What is an ACL Tear
The anterior cruciate ligament, or ACL, is one of the key ligaments that helps stabilize your knee joint. It connects the thigh bone (femur) to the shin bone (tibia) and promotes stability by keeping your knee from sliding too far forward or excessively rotating. When the ACL is torn, it can cause pain, swelling, and instability in the knee, making everyday activities difficult or impossible. Understanding what causes it, the symptoms, and treatment options is important for anyone who wants to protect their knees and recover well.
Who’s Most Likely to Sustain an ACL Tear?
ACL injuries are surprisingly common. Research shows that approximately 200,000 ACL tears occur annually in the United States alone. These injuries are especially frequent among athletes involved in sports requiring sudden stops, pivots, or jumps, like soccer, basketball, football, skiing, and volleyball. Statistically, females have a higher risk of ACL tears compared to males, with some studies suggesting as much as 2 to 8 times greater risk. This difference is often attributed to anatomical, hormonal, and neuromuscular factors. However, anyone, regardless of gender or age, can sustain an ACL injury.
ACL Tear Causes
ACL tears typically happen in two main ways: contact and non-contact injuries.
Contact Injuries
These occur when an external force directly impacts the knee, such as a tackle in football or a collision in soccer. Examples include:
- A player being hit on the side of the knee, causing it to buckle inward (valgus force)
- Landing awkwardly after a jump with someone else landing on your leg
- Hyperextension of the knee caused by a sudden force
Non-Contact Injuries
Interestingly, the majority of ACL tears (up to 70%) happen without direct contact. These usually happen during sudden changes in direction, rapid deceleration, or improper landing from a jump. Common mechanisms include:
- Cutting or pivoting quickly while running
- Twisting the knee while the foot is planted
- Landing from a jump with the knee in an unstable position
The ACL is vulnerable during these movements because they may place stress on the ligament that exceeds its capacity to resist twisting or forward motion of the tibia relative to the femur.
ACL Tear Symptoms
If you tear your ACL, you may notice several signs right away:
- A sudden “pop” or snapping sensation in the knee at the time of injury
- Immediate swelling within a few hours
- Pain, especially when trying to bear weight or walk
- Loss of full knee range of motion (difficulty straightening or bending fully)
- A feeling of instability or the knee “giving way,” especially when walking or changing directions
Although an MRI is the gold standard for an ACL tear diagnosis, physical therapists can perform special testing which can help rule in/out the possibility of a tear.
Is Surgery Required?
One of the biggest questions after an ACL tear is whether surgery is necessary. Research shows that the ACL has limited capacity to heal on its own once torn. However, not everyone with an ACL tear requires surgery.
Patients can be categorized into two groups: “copers” and “non-copers.” Copers are individuals who can compensate for the lack of a functional ACL by improving strength, stability, and movement patterns, often through targeted physical therapy. Some high-level athletes, like Tiger Woods and John Elway, have successfully played sports with a torn ACL.
That said, non-copers typically experience persistent instability, repeated knee giving way, or inability to return to desired activities without surgical reconstruction.
While surgery can restore mechanical stability, long-term research on return-to-play rates and functional outcomes is still evolving. Many people live active, fulfilling lives without an ACL, but it’s a decision best made with a healthcare professional’s guidance.
How Can Physical Therapy Help?
Physical therapy (PT) is a cornerstone of both non-surgical and surgical management of ACL tears. It’s often the only treatment for those who choose the non-operative route, and it plays a crucial role in preparing patients for surgery and in post-operative recovery.
Non-Operative Approach
For copers, PT focuses on building strength, especially in the muscles around the knee and hip, improving balance and proprioception (your body’s sense of position), and retraining movement patterns to avoid instability. With consistent guided rehab, many patients regain function without surgery.
Pre-Operative (Prehab) Phase
If surgery is planned, physical therapy beforehand is essential. Getting the knee as strong, mobile, and pain-free as possible before surgery leads to better post-operative outcomes. Prehab helps reduce swelling, restore range of motion, and build strength.
Post-Operative Rehab
After ACL reconstruction, physical therapy guides the recovery process through phases:
- Regaining full knee motion and controlling swelling
- Rebuilding strength and stability
- Retraining gait and functional movement
- Progressing to running, jumping, and sport-specific drills
- Restoring confidence in the knee to safely return to prior levels of activity
Physical therapists are experts at balancing progression, pushing you enough to improve but not so fast that you risk re-injury. They use a combination of time-based milestones (weeks since surgery) and functional milestones (strength tests, movement quality) to safely guide your return to activity.
Final Thoughts
An ACL tear is a serious injury but not the end of an active lifestyle. Regardless of your chosen surgical or non-operative route, physical therapy is essential to regain knee function and confidence.
Find a PT Clinic Near You!
If you suspect an ACL injury, seek evaluation from a physical therapist who can guide you on the best treatment path for your goals and lifestyle. Use our interactive map tool to find a physical therapist near you and start your recovery journey with expert care.