By Cory Calendine, MD · Updated September 11, 2026, Board-Certified Orthopedic Surgeon
A knee dislocation is one of the few knee injuries every orthopaedic surgeon treats as a true emergency. It is not a sprain, and it is not a kneecap that slipped out of place. The whole knee joint has come apart, and the leg itself can be at risk.
I’m Dr. Cory Calendine, a board-certified, fellowship-trained orthopaedic surgeon at the Bone and Joint Institute of Tennessee in Franklin. I trained at Vanderbilt University Medical Center, a Level I trauma center, and today I perform more than 700 joint replacements a year. Here’s what I want every patient and parent in Middle Tennessee to know.
What Is a Knee Dislocation?
A knee dislocation happens when the thigh bone (femur) and the shin bone (tibia) are forced completely out of line with each other. The knee is a very stable joint, so it takes a large force to do this. The ligaments, blood vessels, and nerves around the knee get stretched or torn in the process.
Is a Dislocated Knee the Same as a Dislocated Kneecap?
No. A dislocated kneecap (patella) is far more common and far less serious; the kneecap slides out of its groove and rarely harms major blood vessels. A true dislocated knee means the main joint itself has separated.
I hear people mix up the two terms all the time, but the difference matters. One is usually treated with a brace and therapy. The other is a surgical emergency.
What Causes a Knee Dislocation?
Most knee dislocations come from high-energy trauma. It usually takes a violent event to pull this joint apart:
- Motor vehicle crashes, including “dashboard injuries,” where a bent knee slams into the dashboard.
- Falls from a height, such as off a ladder, a roof, or a hunting stand.
- Contact sports, such as football, when a hard hit lands on a planted leg.
- Pedestrian, work, and crush injuries, such as being struck by a car or pinned by equipment.
In Middle Tennessee, that means busy roads like I-65 and I-840, job sites, and Friday night football. Men have this injury about four times as often as women.
Can a Knee Dislocate From a Simple Misstep?
Yes, though it is less common. In people with severe obesity, a knee can dislocate from something as simple as a misstep. Doctors call this an “ultra-low-energy” dislocation, and it is easy to miss because the event seems so minor.
Why Is a Knee Dislocation a Limb-Threatening Emergency?
A knee dislocation is an emergency because it can tear or bruise the popliteal artery, the main blood vessel behind the knee that feeds the lower leg. If blood flow is not restored in time, the tissue below the knee starts to die. That can lead to amputation.
Studies report artery damage in roughly 5 to 15 percent of all knee dislocations, and more often with certain patterns. When blood flow stays cut off for more than six to eight hours, amputation rates as high as 86 percent have been reported, according to a clinical review from the National Library of Medicine.
Here’s the tricky part: a normal pulse in the foot does not rule out an artery injury. Small side branches around the knee can keep a pulse going even when the main artery is badly damaged, so emergency teams keep checking for hours.
Can a Knee Dislocation Pop Back Into Place on Its Own?
Yes. Up to half of all knee dislocations slip back into place before the patient reaches the emergency room. That sounds like good news, but it is one of the most dangerous parts of this injury.
A knee that looks normal can still hide a torn artery, a stretched nerve, and several torn ligaments. If you saw the knee bent at a strange angle, even for a moment, tell the emergency team.
Nerves are at risk too. The peroneal nerve, which controls the muscles that lift your foot, is injured in about one in four cases and can cause foot drop (toes that drag when you walk).
What Ligaments Are Damaged in a Knee Dislocation?
Nearly every knee dislocation is a multi-ligament injury, meaning several of the knee’s major ligaments tear at once. The damage often involves the ACL, PCL, and MCL, along with the posteromedial corner, the LCL, and the posterolateral corner. Say that ten times fast.
- ACL and PCL: the two ligaments that cross in the center of the knee and stop the shin bone from sliding forward or backward.
- MCL and LCL: the ligaments on the inner and outer sides that keep the knee from buckling sideways.
- Posteromedial and posterolateral corners: groups of ligaments and tendons at the back corners of the knee that control twisting.
Broken bones are common too. Studies find fractures in roughly 40 to 60 percent of knee dislocations.
What Are the Signs of a Dislocated Knee?
The signs of a dislocated knee are usually hard to miss: severe pain, fast swelling, and a leg that will not hold weight. Watch for:
- A knee that looks deformed or bent at the wrong angle
- Numbness, tingling, or weakness in the leg or foot
- A foot that feels cold or looks pale or bluish
- Trouble lifting the front of the foot
If you suspect a dislocated knee, call 911. Do not try to push it back into place, walk on it, or drive yourself to the hospital. Keep the leg still until help arrives.
How Is a Knee Dislocation Treated?
Knee dislocation treatment happens in stages: first save the leg, then steady the joint, then rebuild the ligaments. Most patients need surgery at some point.
Emergency Care for a Knee Dislocation
In the emergency room, the doctor gently guides the bones back into line, called a reduction, and places the leg in a splint. Next comes a close look at blood flow. A quick test called the ankle-brachial index (ABI) compares blood pressure at the ankle with pressure in the arm.
A low reading or weak pulse leads to a CT angiogram, a scan that maps the arteries. X-rays check for fractures, and an MRI later shows the torn ligaments.
Surgery After a Dislocated Knee
If the artery is damaged, a vascular surgeon repairs it first. Some patients also need an external fixator, a frame outside the leg attached to the bones with pins, to hold the knee steady while swelling settles.
The torn ligaments are then repaired or rebuilt, often within the first few weeks. Some of this work is done with a camera through small incisions, called knee arthroscopy. At the Bone and Joint Institute of Tennessee, our sports medicine knee specialists handle this reconstruction.
What Is Recovery Like After a Knee Dislocation?
Recovery after a knee dislocation takes many months of bracing, crutches, and physical therapy. I want patients to start with honest expectations. With prompt treatment, about 60 to 70 percent end up with a stable, painless knee.
Only about 22 to 33 percent return to the same level of sport. Stiffness from scar tissue (arthrofibrosis) affects up to 38 percent of patients, and some looseness affects up to 37 percent. Early, guided motion helps prevent stiffness.
Can a Knee Dislocation Lead to Arthritis Later?
Yes. A knee dislocation raises the risk of arthritis later in life, because cartilage, meniscus, and ligaments are often injured all at once. Doctors call this post-traumatic arthritis.
This is where my practice connects to the story. After more than twenty years doing this, I regularly see patients whose knee arthritis traces back to a serious injury years earlier: a car wreck, a football hit, a bad fall.
Many start with nonsurgical joint pain treatment. When pain keeps winning, a total knee replacement can often restore comfort and function. Knees with old ligament damage take careful planning, and that experience matters.
Where Can You Get Care for a Knee Injury in Middle Tennessee?
For a new knee dislocation, call 911 and go to the nearest emergency room. For the months and years that follow, our team at the Bone and Joint Institute of Tennessee cares for patients from Franklin, Nashville, Columbia, and across Middle Tennessee.
Living with pain or arthritis after an old knee injury? You can schedule a consultation with Dr. Calendine or call (615) 791-2630. Our office is at 3000 Edward Curd Lane, Franklin, TN 37067.
Thinking ahead to surgery? My free knee replacement guide walks you through every step.
Prefer video? Watch my one-minute explanation below.
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This article is for educational purposes only and is not a substitute for professional medical advice. A suspected knee dislocation is a medical emergency: call 911. Individual results may vary.
References
- Mohseni M, Mabrouk A, Simon LV. Knee dislocation. StatPearls. 2024.
- Constantinescu D, et al. Vascular injury after knee dislocation: a meta-analysis update. J Am Acad Orthop Surg. 2023;31(4):e198-e206.
- Stannard JP, Schreiner AJ. Vascular injuries following knee dislocation. J Knee Surg. 2020;33(4):351-356.
- Ramirez-Bermejo E, et al. Management of acute knee dislocation with vascular injury: the use of the external fixator. Arch Orthop Trauma Surg. 2022;142(2):255-261.
- Medina O, et al. Vascular and nerve injury after knee dislocation: a systematic review. Clin Orthop Relat Res. 2014;472(9):2621-2629.
- Kelleher HB. Knee dislocation: background, prognosis. Medscape. Updated May 15, 2025.
