Pediatric Knee Injuries

Because the knee has a lot of strong ligaments around it and because the ligaments are considered stronger than bone in the pediatric population, there are more bony injuries and avulsion fractures around the knee in kids.  The patella is considered a sesamoid bone in kids and doesn’t ossify until 3-5 years of age. 

Distal Femoral Physeal Fractures

This is the most commonly injured physis around the knee.  Even so, it represents only 1 percent of all fractures in children.  Two thirds of these injuries are Salter-Harris type II fractures.  The mechanism of injury is direct trauma to the distal femur in a motor vehicle accident or a fall onto the flexed knee.  Some of these fractures occur during football when another player exerts a lateral blow to a foot that is firmly planted to the ground.  Indirect injuries can occur with varus or valgus forces.  Some can occur because of hyperextension or hyperflexion of the knee area.  An indirect force can result in separation of the epiphyseal plate.  This type of injury can occur in a breech delivery as well.  The area can be fractured under minimal trauma in cases of pathological weakness of the growth plate from osteomyelitis, myelodysplasia, or leukemia.

When the distal femur is fractured, the patient is unable to bear weight on the leg, with the exception of some low energy athletic injuries, in which the patient has a limp.  Often there is an audible pop at the time of injury and the knee swells quickly.  There is usually spasm of the hamstrings so that the knee is partially flexed.  There may be shortening of the leg or an angulation noted.  Neurovascular injury is possible and so must be evaluated at the time of injury and after reduction. 

X-rays of the front and side of the leg must be done along with oblique views which should show the presence of a fracture.  X-rays of the opposite side of the body can be done for comparison with the injured side.  CT scanning can be used to make the decision of whether to do surgery or not. MRI scanning can help define occult fractures and stress views can be done to differentiate between a ligamentous injury versus an occult fracture.  Ultrasound or an arthrogram may show the injury in some cases. 

Treatment involves closed reduction in cases of nondisplaced fractures.  If there is a lot of blood and fluid in the knee, it can be aspirated to reduce pain.  In general, the closed reduction should be done under general anesthesia to get a stable result.  The position of the immobilization depends on the direction of displacement of the fracture.  The individual can use crutches and toe touch weight bearing after three weeks of immobilization.  The cast can be removed at 4-8 weeks post injury. 

Surgery is necessary if there is an irreducible Salter-Harris II fracture.  Screws can be placed to hold the fracture fragments together.  If the reduction yields an unstable result, surgery is necessary.  Surgery is also necessary in Salter-Harris III and IV injuries to restore the joint to its normal position.  After surgery, a long leg cast is used with about 10 percent knee flexion.  Crutches and non-weight bearing can then be used for an additional 4 weeks.  A posterior splint can then be applied until the fracture heals.  Normal activities can be resumed in 4-6 months.

Complications include injury to the popliteal artery in hyperextension injuries, peroneal nerve injury and recurrent displacement of the fracture.  Late complications include instability of the knee due to ligamentous injury, angular deformity, and knee stiffness.

Proximal Tibial Fractures

Most of these injuries occur in adolescent boys.  This area is relatively protected from being fractured because of soft tissue in the area.  The mechanism of injury include direct trauma in a lawnmower accident or from an automobile bumper.  Indirect injuries are more common and occur when there is hyperextension, hyperflexion, or abduction forces such as is seen in an athletic injury, motor vehicle accident, a fall, or landing after a jump.  A fracture can happen in a breech delivery as part of a birth trauma and hyperextension of the knee.  There can be pathological fractures of this area as well.

When fractured, the patient cannot walk on the leg and may have a large amount of blood in the knee joint.  Hamstring spasm causes the knee to be a little bit flexed.  There is tenderness just distal to the knee joint and there may be a deformity of the affected area.  The person needs to be evaluated for a popliteal artery or peroneal nerve injury.  Compartment syndrome is possible.  There may also be ligamentous injuries associated with the fracture but they may not be diagnosed right away. 

X-ray of the front, side, and oblique aspects of the knee can show the fracture, especially if compared to the uninjured knee.  Stress views can show some fractures.  An MRI examination can help define soft tissue injuries and a CT scan can be done to better define the fractures of the growth plate.  If the popliteal artery is suspected to be disrupted, an arteriography may be necessary. 

Treatment may be nonoperative, especially if the fracture is nondisplaced.  A long leg cast is applied with the knee partially flexed.  Follow up x-rays should be done to see if any displacement has occurred. Displaced fractures may be reduced externally with the placement of a long leg cast.  The cast can remain for 4-6 weeks.  If healing is documented then physical therapy can begin. 

Surgery is necessary in displaced fractures that cannot be stabilized with external reduction.  For Salter-Harris III and IV injuries, surgery is required to repair the joint.  After surgery, a long leg cast is applied for about 6-8 weeks and then physical therapy is performed.

Complications include recurrent displacement, popliteal artery injury and peroneal nerve injury.  Late complications include an angular deformity of the fracture, and leg length discrepancy.

Tibial Tubercle Fractures

These fractures are commonly seen in athletes around 14-16 years of age.  The fractures can look like Osgood-Schlatter’s disease so this must be identified as to which is going on.  The mechanism of injury is usually indirect and results from a sudden acceleration or deceleration force involving the quadriceps muscle.  The patient usually presents with a limited ability to extend the knee.  The hamstrings are in spasm.  There is swelling and tenderness over the tibial tubercle.  There can be blood in the knee joint. X-ray of the front and side views of the knees can usually show the fracture.

Treatment is done without surgery in some cases.  A long leg cast is placed with the knee extended and molding around the patella.  The cast is placed for 4-6 weeks followed by placement in a posterior splint for another two weeks.  After than physical therapy begins. 

Surgery is required if the fracture is displaced and pins, screws or a tension band is used to hold the fracture segments together.  After surgery, a long leg cast is used for 4-6 weeks after which a posterior splint is used for another two weeks.  After that, physical therapy can be used to strengthen the knee. 

Tibial Spine Fractures

These are rare injuries that usually come from a fall from a bicycle.  The mechanism of injury is usually indirect and results from a rotational, hyperextension or valgus force on the knee. Direct injury leading to tibial spine fractures are uncommon and part of a multiple injury situation.  Patients often do not want to bear weight on the affected leg and there is often blood within the joint.  The medial and lateral collateral ligaments can be damaged as well. 

X-ray of the front and sides of the leg will often show the fracture. Stress views can be used to see if there is a ligamentous injury. 

The leg can be treated nonoperatively with immobilization of the knee for 4-6 weeks followed by active physical therapy.  Surgery is used in some cases with screws, pins, or sutures to hold the fracture segments together and restore alignment.  After surgery, a long leg cast is used for 4-6 weeks, after which physical therapy is begun. 

The main complications are loss of complete extension of the knee and instability of the knee.

Patella Fractures

These are very rare in children.  It is most commonly fractured because of a direct injury, such as is seen in a motor vehicle accident.  An indirect injury can occur with a sudden acceleration or deceleration force on the quadriceps muscle. 

Patients who have this cannot bear weight on the leg.  There is often blood in the knee joint and swelling/tenderness to palpation of the knee.  X-ray involves a frontal, side, and sunrise view of the patella. 

This can be treated without surgery if not displaced using a well molded cylinder cast with an extended knee.  The cast is removed after 4-6 weeks.  Surgery is used in displaced fractures and sleeve fractures of the patella. After surgery, the leg is kept in a well-molded cylinder cast for 4-6 weeks.  If the fracture is comminuted, part of the patella may need to be removed. 

Complications include weakness of the quadriceps muscle and post traumatic arthritis of the knee.

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