Tibial Spine (ACL Avulsion) Fracture

Description

In this injury, the ACL, a major knee ligament, pulls off a piece of bone where it attaches to the top of the shin, instead of tearing in its middle. It is a children’s version of an ACL injury, usually from a twisting fall or a sports injury.

How it happens (the mechanism)

This usually happens from a twisting fall, a hard landing, or a fall from a bike. In an adult, that same force would usually tear the ACL itself. In a child, the ligament is actually stronger than the bone it attaches to, because that bone is still partly soft cartilage. So instead of the ligament tearing, the force pulls off the piece of bone where the ACL anchors, at the top of the shinbone. The ligament itself is usually intact, though it may be slightly stretched. If the piece lifts up, it can catch in the front of the knee and stop the knee from fully straightening, and the ACL is left loose. Putting the piece back where it belongs restores both the ligament's tension and the smooth joint surface.

What matters

The reassuring part is that the ligament itself is usually intact: it is the bony attachment that came loose, and reattaching bone restores a normal ligament. The priority is full knee straightening, because a lifted fragment can otherwise block the knee from extending.

Symptoms

A painful, swollen knee after a twist or fall, often with difficulty fully straightening it and a feeling of the knee giving way.

Doctor examination and imaging

The doctor checks knee motion, stability, and swelling; X-rays show the fracture, and an MRI or CT is sometimes used to judge the size and position of the piece.

Nonsurgical treatment

A piece that is barely lifted may be treated by gently straightening the knee and holding it in a cast or brace, with follow-up X-rays.

Surgical treatment

A displaced piece is usually reattached with a short camera-assisted (arthroscopic) operation using sutures or a small screw, restoring the ligament’s anchor and a smooth joint.

Recovery and long-term outlook

Healed in good position, the knee is typically stable and returns to sport. Rebuilding motion and strength, and regaining full straightening, are the focus of recovery.

When to call the doctor

Call the office right away if your child’s toes become numb, pale, blue, or cold; pain keeps worsening even after raising the leg and giving medicine; swelling does not improve with elevation; the cast feels too tight, cracked, or wet, or smells bad; or your child develops a fever.

Learn more

OrthoInfo (AAOS), Growth Plate Fractures: orthoinfo.aaos.org (opens in a new tab)

This information is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. For specific concerns about your child, consult a board-certified, fellowship-trained pediatric orthopaedic surgeon.

More for families

OrthoKids · POSNA

POSNA's OrthoKids: illustrated, family-friendly information on this condition.

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