What Achilles never knew about his heel: a pictorial review
of common disorders of the Achilles tendon
Poster No.:
C-1543
Congress:
ECR 2014
Type:
Educational Exhibit
Authors:
L. L. Chew, R. Dutta, M. George, K. Kaliyaperumal, K. M.
GUMMALLA, N. T. Than; Singapore/SG
Keywords:
Athletic injuries, Surgery, Ultrasound, Plain radiographic studies,
MR, Musculoskeletal soft tissue, Anatomy
DOI:
10.1594/ecr2014/C-1543
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Page 1 of 26
Learning objectives
The purpose of our educational exhibit is to:
1.
2.
3.
Illustrate the radiological anatomy of the Achilles tendon.
Describe common pathologies of the Achilles tendon.
Outline treatment options available for different types of Achilles tendon
injuries.
Background
The Achilles tendon, named after the hero of Homer's Iliad, is the thickest and strongest
tendon in the human body. The Achilles tendon experiences repetitive strain from
running, jumping, and sudden acceleration or deceleration, making it susceptible to
rupture and degenerative changes [1]. Other mechanisms include direct trauma, or
sudden activation after prolonged inactivity.
Pathologic findings can be acute or chronic, and range from inflammation of the
peritendinous tissue (peritendonitis) or structural degeneration of the tendon (tendinosis)
to partial or complete tendon rupture [2]. A thorough clinical history and physical
examination with appropriate radiological imaging are essential for accurate diagnosis
and timely treatment.
GROSS ANATOMY
The Achilles tendon constitutes the distal insertion of the gastrocnemius and soleus
muscles. The bulk of the Achilles tendon is formed by the gastrocnemius. The fibers in
the tendon spiral up to 90 degrees from the proximal to the distal end at its insertion on
the calcaneal tuberosity.
Unlike other tendons around the ankle, which have a synovial sheath, the Achilles
tendon is enveloped by a paratenon, a membrane consisting of 2 layers: a deeper layer
surrounding and in direct contact with the epitenon, and a superficial layer, the peritenon
[3]. The paratenon provides nutrition for the tendon [4]. Together, the epitenon and the
paratenon comprise the peritendon.
Page 2 of 26
A zone of relative avascularity 2-6 cm from the calcaneal insertion is the common site
of pathologic findings [5]. Proximal tears are uncommon due to nutrition provided by the
muscular branches from the gastrocnemius. Distal tears are also rare because the blood
supply from the periosteal vessels is near the calcaneal insertion [4].
The insertion site of the Achilles tendon is an enthesis, made up of fibrocartilage directly
intermeshing into the marrow of the calcaneus. This direct meshing of tendon fibrils into
marrow provides significant strength at the enthesis, making it a rare site of tendon failure
[4].
Anterior to the insertion of the Achilles tendon is the synovial fluid-filled, horseshoe
shaped retrocalcaneal bursa. The retrocalcaneal bursa protects the distal Achilles tendon
from frictional wear against the posterior calcaneus. It is surrounded anteriorly by Kager's
fat pad. The retro-Achilles bursa (also called the subcutaneous calcaneal bursa) is an
acquired bursa, which lies posterior to the tendon [4] (Fig. 1).
Images for this section:
Page 3 of 26
Fig. 1: Diagram illustrating the anatomy of the Achilles tendon and its adjacent structures.
Page 4 of 26
Findings and procedure details
RADIOGRAPHIC FINDINGS
On lateral radiographs of the ankle, the normal Kager's fat pad appears as a sharply
marginated, radiolucent triangle. The boundaries of the triangle are formed by the flexor
hallucis longus muscle and tendon anteriorly, the calcaneus inferiorly, and the Achilles
tendon posteriorly [6] (Fig. 2).
Signs of ruptured Achilles tendon
•
•
•
•
Increased and ill-defined soft-tissue density in Kager's fat pad/obliteration or
distortion of its borders (Fig. 3).
Thickening of the Achilles tendon
Positive Arner's sign = anterior contour of the ruptured Achilles tendon
curves away from the calcaneus at its insertion zone and shows forward
deviation and non parallelism in the tendon and the skin surface in the
supracalcaneal zone [6].
Diminished Toygar's angle = angle of the posterior skin surface adjacent to
the Achilles tendon on lateral ankle radiographs < 150° [6] (Fig. 4).
Ossification of the Achilles tendon may occur at the insertion of the tendon into the
calcaneus, such as enthesopathy, or in the tendon itself following trauma.
ULTRASOUND FINDINGS
The normal Achilles tendon has a fibrillar appearance. In the longitudinal plane, the
tendon is equally thick or slightly thickened distally (Fig. 5). It is ovoid in shape in the
transverse plane.
When there is disease, it may be thickened or show disruption of the fibers. Normal
Achilles tendons are typically 5-7mm in anteroposterior dimension on a transverse scan.
Tendon thickness greater than 10mm suggests a partial thickness tear or tendinosis [7].
Sonographic findings in full thickness tears:
•
•
•
Posterior acoustic shadowing at the site of tendon abnormality
Tendon retraction
Visualization of fat herniation
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•
Visualization of the plantaris tendon
Shadowing from calcification can be distinguished from refractive shadowing from the
end of a torn tendon. Shadowing from calcification originates from a linear or round
echogenic structure, whereas refractive shadowing originates from a fibrillar-appearing
tendon stump.
In cases of full-thickness tears, Kager fat and the plantaris tendon can move posteriorly
into the tendon gap and become more visible at sonography. Blood products of variable
echogenicity or debris may also be noted at the site of the tendon gap in acute full
thickness tears. Hypoechoic or isoechoic scar tissue fills the gap in long standing cases.
MR FINDINGS
The normal Achilles tendon is usually dark on all imaging sequences. An abnormal
signal without change in tendon thickness must be interpreted with caution. The normal
fascicular anatomy of the Achilles tendon may be visible as a single line and can mimic
an interstitial tear, usually not present or fades on T2-weighted images [4]. The magic
angle phenomenon can also result in a false positive high signal intensity of normal
tendon tissue [3]. This phenomenon occurs in the Achilles tendon because the fibers
twist internally [4].
On sagittal images, the anterior and posterior margins of the Achilles tendon should be
parallel below the soleus insertion [4]. It has a flattened or slightly concave anterior border
and is usually less than 1 cm in anteroposterior thickness [8] (Fig. 6).
The normal retrocalcaneal bursa is visible on MR imaging but should measure less
than 6mm craniocaudally, 3mm transversely, and 2mm anteroposteriorly [9]. Fat should
normally be seen anterior to the tendon in Kager's fat pad. Occasionally, vessels within
Kager's fat pad can mimic edema, although their tubular morphology should allow
differentiation [4].
MR imaging is superior to ultrasound in the depiction of pathology due to its excellent
soft tissue contrast resolution and multiplanar capabilities. It precisely demonstrates the
extent and nature of the injury, thereby also helping in planning the treatment approach.
COMMON PATHOLOGIES
Page 6 of 26
•
Peritendonitis
On T2-weighted MR sequences, peritendonitis appears as partially circumferential high
signal around the Achilles tendon (Fig. 7). Fat suppression is usually necessary to
visualize this high signal. In isolated peritendonitis, the tendon itself is normal.
Acute peritendonitis is treated basically as tendinosis but pharmacological therapy such
as non-steroidal anti-inflammatory drugs have better effect on acute phase than on
chronic phase. In chronic cases, operative treatment includes crural fasciotomy, removal
of adhesions, and liberation of clearly hypertrophied portions of the paratenon [10].
•
Tendinosis
This disorder is characterized by intratendinous degeneration without a significant
inflammatory response. The Achilles tendon is protected against inflammatory processes
because no true synovial sheath is present. However, inflammatory processes involving
the retrocalcaneal bursa may sometimes secondarily affect the Achilles tendon [4].
Tendon degeneration leads to microscopic tears, which evolve and coalesce to form focal
mycoid regions and interstitial tears along the long axis of the tendon [4].
On MR imaging, there is thickening of the tendon with a convex anterior margin and focal
or diffuse intratendinous high signal (Fig. 8). It may be associated with peritendonitis and
edema of Kager's fat pad.
Favourable long-term prognosis has been reported with conservative treatment
•
•
•
•
Relative rest
Anti-inflammatory drugs
Physiotherapy (includes gentle static stretching and eccentric strengthening
of the gastrocnemius-soleus complex)
Orthoses
Surgery is recommended only after exhausting conservative methods of management,
often tried for at least 6 months. At surgery, longitudinal splits are made in the
tendon to identify the abnormal tendon tissues and excise the areas of degeneration.
Reconstruction procedures such as tendon transfer may be required if excision of the
degenerated area has left a major defect in the tendon (>50%) [3].
•
Achilles tears
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The spectrum of tears ranges from micro tears to interstitial tears (parallel to the long axis
of the Achilles), to partial tears, and eventually to complete tears. Almost all tears show
high signal on T2-weighted imaging. Tendon-end retraction may be seen occasionally in
acute tears (Fig. 9).
In chronic tears (Fig. 10, 11), the tendon edges are retracted from each other and there
is ongoing atrophy of the Achilles tendon fibers. The calf muscles also show atrophy.
Atrophy occurs first in the soleus because of the predominance of slow-twitch fibers.
Occasionally gastrocnemius atrophy may be seen.
Surgery is the recommended treatment for both partial and complete tears [1]. There is
no single, uniformly accepted surgical technique, and the options include open repair
(Fig. 12), minimally invasive and percutaneous techniques. Sometimes the repair is
augmented using fascia or tendon [11] (Fig. 13).
Open surgery is associated with a much lower rate of re-rupture than conservative
treatment but has a higher rate of complications [12]. The rate of major surgical
complications (deep wound infection, skin necrosis, deep vein thrombosis, etc) has varied
from 1.9% to 5.4% [13,14].
A few randomized controlled trials comparing surgery to conservative management have
shown no significant difference in functional outcomes after one year [15,16]. Because
outcomes can be similar for conservative or surgical management, it is useful to known
which patients are most suitable for surgery. Non-surgical management is generally best
for older, less active patients or those with poor skin integrity or wound healing problems.
Surgical management is recommended for younger people, active high level athletes,
and those in who non-surgical has been unsuccessful [1].
•
Insertional tendonitis
Achilles tendonitis involving the calcaneal insertion of the tendon is known as insertional
tendonitis. It is commonly caused by repetitive trauma and microscopic tears due to
excessive use of the calf muscles, seen commonly in ballet dancers, runners and athletes
engaged in sports that involve jumping. It is also seen in patients with rheumatoid arthritis
and seronegative spondyloarthropathies.
MR imaging shows thickening of the tendon at its insertion with loss of the normal
concavity of its anterior margin and intratendinous areas of increased signal intensity
[8] (Fig. 14). Achilles tendonitis related to rheumatoid arthritis is characterized by
Page 8 of 26
the absence of tendinous enlargement and association with retrocalcaneal bursitis.
Peritendonitis may precede or be associated with insertional tendonitis.
Conservative treatment, including eccentric loading exercises and shock wave therapy,
is usually attempted before operative intervention [1].
•
Retrocalcaneal bursitis/Haglund's disease
Retrocalcaneal bursitis may manifest as an inflammatory arthropathy (rheumatoid
arthritis, seronegative spondyloarthropathies), accompany Achilles tendinitis, or occur
as an isolated disorder. Isolated retrocalcaneal bursitis is usually a result of repetitive
trauma due to athletic over activity, particularly in runners. MR imaging shows a bursal
fluid collection [8] (Fig. 15). A bursa larger than 6mm craniocaudally, 3mm transversely,
and 2mm anteroposteriorly is considered abnormal [9].
Haglund's disease is frequently associated with "pump"-style shoes. The stiff heel counter
compresses the retro-Achilles bursa against the posterior lateral calcaneal prominence.
The calcaneal tuberosity may focally enlarge in response to local irritation. MR imaging
shows excessive fluid in the retrocalcaneal bursa, fluid in the retro-Achilles bursa, and
an enlarged calcaneal tuberosity [4](Fig. 14).
Rest, activity modification, slight heel elevation with a felt heel pad, and nonsteroidal drug
therapy are sufficient for most cases [8]. A cautious corticosteroid injection into the bursa
is sometimes required. Surgical bursectomy and resection of the superior prominence of
the calcaneal tuberosity are rarely indicated.
•
Associated osseous abnormalities
The most common associated osseous abnormality in Achilles disorders is an
enthesophyte at the insertion of the Achilles into the calcaneus. Occasionally, these
enthesophytes show evidence of marrow edema on MR imaging.
Tendon ossification predominates distally in the tendon, appearing as focal fatty marrow.
This calcification is related to insertional enthesopathy. True Achilles enthesopathy
occurs at the edge of rather than within the tendon. This dystrophic ossification may
have the appearance of a broken enthesophyte. Distal ossification appearing as a broken
enthesophyte is thought to be due to partial insertion tears [4].
Page 9 of 26
Images for this section:
Fig. 1: Diagram illustrating the anatomy of the Achilles tendon and its adjacent structures.
Page 10 of 26
Fig. 2: Lateral radiograph of the ankle showing normal appearance of the Achilles tendon
and Kager's fat pad.
Page 11 of 26
Fig. 3: 51-year-old female patient with acute partial tear of the Achilles tendon. Lateral
radiograph shows abnormal soft-tissue density in Kager's fat pad. Note the ill defined
outline of Kager's fat pad compared to Figure 2. Dystrophic ossification is also seen in
the distal Achilles tendon.
Page 12 of 26
Fig. 4: Lateral radiograph of the ankle showing normal Toygar's angle.
Page 13 of 26
Fig. 5: Ultrasound examination showing the echogenic fibrillar structure in the normal
Achilles tendon.
Page 14 of 26
Fig. 6: Appearance of normal Achilles tendon on MR. (A) Sagittal PD image shows normal
parallel anterior and posterior margins of the tendon. Note normal volume of fat in Kager's
fat pad anterior to tendon. (B) Axial PD image shows normal concave anterior margin
of tendon.
Page 15 of 26
Fig. 7: Axial T2-weighted MR image with fat suppression showing rim of high signal
surrounding the Achilles tendon, consistent with peritendonitis.
Page 16 of 26
Fig. 8: 24-year-old male patient (A) Sagittal STIR image showing thickening of the
Achilles tendon with increased intra-substance signal at the myotendinous junction
suggestive of tendinopathy/partial tear. (B) Intrasubstance degeneration confirmed at
surgery.
Page 17 of 26
Fig. 9: 44-year-old female patient. Sagittal STIR MR image showing acute complete tear
of the Achilles tendon with tendon retraction. Edema is seen in Kager's fat pad.
Page 18 of 26
Fig. 10: 48-year-old male patient. Sagittal STIR MR image shows a chronic high-grade
partial tear at the musculotendinous junction of the Achilles tendon with tendon retraction.
Page 19 of 26
Fig. 11: 40-year-old female patient. Sagittal STIR and axial T2-weighted with fat
suppression MR images show an ovoid cystic lesion within the Achilles tendon likely due
to chronic interstitial tear.
Page 20 of 26
Fig. 12: 35-year-old male patient (A) At surgery, found to have complete rupture of the
Achilles tendon. (B, C) Primary repair of Achilles tendon using Krackow locking loop
technique.
Page 21 of 26
Fig. 13: 44-year-old female patient (A) Sagittal STIR MR image shows a high-grade
partial tear of the Achilles tendon. (B) Chronic partial tear with background mucinous
degeneration confirmed at surgery. Unhealthy tissue debrided till only a thin sliver of
tendon remains. (C, D) Flexor hallucis longus tendon harvested and transferred for
reconstruction of the Achilles tendon.
Page 22 of 26
Fig. 14: 52-year-old female patient (A) Sagittal PD image shows prominent calcaneal
tuberosity consistent with Haglund's deformity. (B) Sagittal STIR image shows thickening
of the tendon and high-grade partial thickness tear at the Achilles insertion.
Page 23 of 26
Fig. 15: Retrocalcaneal bursitis in a 25-year-old woman. Sagittal STIR MR image shows
distension of the retrocalcaneal bursa by high-signal intensity fluid. The Achilles tendon
is also mildly thickened with increased intra-tendinous signal intensity, consistent with
tendinosis.
Page 24 of 26
Conclusion
MRI accurately characterizes the severity and nature of involvement and is therefore the
modality of choice in evaluating Achilles tendon injuries and planning treatment options.
Personal information
Dr Lee Lian Chew is a radiology registrar at Tan Tock Seng Hospital in Singapore.
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