Dangerous Sports Injuries: Knee Dislocations
Last week during the Chicago Bears – New Orleans Saints football game, Bears’ tight end Zach Miller suffered a devastating knee injury while catching a touchdown pass. Replays showed the gruesome nature of this injury, as his knee contorted into unnatural positions when he landed in the end zone. Miller underwent emergency surgery in New Orleans to repair the arterial supply to his leg, saving his limb in the process. Knee dislocations are severe, limb-threatening injuries which, while rare, can occur in contact sports like football. What exactly is a knee dislocation and how worried should athletes and their parents be about injuries like those?
Knee dislocations occur when sufficient force is applied to the knee to tear multiple ligaments (soft tissue structures which connect bones) and completely separate the tibia (shin bone) from the femur (thigh bone). This is not a patellar dislocation, when the knee cap dislocates, but a much more serious injury. The most common cause is a significant traumatic event such as a motor vehicle accident or fall from a height, but they also occur in sports. While these injuries are relatively rare in sports, their consequences can be devastating.
There are four main ligaments in the knee that maintain its structure: the medial collateral ligament/mcl, lateral collateral ligament/lcl, anterior cruciate ligament/acl, , and posterior cruciate ligament/pcl. When viewing the knee from the front, the mcl connects the femur to the tibia on the inside, the lcl on the outside, and the acl/pcl in the middle. The popliteal artery runs from the upper to lower leg directly behind the pcl in the back of the knee, and is the primary blood supply to the leg below the knee. The tibial and peroneal nerves are the neurologic supply to the leg below the knee, and run adjacent to the popliteal artery. These nerves supply muscular function and sensation below the knee.
Knee dislocations are graded by the number of ligaments torn and extent of arterial and neurologic damage. The best case scenario for these injuries is rupture of two ligaments without neurovascular damage. This type of injury can be treated with surgical reconstruction/repair of the injured ligaments on a non-emergent basis with, generally, a good outcome and high likelihood of return to previous level of activity, including sports.
On the other end of the spectrum are knee dislocations like Zach Miller sustained. These generally involve rupture of 3-4 ligaments, with arterial and nerve disruption in the most severe cases. Treatment requires emergent repair of the arterial injury to save the leg, along with some type of stabilization to prevent the knee from shifting and disrupting the arterial repair. External fixators are often used temporarily, placing pins into the leg above and below the knee and connecting them with bars to immobilize the leg and allow access to the artery. Nerve injuries may be explored and repaired or decompressed from surrounding injured structures. Ligament injuries are often treated with delayed reconstruction or repair, when the arterial supply is stable. These are very complex reconstructions due to the involvement of multiple ligaments, and are a completely different injury from an isolated acl tear. Surgical repair often requires use of allografts (donor tissue) to reconstruct the injured structures, as the severe nature of the injury often precludes use of the patient’s own tendons for total reconstruction. The goal of this type of surgery is to preserve a functional leg on which a patient can ambulate effectively. If the patient is able to return to sports after recovery this is an added blessing. When severe nerve and vascular damage occurs, the priority is limb salvage. A recent study demonstrated an 18% incidence of vascular injury, with 12% of these leading to amputation, and a 25% incidence of neurologic injury. Other studies showed only 38% of patients had functional recovery when they initially showed complete nerve injury. These statistics are alarming.
When an athlete sustains a knee dislocation, the joint should be immobilized in the most anatomic alignment possible and transported emergently to the ER for reduction (putting the knee back in place) and careful assessment of neurovascular status. Dislocations often reduce spontaneously, but this should not cause you to underestimate the severity of the injury. A missed arterial injury will result in amputation, so vigilance is mandatory in initial and follow up assessment. Appropriate arterial evaluation and emergent repair saved Zach Miller’s leg, and this is the standard of care required for these injuries.
Thankfully, knee dislocations are a relatively rare injury, and the likelihood of experiencing such damage in sports is extremely low. I hope this information has been helpful. If you or your family member need help with a knee ligament injury, feel free to call us at 205-443-2797 or 802-6700.