Patella (kneecap) fractures (broken kneecap) are common injuries. About 1% of all broken bones are broken kneecaps.
Fractures of the patella are most often caused by a direct blow to the knee, such as a fall or motor vehicle accident.
Kneecap fractures can be simple or complex. Complicated patella fractures, which result in displaced pieces of bone, may require surgery.
Rehabilitation focuses on improving range of motion, building up muscle strength and decreasing knee stiffness. Recovery can take several months.
What is a kneecap/ Patella fracture?
A kneecap (patella) fracture is a break of the bone located on the front of the knee joint. The patella is a sesamoid bone: a round bone embedded in a tendon that shields and protects a joint. In the case of the patella, ligaments attach it to both the thigh muscles (quadriceps) and the shinbone (tibia).
In some cases, kneecap fractures can be accompanied by injuries to knee tendons and ligaments due to the initial impact to the knee.
Types of Kneecap Patella Fractures
The type of patella fracture depends on the mechanism and severity of the injury. It can be affected by your weight and general health.
Displaced and Nondisplaced Kneecap Patella Fractures
Nondisplaced kneecap fractures occur when the patella is broken but hasn’t moved out of place.
In displaced patella fractures, the patella is broken and the pieces of bone have moved out of place.
Closed and Open Kneecap Patella Fractures
A kneecap fracture is considered closed if the broken pieces of patella do not pierce the skin.
In open kneecap fractures, the bones stick out of the skin, creating a complex wound.
Comminuted, Noncomminuted and Hairline Kneecap Fractures
A comminuted patella fracture is one in which the bone is shattered into three or more pieces.
In a noncomminuted patella fracture, the kneecap is broken in two pieces.
A hairline kneecap fracture is a simple crack in the bone (the patella is still in one piece). Hairline fractures are also known as stress fractures, and are rare in the kneecap. They can occur in athletes, such as marathon runners, and may be due to overuse. A stress fracture of the patella may be difficult to see on an X-ray. The main symptom is pain in the front of the knee that gets worse over time.
Patellar Sleeve Fractures
Patellar sleeve injuries can affect children, most commonly between ages 8 and 12 when the bony portion of the knee is still forming. The injury happens when the bony part of the patella gets pulled out of its sleeve of cartilage. The bone is not broken, so technically this is not a fracture, although it is treated in a similar manner.
What causes kneecap Patella fractures?
Patella fractures are injuries often associated with a blow to the knee. Common causes include:
Falling directly on the knee, especially on a hard surface such as concrete
Sports where the knee may be directly hit by a ball, bat or stick
Car accidents where the knee hits the dashboard
Sudden contractions (pulling) of the quadriceps muscle that causes the tendon to pull on the kneecap and break it apart
Kneecap Fracture Symptoms
The symptoms of a patella fracture may include:
Pain around the kneecap or in the knee
Swelling, which can be severe, even with relatively minor kneecap fractures
Inability to bend or straighten the knee or to hold the leg out straight
Inability to bear weight, stand or walk
Deformed appearance of the knee, especially with severe fractures
Bone protruding from the skin of the knee in the case of an open patellar fracture
If you have these symptoms after hitting or injuring your knee or leg, call your doctor or visit an urgent care clinic for an examination.
Kneecap Fracture Diagnosis
Your doctor may use some of the following techniques to determine if you have fractured your patella:
History: The doctor will ask you about any recent trauma, such as sports injuries, automobile accidents or falls.
Physical examination: The doctor will examine the knee and check for deformity that can be felt through the skin such as gaps or edges of bone.
The doctor may put mild pressure on the kneecap, and may bend or straighten the leg to see if those actions cause or increase pain or reveal a deformity.
X-rays help the doctor identify a fracture and see if there are fragments.
Treatment for a Fractured Kneecap
Treatment for patella fracture varies depending on how severe the break is, as well as your age, health and other factors.
Patella fractures can cause extensive bleeding into the joint. Emergency treatment may include draining blood and fluid from the joint to reduce swelling and pain and to make it easier to diagnose the problem.
Nonsurgical treatment is typically recommended for more stable patellar fractures or less severe breaks and may include:
A cast or splint to hold the leg in place while the bone heals
Preventing or reducing weight-bearing
Pain medications (opioid pain medication may be appropriate for the first few days after a severe kneecap fracture, followed by non-opioid options)
Physical therapy and walking aids to help you regain strength and independence.
Surgical treatment is typically recommended for more severe kneecap fractures. Surgical repairs may:
Use screws, pins and wires to hold larger pieces of patella together
Remove fragments of bone that are too small to reattach. In very severe comminuted fractures, removal of part or all of the kneecap may be necessary, but the surgeon will attempt to preserve and reattach as much of the kneecap as possible.
Address damage to the patellar ligament and other structures in the knee joint associated with the fracture (for example, in the case of an open fracture where bone pieces have damaged the skin and soft tissue)
Recovery and Complications After a Patella Fracture
The knee is a complex joint that bears weight. Even after treatment, you may experience continued pain and reduced range of motion. Post-traumatic arthritis (thinning of cartilage due to trauma) of the knee is a common complication of patella fractures and other knee injuries.
After weeks or months of immobilization with a cast or splint, there may be muscle loss (atrophy) in the leg. Physical therapy can help minimize atrophy and prevent it from becoming permanent, as well as recover muscle strength, flexibility and range of motion. Physical therapy and occupational therapy may also be recommended if you had surgery to repair the kneecap.
Depending on your age and health, it takes about three to six months to recover from a broken kneecap, but very severe patellar injuries may take longer.
For a time, you may be advised to avoid climbing stairs, squatting, kneeling or other activities that place strain on the knee joint. In most cases, you should still be able to walk with a fractured kneecap while the knee is immobilized and healing. Your care team will recommend exercises and weight-bearing restrictions appropriate for each stage of recovery.
Persistent pain or severe post-traumatic osteoarthritis in the knee can call for continued reassessment and further surgery, including knee replacement.
The patellar tendon is the structure that connects the kneecap (patella) to the shinbone (tibia). A ligament is a structure that connects one bone to another bone, and therefore some people refer to this as the patellar ligament.
However, this structure is really connecting the quadriceps muscle to the shin bone, and a tendon connects muscle to bone, and therefore patellar tendon is the more common description.
The patellar tendon is an important part of the extensor mechanism of the lower extremity. The extensor mechanism includes the quadriceps muscle, quadriceps tendon, patella (kneecap), and patellar tendon. These structures function together to allow the knee to straighten, and can do so with significant force.
The extensor mechanism is critical to normal functions ranging from walking and stair climbing to athletic activities including running and kicking. Without an intact extensor mechanism, all of these activities can become difficult to perform.
Patellar Tendon Tear Symptoms
The typical individual who sustains a torn patellar tendon is a young, male athlete. As more middle-aged people are remaining physically active, this injury is becoming more common in an older population.1
The injury usually involves an awkward landing from a jumping position where the quadriceps muscle is contracting, but the knee is being forcefully straightened. This is a so-called eccentric contraction and places tremendous stress on the tendon.
Athletes who sustain the injury may feel a snapping or popping sensation and will typically be unable to walk following the injury.
The typical signs of a torn patellar tendon include:
Pain directly under the kneecap
Swelling and bruising in the front of the knee
A defect, or soft spot, where the tendon should be tight
Difficulty walking or doing sports activities
It has been found that in nearly all patients who sustain a patellar tendon rupture there is abnormal tendon tissue consistent with a chronic tendinosis.2 The patellar tendon is usually injured in the watershed region of the tendon, where blood flow to the tissue is poor, and the tendon is weakest.
Tendon tears can also occur in non-athletic settings. Usually, there is a reason for the patellar tendon to be weakened in these individuals, such as a systemic disease that weakens tendons or recent surgery on the knee the caused tendon weakening. Treatment is usually similar in athletes and non-athletes alike.
Making the diagnosis of a torn patellar tendon is usually obvious on clinical examination. People who tear the tendon will be unable to extend their knee against gravity, and unable to perform a straight leg raise test. The examiner can usually feel the gap in the tendon, just below the kneecap.
An X-ray will be obtained, as a patellar fracture can cause similar symptoms, and should be excluded as a possible diagnosis. On the X-ray, the patella is usually up higher when compared to the opposite knee, as the quadriceps pulls up on the kneecap, and nothing is holding it down in its normal position.
While often not needed, an MRI may be used to confirm the diagnosis and inspect the knee for any other damage that may have occurred.1
A torn patellar tendon does not heal well on its own, and left untreated will lead to weakness of the quadriceps muscle and difficulty with routine activities, including walking. Surgery to repair the torn tendon is relatively straightforward in concept but can be difficult to perform.
The torn ends of the tendon need to be sewn together. The difficulty lies in the fact that it is important to restore proper tension to the tendon, not making it too tight or too loose.
Also, it can be difficult to get a good repair, especially if the tendon has torn directly off the bone. In these situations, the sutures used to repair the tendon may have to be attached directly through the bone.1
Recovering from a torn patellar tendon is difficult and takes time. One of the most important prognostic factors for recovery is the time to surgery, and surgery delayed beyond a few weeks can limit recovery ability.
It is known that early mobility after surgery, protected strengthening, and preventing excessive stress on the repair will speed overall recovery. Even with these steps, there is a minimum of three months until the return of normal daily activities, and four to six months until sports should be resumed.3
While most people heal completely from a patellar tendon surgery, there can be long-term weakness even with a successful repair.
Athletes who are attempting to return to competitive sports may take a year or longer to return to their preinjury level of function. Performing guided physical therapy can be helpful to ensure athletes are able to resume their normal sports activities.