Patellar Fractures

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Original Editors - Lise De Wael, Stephanie Geeurickx

Top Contributors - Marie AVAU , Debby Decock, Ellen Van Dyck, Tamara Kindekens

Definition/Description

Patellar fracture is a very common knee injury. They can be divided into three types.
The first type is caused by direct violence and is called comminuted (this is a bone fracture that results in more than 2 separate bone components, the bone breaks into several pieces). These type of fractures are usually associated with a blow or a fall on a flexed knee.
The second type is caused by muscle violence and is called transverse. These type of frac-tures are usually associated with rupture of structures at the lateral site of the knee such as the collateral ligament.
Finally, the third type is a minor marginal fracture, which is usually caused by a fall on the knee. [10]

Approximately 1% of all skeletal injuries are patellar fractures. [1][2]
Thereby, fractures may be accompanied by a sprain or rupture of the ligaments or tendons that are attached to the patella. This injury can lead to stiffness, extension weakness, and patellofemoral arthritis.[11]

Clinically Relevant Anatomy

The patella is the largest sesamoïd bone in the body.
The patella is a triangular bone that is situated on the anterior surface of the knee at the distal end of the femur, it's a part of the articulatio patello-femoralis. In combination with the capsuloligamentar ligaments and the meniscus medialis and lateralis it forms the knee joint. .[17,13]
On the anterior side of the patella we can find: facies anterior, basis patellae and apex patellae. On
the posterior side of the patella we have: facies articularis patellae, one lateral and one me-dial separated by a ridge. On The basis patellae is the insertion of the quadriceps tendon and the apex patellae is the origin of the patellar ligament. The patella has the thickest articular cartilage of the body, it may be as thick as 1 cm. The patella is surrounded by several structures going from muscles to menisci. The two muscles that control the move-ment of the patella are the vastus medialis and the vastus lateralis. [5]

Epidemiology /Etiology

Because of its subcutaneous location, the patella is very vulnerable to injury. Patellar frac-tures occur as a result of a compressive force, a sudden tensile force (as occurs with hyper flexion of the knee), or a combination of these two causes. [16,17,13]
These fractures can be caused by direct blows to the knee in sports injuries or accidents, or from indirect stresses caused by twisting actions or violent contractions in the muscles sur-rounding the knee.[10,12]

As a result of these forces, various fracture patterns result, which depend on the mechanism of the injury.
The most common pattern is often described as transverse or stellate. (in this case the prox-imal blood supply may be compromised leading to avascular necrosis of the proximal seg-ment.)[14,16]
Less common patterns include vertical, marginal, osteochondral, and sleeve fractures (exclu-sively seen in the pediatric population).

Causes of fractures:
A direct blow to the patella: most often results in a stellate fracture. The compressive forces applied to the patella result in a comminuted pattern. The energy of the blow is absorbed by the fracture and causes damage to the articular cartilage of both the patella and the femoral condyles.
Another mechanism is a tensile force: this is sustained with hyper flexion of the knee, this is equal to an eccentric contraction of the quadriceps.
A combination of these two mechanisms: leads to a variety of other fracture patterns. A dis-placed transverse fracture can have “comminution”(see figure 3).[16,17,13

Characteristics/Clinical Presentation

Patellar fractures are classified in two groups: displaced or non-displaced, these 2 groups consist of several types.
Non- displaced fractures can be recognized when the broken bone is stable and has re-mained in place.
Displaced fractures, in which the pieces of broken bone have shifted out of position, logically these fractures are unstable.(transverse, vertical, comminuted or lower/upper pole)[10,15]

Differential Diagnosis

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Diagnostic Procedures

Sometimes the edges of the fracture can be felt through the skin. Normally one would also look for hemarthrosis, this is the swelling deep inside the joint. But there isn't some kind of specific test to identify a patellar fracture. We always need an X-ray to confirm the diagnosis. The X-ray can show front and side views of the fracture. 

Outcome Measures

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Examination

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Medical Management

Surgical treatment is usually used with a displaced fracture. Sometimes surgery is necessary because the thigh muscles are very strong and can pull the broken pieces out of place and apart from each other so callus cannot form and the healing with ossification is impossible. The type of procedure isn't always the same. It depends on the type of fracture you have. If you have a transverse fracture the most common procedure is to use pins and wires and 'a figue of eight' to press the pieces together. When you have a comminuted fracture, which is a type of fracture that is usually associated with a blow or a fall on a flexed knee, the small crushed pieces of the patella will be removed. When the kneecap is broken in its centre the doctor can use wires and screws to fix it. A patellectomy is the last treatment for a comminuted fracture. Nonsurgical treatment is indicated when the broken pieces of the patella aren't displaced. The patient need casts or splints to immobilize the fractured pieces so callus formation can take place. And you will also need crutches during the 6 to 8 weeks that the bone needs to heal completely. 

Physical Therapy Management

Treatment with heat and cold can be used to control pain and oedema. During the immobilization of the knee the patient is encouraged to train other leg muscles. After removing the cast or splint, and the fracture is considered healed, the therapy to regain range of motion starts.

There are instructions to prevent loss of motion and strength in adjacent joints. Ankle exercises are taught to promote circulation. 

The patients body decides the range of motion, strengthening, and proprioceptive exercises of the involved joint. 

Key Research

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Resources

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