14 Signs You Have an ACL Tear

2. Intense Pain in the Knee

You may feel intense pain in your knee right after the injury, often starting fast and feeling sharp or deep inside the joint. This pain can stop you from continuing activity right away and may begin during a sudden twist, landing, or quick stop. The knee may not feel strong enough to support your weight.

The pain often worsens when you try to walk, bend, or turn. Even small movements can feel uncomfortable, and you may feel the pain more on the inside or center of the knee. As time passes, the pain can shift from sharp to a constant ache, sometimes present even at rest.

Swelling can increase the pain by making the knee feel tight and stiff. You may try rest, ice, compression, or elevation to ease discomfort, but the pain often returns when you move again. Intense knee pain after an injury often signals damage inside the joint, especially when combined with swelling or instability.

3. Swelling of the Knee

Knee swelling often appears soon after you tear your ACL. Your knee may look larger than normal and feel tight because fluid builds up inside the joint after the injury. Swelling can grow fast and limit how much you can bend or straighten your knee, which makes the skin feel warm and the joint heavy or stiff.

Swelling can make it hard to walk or put weight on your leg, and you may feel pressure inside the knee even when you rest. The knee may show a visible increase in size, and the tightness can limit movement. A full or pressured feeling can also develop inside the joint.

The swelling may go down after a few days, but it often returns with activity. Ongoing swelling can affect balance and make your knee feel less steady during daily tasks. Repeated swelling can also slow recovery and make simple movements during upright posture or direction changes feel less controlled overall.

4. Difficulty Stretching the Knee

You may notice trouble when you try to fully bend or straighten your knee. The joint can feel tight, stiff, or blocked, often soon after an ACL tear. Swelling inside the knee limits how far the joint can move, and extra fluid takes up space that your knee needs to stretch.

You might feel resistance when you try to straighten your leg all the way, sometimes described as a pulling or catching feeling. Pain can also cause your body to guard the joint and stop the movement early.

Difficulty stretching the knee can show up as trouble locking the knee straight or reduced bending when sitting or squatting. Stiffness may feel worse after resting or sleeping, and discomfort can appear during simple leg movements. These limits can affect daily tasks. Walking, climbing stairs, or getting out of a chair may feel awkward.

5. The Knee Feels Unstable

You may notice that your knee does not feel solid or reliable. It can feel loose, shaky, or like it might slip out of place, especially when you stand, walk, or turn. Your knee may give way during simple moves, such as changing direction, stepping off a curb, or walking on uneven ground.

Instability often becomes clear during active movements. Sports, quick stops, or side steps can trigger it, but some people feel it during daily tasks like climbing stairs or getting out of a chair. The ACL helps keep your lower leg in the right position, so when it tears, your knee can move in ways it should not, causing the unsafe feeling.

You may try to protect your knee without thinking, walking slower, avoiding turns, or keeping weight off one leg. This can show up as buckling or giving way, trouble with turning or pivoting, and fear of putting full weight on the leg. Loss of confidence in the knee during movement is also common.

6. Difficulty Walking

You may notice trouble walking soon after an ACL tear. Your knee can feel weak, loose, or unsteady when you put weight on it, which makes normal steps feel hard or unsafe. You might walk slower than usual, take short steps, or limp without trying.

Swelling and pain can also change how you walk, as a swollen knee may not bend or straighten fully. You may feel worse when you try to go up or down stairs, since stairs require knee control and balance.

Walking changes can include limping to avoid pain and trouble turning or changing direction. You may also feel unstable on slopes or uneven surfaces, and you might need support from walls or furniture. Difficulty walking affects daily tasks like shopping, working, or caring for your home.

7. Difficulty Bearing Weight

You may struggle to put weight on your injured leg after an ACL tear. The knee can feel weak, unstable, or unsafe the moment you try to stand, and this often starts right after the injury. You might notice pain when your foot hits the ground, and swelling inside the knee can make movement stiff and limit how much force you can handle.

Your body reacts by shifting weight to the other leg to avoid pain. Some people feel like the knee might give out when they walk, on flat ground, or when using stairs. You may walk short distances but need to move slowly, at the same time relying on walls, furniture, or another person for support.

How your knee reacts during daily tasks, such as standing from a chair or stepping off a curb, can provide useful information. Trouble with these simple actions can signal a deeper knee injury.

8. Abnormal X-Ray Imaging

You may get an X-ray after a knee injury when a provider wants to rule out bone damage. An X-ray does not show the ACL itself, but it can show changes that often happen with this type of injury. These clues help guide the next steps.

X‑ray results linked to an ACL tear can include small bone breaks where the ligament pulls on the bone and a shift in how the thigh bone and shin bone line up. Images may also show signs of joint swelling inside the knee or damage to nearby bone caused by impact during the injury.

One example is a small chip of bone pulled off the shin bone, which can happen when the ACL tears and tugs hard on its attachment point. You may also have a normal X-ray even if you tore your ACL, since the ligament injury does not always affect the bone. When symptoms continue but the X-ray looks normal, providers often order more detailed imaging to confirm the cause of knee pain, swelling, or instability.

9. Abnormal Physical Exams

A physical exam can show clear signs that your ACL is torn. During the exam, a clinician compares both knees to check for differences. You may notice that the injured knee moves more than it should or feels loose during testing.

One common finding is extra forward movement of your lower leg when the knee bends, which suggests the ACL no longer holds the knee steady. You might feel a soft or unstable stop instead of a firm one when the leg moves.

Your knee may also fail simple movement checks, such as struggling to fully straighten or bend it without pain. Grinding or cracking sounds can appear when the knee moves, which may point to joint damage or swelling.

Balance and walking tests can also look abnormal. You may limp, avoid putting weight on the leg, or feel the knee shift when you turn. Swelling and warmth around the knee are common exam findings, and rapid swelling soon after injury raises concern for a ligament tear.

10. Tenderness Along the Knee Joints

Tenderness along the knee joint often signals deeper injury, especially after an ACL tear. You may notice soreness when pressing along the sides or front of your knee, even if the knee looks normal. Simple actions like kneeling, squatting, or climbing stairs can trigger discomfort.

Swelling adds pressure and makes the area sore to touch, especially after activity or later in the day. You may feel uneven soreness from one side of the knee to the other because the injury changes how your knee carries weight. The joint works harder to stay stable.

Pain may increase when you bend or straighten your leg fully, and stiffness can appear after sitting for a while. Touching the joint line can bring a sharp or dull ache. These signs often appear with swelling, weakness, or a sense that the knee might give way, suggesting damage inside the knee rather than a surface problem.

11. Creaky Joints

Creaking, cracking, or popping sounds in your knee may appear when you move, especially when you bend, straighten, or stand up. These sounds often show up during daily tasks like walking upstairs, getting out of a chair, or turning quickly, and they can feel strange even if they do not hurt.

The ACL helps guide smooth movement, so when it stretches or tears, the bones and soft parts stop gliding as they should. Some people feel stiffness along with the sound, which may loosen a bit after moving but can return later.

You may notice these sounds more during sports or fast movement, as quick stops and turns place extra stress on the knee. A damaged ACL struggles to handle that stress, which leads to noise and uneven motion. Creaky joints alone do not always mean an ACL tear, but when they pair with swelling, pain, or a sense that your knee gives way, they can signal deeper trouble.

12. Hemarthrosis

Hemarthrosis means bleeding inside your knee joint and often occurs after an ACL tear. Blood can leak into the joint space within hours, and this causes rapid swelling that feels tight and warm. Your knee may look larger than the other side, feel stiff, and you might struggle to bend or straighten it because the pressure inside the joint limits movement.

Pain often increases as the swelling grows, and the knee can feel heavy or full even when you rest. Hemarthrosis often happens with ligament injuries because the ACL has a blood supply, so bleeding starts quickly. This explains why ACL injuries often cause sudden and visible swelling, unlike mild knee strains. The swelling from hemarthrosis can make your knee feel unstable, and you may feel like the joint cannot support you. This sensation often appears early and can signal a serious internal injury.

13. Numbness and Tingling

Numbness or tingling in your knee or lower leg can follow an ACL tear. This appears soon after the injury or later as swelling increases. The ACL contains small nerves that help your brain sense knee position, so when the ligament tears, these nerves may stop sending clear signals and cause odd sensations.

Swelling can press on nearby nerves, which can lead to pins-and-needles feelings around the knee, shin, or foot. You might feel these sensations as light tingling like static, partial numbness around the kneecap, or a dull, buzzing feeling down the leg.

These symptoms often reflect irritation or pressure from the injury rather than direct nerve damage. As knee motion becomes unstable, nearby tissues can react and affect how the area feels.

Numbness and tingling can make it harder to trust your knee, and you may feel unsure where your leg is when you step or turn. This loss of clear feedback can add to the sense that your knee may give way during normal movement.

14. Redness, Bruising, Warmth in the Joint

After an ACL tear, you may notice redness, bruising, and warmth around your knee. These changes often appear soon after the injury and can vary in strength from person to person. The size of the tear and how quickly you rest the knee can affect these symptoms.

You may notice redness around your knee soon after an ACL tear. Blood flow increases as your body reacts to the injury, which makes the skin look flushed compared to the other knee.

Bruising often follows within hours or days. Small blood vessels break when the ligament tears, and the blood spreads under the skin. This causes purple, blue, or yellow marks that may travel down your leg.

Warmth in the knee is another common sign. Your body sends extra blood and fluid to protect the injured area, and when you touch the knee, it may feel warmer than the surrounding skin.