Zach Miller, tight end for the Chicago bears, suffered a significant knee injury on 10/29/2017 playing against the New Orleans Saints. The images were very gruesome as Miller unfortunately suffered a dislocated knee. A knee dislocation is a devastating injury that can be from 1 of 2 different types of traumas. High-energy traumas are usually from either a fall or motor vehicle accident, commonly where a flexed knee hits the dashboard. A low-energy knee dislocation, as in the case with Miller, result from athletic injuries, typically secondary to a rotational component, and morbid obesity is a risk factor.
Due to the severe nature of these injuries, 3 of the 4 major ligaments of the knee (ACL, PCL, MCL, LCL) are usually torn. In most cases, both cruciate ligaments are ruptured, and approximately 75% are either anterior or posterior dislocations. Vascular injury, that is injury to the artery supplying blood to the lower part of the leg, can be compromised in 5-15% of all dislocations. However, those odds increase significantly to approximately 32-45% with an anterior or posterior dislocation, with an increased incidence in posterior displacement. This is due to a tearing of the popliteal artery as it runs behind and deep inside of the knee. Nerve damage occurs in 16 – 40% of patients, as the common peroneal nerve injury is the most commonly injured nerve, as it wraps around the proximal head of the fibula, occurring approximately 25% of the time. Fractures occur in approximately 60% of knee dislocations.
How are knee dislocations classified? There is a Kennedy classification system based on the direction of the displacement of the tibia. Anterior displacement is the most common, with posterior displacement being the second most, followed by lateral, medial and rotational displacements. There is also a Schenck classification system, which based on the number of ligaments injured, ranging from a single ligament damaged all the way to four with the addition of a periarticular fracture.
THIS IS ONE OF THE FEW EMERGENCIES IN ORTHOPEDICS! As a delay in management can result in loss of blood flow to the lower leg below the knee, leading to loss of that lower leg. Palpation for pulses is an important place to start upon realization that the knee is dislocated. Any concern for loss of pulse, or a weak pulse, should be emergently sent for evaluation of the artery with CT angiography. Ankle brachial indexes (ABIs) have also been shown to be highly sensitive and specific as a screening tool for vascular injury. Any patient with an ABI less than 0.9 should undergo further workup, and is likely to require surgery. Evaluation of the nerves, including sensory and motor exams, are important to evaluate severity of damage to the nerves.
Emergent surgery is indicated for patients with a vascular injury. Other surgical emergencies associated with knee dislocations include compartment syndrome, open injury, and irreducible dislocation. Posterolateral dislocations are most likely to be irreducible because of the anatomy in this region. Vascular compromise more than 8 hours has a high association for above-the-knee amputations (86%). In the absence of a surgical emergency, the knee should be splinted in extension, and serial vascular evaluations should be completed over the next 24-48 hours. While most patients are able to return to their everyday lives after this injury, unfortunately few are able to return to competitive sports.
In the case of Miller, the reports have been very good as it appears the team physicians and medical staff at the stadium was able to address and diagnose this serious injury quickly and efficiently. He was rushed to the hospital and underwent emergent vascular surgery. The good news is that it appears the surgeons were able to re-vascularize Miller’s leg in the appropriate amount of time, and were able to resupply his lower leg with blood. Coach John Fox reported today that Miller had good pulses in his lower legs, meaning that the long-term possibility of him requiring an above-the-knee amputation is less likely. Once the vascular aspect of his care has calm down, Miller will likely undergo an MRI, and then subsequent surgery to repair the ligaments that are torn (despite not being mentioned at this time).
This was written by Dr. Jesse Morse, I am a Board-Certified Family Medicine physician, and I am currently completing a Sports Medicine Fellowship at the University of South Florida in Tampa. This information should be used for entertainment only, and not for medical advice. If you have any questions or comments, you can contact me directly at @DrJesseMorse or visit my website at: www.DrJesseMorse.com. Keep an eye out for my next article!
Patel, Anay. “Knee Dislocation.” Orthobullets, Orthobullets, www.orthobullets.com/trauma/1043/knee-dislocation.
O’Connor, Francis G. ACSM’s Sports Medicine: a Comprehensive Review. Wolters Kluwer Health, 2015.