Growth Plate Injuries to the Knee
A growth plate injury is a fracture of the physis, an area of supple, delicate tissue found near each end of the long bones in a growing child. Fractures may be confined to the physis itself, or they may involve the metaphysis (bone shaft), the epiphysis (head of the bone), or both.
The growth plates determine the eventual length and shape of each long bone. During periods of growth, and particularly during an adolescent growth spurt, they are particularly vulnerable to damage as they are weaker than the surrounding ligaments and connective tissues. They are in fact the weakest part of the skeleton. Over time the cells in the physis harden, and by the time the child has stopped growing, the physis has been entirely replaced by solid bone.
Injuries to the growth plate are therefore unique to children and young people who have yet to finish growing. Boys are twice as likely as girls to suffer a growth plate fracture, primarily because girls mature physically at a younger age, but also because boys tend to be more physically adventurous. Children between the ages of 10 and 16 are most at risk.
About 30% of growth plate fractures happen as a result of direct trauma to the physis while playing competitive sports such as football, basketball or gymnastics. A further 20% of injuries are sustained during recreational activities. Overuse can also cause damage to the physeal tissues.
Less common, but not unknown, causes are:
- Abuse: A growth plate fracture is the second most common injury found in physically abused children.
- Steroids or other medications
- Bone infections
- Radiation treatment
- Neurological disorders
Because children heal so quickly, symptoms can be ignored. This is dangerous as lack of proper treatment can result in permanent damage to the growth plate, which may mean stunted or crooked limb growth.
A child or adolescent should never work through any joint pain. If your child complains of any of the following symptoms, arrange to see your doctor as soon as possible.
- Localized joint pain, particularly after a trauma
- Tenderness and warmth over the physis
- Inability to bear weight on the leg
- Knee may appear crooked in comparison with the unaffected leg
Your doctor will ask about the circumstances of the injury, and then perform a physical examination. The affected knee will be compared with the other knee. X-rays will be taken, usually of both legs: on an x-ray, a growth plate only shows up as a gap between the shaft and head of a bone. Taking an x-ray of each knee allows the doctor to compare the two. The results of x-rays can often be negative, in that the ends of the bone are not separated, but a diagnosis of an undisplaced growth plate fracture may still be made, based on tenderness of the physis.
Imaging tests such as CT, MRI and ultrasound clearly show the soft tissues and are often used as an aid in evaluating the type and extent of the injury.
The Salter-Harris classification system describes five types of growth plate fracture. There is now also the Peterson classification, which adds a sixth type.
Type I: The fracture extends from the bone shaft into the growth plate, separating the head of the bone from the shaft.
Type II: This common type of fracture involves part of the growth plate and the metaphysis, but not the epiphysis.
Type III: This uncommon fracture passes through part of the growth plate and breaks off a portion of the epiphysis.
Type IV: The fracture extends through the shaft, growth plate and end of the bone.
Type V: These rare fractures result from the end of the bone being crushed, thus compressing the growth plate.
Type VI: This type describes an injury in which a portion of the shaft, growth plate and end of bone is completely missing as a result of a wound.
If a growth plate fracture is sustained and treatment is delayed, permanent damage to the bone may result. Early diagnosis, treatment and careful follow up monitoring are extremely important in order to achieve the best outcome.
Treatment depends on the age of the child and the type of fracture. The knee is a particularly complex joint with many blood vessels and nerves that may be involved in a growth plate fracture. Damage to such structures can impair further bone growth. Younger children who still have more growing to do are at increased risk of stunted bone growth than older children whose physes are nearly closed. An orthopedic surgeon will often advise delaying surgery to repair a growth plate fracture until the child is older.
Type I, II, and V fractures are often treated by manipulating the bones to realign them, and immobilizing the leg in a cast or splint during healing. Sometimes the bones need to be surgically fixed with screws or pins to keep them in correct alignment while the fracture heals. Types III, IV and VI nearly always require surgery and immobilization in a cast for a few weeks or even a few months, depending on the type of injury.
Physiotherapy to strengthen the muscles surrounding the knee, to improve and maintain the function of the joint, is required once the cast has been removed.
Follow up treatment consists of x-rays every 3-6 months, for at least a year and sometimes until the bones have completely matured.
Occasionally bones respond to a fracture by growing excessively, leading to uneven leg length. These cases can be surgically treated to achieve similarity. A bone can also respond to a fracture by forming a bony bridge across the injured area that restricts normal bone growth or causes the lengthening bone to curve. This bridge can be surgically removed and replaced with another material such as fat or cartilage to prevent it reforming.
Due to the complexity of the joint, a growth plate injury to the knee carries the greatest potential for stunted or deformed bone growth. The long-term outcome depends on the severity of the original fracture, with Types IV, V and VI injuries being the most serious.
Most cases, about 85%, have an excellent prognosis and resolve successfully with no lasting damage.