The classic ACL tear symptoms are a pop felt or heard at the moment of injury, pain and rapid swelling within hours, difficulty fully straightening or bending the knee, and — once the swelling settles — a knee that feels unstable or “gives way” when you twist or change direction.
Symptoms of a torn ACL
- A pop at the moment of injury, usually while pivoting or landing.
- Rapid swelling within the first few hours from bleeding inside the joint.
- Pain that usually stops you continuing to play.
- Loss of movement — the knee will not fully straighten or bend.
- Instability: the knee shifts or gives way on stairs or when turning, most obvious after the swelling goes down.
- Joint-line pain or locking, which can point to an associated meniscus tear.
When to see a doctor straight away
- Major swelling within hours of the injury.
- You cannot put weight on the leg.
- The knee is locked and will not straighten.
- Numbness, coldness or colour change in the foot — this is an emergency.
What causes an ACL tear?
- Sudden change of direction or pivoting with the foot fixed on the ground.
- Landing badly from a jump with the knee collapsing inward.
- Stopping suddenly while running.
- A direct blow to the side of the knee, as in a football tackle.
Sprain, partial tear or complete tear?
| Injury | Usual symptoms | Knee stability | Usual treatment |
|---|---|---|---|
| Sprain (grade 1) | Mild pain and swelling | Stable | Rest and physiotherapy |
| Partial tear (grade 2) | Moderate pain and swelling | Sometimes mildly unstable | Usually physiotherapy; surgery if instability persists |
| Complete tear (grade 3) | Pop, fast swelling, then clear instability | Unstable when twisting | Arthroscopic reconstruction for active people, or non-surgical care for selected patients |
How is an ACL tear diagnosed?
Diagnosis combines the history, a clinical examination and imaging. In experienced hands the Lachman test is very accurate for a complete tear; an MRI confirms it and shows associated damage to the meniscus, cartilage or other ligaments. X-rays are used to rule out fractures.
Video: arthroscopic treatment of an ACL injury
Frequently asked questions about ACL tear symptoms
What are the symptoms of a partial ACL tear?
Pain and swelling are usually milder than with a complete tear, and the knee may feel stable in daily life but untrustworthy when running or turning.
Can you walk with a torn ACL?
Usually yes within days, once the swelling settles. Walking does not mean the ligament is intact — instability shows up with twisting and sport.
Does swelling after a twist mean the ACL is torn?
Swelling within hours of a twisting injury makes an ACL tear much more likely, but it also happens with kneecap dislocation and fractures, so the knee needs examining.
Is an MRI enough to diagnose an ACL tear?
MRI is accurate in most cases, but treatment decisions combine the MRI with the examination of knee stability and your activity goals.
Is a torn ACL the same as a ruptured ACL?
Yes. “Torn” and “ruptured” describe the same injury; what matters medically is whether the tear is partial or complete and how stable the knee is.
To have your knee assessed, book a consultation, call +20 155 240 4488 or message us on WhatsApp at +20 155 554 7181.
Medically reviewed by Prof. Dr. Ibrahim Shaarawi, Professor of Orthopaedic Surgery. This article is general medical education and does not replace an examination or the plan your surgeon sets for you. See our medical disclaimer.
Related ACL guides
Once you recognise the symptoms, see the treatment options on ACL reconstruction surgery, or read:
- ACL reconstruction surgery
- The anterior cruciate ligament (ACL)
- Partial ACL tear
- The posterior cruciate ligament (PCL)
- ACL treatment without surgery
References
- Benjaminse A, et al. Clinical diagnosis of an anterior cruciate ligament rupture: a meta-analysis. J Orthop Sports Phys Ther. 2006;36(5):267-88.
- American Academy of Orthopaedic Surgeons (OrthoInfo). Anterior Cruciate Ligament (ACL) Injuries.
- Kiapour AM, Murray MM. Basic science of anterior cruciate ligament injury and repair. Bone Joint Res. 2014;3(2):20-31.
- Filbay SR, Grindem H. Evidence-based recommendations for the management of anterior cruciate ligament (ACL) rupture. Best Pract Res Clin Rheumatol. 2019;33(1):33-47.