Patellar Fractures

Patellar Fractures

Patellar fractures can involve different topic, and I am going to try and highlight the important points related to patellar fractures. The medial patellofemoral ligament is the primary stabilizer of the patella, so when the patella dislocates, you will have an injury to that ligament and also an injury to the medial patellar facet articulation cartilage or an osteochondral fragment. In addition to the medial patellar facet injury, you will get a lateral femoral condyle injury. Bipartite patella occurs in about 8% of the population. It could be bilateral in about 50%, and it usually occurs in the superolateral aspect of the patella. You should observe it and not fix it. It is not an acute fracture that may need excision or lateral retinacular release. It can occur in children between 8-10 years old. It is a rare condition. The patient will be unable to do straight leg raising, so you suspect that the extensor mechanism is injured. The patient may have a high riding patella on x-ray with a palpable gap when you examine the patient. The x-ray may show small flecks of bone as the patellar tendon avulses with a portion of the distal pole of the patella. Sometimes the bony injury is so small that the condition can be missed. You should have a high index of suspicion. You may need to get an MRI to confirm diagnosis. The treatment is usually ORIF if the fracture is displaced.

The patella is a large sesamoid bone. The quadriceps muscle is inserted at the proximal pole and the distal pole gives attachment to the patellar tendon. The patella is triangular in shape. The proximal 3/4 of the patella is covered with cartilage, however the distal 25% of the patella is not covered with cartilage. The patella increases the power of the extensor mechanism by about 50% because it displaces the extensor mechanism anteriorly, and that will increase the moment arm.

Transverse fractures of the patella can be non-displaced or displaced. The patella can be pulled apart by the attached quadriceps tendon. The patient will be unable to do active extension of the knee. Upper or lower pole fractures of the patella are fractures at the site of attachment of the patellar tendon. Comminuted fractures of the patella can be non-displaced or displaced. Comminuted fractures have multiple pieces, are very unstable, and are difficult to fix. Vertical fractures of the patella are the most common, and they are stable and nondisplaced. Osteochondral fractures are small fractures of the patella usually associated with acute dislocation of the patella.

In examination, you may feel a palpable gap. The area of the knee is usually swollen. The patient will be unable to do straight leg raise. The lateral view of the knee is the best view to see the fracture. 2-3 mm of displacement will probably mean that the patient will need surgery.

If you think that the patient’s extensor mechanism is intact, and the patient is able to do straight leg raise, and the fracture is nondisplaced or minimally displaced, it is usually a transverse fracture in this situation, then immobilize the knee straight in a hinged knee brace for 4-6 weeks with weight bearing as tolerated. Sometimes the patient cannot move the knee because of the pan and injection of lidocaine inside the knee can help to assess the integrity of the extensor mechanism. If the patient has a total knee with 2mm displacement of the patella, and the extensor mechanism is intact, then the patient will be treated conservatively in a brace or in a knee immobilizer (no surgery).

Indication for surgery is a displaced patellar fracture and the inability to do straight leg raising.

First, preserve the patella (if possible). The tension band fixation technique is the gold standard for the treatment of displaced patellar fractures (the fracture is usually a transverse fracture), and the tension band technique is the one that gives us the most complications. The first step in the tension band technique is to reduce the fracture with reduction clamps. Next, at least two K-wires are placed across the fracture. An anterior tension band is applied, organized in a Figure-8 pattern. You need to put the Figure-8 tension band wire close to the patella superiorly and not far away from the patella because that may cause construct instability and fracture displacement. A second wire may be placed circumferentially around the patella. Bending the K-wires from both ends may decrease migration of the wires and decrease the complications. The wire that is bent at both ends may be difficult to remove. Tension band fixation technique may be done with K-wires or also with cannulated screws (through the cannulated screws, you place the wires). It does not matter if you have an open or closed fracture, you treat it the same way. When you place K-wires, it means symptomatic hardware and thus a secondary reoperation. It was found that the longitudinal screws and the tension band wires are a more superior fixation. The tension band construct when performed correctly will provide absolute stability and will convert the tension forces from the muscle pull into compression forces at the articular surface. You want to have anatomic reduction and stable fixation; don’t judge the reduction by what you see at the surface of the fracture. Try to see and feel the joint if you can. Check the x-rays carefully. The surface of the patella may be well reduced, however, the joint may be distracted or displaced. If you tighten the cerclage wire aggressively, you may have a good looking surface, but you may have a distracted join. After you fix the patella, you will do a range of motion of the knee before closure and give the patient a hinged knee brace, locked into extension with weight-bearing as tolerated. Weight-bearing is controversial. Some people start weight-bearing early, and some people start weight-bearing after 4-6 weeks. A can may be helpful to the patient. You will begin active flexion at 2-3 weeks (patient will lie prone, flexing and extending the knee). When the patient is prone, it avoids active knee extension and avoids excessive stress on the fracture site. At 6 weeks, you can unlock the brace and start moving the knee, gradually increasing the flexion.

If the patellar fracture is comminuted, you can use the peripatellar circumferential wire loop fixation, which is commonly used as an addition to other methods of fixation. You can also use a plate fixation utilizing a low profile implant and providing stable fixation. This technique is becoming more popular.

You can also excise the patella partially or completely. In a partial patellectomy, the distal pole is extra-articular, and if it is severely comminuted and less than 40% of the patella, then you can excise it (in general, you would like to preserve the patella). If you can’t preserve the patella and ORIF is not possible, then do partial patellectomy and preserve the largest piece. Partial patellectomy may be necessary, but open reduction and internal fixation (if possible) is associated with a better outcome. You will do the partial patellectomy in several comminuted inferior pole fractures. You will do medial and lateral retinacular repair, and a poor outcome may occur with removal of more than 40% of the patella. Total patellectomy will be done when the fractured patella cannot be fixed. Total patellectomy can cause extensor lag and loss of the extensor strength. The quadriceps torque is reduced by about 50%.

Symptomatic hardware and knee pain is the most common complication after patellar fracture fixation, especially if you use the tension band technique. It requires implant removal in about 50% of the time. This complication will include the hardware migration. Failure after patellar fracture fixation occurs in about 20% of the time due to increasing age, fixation with wires, technical errors and noncompliance.