knee dislocation…it’s about the complication

Sunday, October 28, 2012

When a joint is injured, it’s all about the complications, especially when the knee dislocates. The tibia is literally torn from its relationship to the femur and at least three of the four ligaments that hold the knee stable (ACL, PCL, MCL. LCL) have been torn. It is a gruesome injury and Marcus Lattimore, the University of South Caroline running back, has the distinct displeasure of suffering his injury on national television and knowing that it is being rebroadcast on a variety of websites with the “don’t watch this if you have a weak stomach” disclaimer. At least the doctors caring for Mr. Lattimore can review the mechanism of injury and predict the potential disaster that might come his way. The knee can dislocate in many directions but for Mr. Lattimore, the knee was hyperextended or bent so far the wrong way that everything inside tore. The CBS Sports headline read: “Official word on Lattimore injury: extensive ligament damage, no fracture.” While the focus may be on the bones, joints and torn ligaments, it’s all about the blood and evaluating the artery.

Arteries run along the back of the thigh hugging tight to the femur and passing across the back of the knee to then supply the lower leg and foot with blood. The femoral artery in the thigh is connected to the popliteal artery (in the back of the knee) that is connected to the anterior tibial, posterior tibial and peroneal arteries in the lower leg. When the knee dislocates, the popliteal artery is stretched and can potentially be damaged. Like any other part of the body, should blood supply be lost to the lower leg, muscles start to die. There are just a few hours to recognize the situation and repair the artery or else the complication is potential amputation and loss of the leg. Unfortunately, it’s not that simple and straightforward.

In the case of an isolated injury like Mr. Lattimore, the focus can be placed just of the knee but too often, knee dislocations occur in major trauma victims and other life threatening injuries may take precedence and distract the trauma team from appreciating the severity of the knee injury. Making it even more of a challenge is that knee dislocations often reduce themselves, meaning that the bones have realigned; the trauma patient is usually lying flat on their back and the knee can appear normal on first blush.

Even recognizing the knee dislocation and appreciating the potential artery damage, the physical exam can fool the doctor. The diagnosis is easy if the foot is cool and no pulses can be felt. A vascular surgeon will have to repair the damaged artery to re-establish blood supply. But if the pulses in the foot can be felt, a false sense of security may suggest that the arteries aren’t damaged and disaster has been averted. So not true. Occult or hidden injuries to the popliteal artery may occur. A partial tear of the artery can allow blood flow initially, but soon the artery may clot and put the leg at risk.

The gold standard for making the diagnosis of a damaged artery is an arteriogram (CT angiography is closely catching up) where dye is injected into the artery to look at itsanatomy. Less invasive testing using ultrasound may be just as reliable, especially if it is coupled with close observation. But the most important first step is recognizing that the knee has been dislocated, then having the knee jerk response to look at the artery. Timing is everything. If the leg is without blood supply and the artery repair is delayed, by more than 8 hours, the amputation rate can be greater than 80%. Find the problem and operate within 6 hours allows amputations to drop to about 10%. The best news always is a normal artery is and then it’s all about the ligaments and bones.

Mr. Lattimore has a tough next few months. He has to begin pre-op physical therapy to keep his quads and hamstrings strong, make it through the surgery to repair the torn ligaments and finally, start the months of rehab to give him the opportunity to play football. There is no guarantee that the knee will recover enough to allow him to play again but he does have a role model. Denver Broncos running back, Willis McGahee, dislocated his knee in the 2003 Fiesta Bowl and is now in his ninth NFL season. Best wishes to Mr. Lattimore as he chases his NFL dream.

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