Volume 6, Case 6
Loren G. Yamamoto, MD, MPH
Kapiolani Medical Center For Women And Children
University of Hawaii John A. Burns School of Medicine
This is a 16 year old male with a chief complaint of right knee pain. He was jumping off a bench when he struck his knee on a nearby shopping cart twisting it as he fell onto the concrete surface. He noted swelling of his knee and he was unable to bear weight on that side. He denies pain within the patella.
His past medical history is unremarkable.
Exam: VS T36.7 (oral), P70, R18, BP 115/70. He is healthy appearing and comfortable. He has no areas of tenderness except for his right knee which is visibly swollen. There are no abrasions, lacerations or visible bruises. Swelling can be palpated beneath (posterior to) the patella. The patella itself is not tender. There is limited and painful range of motion. The drawer sign is negative and his lateral stability appears to be good. The femoral condyles and the proximal tibia are non-tender. His mid femur and hip are non-tender. Function, sensation, pulses and perfusion are all intact distally.
He is told that he has a traumatic knee effusion probably due to a soft tissue injury. Radiographs of his knee are ordered to rule out a fracture. What is the likelihood that he has a fracture?
View knee radiographs: AP, Lateral, Oblique
View AP view.
View lateral view.
View oblique view.
AP, lateral, and oblique views of the knee are obtained. There is a non-displaced intercondylar fracture of the distal femur extending vertically. The fracture is only appreciated on the AP view. These radiographs demonstrate that it may be very difficult to see some fractures at the wrong angle. If a fracture is suspected, but not demonstrated on radiographs, consider obtaining other views to more definitively identify it.
An orthopedic surgeon was consulted by phone. He was placed in a long leg splint and orthopedic follow-up the next day was arranged.
Discussion
Fractures of the knee may be very obvious clinically, but some of them are not. Most radiographs of the knee will be normal, but it may be difficult to identify small fractures of the knee with only two views.
Fractures of the distal femur are uncommon injuries. These can be classified as supracondylar, condylar, intercondylar and physeal. Most of these fractures are large and are easily visible on AP and lateral radiographs. In our patient's case, the intercondylar fracture is small. Such intercondylar fractures often extend further superiorly forming a "T" or "Y" shape as they extend into the metaphysis of the distal femur.
Distal femur fractures are usually due to fairly severe trauma. They may be associated with ipsilateral hip fracture or dislocation, vascular injury, peroneal nerve injury or damage to the quadriceps insertions.
References:
The Distal Femur (Chapter 17). In: Simon RR, Koenigsknecht SJ. Emergency Orthopedics: The Extremities, third edition. 1995, Norwalk, CT, Appleton & Lange, pp. 267-272.