At 0100 HRS, EMS responded Code 3 (lights and siren) to a 23-year-old female lying on a sidewalk. She complained of severe pain to the left knee and leg, as well as numbness.
The patient advised the crew that she had left a bar with her friends and walked toward the parking lot. She stepped off a curb and then either tripped slightly or twisted her knee, falling to the ground. She experienced immediate pain, followed by a tingling sensation that extended down the leg and into the foot.
She denied any other injury. The past medical history was negative, and she was on no medications. She admitted to consuming alcohol, but she did not appear to be acutely intoxicated.
Physical assessment by the crew demonstrated a morbidly obese female in significant distress, complaining of pain in her left leg. She was alert and oriented. Blood pressure was 118/88 mmHg; the pulse rate was 110 and regular, respirations 18. There was no abnormality noted on the detailed survey, except for a "deformity of the left mid leg and knee and, surprisingly, apparent absence of distal pulses of the foot." The skin color and temperature of the lower extremity appeared normal.
An intravenous line was established, and 100 micrograms of fentanyl with 5 mg of diazepam were administered. The patient's leg was then placed in an air splint. End tidal carbon dioxide and pulse oximetry were monitored after the narcotic/benzodiazepine combination was given. Both remained normal.
The ambulance transported the patient Code 3 to the hospital, which was seven minutes away, because pulses could not be detected. No change was noted en route.
When later asked why this patient was transported Code 3 to an ED a close distance away at 1 a.m. with no traffic in the area, the crew responded, "We thought we only had an hour before the patient would lose her leg to an amputation."
Upon arrival to the emergency department (ED), the patient was promptly attended by the staff and the emergency physician. The patient was markedly obese. (Later assessment revealed her height to be 5'5" with a weight of more than 300 pounds). Dorsalis pedis and posterior tibial pulses seemed to be present but only intermittently both by palpation and doppler. The physician concurred with the findings of the EMS providers and was also very concerned about the examination of the knee. Aside from the left lower extremity, the physical findings were normal.
A radiograph was ordered of the left knee. A lateral view of the patient's x-ray is shown in Figure 1. What is your opinion as to the nature to the patient's injury?
The injury is, in fact, a posterior knee dislocation. Knee dislocations are defined by the position of the tibia, relative to the femur and are fairly uncommon. But they should never be confused with patella (knee cap) dislocations. Patella dislocations are usually minor injuries that are easily reduced often by the patient themselves and have very few complications. Knee (femur/tibia) dislocations are a very different animal.
Anterior tibial dislocations are reported to be somewhat more common than posterior dislocations. There are other even less common variants of knee dislocations, defined by the ultimate position of the tibia.
However, what is very unusual about this case is that the dislocation occurred in a previously non-injured knee, with seemingly minor trauma. Almost all knee dislocations are thought to result from very high velocity traumatic injuries, such as major motor vehicle crashes and long falls onto a flexed knee.
This patient likely fell onto her flexed knee after initially twisting it or tripping off the curb. What made this appear trivial was that she injured it stepping off a curb. However, her weight likely increased the force on her knee as she landed on it, and suddenly the mechanism became a high energy one.
Invariably, knee dislocations occur after severe disruption of the ligaments holding the knee in a normal position. Patients with this kind of injury can expect prolonged orthopedic care to repair the associated ligaments.
The most feared complication of knee dislocations, though, is vascular occlusion (or acute blockage of blood flow into the leg below the knee). The popliteal artery, which passes behind the knee in the popliteal fossa, is the most commonly injured artery. Some estimates place the risk of arterial occlusion as high as 50% of all posterior knee dislocations.
Signs of diminished or absent blood flow are usually present in these cases, but not always. The presence of an arterial occlusion may not be evident in up to 40% of vascular injuries associated with knee trauma. Arterial blockage may well persist despite prompt reduction of the tibia as happened in this case. This is because pressure on the blood vessel from the tibia will eventually cause a clot to develop in the vessel (or cause damage to its lining) continuing the flow problem after the tibia has been placed back in normal position.
A later complication related to an arterial blockage is the development of a compartment syndrome. Compartment syndrome can occur in any extremity in which there is continued, unrelieved swelling leading to muscle damage and further swelling. The accumulation of this fluid and the resultant increase in tissue pressure leads to death of extremity muscle, nerves and other blood vessels.
Compartment syndromes are typically treated by a surgical procedure known as a fasciotomy. A fasciotomy involves the placement of longitudinal incisions around the involved extremity to the level of the deep subcutaneous tissue (the fascia). The idea is to open the skin deep tissue and compartments decreasing the pressure on the nerves, blood vessels and muscles. This procedure then protects the underlying vital structures from death due to compression.
As soon as the posterior knee dislocation was confirmed by x-ray, both a vascular surgeon and an orthopedic surgeon were consulted. The knee dislocation was reduced (put back into normal position) by the emergency physician (see Figure 2).
Additionally, a dye study of the blood vessels of the knee and leg (angiogram) was obtained. This patient did demonstrate a blocked popliteal artery as a result of the knee dislocation (see the angiogram study in Figure 3).
The patient was taken promptly to the operating room. After a prolonged surgery, blood flow was restored to the lower leg. However, she did develop a compartment syndrome, requiring a fasciotomy.
Ultimately, she maintained good blood flow in the leg, and the fasciotomy prevented further compromise to the deeper structures of the leg. Rehabilitation services had a difficult time with the patient in her recovery, as she was quite resistant to participate in the necessary exercises to facilitate full use of her leg. However, primarily due to her therapists' continued efforts, the patient regained good function of her leg.
What Can We in EMS Learn from this Case
The take home point of this case is the importance of prehospital recognition of the presence of reduced or absent blood flow, despite the history of this particular injury. Indeed, the story would not suggest a posterior knee dislocation with subsequent risk of arterial blockage and compartment syndrome. Once that recognition took place, a prompt but non-emergent return to the hospital would have been quite sufficient and is always safer.