A Bumper fracture is a fracture

Bone fracture

A bone fracture is a medical condition in which there is a break in the continuity of the bone...

 of the lateral tibia

Tibia

The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....

l plateau caused by a forced valgus

Valgus deformity

In orthopedics, a valgus deformity is a term for outward angulation of the distal segment of a bone or joint. The opposite deformation, medial deviation of the distal bone, is called varus....

 applied to the knee

Knee

The knee joint joins the thigh with the leg and consists of two articulations: one between the fibula and tibia, and one between the femur and patella. It is the largest joint in the human body and is very complicated. The knee is a mobile trocho-ginglymus , which permits flexion and extension as...

. This causes the lateral part of the distal femur

Femur

The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...

 and the lateral tibial plateau to come into contact, compressing the tibial plateau and causing the tibia to fracture. The name of the injury is because it was described as being caused by the impact of a car bumper on the lateral side of the knee while the foot is planted on the ground, although this mechanism is only seen in about 25% of tibial plateau fractures.

Fracture of the neck of the fibula may also be found, and associated injury to the medial collateral ligament

Medial collateral ligament

The medial collateral ligament of the knee is one of the four major ligaments of the knee. It is on the medial side of the knee joint in humans and other primates. It is also known as the tibial collateral ligament, or abbreviated as the MCL.- Structure :It is a broad, flat, membranous band,...

 or cruciate ligament

Cruciate ligament

Cruciate ligaments are pairs of ligaments arranged like a letter X. They occur in several joints of the body, such as the knee...

s occurs in about 10% of cases.