What Does a Ruptured Achilles Tendon Look Like?

A ruptured Achilles tendon produces a distinctive set of visible signs: the ankle and lower calf swell rapidly, bruising spreads over the back of the heel within hours, and there is often a palpable gap or indentation in the tendon a few centimeters above the heel bone where the fibers have separated. The injured foot also hangs differently, resting in a flatter position than the uninjured side. These surface clues are often enough to identify the injury, but imaging and clinical tests add much more to the picture, and the appearance varies depending on whether the tear is partial or complete, acute or old.

What You See From the Outside

The most recognizable visual sign is swelling along the back of the lower leg, concentrated just above the heel. The area becomes puffy and warm, and within a day or so discoloration appears as blood pools under the skin. Bruising can spread across the heel, the sole, and even partway up the calf. Some people describe the initial moment of rupture as feeling like being kicked in the back of the leg, followed by immediate difficulty pushing off the foot.

If you run your fingers along the tendon, you can often feel a distinct gap or depression at the rupture site. In a healthy Achilles, the tendon feels like a firm cord running from the calf muscle to the heel bone. After a full rupture, that cord is interrupted by a soft, boggy zone. The gap is usually located two to six centimeters above the heel bone, an area sometimes called the “watershed zone” because of its relatively sparse blood supply.¹

Another telling sign is the resting position of the foot. When someone with a ruptured Achilles lies face down on an exam table, the injured foot drops into a flatter, more dorsiflexed posture compared with the uninjured side. This altered “angle of declination” reflects the loss of the tendon’s normal resting tension, and it is visible without any special equipment.²

How Doctors Confirm It on Exam

A set of bedside findings, sometimes called Simmonds’ triad, can detect a rupture in nearly all cases. The triad consists of the altered foot angle described above, a palpable gap along the tendon, and loss of plantarflexion when the calf muscle is squeezed. That last test, known as the Thompson test or calf-squeeze test, is the single most commonly used check. With the patient lying prone, the examiner squeezes the calf muscle firmly. In a healthy leg, squeezing the calf makes the foot point downward. If the Achilles is torn, the foot barely moves or does not move at all.²

A study comparing clinical diagnostic criteria against MRI confirmed that the combination of an abnormal Thompson test, decreased resting tension, and a palpable defect is reliable enough to diagnose the injury without imaging in many straightforward cases.³ That said, imaging is still used when the picture is ambiguous, when a partial tear is suspected, or when surgeons need to measure how far apart the torn ends have retracted.

What a Rupture Looks Like on Ultrasound

Ultrasound is often the first imaging study done because it is fast, inexpensive, and can be performed in a clinic or emergency department. A normal Achilles tendon appears on ultrasound as a dense, bright band of parallel fibers. When the tendon ruptures, that neat fibrillar pattern disappears at the tear site. Instead, you see a dark gap between the retracted ends of the tendon, with the two stumps no longer in continuity.⁴

Full-thickness tears show up as a complete discontinuity of the tendon fibers with a dark or nearly black gap. Partial tears look different: you see a dark area within the tendon, but some intact fibers are still visible bridging across the zone of damage. Fluid and debris often collect in the fat pad behind the ankle, and color Doppler imaging may show increased blood flow around the tear, a sign that the body’s inflammatory response has kicked in.⁵

Clinicians use a grading system to categorize what they see. A Grade I tear is partial, involving less than half the tendon’s width. Grade II is a complete rupture with a gap under three centimeters. Grade III has a gap between three and six centimeters. Grade IV is a gap wider than six centimeters. Dynamic scanning, where the examiner moves the foot up and down during the ultrasound, helps confirm the diagnosis by showing the two ends failing to come together with movement.⁵

Telling a Partial Tear From a Complete Tear

This distinction matters because treatment decisions often depend on it. On ultrasound, certain features strongly correlate with a full-thickness tear rather than a partial one. Tendon retraction, where the torn ends pull apart and leave a visible gap, is one of the clearest markers of a complete rupture. Another is a shadowing artifact behind the damaged zone, and thickening of the tendon itself.⁶

Fat from the surrounding tissue can sometimes be seen herninating into the gap left by a full tear. Interestingly, the brightness or darkness of the damaged area alone does not reliably distinguish partial from complete tears. It is the structural disruption, retraction, and associated findings that help the clinician sort out whether any fibers remain intact.⁶

What the Tissue Looks Like Under a Microscope

If you could examine a ruptured Achilles tendon under a microscope, you would not simply see fibers that snapped cleanly. The tissue almost always shows signs of pre-existing degeneration, even in areas that looked normal to the naked eye before the tear happened. Compared with healthy tendons, ruptured ones show disorganized collagen fibers, rounded cell nuclei instead of the usual elongated ones, abnormal clusters of cells, increased blood vessel growth, and areas where the collagen has lost its normal staining pattern.⁷

These degenerative changes are not confined to the tear site. Research on tissue samples taken from areas well away from the actual rupture found the same abnormalities. Even regions that appeared healthy on gross inspection scored markedly worse than tissue from unruptured tendons on every measure of structural quality. In other words, by the time a tendon ruptures, the damage has been brewing throughout its length for some time.⁸

At an even finer level, the individual collagen fibers themselves are affected. Ruptured tendons contain fewer medium-to-large-diameter collagen fibrils, particularly in the deeper and more distal portions of the tendon.⁹ Thinner fibrils produce a mechanically weaker tendon, which helps explain why a seemingly sudden rupture usually has a long silent buildup.

Why the Achilles Is Prone to Rupture in the First Place

The Achilles is the thickest, strongest tendon in the body, yet it ruptures more than almost any other. Part of the vulnerability comes from its blood supply. The tendon receives blood from three areas: where it connects to the calf muscle at the top, where it attaches to the heel bone at the bottom, and from the thin sheath surrounding it. Quantitative studies of vessel density found that overall, the tendon has relatively poor blood flow along its entire length.¹ Limited blood supply means limited capacity for ongoing repair, so micro-damage from everyday loading can accumulate without being fully healed.

Certain medications compound the problem. Fluoroquinolone antibiotics, a class of drugs prescribed for urinary tract infections and other bacterial infections, can weaken tendon structure. Animal studies have shown that these drugs cause collagen fiber disarrangement and a specific type of tissue breakdown in the tendon, along with measurable reductions in the force the tendon can withstand before failing.¹⁰ Corticosteroid injections near the tendon can have a similar effect by inhibiting collagen production and further compromising the already limited local blood flow.¹¹

What a Chronic (Missed) Rupture Looks Like

Not every Achilles rupture gets diagnosed right away. Some people assume they have a bad sprain and only seek care weeks or months later, when they notice persistent weakness and an odd gait. A chronic rupture looks quite different from an acute one, both on the surface and on imaging.

The palpable gap that is so characteristic early on may disappear entirely as scar tissue fills the space between the torn ends. The patient can often still point their foot downward, which is confusing because it seems like the tendon must be intact. In reality, other muscles in the leg, including the tibialis posterior, the peroneals, and the long toe flexors, are compensating for the lost Achilles function. The giveaways are calf weakness, a limp, and a tendon that feels elongated and boggy rather than firm.¹²

On MRI, a chronic rupture shows disrupted signal within the tendon substance on one type of image and generalized bright signal on another, reflecting the disorganized scar tissue that has replaced normal tendon. Ultrasound of a chronic tear typically shows a gap filled with thick, irregular edges rather than the clean dark void of an acute rupture.¹²

Conditions That Can Look Like a Ruptured Achilles

A few other injuries in the same part of the leg can mimic an Achilles rupture closely enough to cause diagnostic confusion. The most common is a tear of the medial head of the gastrocnemius, the inner calf muscle. This injury, sometimes called “tennis leg,” produces sudden calf pain, swelling, and difficulty walking. In a large review of patients presenting with the clinical picture of tennis leg, a partial tear of the gastrocnemius turned out to be the cause about two-thirds of the time, while an actual plantaris tendon rupture, despite its reputation, accounted for barely one percent of cases.¹³

The plantaris tendon is a small, thin tendon that runs alongside the Achilles. When it ruptures, it causes a sharp pain in the calf. Complicating matters, an intact plantaris can sometimes mask a ruptured Achilles: because the plantaris still produces a small amount of ankle motion, it can fool the examiner into thinking the Achilles is functioning.¹⁴ Imaging usually sorts this out, but it is worth knowing that sudden posterior ankle and calf pain has more than one possible cause.

What the Tendon Looks Like After Repair

Whether treated surgically or managed with bracing and physical therapy, a healed Achilles tendon never looks the same as it did before on imaging. The repaired tendon is thicker and wider than the original, and its internal fiber pattern remains disorganized. Surgical suture material may be visible within the tendon substance, and there is typically more blood flow around the repaired zone for an extended period.¹⁵

On MRI three months after surgery, nearly all repaired tendons show a bright internal signal that might, in a different context, look worrying. In most cases, this signal simply reflects the ongoing remodeling process and does not indicate a problem. The tendon also reaches its maximum thickness around three months, gradually slimming somewhat over the following year but never returning to its pre-injury dimensions.¹⁶ What does predict trouble is the size of that bright area: patients whose bright lesion was particularly large at three months were more likely to have a poor clinical outcome and a noticeable limp.¹⁶

The key imaging distinction after surgery is between expected remodeling and re-rupture. A higher-than-normal signal throughout the tendon is a normal post-repair finding that can persist for years. But if a clearly defined pocket of fluid appears at the repair site, that is a red flag suggesting the tendon has torn again.¹⁷ Clinicians evaluating a post-surgical Achilles need to read the imaging alongside the patient’s symptoms, because the tendon will look abnormal by normal standards for a long time even when healing is going well.

Long-Term Changes in the Calf Muscle

The visual aftermath of an Achilles rupture extends beyond the tendon itself. The calf muscles on the injured side often shrink noticeably, and this asymmetry can persist long after the tendon has healed. Loss of muscle mass, strength, and function after an Achilles rupture can in some cases be permanent.¹⁸ The repaired tendon is often longer than the original, which changes the mechanical leverage of the calf muscles and reduces their ability to generate force even when the muscle itself is intact.

MRI measurements show that the soleus and the two heads of the gastrocnemius, the three muscles that together form the bulk of the calf, all lose cross-sectional area on the injured side.¹⁹ Fatty tissue infiltrates the muscle over time, further reducing its functional capacity.²⁰ For many people, the smaller calf is the most visible long-term reminder of the injury, noticeable even years later when the tendon scar is no longer tender.

Re-Rupture and What It Looks Like

A small but real percentage of surgically repaired Achilles tendons tear again. Published rates for re-rupture after surgical repair range from roughly two to six percent.²¹ Most re-ruptures happen under the skin, producing the same set of signs as the original injury: renewed swelling, a palpable gap, and loss of push-off strength. On rare occasions, re-rupture has occurred as an open wound, with the skin breaking at the surgical incision site. Re-ruptures tend to happen in the first few months after surgery, when the tendon is still at its most vulnerable and the repair tissue has not yet matured enough to handle high loads.

On imaging, a re-rupture looks distinct from normal post-surgical changes. Where normal healing produces a diffuse, somewhat bright signal through the thickened tendon, a re-rupture creates a focal fluid-filled gap at the repair site, often with retraction of the tendon ends.¹⁷ Distinguishing this from expected post-operative abnormality is one of the trickier judgment calls in musculoskeletal imaging, and it almost always requires correlating the scan with the patient’s clinical picture.

1
PubMed. Blood supply of the Achilles tendon
2
PubMed. Acute Achilles tendon rupture
3
PubMed Central. MRI is unnecessary for diagnosing acute Achilles tendon ruptures: clinical diagnostic criteria
4
PubMed Central. Ultrasound assessment of acute Achilles tendon rupture and measurement of the tendon gap
5
PubMed Central. Diagnostic Musculoskeletal Ultrasound of the Achilles Tendon
6
PubMed. Full- versus partial-thickness Achilles tendon tears: sonographic accuracy and characterization in 26 cases with surgical correlation
7
PubMed. Light microscopic histology of achilles tendon ruptures. A comparison with unruptured tendons
8
PubMed. Marked pathological changes proximal and distal to the site of rupture in acute Achilles tendon ruptures
9
Matrix Biology. Collagen fibril size and crimp morphology in ruptured and intact Achilles tendons
10
The Journal of Toxicological Sciences. Oral toxicity of pefloxacin, norfloxacin, ofloxacin and ciprofloxacin: comparison of biomechanical and histopathological effects on Achilles tendon in rats
11
PubMed Central. Complete Achilles tendon rupture after local infiltration of corticosteroids in the treatment of deep retrocalcaneal bursitis
12
The Open Orthopaedics Journal. Chronic Achilles Tendon Rupture
13
PubMed Central. “Tennis leg”: gastrocnemius injury is a far more common cause than plantaris rupture
14
PubMed Central. Plantaris rupture: why is it important?
15
PubMed Central. Post-operative MRI and US appearance of the Achilles tendons
16
PubMed. Magnetic resonance imaging during healing of surgically repaired Achilles tendon ruptures
17
European Journal of Radiology Open. MRI of the Achilles tendon – a comprehensive pictorial review. Part two
18
PubMed Central. Persistent Deficits after an Achilles Tendon Rupture: A Narrative Review
19
Journal of the Foot & Ankle. Optimization of MRI measurements of calf muscle atrophy following acute Achilles tendon rupture
20
PubMed Central. Muscular and Tendon Degeneration after Achilles Rupture: New Insights into Future Repair Strategies
21
PubMed Central. Open re-rupture of the Achilles tendon after surgical treatment