Patellar Fracture
A break in the kneecap at the front of the knee
Quick Facts
- Type: Bone (fracture) injury
- Main area: The kneecap, front of the knee
- Common causes: Falls onto the knee, direct blows, dashboard injuries
- Key sign: Trouble straightening or lifting the leg
Overview
The patella, or kneecap, is the small bone at the front of the knee that sits within the tendon of the thigh muscles and protects the joint while improving the leverage of the muscles that straighten the knee. A patellar fracture is a break in this bone, most often caused by a direct impact such as a fall onto the knee or a blow against a hard surface.
Because the kneecap is essential for straightening the knee, a fracture often makes it hard or impossible to lift or straighten the leg. Fractures range from a clean crack with the pieces still in place to breaks where the fragments are separated or shattered. Treatment depends on the pattern, and recovery requires protecting the knee while gradually restoring movement and strength.
Symptoms
Symptoms usually begin immediately after the injury and center on the front of the knee.
- Pain and swelling at the front of the knee
- Difficulty or inability to straighten the knee or lift the leg straight
- Trouble walking or bearing weight
- Bruising around the kneecap
- Tenderness directly over the kneecap
- Sometimes a palpable gap if the fragments have separated
An inability to straighten the knee against gravity is an important sign, as it suggests the kneecap and its tendon attachments can no longer do their job.
Causes
Most patellar fractures result from a force applied directly to the kneecap or from a strong muscle pull.
- Direct impact: Falling directly onto the knee, a blow during sport, or the knee striking a dashboard in a car crash.
- Strong muscle contraction: A forceful pull of the thigh muscles can crack the kneecap in some situations.
- High-energy trauma: Such as motor vehicle collisions, which can cause more severe, shattered fractures.
- Weak bone: Less commonly, fractures occur with less force in bone weakened by disease.
Risk Factors
- Falls, especially in older adults
- Contact and high-impact sports
- Motor vehicle collisions
- Osteoporosis or other conditions that weaken bone
- Activities with a high risk of direct knee impact
Diagnosis
A clinician diagnoses a patellar fracture from the history, examination, and imaging.
- Physical exam: Checking swelling, tenderness, any gap in the kneecap, and crucially whether you can straighten the knee or lift the leg.
- X-rays: The main test, showing the break and how far the fragments are separated, including special views of the kneecap.
- CT scan: Sometimes used for complex or shattered fractures to plan surgery.
- Assessment for other injuries: Checking the surrounding ligaments, tendons, and skin, especially after high-energy trauma.
Treatment
Treatment depends on the fracture pattern and whether the pieces are displaced.
- Non-surgical treatment: If the bone fragments are still in place and you can straighten the knee, the leg is held straight in a cast or brace while the bone heals, followed by gradual rehabilitation.
- Surgery: If the fragments are separated, the knee cannot be straightened, or the bone is shattered, surgery is usually needed to put the pieces back together and hold them with wires, screws, or plates. In some severe cases, a portion of the kneecap may be removed.
- Rehabilitation: Physical therapy restores knee movement and rebuilds quadriceps strength, progressing as the bone heals.
- Pain relief and weight-bearing: Managed according to the injury and treatment, often with crutches and a brace early on.
Healing typically takes several weeks to a few months, and regaining full strength and motion can take longer.
Prevention
- Use protective knee pads in sports and high-risk activities
- Wear seatbelts to reduce dashboard knee injuries in car crashes
- Reduce fall risk at home with good lighting, removing clutter, and handrails
- Maintain bone health with adequate calcium, vitamin D, and weight-bearing exercise
- Keep the leg muscles strong for stability and balance
- Address balance problems, especially in older adults
When to See a Doctor
Seek medical care promptly after any significant knee injury, especially if you cannot straighten the knee or lift your leg, cannot bear weight, or have severe pain, swelling, or a visible deformity of the kneecap. Go to emergency care for an open wound over the kneecap with bone visible, a knee that is clearly deformed, or signs of poor circulation such as a cold, pale, or numb lower leg, as these need urgent treatment.
Frequently Asked Questions
How do I know if my kneecap is broken?
Signs include immediate pain and swelling at the front of the knee, trouble bearing weight, and especially difficulty or inability to straighten the knee or lift the leg straight. There may be bruising or a palpable gap. An X-ray is needed to confirm the fracture, so seek prompt medical assessment after such an injury.
Does a broken kneecap always need surgery?
No. If the bone fragments are still in good position and you can straighten the knee, it can often be treated by holding the leg straight in a cast or brace while it heals. Surgery is needed when the pieces are separated, the knee cannot be straightened, or the bone is shattered.
How long does a patellar fracture take to heal?
Bone healing usually takes about six weeks or more, and many people need several weeks to a few months before returning to normal activities. Regaining full knee movement and quadriceps strength through physical therapy can take longer, and recovery time varies with the fracture and treatment.
When is a kneecap injury an emergency?
Seek emergency care for an open wound over the kneecap with bone showing, a knee that looks clearly deformed, severe uncontrolled pain, or signs of poor circulation such as a cold, pale, or numb lower leg. These situations need urgent treatment to protect the leg and joint.
References
- American Academy of Orthopaedic Surgeons (AAOS). Patellar (Kneecap) Fractures.
- Mayo Clinic. Broken bones (fractures).
- MedlinePlus, U.S. National Library of Medicine. Patella fracture.
- OrthoInfo, AAOS. Kneecap Fracture.