ACL Injuries

The knee is a hinge joint where the thigh bone (femur) meets the shin bone (tibia), and it depends on four major ligaments to control motion. The collateral ligaments (MCL and LCL) run along the sides of the knee, while the cruciate ligaments (ACL and PCL) cross in the center of the joint.

The ACL runs diagonally from the back of the femur to the front of the tibia. Its two bundles tighten at different points as the knee bends and straightens, making the ACL the primary restraint against the tibia sliding forward on the femur and an important controller of rotation. The ACL also contains nerve endings that help the brain sense the position of the knee, which contributes to balance and coordinated movement.

Because the ACL sits inside the joint and is bathed in joint fluid, a complete tear does not heal back together on its own the way many other ligaments do.

Most ACL tears are non-contact injuries. They typically occur during a sudden deceleration, a pivot or cutting maneuver, or an awkward landing from a jump, when the knee collapses inward and the leg rotates. Contact injuries occur as well, particularly from a blow to the outside of the knee, and these are more likely to involve additional ligaments. ACL tears often occur alongside meniscus tears, bone bruises, cartilage injury, and injury to the MCL or posterolateral corner.

Several factors increase the risk of an ACL tear:

Sex

Female athletes sustain ACL tears at several times the rate of male athletes in the same sports, a difference driven by anatomy, hormonal factors, and neuromuscular control patterns.

Movement patterns

Landing with the knee collapsing inward and limited hip and core control place greater strain on the ligament.

Anatomy

A narrow notch at the end of the femur, increased slope of the top of the tibia, and generalized ligamentous laxity or knee hyperextension are all associated with higher risk.

Prior injury and family history

A previous ACL tear or a family history of ACL tears raises the risk of future injury.

Symptoms often begin dramatically and then settle, which can lead patients to underestimate the injury. A knee that feels unstable should not be dismissed, as each episode of giving way can damage the meniscus and cartilage and raise the long-term risk of arthritis.

Common symptoms include:

• A “pop” at the time of injury: Many patients describe hearing or feeling a distinct pop, followed by the sense that something shifted inside the knee.
• Rapid swelling: Significant swelling within the first several hours reflects bleeding inside the joint and is a hallmark of an ACL tear.
• Instability or giving way: A sensation that the knee is buckling or shifting, particularly when pivoting, changing direction, or stepping down from a curb or stair.
• Inability to return to play: Most athletes cannot continue the game or practice, even when the initial pain subsides.
• Loss of motion and quadriceps weakness: Difficulty fully straightening or bending the knee, along with rapid loss of quadriceps strength in the days following the injury.
• Pain, locking, or catching: Discomfort with twisting or squatting, or a knee that gets stuck, may signal an associated meniscus tear.

Accurate diagnosis of an ACL tear begins with a thorough evaluation by Dr. Rynecki Baker. She will take a detailed history of how the injury occurred and what activities now provoke instability, then perform a physical exam assessing motion, swelling, and quadriceps function, along with specific maneuvers, including the Lachman, anterior drawer, and pivot shift tests, that identify the degree of ACL insufficiency and rotational laxity.

X-rays are obtained to rule out fracture and to identify a Segond fracture, a small avulsion off the outer edge of the tibia that is strongly associated with an ACL tear. MRI is the gold standard for confirming the diagnosis and, just as importantly, for identifying associated injuries: meniscus tears, ramp lesions at the back of the medial meniscus, cartilage damage, bone bruising, and injury to the surrounding ligaments. In revision cases, a CT scan or alignment x-rays may also be needed.

Decisions about treatment, graft choice, associated injuries, and timing of return to sport all influence how the knee performs years later. Dr. Rynecki Baker’s training at both NYU Langone Health and Hospital for Special Surgery, two of the world’s leading orthopedic institutions, means patients are receiving care from a specialist with deep knowledge of knee mechanics and ligament reconstruction.

Her research focuses on what it takes to return to sport after ACL surgery. She has co-authored studies investigating psychological readiness to return to sport after ACL injury, also known as kinesiophobia, emphasizing her understanding not only the physical obstacles but also the mental ones that must be tackled in returning to sport. Her ongoing work examines quadriceps strength recovery after combined ACL and MCL reconstruction, helping refine how patients with more complex injuries are rehabilitated and cleared for sport.

She also brings a perspective few surgeons can offer: she has been on the other side of this operation. A former collegiate soccer player, Dr. Rynecki Baker underwent two ACL reconstructions of her own and completed the same long rehabilitation she now guides her patients through. She understands the mental side of an ACL tear as well as the physical one. She returned to play college soccer after her injuries, and she sets the bar just as high for her own athletes.