Patellar Sleeve Fracture (Kneecap)

Description

A patellar sleeve fracture is a piece of cartilage and bone pulled off the edge of the kneecap — usually the lower tip — during a forceful straightening of the knee. It is a children’s injury, because a child’s kneecap has a cartilage “sleeve” that can peel away.

How it happens (the mechanism)

A sudden, powerful contraction of the thigh muscle can strip a sleeve of cartilage (with a small piece of bone) off the kneecap. Because a child’s kneecap is mostly cartilage that has not yet turned to bone, the X-ray may show only a tiny fleck even though a large cartilage piece has come loose — a classic injury that looks minor but is not.

What matters

The tell is function, not the size of the fleck on the X-ray: a child who cannot straighten the knee or hold it straight has disrupted the extensor mechanism, and that needs to be restored. Recognizing this is what prevents a significant injury from being dismissed as a small chip.

Symptoms

A painful, swollen knee with difficulty straightening it or holding it straight, often after a fall or jump.

Doctor examination and imaging

The doctor checks the ability to straighten the knee; because the X-ray can understate it, an ultrasound or MRI is sometimes used to see the cartilage piece.

Treatment

A truly non-displaced injury may be treated in a cast with the knee straight. A displaced sleeve fracture is usually repaired surgically to restore the kneecap and the ability to straighten the knee.

Recovery and long-term outlook

Recognized and treated properly, these do well, with the focus on regaining full, strong knee extension.

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

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.