Most Achilles ruptures can be treated without surgery. Modern non-surgical treatment means walking early in a boot that holds the foot at an angle, rather than spending months in plaster.

Surgery reduces the risk of the tendon re-rupturing, but the difference is small. A large review pooling many trials found re-rupture in around 2.3% after surgery versus 3.9% without — a difference of roughly 1.6 in every 100 patients.

Surgery carries its own risks. The same analysis found other complications in around 4.9% of surgical patients versus 1.6% of those treated in a boot, mostly wound infection.

Early movement narrows the gap further. When non-surgical treatment includes loading the leg early alongside physiotherapy, the difference shrinks — although the studies showing “no difference” rest on very fine margins, a caveat that is rarely mentioned.

A cast is not better than a boot. The UK’s UKSTAR trial randomly assigned 540 patients across 39 hospitals and found no difference in outcome or re-rupture between plaster and a walking boot.

A gap measured in millimetres should not decide it on its own. What matters more is whether the torn ends come back together when the foot is pointed down. The millimetre figure is not measured in a standardised way, and at least one study found it did not predict how well patients did.

Timing matters more than almost anything else. The decision is easiest, and both options work best, when treatment starts within the first two weeks. Achilles ruptures are commonly missed at first presentation.

The description is remarkably consistent: a sudden, sharp pain at the back of the ankle, often described as being kicked or hit from behind — many people turn round to see who did it. Sometimes there is an audible snap. Then the odd part: you can usually still walk, in a flat-footed way.

That last point is the reason so many Achilles ruptures are missed. The other calf muscles can push the foot down well enough to fool both the patient and a busy emergency department. People are sent away with “a calf strain” and return weeks later, by which time the treatment options have narrowed.

The classic picture is someone in their forties or fifties returning to a stop-start sport — badminton, squash, football, tennis or padel — often after a period away from it. In the UKSTAR trial the average age was 49, and around four in five patients were men.

It is largely a clinical diagnosis, made by examining you:

• A gap you can feel. Running a finger along the tendon often finds a dip where the ends have separated.
• The calf squeeze test. With you lying face down, squeezing the calf normally makes the foot point downwards. If it does not move, the tendon is not connected.
• Resting foot position. The injured foot tends to sit flatter than the other side when the knees are bent over the end of a couch.

Ultrasound is useful, and not simply to confirm what the examination already shows. A dynamic ultrasound can show whether the torn ends come back together when the foot is pointed down. If they do, non-surgical treatment is on strong ground; if a large gap persists, that shifts the balance of the conversation. An MRI scan is rarely needed for a straightforward recent rupture.

If you suspect a rupture, get it looked at within a few days rather than waiting to see if it settles.

The old version of this — a rigid plaster with the foot pointed down and no weight allowed through the leg for many weeks — has largely been abandoned. Current practice is an active programme:

• A removable walking boot, either with heel wedges or with an adjustable angle, holding the foot pointed downwards so the tendon ends sit together
• Walking in the boot early, putting weight through the leg, often from the start
• Wedges gradually removed over roughly 8 to 10 weeks, bringing the foot back to a flat position
• Structured physiotherapy alongside, and continuing well after the boot comes off

UKSTAR compared this against traditional plaster casting in 540 UK patients. There was no difference in how patients rated their own recovery at nine months, no difference in re-rupture, and no meaningful difference in cost. Walking early in a boot was just as safe, and rather easier to live with.

Pooled data from 29 studies covering nearly 16,000 patients found:

So surgery roughly halves an already low re-rupture risk, at the cost of roughly tripling an already low risk of other problems. When the patients treated in a boot were encouraged to move and load the leg early, the difference in re-rupture was no longer large enough to be statistically meaningful.

A 2025 review pooling 14 randomised trials reached broadly similar conclusions and added a useful distinction: minimally invasive repair, done through small cuts rather than one long one, appeared to reduce re-rupture without the increase in complications seen with open repair, and allowed an earlier return to work. A separate analysis comparing open with minimally invasive repair found similar function and re-rupture rates, with more surface wound infection after open surgery (6.0% versus 0.4%) and more temporary irritation of the sural nerve, which runs beside the tendon, after minimally invasive repair (3.4% versus none).

There is no formula, but the balance tends to shift towards surgery with:

• Tendon ends that fail to come together when the foot is pointed down on dynamic ultrasound (this is not the same as a large gap measured with the foot flat)
• Being seen for the first time more than two to three weeks after the injury
• Athletes training or competing hard, particularly in sports needing explosive push-off
• A second rupture after previous non-surgical treatment
• Rupture at the point where the tendon meets bone, or with a bony fragment pulled off

And it tends to shift towards a boot with:

• Tendon ends that come together neatly on a moving (dynamic) ultrasound
• Diabetes, poor circulation in the legs, smoking or anything else that makes wound healing riskier
• Older or less physically active patients
• A preference to avoid an operation, which is a legitimate reason in a decision this finely balanced

This is the question patients ask most often once they have had a scan, usually because someone has quoted them a number in millimetres. It deserves a fuller answer than it normally gets, because the number is used more confidently than the evidence justifies.

Two different things get called “the gap”. The first is a static measurement — the distance between the torn ends with the foot in a given position, reported in millimetres. The second is whether the ends actually meet on movement — that is, whether they come back together when the foot is pointed downwards, watched in real time on ultrasound. These are not the same, and it is the second that carries more weight. A tendon can measure a wide gap with the foot flat and still close completely when the foot is pointed down, which is the position the boot holds you in for the next two months.

Why the millimetre figure is less reliable than it sounds. The measurement is not standardised. A 2024 review of ultrasound assessment concluded that the way it is done — including how far the foot is pointed down while measuring — still needs to be agreed and made consistent. The same tendon, scanned by two people with the ankle at different angles, can produce meaningfully different numbers.

Gap size may not predict outcome. A UK study followed 56 patients treated in a boot, with early movement and physiotherapy, for at least twelve months. The average gap on their first scan was 13.7 mm — larger than the level many hospitals use to recommend surgery. Their average score on the standard Achilles recovery questionnaire at twelve months was 85 out of 100, two tendons re-ruptured, and there was no meaningful link between gap size and the final result. The authors concluded that the decision should not be based on gap size. That is one study, from one unit, and not the last word — but it is a direct test of the assumption, and it did not support it.

Where the gap genuinely does matter. In long-standing ruptures that were missed or treated late — typically seen beyond four to six weeks — the gap becomes an important planning measurement rather than a decision rule. It determines whether the ends can be brought together directly, or whether tissue will need to be borrowed from elsewhere (a tendon transfer, flap or graft) to bridge the gap. Here, MRI is often more useful than ultrasound.

Whichever route you take, recovery is measured in months, not weeks. This is the part most often underestimated.

Calf strength recovers slowly and often remains slightly reduced compared with the other side for a year or more. Rehabilitation — particularly heel-raise strength work — is not optional; it is the single biggest factor in how the leg ends up feeling.

Blood clots are a recognised risk while the leg is in a boot and you are moving about less. Your risk should be assessed and discussed at the outset.

An Achilles rupture is one of the few foot and ankle injuries where getting the right advice quickly genuinely changes the options available to you. If you have a suspected rupture, have been told you have a calf strain but are not improving, or have been offered one treatment and want to understand the alternative, an early specialist assessment is worthwhile.

Mr Matthew Welck is a Consultant Orthopaedic Foot & Ankle Surgeon at the Royal National Orthopaedic Hospital, Stanmore, and Honorary Associate Clinical Professor at UCL. He treats acute and neglected Achilles injuries alongside a specialist practice in sports foot and ankle injuries, with clinics across North and Central London.

• Telephone: 07547 395 270
• Email: secretary@matthewwelck.com
• Book a consultation: matthewwelck.com/appointments

Urgent same-day appointments are offered where possible.

This article is general information and does not replace individual medical advice. If you have a suspected Achilles rupture, seek assessment promptly.

References

1. Ochen Y, Beks RB, van Heijl M, et al. Operative treatment versus nonoperative treatment of Achilles tendon ruptures: systematic review and meta-analysis. BMJ. 2019;364:k5120. doi:10.1136/bmj.k5120
2. Costa ML, Achten J, Marian IR, et al. Plaster cast versus functional brace for non-surgical treatment of Achilles tendon rupture (UKSTAR): a multicentre randomised controlled trial and economic evaluation. Lancet. 2020;395(10222):441–448. doi:10.1016/S0140-6736(19)32942-3
3. Xu S, Xiao J, Li Y, et al. Operative versus nonoperative management of acute Achilles tendon rupture: a systematic review and meta-analysis of clinical outcomes from randomized controlled trials. Ann Med. 2025;57(1):2537349. doi:10.1080/07853890.2025.2537349
4. Attia AK, Mahmoud K, d’Hooghe P, et al. Outcomes and complications of open versus minimally invasive repair of acute Achilles tendon ruptures: a systematic review and meta-analysis of randomized controlled trials. Am J Sports Med. 2023;51(3):825–836. doi:10.1177/03635465211053619
5. Bragg JT, Ruelos VCB, McIntyre JA, et al. Reverse fragility index comparing rates of rerupture after open Achilles tendon repair versus early functional rehabilitation: a systematic review of randomized controlled trials. Am J Sports Med. 2024;52(4):1116–1121. doi:10.1177/03635465231178831
6. Mubark I, Abouelela A, Arya S, et al. Achilles tendon rupture: can the tendon gap on ultrasound scan predict the outcome of functional rehabilitation programme? Cureus. 2020;12(9):e10298. doi:10.7759/cureus.10298
7. Fenech M, Ajjikuttira A, Edwards H. Ultrasound assessment of acute Achilles tendon rupture and measurement of the tendon gap. Australas J Ultrasound Med. 2024;27(2):106–119. doi:10.1002/ajum.12384
8. Thermann H. Achilles tendon rupture — Part 1: etiology and diagnostics. Chirurg. 2019;90(10):863–872. doi:10.1007/s00104-019-01024-6

Trial and meta-analysis data above retrieved via PubMed. This article is general information and does not replace individual medical advice.