The anterior cruciate ligament (ACL) is a band of dense connective tissue within the knee, connecting the thigh bone (femur) to the shin bone (tibia). Its primary function is to stabilize the knee by preventing the shin bone from sliding too far forward and limiting excessive rotation. ACL tears commonly occur during activities involving sudden stops, changes in direction, pivoting, or incorrect landing from jumps. While a torn ACL can significantly impact knee function, individuals often can walk after such an injury, though this capability comes with important considerations.
Immediate Experience of an ACL Tear
Many individuals who experience an ACL tear report a distinct “pop” sound or sensation in the knee at the moment of injury. This is often accompanied by immediate pain, which can range from significant to mild, and rapid swelling that typically develops within the first few hours. The swelling occurs as blood vessels within the knee bleed into the joint. A feeling of instability, or the knee “giving out,” is also a common immediate symptom.
Despite these symptoms, some individuals can walk immediately after an ACL tear, particularly in straight lines, and may even manage stairs. This is because the ACL is not the sole weight-bearing structure, and other surrounding muscles may compensate. However, this ability does not indicate injury severity; even complete tears can allow initial walking. Conversely, severe pain, buckling, or associated injuries can prevent walking.
Why Walking with a Torn ACL is Risky
Walking with a torn ACL carries significant risks for further knee damage. The ACL maintains knee stability, especially during twisting, pivoting, or sudden changes in direction. Without a functional ACL, the knee joint becomes unstable, leading to abnormal movement. This instability can cause the knee to buckle or “give way” unexpectedly, even during simple activities like walking or climbing stairs.
Continued weight-bearing on an unstable knee stresses other internal structures. The menisci, cartilage pads that cushion the knee, are vulnerable to injury due to altered mechanics. Meniscus tears are commonly associated with ACL injuries, and walking on an unstable knee can worsen them. Other knee ligaments, such as the medial collateral ligament (MCL), can also be damaged. Over time, chronic instability and repeated episodes of the knee giving out can accelerate articular cartilage wear, increasing the long-term risk of osteoarthritis.
When to See a Doctor
Any suspected ACL tear warrants prompt medical evaluation. Several signs and symptoms indicate the need for a doctor’s visit. Severe pain, an inability to bear weight, or a feeling that the knee is “giving out” are clear reasons to seek medical attention. Even if the initial pain subsides and walking is possible, persistent instability or discomfort means the knee is compromised and requires professional assessment. Consulting a healthcare provider immediately after a knee injury is important for an accurate diagnosis and to determine the most appropriate course of action.
Next Steps After an ACL Injury
After a suspected ACL injury, a healthcare provider will conduct a thorough physical examination of the knee, assessing for swelling, tenderness, and range of motion. Specific physical tests, such as the Lachman’s test, are often performed to evaluate the integrity of the ACL. To confirm diagnosis and check for associated injuries like meniscus tears or bone fractures, imaging tests are typically ordered. An X-ray can rule out fractures, while an MRI scan provides detailed views of ligaments, cartilage, and soft tissues, which helps confirm an ACL tear and assess its severity.
Initial management strategies often include the RICE protocol: Rest, Ice, Compression, and Elevation, to help reduce pain and swelling. Crutches or a knee brace may be recommended to provide support and limit weight-bearing, which helps protect the injured knee. Treatment options for an ACL tear vary based on factors such as the individual’s activity level, age, and the extent of the tear. Non-surgical approaches, focusing on rehabilitation and strengthening the muscles around the knee, may be considered for less active individuals or those with partial tears. For active individuals or those with complete tears and significant instability, surgical ACL reconstruction, followed by extensive physical therapy, is often recommended to restore knee function and stability.