*IMPORTANT: Contact us immediately if you have been diagnosed with or suffered a patella fracture or patella tendon rupture. Ideally, surgical fixation of a patella fracture should take place within two (2) weeks of the initial injury. To schedule an appointment with Dr. Dold, click here. A member of our team will be in contact with you soon – usually within an hour of receiving your request if within regular business hours. Your care should be expedited!*

Patella fractures comprise 1% of all fractures. The critical element to examine on physical examination of a patient with a patella fracture is their extensor mechanism via straight leg raise or knee extension. Treatment options vary based on fracture displacement, classification, and patient factors. Traditionally, nonoperative treatment has been reserved for non-displaced fractures. Many operative treatments are available with differing indications and levels of success. Tension band constructs have been the most commonly employed approach to fixation, with cerclage wiring for comminuted fractures. Recently, both cannulated screws with high-strength suture constructs and plate fixation of patella fractures have become more popular. Plating constructs offer a low-profile design with stable fixation, allowing for earlier mobilization and potentially improved functional outcomes. Data regarding the long-term outcomes of plating techniques are limited, and further studies are needed. Ideally, operative management for displaced patella fractures occurs within 2 weeks of the initial injury.

Anatomy

The patella is the largest sesamoid bone within the body. The superior 3/4 of its posterior surface is covered by articular cartilage, the thickest articular cartilage in body (up to 1cm thick). The inferior 1/4 is devoid of cartilage. It is located at the anterior aspect of the knee and has several functions. One of the functions is to provide protection for the knee, another is to provide an insertion point for the quadricep muscle proximally and the patellar tendon distally, and the most important is that it serves as a fulcrum to maximize efficiency throughout extension of the leg. Without an intact patella, the extensor mechanism is unable to function. The posterior aspect of the patella is composed of thick hyaline cartilage that allows the patella to glide smoothly within the trochlear groove of the femur. It contains a vertical ridge that separates the patella into medial and lateral facets. Often, the superior lateral aspect of the patella fails to fuse, resulting in a bipartite patella which is often mistaken for a fracture. A bipartite patella occurs in approximately 2-3% of th population. Patellar fractures account for approximately 1% of all fractures and more commonly occur in men.

Pathogenesis

Dynamic forces are seen across the patella. Quadriceps contraction extends the leg, creating tension across the patella. The opposite occurs when the knee moves into flexion and compression is seen across the patella. Rapid change in forces can cause the patella to fail and ultimately lead to compromise of the bone leading to a fracture. If the quadricep is contracted and rapid knee flexion occurs, this creates failure in compression and can lead to avulsion fractures or transverse fractures across the patella with displacement of the fracture. There are seven different classifications for patellar fracture, all of which rely on where the fracture occurs and the orientation of the fracture; nondisplaced, transverse with displacement, inferior pole, comminuted without displacement, comminuted with displacement, vertical, and osteochondral.

Presentation

Patella fractures occur via one of two unique mechanisms: (1) Direct impact due to fall, dashboard injury, or other high energy mechanism and (2) indirect eccentric contraction, which occurs from rapid knee flexion against a contracted quadriceps muscle. This causes failure in tension and often results in a transverse fracture or inferior pole avulsion. The patient will present with difficulty walking and often requires crutches . Inspection can evaluate for any soft tissue trauma around the kneecap and can help identify if the injury is open, which would necessitate more urgent surgical management. Further evaluation can reveal a gap within the patella where the fracture has occurred. It is of critical importance to assess the extensor mechanism of the knee through straight leg raise (SLR) or extension of the knee from a flexed position. If the extensor mechanism is intact, this typically indicates that the fracture is non-displaced and can often be managed non-operatively. If the patient is unable to attempt a straight leg raise due to pain, the physician can aspirate a hemarthrosis and inject local anesthetic for pain relief. 

Imaging

Standard plain film radiographs (X-rays) are the initial study of choice to assess a patella injury. These films will be able to visualize the fracture and the location within the patella. Normal AP and lateral films are required to help check for any significant displacement of the fracture fragments. An axial view (sunrise/merchant views) is best to see a vertical fracture. The radiographic assessment should include classification of the patella fracture, including fracture displacement, patella alta, and patella baja. An articular step-off greater than 2-3 mm and displaced fracture gap greater than 3mm dictates the need for operative management. A CT scan is occasionally indicated in the work-up of a patella fracture. The primary indications for a CT scan are: (1) suspected distal pole comminution, (2) patellar stress fracture, (3) a nonunion or malunion. An MRI is not typically indicated. 

Treatment

Treatment of patellar fractures is divided by non-operative and operative management, based on both fracture and patient factors. The obvious goal is to restore the extensor mechanism of the knee. The indications for non-operative management are:

  1. intact extensor mechanism (patient able to perform straight leg raise)
  2. nondisplaced or minimally displaced fractures (2-3mm of step-off and 1-4mm of fracture gap with the extension mechanism intact)
  3. vertical fracture patterns
  4. significant medical co-morbidities

Non-operative management involves placing the knee in a knee immobilizer, hinged knee brace, or cast in extension with full weight bearing. Crutches can be utilized for support.

The indications for surgery include:

  1. extensor mechanism failure (unable to perform a straight leg raise)
  2. open fractures (requires urgent surgical attention)
  3. fracture articular step-off > 2-3 mm
  4. displaced articular patella gap > 3 mm
  5. loose bodies within the knee joint
  6. osteochondral fractures
  7. patella sleeve fractures in children

Many operative treatments are available with differing indications and levels of success. Tension band constructs have been the most commonly employed approach to fixation, with cerclage wiring for comminuted fractures. Recently, both cannulated screws with high-strength suture constructs and plate and screw fixation of patella fractures have become more popular. Plating constructs offer a low-profile design with stable fixation, allowing for earlier mobilization and potentially improved functional outcomes. Data regarding the long-term outcomes of plating techniques are limited, and further studies are needed. Ideally, operative management for displaced patella fractures occurs within 2 weeks of the initial injury. The goal is to preserve the patella at all costs!

Modern treatment options include internal fixation using tension bands with Kirschner wires or cannulated screws, lag screw fixation, partial patellectomy, and rarely total patellectomy. Nondisplaced, closed patellar fractures or fractures with less than 2-mm articular steps can be successfully treated conservatively. Open fractures, articular step of 2 mm or greater, and loss of knee extension are indications for surgical intervention.

*IMPORTANT: Contact us immediately if you have been diagnosed with or suffered a patella fracture or patella tendon rupture. Ideally, surgical fixation of a patella fracture should take place within two (2) weeks of the initial injury. To schedule an appointment with Dr. Dold, click here. A member of our team will be in contact with you soon – usually within an hour of receiving your request if within regular business hours. Your care should be expedited!*

Related Research