Patellar Fractures

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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

A doctor can diagnose a fracture of the patella by asking you about the details of your acci-dent and by examining you. He will inspect your knee, focusing on where it is tender, swol-len or misshapen. Then, he may also ask you to raise your leg or extend your knee, possibly after giving you a local anesthetic to eliminate pain. This helps the doctor to see if there are other injuries in and around your knee. [24]
Most of the times the individual reports pain during this examination of the affected knee.
Common causes that the patients may report for this pain are: an accident, a fall from height or a direct blow to the knee.[10]

The best way to exclude or include a patellar fracture is an X-ray, taken from several angles, to determine the extent of a fractured kneecap and to check for other injuries. If other inju-ries are suspected, a computer tomography (CT) or magnetic resonance imaging (MRI) scan may also be done. [24]

Diagnostic Procedures

A patellar fracture is suspected when there is a history of direct violence, when there are difficulties in standing or when there is a snapping sensation. In most cases there is straight leg raise inability and the inability to extend the knee.
Bruising and abrasion, the presence and site of tenderness, any palpable gap above or be-neath the patella as well as any obvious proximal displacement of the patella can indicate a patellar fracture.
Radiographs are necessary to clarify because there isn't some kind of specific test to identify a patellar fracture. Standard x-rays with special views of the patella are usually sufficient to diagnose a patellar fracture. However in more difficult cases where x-rays are not decisive, CT scan may be necessary. Associated injuries to nearby tendons and ligaments may need to be evaluated by MRI studies.[18,21,22,13]

Outcome Measures

The outcome depends primarily on the quality of articular restoration. Any intra-articular incongruities lead to the development of posttraumatic arthritis.
The prognosis of the injury depends on the amount of chondral damage at the time of injury. Functional outcome depends on the ability to achieve pain-free and stabile range of motion in an early stage.
Manipulation under anesthesia or the arthroscopic releasing of adhesions is required when athrofibrosis occurs.
Future treatment options may include osteochondral allograft reconstructions of the patella, for posttraumatic arthritis. Currently, several fixation methods of patellar fractures includes modified tension band wiring, Circumferential cerculage wires, and screw fixation and re-cently bioabsorbable fixation which may reduce the frequency of hardware symptoms.[18]

Examination

The clinical examination should include an inspection of the whole extremity. Clinical signs of a patellar fracture are swelling and pain in the knee joint. Wounds should be checked to con-firm whether the fracture is open or closed.
In displaced patellar fractures, a defect zone between the fragments may be palpable. Often there is a haemarthrosis of the knee. Flexion and extension in the knee joint is limited and painful. Active extension and lifting of the leg is usually impossible.
However, the ability to extend the knee does not rule out a patellar fracture, because the medial and lateral retinacula may be still intact.
Of course a check of the peripheral pulses, the compartments of the leg, and a neurological examination should always be performed. Special interest should be paid to potential ipsi-lateral concomitant injuries (e.g. acetabular fractures, femoral fractures or tibial fractures) which are signs of serious trauma.[19]

Medical Management

Surgical treatment is usually performed in patients with a displaced fracture and is carried out on an emergency basis if the fracture is open or if an associated traumatic arthrotomy is present.Sometimes surgery is necessary because the strong M. Quadriceps can pull the broken pieces out of place and apart from each other so callus cannot form. When this occurs, healing with ossification is im-possible.
The therapy procedure variates with the characteristics of the patella fracture. If you have a transverse fracture If the fracture is transverse, the most common procedure is to use pins and wires and 'a figure of eight' to press the pieces together (AO tension band wiring). A comminuted fracture is usually associated with a blow or a fall on a flexed knee, and causes the patella to break in several pieces. In this case, the small crushed pieces of the patella will be re-moved.(partial patellectomy). In addition, there is also a procedure called ‘complete pallac-tomy’. In this case the whole patella is removed and the tendon of the M. Quadriceps is at-tached to the ligamentum patellae, to ensure the function of the extensor apparatus. But, this is a relatively old procedure and its effects are controversial. (Günal L. et al ) [24]
A break in the center of the kneecap can be fixed using wires and screws. Note that a patellec-tomy is the last treatment for a comminuted fracture.
Operative treatment aims to restore extensor function, align articular incongruities, and al-low early motion (Fourati M.K. Level 2b: levels of evidence, Mehling, I. et al, Scolaro, J. et al. level of evidence 5, Zhongguo Gu Shang et al. level 2b: levels of evidence, Strauss J. MD Lev-el 5 :levels of evidence) [22, 18, 19,20, 25]

Nonsurgical treatment (Orthopeadic) is indicated when the broken pieces of the patella aren't displaced. The patient needs a casts or splints to immobilize the fractured pieces, this is done in vertical and horizontal fractures. In horizontal fractures, radiographs are taken at weekly intervals to exclude late separation of the pieces. so callus formation can take place. In this way the callus can form. Crutches will be used during the 6 to 8 week healing process.[7][8]
Once radiographic evidence indicates union and clinical signs of healing (nontender to palpa-tion) are present, the patient is changed to a removable brace.( Mehling, I. et al )[18]

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. 

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