knee dislocation disaster

Tuesday, August 30, 2016

While most injuries require some sort of significant trauma, bad luck may be the most ominous cause of disaster. Bad luck has befallen Vikings quarterback Teddy Bridgewater, who dislocated his knee without being touched. Normally, this injury requires high velocity and high impact because the knee joint is held stable by four ligaments in addition to the quadriceps and hamstring muscles.

knee dislocation anterior knee dislocation

Anterior Dislocation                              Posterior Dislocation

Knee dislocations are a big deal and should not be confused with kneecap (patella) dislocations, which are relatively common, affect women more than men because of anatomic and muscle attachment differences and are easily taken care of in the field or the ER. Knee dislocations, though, not only tear ligaments but also potentially tear the popliteal artery that supplies blood to the lower leg.

It is drilled into emergency doctors that a knee dislocation is an injury that can be missed, because the knee can relocate spontaneously before medical care happens. That can lull doctors into a false sense of security but that may lead to disaster. A missed diagnosis may lead to leg amputation if there is a damaged popliteal artery. For that reason, in addition to the orthopedic surgeon, a vascular surgeon usually gets involved in the evaluation and treatment of this injury.

Once the dislocation diagnosis is made, the next step is to evaluate the artery. There are different diagnosis options, whether it is repeatedly measuring blood pressures in the arms and legs (ankle-brachial index) or performing CT angiograms, the index of suspicion for artery injury needs to be very high. And that suspicion needs to be maintained for a few days, just in case there is delayed clotting in the artery.

Not every dislocation is the same. The four ligaments that hold the knee stable can be torn in different combinations depending upon the forces placed on the knee and the direction it dislocates. Regardless, the surgery to repair the ligament damage needs to happen within a few days of injury

This is not an injury that always gets better, even with the best of care. The prognosis for a “normal” knee, one which is stable and without pain happens about 60-70% of the time, 20% will have reasonable function and the last 20% will have a chronically painful, unstable knee.

Knee dislocation is the same injury that derailed the career of Robert Edwards in 1998. He was playing in an NFL flag football game as part of that year’s Pro Bowl events when he was injured. It took four years for him to rehab and return to play one season in the NFL and four more in the CFL.

It seems though that the only good news for Mr. Bridgewater comes from the Minnesota Vikings press release: “Fortunately, there appears to be no nerve or arterial damage”.

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the knee bone’s connected to the rib bone

Monday, August 19, 2013

Doctors who care for trauma victims think differently than the rest of the world. It’s not the injury that they can see but the hidden complication that might rear its ugly head that causes all the worry and hand wringing. It’s also how Dustin Keller’s knee is related to Barkevious Mingo’s chest. The injury that is apparent is not what the doctor cares about; instead, it’s the damage that can happen beneath the surface. It also helps patients and families understand why the doctor is hovering over the foot when it is obvious that the knee is the damaged part.

Football is a great medicine teaching tool but it requires an injured player to provide the lesson. Mr. Keller was newly signed tight end by the Miami Dolphins, but his season ended when he dislocated his knee during a preseason game. The injury involved tearing three of the four ligaments that hold the knee together, the anterior cruciate ligament (ACL), the posterior cruciate ligament (PCL) and the medial collateral ligament (MCL). Even strong quads and hamstrings, the knee cannot tolerate the damage and becomes unstable and can dislocate. This is a critical diagnosis to make because the popliteal artery that runs behind the knee can be stretched or torn and blood supply to the lower leg and foot cut off. If blood flow cannot be re-established, the leg might be lost. As well, the nerves that supply the foot run behind the knee as well and nerve damage would prevent normal ankle and foot function including walking and running.

The recognition of a knee dislocation can be sometimes tricky. Often the knee relocates spontaneously and on exam may look somewhat normal, though the exam will find it to be swollen, floppy and somewhat instable. X-rays may or may not be helpful. Most important will be to assess the pulses in the foot and ankle. Even if pulses are present, there is the possibility that the artery is damaged and delayed problems can occur. How to proceed is debatable. Some patients are observed, others get arteriograms, where dye is used to evaluate the artery anatomy, but all patients get the knee immobilized and admitted for observation. When the focus of the care is on an isolated injury, dislocations are rarely missed, but in the multiple trauma victim, for example a car wreck, a relatively normal looking, unstable knee might be overlooked while other injuries are addressed. The hand wringing is all about the dislocated knee being a limb threatening injury.

It’s the complications that weigh on the minds of the doctor caring for the chest injury sustained by Barkevious Mingo of the Cleveland Browns. There is a disconnect between their worry and that of the patient. A chest x-ray is done to look for the complications of a blow to the chest, including a pneumothorax (a collapsed lung) or pulmonary contusion (a bruised lung). Looking for a broken rib isn’t a priority but often that is the question that the patient want answered. Explaining physiology helps but deep down, patients want to know. In major trauma, the doctor wants to know as well, since the more ribs that are broken, the more likely that the patient will do poorly. When the ability to take a deep breath is compromised, the ability to get oxygen into the body is compromised as well. Interestingly, a pulmonary contusion can occur without any associated rib fractures.

The lung is composed of clusters of small air sacs (alveoli) divided by thin, elastic walls or membranes. Capillaries, the tiniest of blood vessels, run within these walls between the alveoli and allow blood and air to come near each other. The distance between the air in the lungs and the blood in the capillaries is very small, and allows molecules of oxygen and carbon dioxide to transfer across the membranes. If the lung is bruised, not only does blood leak from the capillaries into the alveoli but it sets into motion the body’s inflammatory response and swelling occurs. The swelling increases the distance that oxygen molecules have to travel to get into the blood stream and that may not happen and the more lung that is damaged, the sicker the patient can become. There is also a physiologic problem called pulmonary shunting. When blood is pumped to the lungs, it expects to pick up oxygen molecules but if the alveoli are filled with fluid, some blood returns to the heart without its oxygen load. This is a ventilation perfusion mismatch where blood is flowing to lung tissue that doesn’t work. Even breathing 100% oxygen may not be able to fix this problem if enough lung is involved.

With a pulmonary contusion, the patient usually complains of pleuritic chest pain that hurts to take a deep breath, as well as shortness of breath. Small contusions may have no symptoms but it may take some time for the contusion to fully blossom. Often the chest x-ray lags and the patient may appear sicker than they look in the picture. There is little treatment except for supportive care, observation and hand wringing hoping that the lung recovers before the patient tires from the work of breathing and needs to be put on a ventilator for breathing support.

Mr. Keller and Mr. Mingo will fade from the headlines as newly injured players take their place. Mr. Keller’s knee injury will require surgery and take almost a year of rehabilitation to recover. Mr. Mingo’s chest will heal in 4 -6 weeks with just ice and deep breathing. Time will also fade the fact that both were potential medical disasters.

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