A broken knee is a serious orthopedic injury, accurately described as a fracture involving one or more bones that form the knee joint. The knee is the largest and most complex joint in the body, requiring immediate medical attention if its bony structure is injured. A fracture means the continuity of the bone has been broken, ranging from a hairline crack to a break where the bone shatters into multiple pieces. Because the knee is responsible for weight-bearing and mobility, any fracture severely impacts a person’s ability to walk or move the leg normally.
Bones That Define a “Broken Knee”
A fracture considered a “broken knee” involves the three bony components that meet at this joint: the patella, the distal femur, and the proximal tibia. The patella, or kneecap, is a unique sesamoid bone embedded within the quadriceps tendon. It is the most common site for a direct knee fracture, acting as a shield for the joint and improving the leverage of the thigh muscles.
The distal end of the femur, the long thigh bone, widens into two rounded knuckles called condyles that articulate with the shin bone. Fractures here, often called supracondylar or condylar fractures, can disrupt the smooth joint surface crucial for movement. The proximal end of the tibia, the shin bone, forms a flat surface called the tibial plateau that supports the femur. A tibial plateau fracture often damages this joint surface, leading to instability and long-term joint problems.
How Knee Fractures Commonly Occur
Knee fractures result from significant force, categorized as either high-energy or low-energy trauma. High-energy injuries occur in motor vehicle accidents, such as when a bent knee impacts a dashboard, or in falls from a height. This level of force often results in complex breaks, such as comminuted fractures where the bone is broken into several fragments.
Low-energy trauma includes simple falls, such as slipping directly onto the kneecap, or injuries in older adults with reduced bone density. A direct blow to the patella can cause a stellate fracture pattern, resembling a starburst. The direction of force often dictates the injury pattern.
An indirect mechanism can also cause a fracture without direct impact to the bone. This occurs when the powerful quadriceps muscle contracts suddenly against a bent knee, generating extreme tension that pulls the patella apart. This tensile force commonly results in a transverse fracture, where the bone breaks horizontally. Compressive forces, such as the body’s weight driving the femur into the tibial plateau during a fall, can cause a depression fracture of the tibia.
Recognizing a Fracture and Seeking Help
The symptoms of a knee fracture are immediate and intense, indicating that emergency medical attention is necessary. The most prominent sign is severe, sharp pain centered at the injury site, making any attempt to move the leg agonizing. This pain is accompanied by rapid swelling and bruising around the knee joint.
A person with a knee fracture is usually unable to bear weight on the injured leg or perform a straight leg raise (the inability to lift the leg while keeping the knee straight). If the extensor mechanism—the system of muscles and tendons that straightens the knee—is compromised, the leg cannot be held straight against gravity. In displaced fractures, a visible deformity or an unnatural shape of the knee may be apparent.
If a fracture is suspected, the immediate action is to immobilize the leg where it lies and seek emergency medical care promptly. Do not attempt to move or straighten the leg, as this could cause further damage to the bone fragments or surrounding soft tissues. Initial medical assessment relies on imaging, starting with X-rays to visualize the break and determine the degree of displacement. Further imaging, such as a Computed Tomography (CT) scan, may be used to gain a detailed, three-dimensional view of the joint surface damage, especially in complex tibial plateau fractures.
Treatment depends on the fracture’s stability. Stable fractures (nondisplaced fractures) are those where the bone pieces remain aligned and can often be managed without surgery using a cast or brace for immobilization. Unstable, displaced, or comminuted fractures require surgical intervention to realign the bone fragments and restore the smooth joint surface. Orthopedic surgeons use specialized hardware like plates, screws, or wires to fix the bone pieces in place, ensuring the knee’s stability and function are recovered.