Introduction
Knee care · ACL injuries
Partial vs complete ACL tear: what the difference means
Written by Dr Sean Leo, a consultant orthopaedic surgeon whose clinical focus is the knee, sports injuries and the lower limb.
Last updated: 15 October 2026.
A partial anterior cruciate ligament (ACL) tear leaves some of the ligament’s fibres intact, while a complete tear disrupts the whole ligament. Examination and MRI help tell them apart. The difference shapes the treatment conversation. It does not, by itself, decide whether surgery is needed.[2][3]
Take-home: “Partial” and “complete” describe how much of the ligament is torn. Your symptoms, how stable the knee is, other injuries and what you want to return to decide the plan, together with your clinician.
Dr Sean LeoOrthopaedic Surgeon, Singapore
Clinic enquiries · Not an emergency service
Illustrative image
What do “partial” and “complete” actually mean
What do “partial” and “complete” actually mean
What do “partial” and “complete” actually mean?
An ACL injury can range from a stretch, to a partial tear, to a complete tear. “Complete” can sound final. “Partial” can sound like good news, or like a warning.
- In a partial tear, some fibres are torn and the ligament is loose.[2][3]
- In a complete tear, the ligament is torn into two pieces and the knee is no longer stable.[2][3]
- The terms describe how the ligament looks and how loose it is. They are not a prediction of how things will go.[2][3]
More on partial tears
A partial tear can involve one of the ligament’s two bundles of fibres, called the anteromedial or the posterolateral bundle, or a blended injury of both.[2]
What’s covered on this webpage
Follow the route in order, or jump to the stop you need. Stops you have read are marked.
How common is each type?
How common is each type?
How common is each type?
Partial tears make up roughly 10% to 28% of isolated ACL injuries. The range is wide because the groups studied differed. Most isolated ACL injuries are complete, and partial tears are a sizeable minority.[2]
The ACL is also often not the only structure hurt. About half of ACL injuries happen together with damage to other parts of the knee, such as the menisci (the cartilage cushions), other ligaments or the joint surface.[3]
How are partial and complete tears told apart
How are partial and complete tears told apart
How are partial and complete tears told apart?
A clinician starts with your story: how the injury happened and whether the knee gives way. Then come an examination and usually an MRI scan. These tests are done by a clinician, not to try on yourself.[2]
- Lachman test: with the knee slightly bent, the clinician gently pulls the shin forward to feel whether the ACL holds it back. It is the most sensitive bedside test for an ACL injury.[2]
- Pivot shift test: the clinician gently rotates and straightens the knee to feel the shift that a knee with a torn ACL can make. A positive result is very reliable, but the test is often negative in partial tears. A negative test does not rule a partial tear out.[2]
- Anterior drawer test: with the knee bent further, the clinician pulls the shin forward and feels for extra movement.[3]
- MRI scan: a detailed scan of the knee and the usual imaging for a suspected tear. It is read together with your history and examination.[2]
Partial tears are genuinely difficult to diagnose, so it is reasonable for a clinician to say they are not certain.[2]
More on the numbers and on arthroscopy
In a systematic review, the pivot shift test had a specificity of 0.97 to 0.99 for partial tears, meaning a positive result was almost always right. Its sensitivity was 0.18 to 0.48, meaning it picked up fewer than half of partial tears.[2]
Arthroscopy (a keyhole look inside the knee) is regarded as the gold standard for diagnosing both partial and complete tears. It is not used for diagnosis alone. In arthroscopy studies, partial tears kept between 25% and 75% of continuous fibres. That is a description of what was seen, not a classification.[2]
Partial vs complete ACL tear
Partial vs complete ACL tear
Partial vs complete ACL tear: side by side
This table sets the two types next to each other. It describes; it does not diagnose.
| Partial ACL tear | Complete ACL tear | |
|---|---|---|
| What is torn | Some of the ligament’s fibres are torn; the ligament is loose.[2][3] | The ligament is torn into two pieces.[2][3] |
| How it is found | History, examination and MRI. The pivot shift test is often negative.[2] | History, examination and MRI.[2] |
| What stability may feel like | The ligament is loose. | The knee is described as no longer stable. In daily life, torn knees differ: some cope, others give way. |
| What the label does not decide | Treatment on its own. It informs the conversation. | Treatment on its own. It informs the conversation. |
Can a torn ACL heal on its own?
Can a torn ACL heal on its own?
Can a torn ACL heal on its own?
For a long time, complete ACL tears were considered unable to heal. More recent research has found MRI signs of healing in some torn ACLs managed with a specific, supervised programme. That research is early and contested, and continuity on a scan is not the same as a normal ligament or a stable knee.[1][2][3][5]
Such a programme asks a great deal of the person and needs trained clinicians and physiotherapists. It is not something to copy from a webpage. The numbers and caveats are set out in Can a torn ACL truly heal itself?
Can a partial ACL tear become a complete tear
Can a partial ACL tear become a complete tear
Can a partial ACL tear become a complete tear?
A partial tear can progress, or the knee can come to behave like an unstable knee over time. How this unfolds differs from person to person, and age and activity level shape the conversation.[2]
If a knee with a partial tear keeps giving way, that is a reason to be reassessed rather than watched, calmly and without alarm.
Does a partial or complete tear change whether I need surgery
Does a partial or complete tear change whether I need surgery
Does a partial or complete tear change whether I need surgery?
No single feature — including age, sport, MRI appearance or a description of a “complete tear” — decides treatment on its own. The structure of the knee, how it behaves and what you want to return to are weighed together.
- Complete tears. In the KANON trial of young active adults, rehabilitation with optional delayed reconstruction did as well at two years as early reconstruction, and substantially reduced the number of operations.[1]
- Partial tears. There is no single standard of care. Treatment is tailored to age, activity, instability and other injuries. Many are managed without surgery first; in one review, about half of people returned to their pre-injury sport.[2]
- Overall. A 2024 systematic review found no certain evidence that reconstruction is better than non-operative treatment for an isolated tear. Measured looseness of the knee was lower after surgery. The authors cautioned that the studies were of low quality.[4]
Rehabilitation-led care is not “doing nothing”. Surgery is considered when the knee keeps giving way, when sport or work needs a stable knee for cutting or pivoting, or when other injuries change the balance.
More on who the KANON trial studied, and on the guideline
KANON was a randomised trial of young, active, non-professional adults with a recent ACL tear, so it does not describe every person or every sport.[1]
The American Academy of Orthopaedic Surgeons guideline (2022) strongly recommends early reconstruction when surgery is indicated for a recent isolated ACL tear, because the risk of extra cartilage and meniscal injury starts to rise within 3 months. The published summary notes this applies most to younger and more active people; older or less active people may do well without surgery.[6][7]
The full decision, including repair and reconstruction, is on the ACL reconstruction surgery page. For the journey itself, see what to expect before and after ACL reconstruction surgery.
When should a knee injury be checked urgently
When should a knee injury be checked urgently
When should a knee injury be checked urgently?
Signs that need urgent help
Some symptoms should not wait for a routine appointment. Each item below says where to go.
After an injury
- The kneecap has slipped out of place and is still out, or the knee looks deformed. Go to an emergency department. If the kneecap went back into place by itself, arrange an early assessment.
- The leg looks twisted or bent, a bone is showing, there is a deep cut, or the foot or leg turns cold, pale, numb, blue or white. Go to an emergency department or call 995.
- You cannot lift your leg up with the knee kept straight, and you may feel a gap just above or just below the kneecap. Arrange an urgent same-day assessment.
At any time
- The knee is stuck and will not straighten, or it is very painful and you cannot move it or put weight on it. Arrange an urgent same-day assessment.
- The knee is suddenly very painful, hot, red and swollen, especially with a fever or feeling generally unwell. Go to an emergency department or call 995.
- One calf or thigh is newly painful and swollen. Arrange an urgent same-day assessment. If you also feel short of breath or have chest pain, call 995.
After knee surgery
- The operated knee becomes more painful, swollen or red, a wound is leaking, or you develop a fever. Contact your surgical team straight away. If you cannot reach them the same day, go to an emergency department. If you feel very unwell, go to an emergency department. If you are short of breath or have chest pain, call 995.
If you are admitted by the doctor at the urgent care centre of one of these private hospitals, the Parkway Pantai hospitals (Mount Elizabeth Orchard, Mount Elizabeth Novena, Gleneagles and Parkway East), Farrer Park Hospital and Thomson Medical Centre, you may ask for Dr Sean Leo to be your attending orthopaedic surgeon. If you are instead discharged and referred for orthopaedic follow-up, you may contact the clinic to arrange an appointment. Both are subject to the hospital’s admission processes and to Dr Leo’s availability.
With you through the seasonsMeet Dr Sean Leo
Meet Dr Sean Leo
A consultant orthopaedic surgeon whose clinical focus is the knee, sports injuries and the lower limb.
- Dr Sean Leo is a consultant orthopaedic surgeon. OrthoKinetics is his professional brand; clinical services are provided through OrthoSports Orthopaedic & Sports Surgery at Mount Elizabeth Novena Specialist Centre and Connexion, Farrer Park Hospital.
- His clinical interests include sports injuries, including those in adolescent athletes; ligament reconstruction; realignment surgery; cartilage repair and joint-preservation approaches; knee replacement; and technology-assisted hip and knee surgery.
- The consistent aim is to return people to meaningful function and activity while avoiding unnecessary downtime.
- Qualifications: MBBS, MRCS (Ed), MMed (Ortho), FRCSEd (Ortho).
More detail: Meet Dr Sean Leo
- Training and career: Dr Leo trained in medicine at the National University of Singapore and served in the Singapore Armed Forces Medical Corps from 2000 to 2012, where his work included the care of soldiers in physically demanding roles. He completed postgraduate orthopaedic training in 2009 and a one-year clinical fellowship at Royal North Shore Hospital in Sydney, Australia, before joining Changi General Hospital as an orthopaedic consultant in 2012, where he later held the positions of Senior Consultant and Director of the Hip and Knee Service. With seniority, his educational contribution has evolved towards mentorship and support for junior doctors.
What should I do next?
What should I do next?
What should I do next?
If you are holding a report that says “partial” or “complete”, an assessment is the sensible next step. It brings together what happened, an examination and any tests that help, so you and your clinician can decide what to do next. An appointment supports an informed decision. It is not a commitment to surgery.
- Compare rehabilitation-led care and reconstruction on the ACL reconstruction surgery page.
- Wondering about healing? Read Can a torn ACL truly heal itself?
- Looking at repair? See Is ACL repair viable as a method of treating ACL injury? and Is your ACL injury suitable for repair rather than a replacement?
- Read about ACL tear symptoms.
- Browse the Knee Hub for other knee problems.
- This page provides general information and cannot diagnose an individual condition. OrthoKinetics does not provide emergency or urgent care through this webpage or its WhatsApp contact.
Sources
References
References
- Frobell RB, Roos EM, Roos HP, Ranstam J, Lohmander LS. A randomized trial of treatment for acute anterior cruciate ligament tears. N Engl J Med. 2010;363(4):331-342. doi:10.1056/NEJMoa0907797. PMID:20660401.
- Efficacy of non-surgical management and functional outcomes of partial ACL tears. A systematic review of randomised trials. BMC Musculoskelet Disord. 2022. doi:10.1186/s12891-022-05278-w. PMCID:PMC8991495.
- Conservative vs Surgical Treatment of Anterior Cruciate Ligament Rupture: A Systematic Review. PMCID:PMC11027445.
- Nonoperative Treatment as an Option for Isolated ACL Injury: A Systematic Review and Meta-analysis. Orthop J Sports Med. 2024;12(4). doi:10.1177/23259671241239665. PMID:38601190.
- Filbay SR, Dowsett M, Chaker Jomaa M, Rooney J, Sabharwal R, Lucas P, et al. Healing of acute anterior cruciate ligament rupture on MRI and outcomes following non-surgical management with the Cross Bracing Protocol. Br J Sports Med. 2023;57(23):1490-1497. doi:10.1136/bjsports-2023-106931. PMID:37316199. PMCID:PMC10715498.
- American Academy of Orthopaedic Surgeons. Management of Anterior Cruciate Ligament Injuries: Evidence-Based Clinical Practice Guideline. Rosemont (IL): AAOS; published 22 August 2022. Available from: aaos.org
- Brophy RH, Lowry KJ. American Academy of Orthopaedic Surgeons Clinical Practice Guideline Summary: Management of Anterior Cruciate Ligament Injuries. J Am Acad Orthop Surg. 2023;31(11):531-537. doi:10.5435/JAAOS-D-22-01020. PMID:36727995. PMCID:PMC10168113.
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