the contralateral uninjured ones.
Even though a direct correlation of physiologically and
elastographically assessed values cannot be postulated,
Fig. 3 Results of shear wave velocity (SWV) measurements: a SWV
of formerly ruptured Achilles tendons (distal and proximal measure-
ments combined) is significantly lower than those of the contralateral
non-injured AT and of healthy individuals. b Highly significant dif-
ferences were found in the mid-substance of the Achilles tendons.
(n = 41 for R/C and 36 for H; — Wilcoxon test, ---- Mann-Whitney
test for nonparametric groups; whiskers: 10–90 percentile; p values: *
≤ 0.05; ** ≤ 0.01; *** ≤ 0.0001)

Knee Surgery, Sports Traumatology, Arthroscopy
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this study supports our results of decreased biomechanical
properties.
In accordance with results from the study of Geremia
etal. [20], we also found the CSA to be significantly
increased. A physiological increase of CSA is known in ath-
letes, where repetitive micro-traumas and consecutive struc-
tural remodelling are suggested to cause tendon thickening
[21]. In long-term results after ATR, the CSA is increased,
suggesting permanent changes due to undergone repair
mechanisms and changes in fibril organization, resulting in
scar tissue formation [20]. The significantly bigger CSA in
the contralateral healthy tendon (C) compared to the healthy
control group (H) is most likely due to the younger age of the
control group, and it might indicate an asymptomatic pathol-
ogy in the contralateral tendon. Bleakney etal. have found
differences in the contralateral healthy tendon and healthy
tendons of matched patients, suggesting that patients with
a ruptured tendon have a tendinopathic predisposition for
rupture [22]. However, from our elastography results, this
finding cannot be concluded, since there were no substantial
differences between C and H in SWE.
According to the literature, the contralateral tendon has
a higher risk of rupture; therefore, we also compared the
formerly ruptured tendons to those of healthy individuals
[23]. The highest differences of SWV were found in the
mid-substance of the tendon. A combination of the lowest
blood supply in this area, with the bradytrophic character
of tendon tissue, the mid-substance of the AT, appears to
have inferior resilience and reparation capacity compared
to more proximal and distal portions [24]. This makes this
area not only prone for rupture [25, 26], but may also con-
tribute to an inferior healing capacity after rupture, result-
ing in a significant loss of biomechanical properties. After
injury, tendon healing results in scar tissue formation. The
microstructure of healed tendon and ligament tissue shows
an altered collagen composition [27] and fibril diameters
[28], which may contribute to the change in biomechanical
properties. A similar significant loss of stiffness has been
shown in tendinopathically altered tendons in both physi-
ological [29] and SWE elastographical [30] studies. In tendi-
nopathy, the loss of collagen fiber integrity, changes in struc-
tural components, and water content are discussed as cause
[29, 30]. Change in matrix components significantly affects
biomechanical properties of tendons, but to correlate more
detailed mechanisms of structural organization and organic
elastic properties, further studies are required.
The ROI of 5mm height in some cases exceeded the
thickness of the tendons, particularly those of healthy and
young patients. This certainly resembles a limitation of the
used technique. Like other authors [19, 21], we experienced
an invalid gauging in a considerable amount of measuring
procedures. According to the manufacturer, this occurs when
(a) the value is beyond the measuring range or (b) that the
software was not able to gather enough information to com-
pute the SWV. The variety of SWE technologies and manu-
facturer specific modifications do not allow a comparison of
SWV results expressed in [m/s] [16, 31]. Moreover, differ-
ent measuring methods and measuring units complicate the
direct comparison of SWE result outcomes. For example,
Ruan etal., using the same method as ours, have shown that
tendon elastographic stiffness increases with both age and
tension [8]. Their study investigated SWV in four different
age groups in a relaxed and tense state, also using VTTQ
mode under the same conditions. The range of values for
their young healthy population corresponds to our results
for the young and healthy population [2.5 ± 0.9; (0.7–3.4)
vs. 2.8 ± 1.6; (0.7–7.3)]. In contrast, Fu etal. showed no
differences in age, using the same manufacturer and same
conditions as ours (9L4 linear transducer, mid-substance of
the tendon, relaxed tendon, and no standoff) but a different
technique (Virtual Touch IQ, Siemens Acuson 3000) [32].
These differences highlight the technique-dependent varia-
tions of SWE.
In the clinical context, no significant differences were
found between non-operatively and operatively treated ten-
dons regarding SWV results. This is not unexpected, since
no long-term biomechanical advantages of one of the two
options had been shown so far in other correlated studies [6].
The clinical scores of our study population had a wider range
compared to other studies, resembling a broad variety of the
outcome. Nevertheless, no correlations were found between
SWE and both clinical scores. To our knowledge, there is no
validated ATR score; therefore, we used two common scores
that are designed for Achilles tendinopathy (VISA-A) and
a variety of foot and ankle-related problems (FAOS). Both
focus on the clinical aspects (e.g., pain, symptoms, function,
sport- and quality-of-life-related abilities); thus, they are not
necessarily associated with biomechanical properties. In
addition, clinical scores are subjective and do not address
the quality of the tendon. In the context of our study, the
question of clinical relevance of SWE directs into the post-
operative biomechanical monitoring rather than evaluation
of treatment outcome. Sufficient biomechanical properties
are crucial for unobstructed function and provide a basis
for resilience for future loads and performances, especially
in active patients and athletes. The rather stiff properties of
healthy tendons are important for responsiveness and also
correlate with the ultimate stress failure [33]. Since all our
healthy tendons (C + N) had higher elastographic stiffness,
future ATR treatment should be directed to regain this range
of stiffness. Tendon fatigue, atrophy, adhesions, and the risk
of re-rupture are typical complications [34]. To focus and
prevent these post-rupture complications, the non-invasive
SWE technology might be a promising diagnostic tool.
Especially, in young and active patients, who often tend to
recover more aggressively, an overuse of the still weakened

Knee Surgery, Sports Traumatology, Arthroscopy
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tendon could be prevented and minimize the risk of re-
rupture. As tendon tissue heals very slowly and results in
scar tissue formation (not gaining its original properties),
monitoring of tendon healing remains a clinical challenge.
Therefore, more longitudinal studies, especially during the
healing phases, are necessary to correlate SWE findings with
biomechanically relevant and histological parameters.
A major limitation of the study was that the elastographi-
cally measured values were not correlated with biomechani-
cal ones from dynamometric gauges. In general, a high
number of patients refused to participate, which is often the
challenge in clinical studies, especially so long after treat-
ment. In comparison, Geremia etal. recruited 18 patients
for a study 2 years after their hospital visit [20]. In spite of
the small sample group of 41 patients in our study, strong
significances were found between our study groups which
support our hypothesis. Another limitation is that the exami-
nation was performed by one examiner only. However, an
advantage of the SWE compared to strain elastography and
other evaluation methods is the examiner-friendly applica-
tion and a high examiner-independency [35]. The small ROI
of 5 × 6mm is a limitation of the technology we used. In that
case, interfering structures (e.g., cysts, adjacent, or irregular
peritendineum) may influence the measuring process. For
this reason, a second independent reviewer was called to
exclude all invalid measurements. As discussed above, the
utilization of clinical scores is certainly a limitation. Clinical
scores mostly resemble the individual subjective impression
of the patient and are inferior to objective physical measure-
ment methods.
Clinically, using non-invasive sonoelastography allows
measurements of biomechanical properties of Achilles
tendons that will be useful to provide objective insights in
tendon recovery. This may be especially useful in advising
patients and athletes whether or not to return to sports activi-
ties or in guiding long-term rehabilitation programs.
Conclusion
In conclusion, this study was aimed to determine changes in
biomechanical properties of formerly ruptured Achilles ten-
dons (i). It revealed that the AT has inferior elastic properties
even after long-term healing. The differences in elastic prop-
erties after rupture mostly originate from the mid-substance
of the AT, in which most of the ruptures occur. A correlation
of elastographical and subjective clinical outcome could not
be proven (ii).
Compliance with ethical standards
Conflict of interest The authors declare that there is no competing in-
terest.
Ethical approval The study was performed after approval of the uni-
versity’s ethical review committee (University of Regensburg, AZ
15-101-0019).
Informed consent Informed consent was obtained from all individual
participants included in the study.
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