Overview

A patellar fracture is a break in the kneecap — the small bone at the front of the knee that protects the joint and connects the front-of-thigh muscles to the shinbone. It usually happens from a direct fall onto the knee, a hard blow or a dashboard-style impact in a vehicle collision.

Because the kneecap is part of the knee's straightening mechanism, a patellar fracture is a serious injury. It can make straightening the knee — or even walking — difficult or impossible.

This Needs Urgent Care

See a doctor promptly after a fall or blow to the knee if you:

Cannot straighten the knee or hold it straight (a straight-leg raise)
Cannot stand or put weight on the leg
Have severe swelling, bruising or a visible gap or deformity over the kneecap
Have an open wound over the kneecap — especially if bone is visible or the wound goes down to the bone

These signs mean the fracture may be displaced or may have damaged the straightening mechanism, and treatment decisions need to be made promptly.

Types of Patellar Fractures

Stable (nondisplaced): the bone pieces stay in place, so healing can happen without surgery
Displaced: the broken ends separate and do not line up; the strong thigh muscles can pull the pieces apart during healing, so surgery is usually needed
Comminuted: the bone breaks into several pieces
Open: a wound penetrates down to the bone, which raises the risk of infection and requires urgent treatment

Symptoms

Pain and swelling at the front of the knee
Bruising
Difficulty or inability to straighten the knee
Difficulty bearing weight or walking

How It Is Diagnosed

After examining the knee and checking your ability to straighten it, a clinician will order X-rays from several angles to see the fracture and check alignment. In some people a harmless condition called bipartite patella (an extra bone fragment that never fused) looks similar on X-ray, which is why the images are read carefully — sometimes with the other knee for comparison.

Treatment

Treatment depends on whether the bone pieces are in place and whether the straightening mechanism still works:

Nondisplaced fractures are often treated without surgery: a cast, splint or locked brace keeps the knee straight while the bone heals, with weightbearing allowed in stages
Displaced or open fractures usually need surgery to put the pieces back together and restore the straightening mechanism, using wires, screws or plates
Open fractures need urgent cleaning and antibiotics because of the infection risk

Recovery

Rehabilitation matters regardless of whether surgery was needed. After a period of keeping the knee straight, a physiotherapist guides you through regaining range of motion and rebuilding thigh strength. Most people return to normal daily activities within 3 to 6 months, though severe fractures can take longer.

Long-term, some people experience posttraumatic arthritis, stiffness, quadriceps weakness or chronic front-of-knee pain. Some loss of motion is common but is not usually disabling.

References

American Academy of Orthopaedic Surgeons. "Patellar (Kneecap) Fractures." OrthoInfo. https://www.orthoinfo.org/diseases--conditions/patellar-kneecap-fractures
StatPearls. "Patella Fractures." https://www.ncbi.nlm.nih.gov/books/NBK513330/

This information is for education only and is not a medical diagnosis. InjuryAtlas does not replace an assessment by a qualified health professional. If you have severe pain, visible deformity, numbness, loss of function, or symptoms that are getting worse, seek medical care promptly.

Patellar Fracture