A person who experiences an acute anterior cruciate ligament (ACL) tear of the knee is likely to report some combination of the following knee symptoms

  • Initial sharp pain. Unlike progressive knee conditions, such as knee osteoarthritis, symptoms of an ACL tear are sudden onset and can almost always be traced back to a specific incident or injury.
  • Swelling after the injury. Swelling often occurs immediately after the injury. In some cases, swelling may develop up to 24 hours later. Swelling may last up to a week.
  • Deep, aching pain in the knee. The pain may be worse when walking or climbing stairs.
  • A feeling the knee is “giving out.” Instability may be especially noticeable during activities that strain the knee joint, such as walking downstairs and pivoting on one leg.

See Guide to Knee Joint Anatomy

  • Restricted range of motion. It may be particularly difficult to straighten the affected knee.
  • The knee may feel warm to the touch. This is due to bleeding within the knee joint.
  • Inability to bear weight. In Grade II or III injuries, the pain and swelling may be too severe to stand or walk without assistance or limping.
  • Tenderness around the knee joint. This area may be painful to the touch.
  • Bruising around the knee. Bruising can occur all around the knee area.
  • Numbness. In some cases, such as a severe ACL tear, a person may lose feeling (numbness) down the leg, below the knee.

While some symptoms occur immediately after injuring the ACL, such as swelling and tenderness, others may appear or get worse in the days following the injury, such as bruising.

See Common Running Injuries: Knee Pain

Without treatment, the swelling and pain in the knee generally subside over a period of several weeks; however, knee instability may often persist. Instability can limit the person’s ability to participate in athletics and even do normal, daily activities. In particular, it may be difficult for the person to stand up from a seated position or go down stairs.

See The P.R.I.C.E. Protocol Principles


Additional Symptoms

Other structures in the knee, such as the meniscus and medial collateral ligament (MCL), are often damaged with ACL injuries. These other injuries may cause additional symptoms, such as knee locking—the inability to bend or straighten the knee—to occur and may require additional treatment.

See Soft Tissue of the Knee Joint

Dr. Michael Khadavi is a sports medicine physician specializing in spine care, musculoskeletal ultrasound, regenerative medicine, and sports-related injuries. He practices at Apex Orthopedics & Sports Medicine. Dr. Khadavi is an educator in regenerative medicine and has been an invited lecturer at the American Academy of Physical Medicine and Rehabilitation, Association of Academic Physiatrists, Major League Soccer, and Stanford University.

Dr. Michael Fredericson is a sports medicine physiatrist with more than 25 years of experience. He serves as a Professor and the Director of Physical Medicine and Rehabilitation Sports Medicine at Stanford University School of Medicine.