ACL injuries, explained simply.
Clear, plain-English information. Not a substitute for your surgeon or physio. Just a starting point so you know what questions to ask.
Jump to diagnosis4 main ligaments
The ACL is one of four key ligaments in the knee joint.
Rotational stability
Controls rotation during cutting, pivoting, and landing.
Common in sport
Basketball, football, netball, skiing, and other change-of-direction sports.
Often not isolated
ACL injuries often occur alongside meniscus or cartilage damage.
Anatomy
What is the ACL?
The anterior cruciate ligament (ACL) is one of four main ligaments in the knee. It sits deep inside the joint, connecting the thigh bone (femur) to the shin bone (tibia). Its job is to limit the shin from sliding forward and help control rotational stability, the kind of movement you rely on when cutting, pivoting, or landing from a jump.
When the ACL tears, the knee can lose some of that rotational stability. For some people, this means the knee feels unreliable during sport or certain movements. An ACL tear is common in sports that involve sudden changes of direction, landing, or contact, including basketball, football, netball, skiing, and others. ACL injuries often occur alongside other knee injuries, particularly damage to the meniscus or cartilage.
The knee can lose some of that rotational stability.
Signs & Symptoms
What an ACL tear often feels like
Every injury is different. But people commonly report some or all of the following:
A pop or snap
Many people describe hearing or feeling a distinct "pop" at the moment of injury. Not everyone does, but it is one of the most commonly reported signs.
Rapid swelling
The knee often swells significantly within a few hours, although swelling can sometimes appear later. This swelling is typically caused by bleeding inside the joint.
Instability or giving way
The knee may feel loose or unstable, as though it could buckle or give way, particularly with twisting or pivoting movements.
Difficulty bearing weight
Continuing to walk or play is often difficult immediately after the injury. Some people can walk; others cannot. Both are normal.
If your knee injury feels serious, seek medical attention. A clinician can assess your knee properly.
Diagnosis
What happens next: diagnosis
X-ray
An X-ray is often the first imaging done, usually in A&E or an urgent care setting. It is useful for ruling out fractures, but it does not show soft tissue like ligaments. An X-ray cannot confirm or rule out an ACL tear on its own.
MRI
An MRI (magnetic resonance imaging) is commonly used to confirm a ligament injury. It produces detailed images of the soft tissues in and around the knee. Getting an MRI may take days or weeks depending on availability and referral pathways. The waiting can be stressful. That is completely normal.
Clinical examination
An experienced clinician can often suspect an ACL tear through physical tests (like the Lachman test or anterior drawer test). These tests assess how much the tibia moves relative to the femur. MRI is commonly used to confirm or support the diagnosis, but clinical assessment is often the first strong indicator.
Results timing varies. Some people wait days; others wait weeks. If you are waiting and unsure, it is reasonable to contact your referral team or GP for an update.
Be Prepared
Questions to ask your clinician
These may be helpful to bring to your physio, surgeon, or GP appointment. Not all will apply to your situation.
What does my MRI show, and what does that mean for me?
Do I need surgery, or is non-operative management an option?
If surgery, what type of graft is recommended, and why?
What should I be doing right now for my knee?
When can I start physiotherapy?
What does a realistic recovery timeline look like for me?
How will we decide when I'm ready to return to sport?
Are there any movements I should avoid at this stage?
Work with your physio and surgeon for your plan. This list is a starting point, not a replacement for clinical advice.
Getting Started
Early priorities
In the early period after an ACL injury, early rehabilitation often focuses on a few key goals. Your physio will tailor these to you.
Reduce swelling
Your physio may recommend ice, compression, elevation, and rest in the early days to help manage swelling and pain.
Restore range of motion
Many rehabilitation approaches prioritise regaining full extension (straightening) early. Flexion (bending) is typically restored progressively over time.
Rebuild strength
Strengthening the muscles around the knee, particularly the quadriceps and hamstrings, is a cornerstone of ACL rehabilitation.
Work with your physio and surgeon to determine the right approach and timing for you.
Common Inquiries
Questions people often ask
Will I need surgery?
It depends on your activity level, knee stability, and goals. Your surgeon will help you decide.
How long is recovery?
Most ACL recoveries take 9 to 12 months, sometimes longer. Everyone's timeline is different.
Can I play sport again?
Many people return to sport after ACL reconstruction, but the timeline and process vary widely.
Is non-operative management an option?
For some people, yes. It depends on knee stability, activity demands, and whether other structures are injured.
How long until I can walk properly?
Most people are walking within a few weeks, sometimes with crutches initially. Your physio will guide your progression.
Why is everything taking so long?
The pathway from injury to diagnosis to treatment can feel slow. Waiting for scans, referrals, and appointments is normal but frustrating.
Am I doing enough, or too much?
It is common to feel unsure about activity levels early on. Your physiotherapist can help you find the right balance for your stage of recovery.
Surgery
ACL Graft Options: What to Know Before Surgery
If you're having ACL reconstruction, one of the biggest decisions is which graft to use. There is no single best option. It depends on your age, sport, goals, and what trade-offs you're willing to accept.
This guide synthesises current research and what people actually say after living with their choice. Always discuss graft selection with your surgeon.
Patellar Tendon Autograft
Bone-Patellar Tendon-Bone
A central third of your patellar tendon, connecting the kneecap to the shin, with bone plugs taken from the kneecap and shinbone. Often called the “gold standard” for athletes.
+Benefits
- Strong fixation. Bone-to-bone healing happens quickly and reliably.
- Lowest rerupture rate in athletes under 25 returning to cutting and pivoting sports (Kaeding et al., 2017 AJSM).
- No hamstring weakness. The hamstring muscle is left untouched.
!Trade-offs
- Anterior knee pain. Up to 10 to 30% report pain with kneeling (Mohtadi et al., 2016 JBJS).
- Small risk of patellar fracture or tendonitis.
- More pain early post-op compared to hamstring grafts.
Sources: Kaeding, C. C., et al. (2017). AJSM. MOON cohort, 2-year rerupture rates. Mohtadi, N. G., et al. (2016). JBJS. RCT patellar vs hamstring.
Hamstring Tendon Autograft
Semitendinosus & Gracilis
Two tendons from the inner thigh are harvested, folded, and used to create a new ACL. No bone plugs.
+Benefits
- No kneeling pain. Leaves the front of the knee untouched.
- Smaller incision. Often considered cosmetically better.
- Good for patients who kneel often, such as wrestlers, volleyball players, or those in construction.
!Trade-offs
- Hamstring strength deficit. Some patients report lasting weakness in hamstring curl strength (Lind et al., 2020 AJSM).
- Slightly higher rerupture rate in young, high-activity patients compared to patellar tendon (Kaeding et al., 2017).
- Slower graft incorporation due to soft-tissue to bone healing.
Sources: Lind, M., et al. (2020). AJSM. Danish registry, hamstring strength outcomes. Mohtadi et al. (2016) JBJS. Functional outcomes and kneeling pain.
Quadriceps Tendon Autograft
A graft taken from the quadriceps tendon just above the kneecap. It can be harvested with or without a bone plug.
+Benefits
- Thicker, stronger graft than hamstring, with excellent collagen properties.
- Less kneeling pain than patellar tendon.
- No hamstring weakness. Preserves hamstring function.
- Increasingly popular as a versatile alternative to patellar tendon.
!Trade-offs
- Quadriceps weakness early on. Requires dedicated rehab to regain strength.
- Small incision above kneecap, which may be cosmetically noticeable.
- Less long-term outcome data compared to patellar and hamstring, though growing.
Sources: Mouarbes, D., et al. (2019). OJSM. Systematic review: quadriceps vs patellar/hamstring, comparable stability, less kneeling pain. Lind et al. (2020) AJSM. Registry data showing quadriceps graft trends.
Allograft (Donor Tissue)
Graft taken from a cadaver donor. Common types include patellar tendon, hamstring, or Achilles tendon.
+Benefits
- No harvest site pain or weakness. Recovery is often less painful early on.
- Shorter surgery time.
- Often preferred for patients over 35 to 40 or those with lower activity demands.
!Trade-offs
- Higher rerupture rate in young, active patients (Kaeding et al., 2017), especially under 25.
- Theoretical infection risk, though extremely low with modern processing.
- Slower incorporation. Some surgeons use a longer bracing protocol.
Sources: Kaeding, C. C., et al. (2017). AJSM. Rerupture rates: autograft 2.5%, allograft 5.4% in under-25 athletes. Wasserstein, D., et al. (2015). JBJS. Increased revision risk with allograft in young patients.
Graft Comparison Summary
| Factor | Patellar Tendon | Hamstring | Quadriceps | Allograft |
|---|---|---|---|---|
| Rerupture risk (young) | Lowest | Moderate | Low (emerging) | Highest |
| Kneeling pain | 10 to 30% | Very low | Low | None from harvest |
| Early recovery pain | Higher | Lower | Moderate | Lowest |
| Best for | High demand sports | Avoiding kneeling pain | Strong graft, no kneeling pain | Lower demand, older patients |
How to Choose: Questions to Ask Your Surgeon
What graft do you use most often, and why?
What are your personal rerupture rates with each graft?
How does my age, sport, and activity level affect the recommendation?
What does recovery look like for each option, especially early pain and return to sport timeline?
Graft choice is one part of a successful ACL reconstruction. Surgeon experience, rehab quality, and your own dedication matter just as much. This guide is based on peer-reviewed research. It is not medical advice. Use it to have a more informed conversation with your medical team.
Sources
Kaeding, C. C., et al. (2017). American Journal of Sports Medicine. MOON cohort, 2-year rerupture rates.
Mohtadi, N. G., et al. (2016). Journal of Bone and Joint Surgery. RCT patellar vs hamstring.
Lind, M., et al. (2020). American Journal of Sports Medicine. Danish registry, hamstring strength outcomes.
Mouarbes, D., et al. (2019). Orthopaedic Journal of Sports Medicine. Systematic review, quadriceps vs patellar/hamstring.
Wasserstein, D., et al. (2015). Journal of Bone and Joint Surgery. Increased revision risk with allograft in young patients.
Medical Disclaimer
This is not medical advice.
ACL Story is an informational resource created by a patient, not a medical professional. The content on this website is intended to help people understand the general shape of ACL recovery and ask better questions of their clinical team.
Nothing on this site should be interpreted as medical diagnosis, treatment advice, or a substitute for professional clinical guidance. Every injury is different. Recovery timelines, exercises, and treatment decisions should always be made in consultation with your surgeon, physiotherapist, or other qualified healthcare provider.
The information presented here is based on publicly available research, published clinical guidelines, and personal experience. While every effort has been made to ensure accuracy, medical knowledge evolves and individual circumstances vary. ACL Story cannot be held responsible for decisions made based on the content of this website.
If you are experiencing a medical emergency or are unsure about your symptoms, please contact your doctor or emergency services immediately.