If you have recently hurt your knee during sport or physical activity, it is natural to wonder whether something serious has happened. The ACL is one of the most commonly injured structures in the knee, and knowing what signs and symptoms to look out for can help you seek the right care at the right time.
It is important to note that only a thorough clinical assessment — and in many cases imaging — can confirm an ACL tear. However, understanding the common signs can help you recognise when something is not right and when professional evaluation is needed.
The Most Common Signs of an ACL Tear
1. A “Pop” Sound or Sensation
One of the most frequently reported features of an ACL tear is a distinct popping sound or sensation at the moment of injury. This is not always present, but when it occurs it is often described as audible and felt through the knee. It typically happens during a sudden deceleration, pivot, or landing movement.
2. Immediate Swelling
Significant swelling developing within the first one to two hours after a knee injury is a common indicator of an ACL tear. This rapid swelling — known as a haemarthrosis — occurs because blood fills the joint space following ligament rupture. Swelling that develops slowly over several hours may suggest a different type of injury.
3. Feeling of Instability or Giving Way
Many people describe a sensation that the knee has “given out” or feels unreliable following an ACL injury. This feeling of instability — particularly during weight bearing, pivoting, or directional changes — is a hallmark symptom of ACL disruption and should always be assessed promptly.
4. Pain at the Time of Injury
Pain is common immediately following an ACL tear, though its severity can vary. Some individuals report significant pain at the time of injury, while others describe a surprisingly brief period of pain followed by a dull ache or pressure from swelling. The absence of severe ongoing pain does not mean the injury is minor.
5. Difficulty Bearing Weight
Following an ACL tear, many people find it difficult or uncomfortable to fully bear weight on the affected leg, particularly in the immediate period after injury. This is often related to a combination of pain, swelling, and the feeling of instability rather than a fracture or bone injury.
6. Loss of Full Range of Motion
Swelling and pain following an ACL injury can limit the knee’s ability to fully straighten or bend. Difficulty achieving full knee extension in particular is a common early sign and should be monitored closely during the initial recovery period.
What to Do if You Suspect an ACL Tear
If you or your child has experienced any of the above symptoms following a knee injury, the following steps are recommended:
- Stop the activity immediately and avoid pushing through pain
- Apply ice wrapped in a cloth to reduce swelling — avoid direct ice contact with skin
- Elevate the leg where possible to support swelling management
- Seek professional assessment as soon as possible — do not wait for symptoms to settle on their own
Early assessment is important not only to confirm the diagnosis but to identify whether associated structures such as the meniscus or cartilage have also been injured.
Why Early Assessment Matters
Delaying assessment after a suspected ACL injury can increase the risk of secondary damage to the knee. Continuing to load an unstable knee — even during everyday activities — places the meniscus and cartilage at risk of further injury. Early assessment also allows rehabilitation to begin promptly, which is associated with better long-term outcomes regardless of whether surgery is ultimately required.
Ahmad at Aret Chiropractic has a specialist focus in lower limb rehabilitation for young athletes, with a primary interest in ACL injury assessment and management. If you are concerned about a recent knee injury, do not wait.
Call us on (02) 8018 8883 to speak with Ahmad or one of our Chiropractors at Aret Chiropractic in North Ryde, or book online for a consultation.
References
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Boden, B. P., et al. (2000). Mechanisms of anterior cruciate ligament injury. Orthopedics, 23(6), 573–578.
Kaplan, Y. (2011). Identifying individuals with an ACL-deficient knee as copers and non-copers: a narrative literature review. Journal of Orthopaedic & Sports Physical Therapy, 41(10), 758–766.
Logerstedt, D. S., et al. (2010). Knee stability and movement coordination impairments: knee ligament sprain. Journal of Orthopaedic & Sports Physical Therapy, 40(4), A1–A37.
Swenson, D. M., et al. (2013). Epidemiology of knee injuries among US high school athletes, 2005–2011. Medicine & Science in Sports & Exercise, 45(3), 462–469.