ConditionInjuries & poisoning
Fracture of the Patella (Broken Kneecap)
A fracture of the patella is a break in the kneecap, the small bone at the front of the knee that helps the thigh muscles straighten the leg. It usually results from a direct blow, such as a fall onto the knee or hitting a dashboard, or from a sudden forceful contraction of the thigh muscle. It causes immediate pain and swelling, and often you cannot straighten the leg or lift it. Undisplaced breaks heal in a brace, while displaced fractures usually need surgery.
Also called: Kneecap fracture, broken kneecap, patella fracture, patellar fracture
At a glance
- What it is
- A break in the kneecap.
- Causes
- Falls onto the knee, dashboard injuries, sudden powerful thigh muscle contraction.
- Key sign
- Pain and swelling at the front of the knee and difficulty straightening the leg or doing a straight-leg raise.
- Diagnosis
- Examination and X-rays, sometimes CT.
- Treatment
- A straight-leg brace for undisplaced breaks. Surgery with wires, screws or plates for displaced breaks.
- Recovery
- Bone heals in 6 to 8 weeks. Full strength often takes 4 to 6 months or longer.
When to get help
Call 911 or go to the ER
- An open wound over the kneecap with bone visible or bleeding
- A cold, pale or numb foot after a knee injury
- Severe, increasing pain and tightness in the leg (possible compartment syndrome)
See a doctor within a day or two
- A fall onto the knee followed by swelling and inability to straighten the leg or lift it while lying down
- A gap you can feel in the kneecap or just above or below it
- A knee that cannot bear weight after an injury
Book a routine appointment
- Knee pain that persists weeks after a fall onto the kneecap
- Stiffness or weakness that is not improving during recovery
Usually safe to manage at home
- A bruised knee after a minor bump, with full ability to straighten and walk
First aid for a suspected broken kneecap
- Keep the leg still and straight, supported on a pillow or rolled blanket.
- Apply ice wrapped in a cloth for 15 to 20 minutes.
- Raise the leg above heart level.
- Cover any wound with a clean dressing.
- Do not try to walk on it. Seek care in an urgent care center or ER.
- Call 911 if there is an open wound, deformity or numbness of the foot.
How the kneecap works
The patella sits within the tendon that connects the quadriceps (front thigh muscles) to the shinbone. It acts like a pulley, increasing the leverage of the quadriceps as they straighten the knee. This extensor mechanism is what lets you kick, climb stairs and stand from a chair. A displaced patella fracture breaks this mechanism, which is why straightening the leg becomes impossible.
Types of patella fracture
| Type | What it looks like | Typical treatment |
|---|---|---|
| Undisplaced (stable) | Bone pieces remain in place | Brace, no surgery |
| Displaced | Pieces separated by more than about 2 to 3 mm | Surgery |
| Transverse | A crack across the middle, the most common pattern | Often surgery if displaced |
| Comminuted | Shattered into three or more pieces | Surgery |
| Pole (sleeve) fracture | Small piece pulled off the top or bottom edge | Depends on displacement |
| Open | The skin is broken over the fracture | Urgent surgery and antibiotics |
A bipartite patella, where the kneecap has naturally developed in two pieces, can look like a fracture on X-ray but is a harmless variation.
Symptoms
- sudden knee pain at the front of the knee
- rapid knee swelling and bruising
- difficulty or inability to straighten the knee or do a straight-leg raise
- difficulty walking or bearing weight
- a deformity or gap you can feel in the kneecap
Diagnosis
A doctor examines the knee and asks you to lift the straight leg while lying down to test the extensor mechanism. X-rays from the front, side and an angled "sunrise" view confirm the fracture and show displacement. CT helps plan surgery for complex breaks. MRI may be used if a tendon rupture or cartilage injury is suspected. Similar symptoms come from a quadriceps tendon rupture or patellar tendon rupture, which are distinguished on examination and imaging.
Treatment
Nonsurgical
Undisplaced fractures with an intact extensor mechanism are treated with:
- a hinged knee brace or cylinder cast locked straight for about 4 to 6 weeks
- weight bearing as tolerated with the knee straight, often with crutches at first
- gradually adjusting the brace to allow more knee bending, guided by your surgeon
- physical therapy to restore movement and strength
Surgery
Displaced, comminuted and open fractures usually need surgery to restore a smooth joint surface and the extensor mechanism:
- Tension band wiring: pins and a figure-of-eight wire hold the pieces together.
- Screws or plates: used alone or in combination, especially for comminuted fractures.
- Partial patellectomy: removing small, unrepairable fragments and reattaching the tendon.
- Total patellectomy: rarely needed today.
Hardware sometimes irritates the skin and may be removed after healing.
Recovery timeline
- 0 to 6 weeks: brace locked straight or limited bending. Ankle and hip exercises, and isometric quadriceps tightening.
- 6 to 12 weeks: bone usually healed. Gradually increase bending and start strengthening with physical therapy.
- 3 to 6 months: return to most normal activities.
- 6 to 12 months: return to sports and full strength, depending on the injury.
Complications
- knee stiffness and loss of full bending
- quadriceps weakness
- pain at the front of the knee, especially kneeling
- painful or prominent hardware
- knee arthritis in the patellofemoral joint over time
- infection, delayed healing or non-healing (uncommon)
- blood clots during reduced mobility
Frequently asked questions
How do I know if my kneecap is broken?
Signs include immediate pain and swelling at the front of the knee after a fall or blow, bruising, and difficulty straightening the leg or lifting it while lying down. You may feel a gap in the kneecap. An X-ray is needed to confirm it.
Can you walk with a broken kneecap?
With an undisplaced fracture, you may be able to walk with the knee held straight in a brace. With a displaced fracture, walking is usually very difficult because the knee cannot straighten. Do not walk on a suspected fracture until it is assessed.
How long does a broken kneecap take to heal?
The bone usually heals in 6 to 8 weeks. Regaining full knee bending and thigh strength takes longer, with most people back to normal activities within 3 to 6 months and sports in 6 to 12 months.
Does a broken kneecap always need surgery?
No. Undisplaced fractures where you can still straighten the leg usually heal in a brace. Surgery is needed when the pieces are separated, the joint surface is uneven, or you cannot straighten the knee.
Is this the same as a patellar fracture?
Yes. Fracture of the patella, patellar fracture, kneecap fracture and broken kneecap all describe the same injury. See also patellar fracture for related information.
Sources
This guide was written from current patient and clinical guidance, including:
- American Academy of Orthopaedic Surgeons (OrthoInfo): Patellar (Kneecap) Fractures
- Orthopaedic Trauma Association: Patella fracture patient education
- NHS: Broken kneecap
- MedlinePlus: Kneecap fracture
- American Academy of Family Physicians: Fractures of the patella