X-rays rarely nail diagnoses of acute knee injuries. They are no substitute for a good history and physical, Dr. Steven Anderson said at a sports injury meeting sponsored by the American Academy of Pediatrics.
When treating acute injuries, focus on the effects of the injury--swelling, instability, deformity--and get a history to find out how the injury occurred, said Dr. Anderson of the University of Washington, Seattle.
"My receptionist can make the diagnosis of an acute knee injury with about 90% accuracy based on what she gets over the phone, so I hope we [physicians] can all do at least that well," he said.
Acute knee injuries usually involve a limited number of structures. When a patient presents with an acute knee injury, check these: bones and growth plates, ligaments, menisci, tendons, and bursa, Dr. Anderson advised.
Start by asking patients about the mechanism of the injury:
* Was it a contact or noncontact injury?
* Was there hyperextension or hyperflexion?
* Were there any noises--a snap, pop, or tearing sensation?
Then ask about specific mechanical symptoms.
* Can the patient bend and straighten the knee?
* Does it lock or catch?
* Does it buckle or give way?
Ask about the exact location of pain: medial, lateral, anterior, or posterior. These questions should provide most of the information needed to narrow down the diagnostic possibilities, Dr. Anderson said.
Some children with an acute knee injury have minimal pain or swelling, and can stand and walk, but if asked to do something more demanding--run, jump, or hop--they'll hurt or have functional limitations.
Although acute knee injuries don't always require x-rays, they may be helpful if the child is skeletally immature or if the diagnosis is uncertain after a history and exam.
"You will never be faulted for taking an x-ray on someone who has open growth plates with acute swelling in the knee," Dr. Anderson said, but he warned against reliance on images alone--the majority of serious acute knee injuries appear normal on x-rays.
The most common acute knee injuries are sprains to the anterior cruciate ligament (ACL), medial collateral ligament (MCL), and posterior cruciate ligament (PCL); patellar subluxation or dislocation; and meniscal tears. Pediatricians who are familiar with these areas should be able to accurately diagnose the majority of their pediatric patients with acute knee injuries.
* ACL injuries. "The typical history of an ACL is twisting or hyperextension," Dr. Anderson said. Most ACL injuries are noncontact and stem from pivoting or jumping, and are usually associated with a popping noise.
These injuries usually involve swelling, posterolateral pain, and a sense of instability when the patient tries to jump or pivot. There may also be pain or physical findings due to concurrent injuries to the MCL or meniscus.
Treatment includes short-term icing, compression, and a splint, but if the ligament is torn, surgical reconstruction is the treatment of choice to get children back to play, Dr. Anderson said. "This ligament doesn't heal by resting."
* Patellar subluxation/dislocation. Patellar problems are part of the differential diagnosis if the knee twisted and gave way. A patellar dislocation has a distinctive sound--like canvas ripping or tearing--as opposed to the discrete snap or pop of an ACL injury.
The patient will have tenderness on the medial patella and apprehension if it's nudged to one side. "You can just push the patella back in," Dr. Anderson said. "Some x-rays show a fragment but it's not important to get x-rays unless you think there's a fracture, and you don't fracture the patella by pivoting the knee."
The initial treatment is ice and compression, with optional use of crutches. Surgery is not indicated initially, but if stability problems persist, surgical procedures can stabilize or realign the patella.
* MCL sprain. This is a fairly common injury. It usually is caused by stress on the outside of the knee while the foot is planted.
The point of tenderness is typically over the adductor tubercle or proximal attachment of the medial ligament on the femur. Tenderness more distally should raise concern about a meniscal tear.
Once an MCL injury is diagnosed, keep evaluating the knee for associated injuries. MCL injuries often occur in conjunction with ACL injury or patellar subluxation. An isolated MCL injury can be treated effectively with rest that allows the ligament to heal and rehab exercises to regain strength and range of motion.
* PCL injuries. A blow to the anterior portion of a flexed knee can sprain the PCL. These injuries are most common in baseball or softball catchers or other athletes who spend a lot of time on flexed knees. Most sprains can be treated with rehab and bracing, but injuries with significant instability may require surgery.
* Meniscal tears. Meniscal tears can occur in isolation or with other injuries and are less common in children than adults, Dr. Anderson said. A meniscal tear usually causes localized pain and restricted motion, and there may be clicking, catching, or popping. The medial meniscus is more often injured than the lateral meniscus. A meniscal tear is the one acute knee injury that requires an imaging test--MRI is best--to confirm the diagnosis.
RELATED ARTICLE: Seven signs of serious harm.
1. Snap, pop, or tearing sensation at the time of injury.
2. Feeling that bones have shifted or given way.
3. Immediate swelling after injury.
4. Locking of the knee or restricted joint motion.
5. Visible deformity.
6. Cross instability.
7. Diminished sensation or circulation distal to injury.