Any fracture affecting the growth plate of bones in children can result in stopping growth. Disturbance of growth after fracture of the distal femur (bottom end of the thigh bone just above the knee) is a particularly vexing problem. That’s because this is where the fastest growth plate in the body is located. Young children can experience as much as a three-inch difference in leg length from a fracture of this type.
In addition to creating a difference in leg length from one side to the other, growth arrest affecting the distal femur can cause a change in the angle of the knee. Later, posttraumatic arthritis can occur because of the affect of the fracture on the joint itself. In this article, pediatric orthopedic surgeons from Cincinnati Children’s Hospital and Texas Children’s Hospital join together to explore treatment for fractures of the distal femur that affect the growth plate.
Growth plate fractures are diagnosed and classified using a standard model called the Salter-Harris (SH) classification. Fractures in this area are divided into four groups (SH I, II, III, and IV) depending on severity. Severity is determined by the number of bone fragments, presence of displacement (separation), and size of displacement.
As you might imagine, more severe fractures (SH III and IV) are the most likely to develop growth arrest, arthritis, and other complications. Assessment isn’t always easy. There can be more damage present than is visible with standard X-rays. As a precaution, any suspicion of growth plate disruption is treated with a full leg cast (up to the groin) for four weeks. Obese or young patients may need a full hip-to-foot (spica) cast to hold the leg still during the healing phase.
Surgery is advised whenever the fracture is displaced (even for SH I fractures). The pieces of bone are put back in place and held stable with wires, pins, or screws until healing has occurred. Wires are used for small fragments. Pins and screws are used for large bone fragments. The surgeon can place the hardware through the growth plate but must try and avoid going through the knee joint itself. The child is always put in a cast for at least a month (up to six weeks).
Besides growth arrest, infection is the next biggest concern with these fractures. Bacteria entering through the pin sites can travel along the pin tract to the joint. Every effort is made to avoid this nasty complication. When it occurs, the surgeon may have to perform another procedure (irrigation and debridement) to clean out the area.
One other potential complication to watch out for is vascular injury. Damage to the blood vessels supplying oxygen and nutrients to the growth plate can also arrest or disturb growth. The surgeon can check pulses and blood pressure of the foot and ankle to detect or monitor arterial injury. There are other more specific tests that can be done to assess blood flow such as a Doppler ultrasound or arteriogram.
The authors of this article advise monitoring for complications and especially for growth arrest for up to 12 months following a distal femur fracture in children who have not reached their full growth yet. Fracture position is also monitored with serial X-rays (taken weekly) during the first eight to 10 weeks.
Any sign that the fracture is not healing or healing in a misaligned position is an indication that surgery is needed.
In summary, every effort should be made to line up the joint surface during treatment for fractures of the distal femur. This will reduce the risk of growth arrest and/or the development of posttraumatic arthritis in young children who have not yet reached full skeletal maturity (i.e., they are still growing). Patients must be closely monitored for any potential complications including infection, loss of reduction (the fracture opens up again), loss of blood supply, and of course, growth arrest.