Dear Doctors: I was on the couch with my right leg on an ottoman when our black Lab rammed into the inside of my knee. The next day, it really hurt to extend or turn my knee. (Not painful to the touch, though, which seemed weird.) It felt better in a week, but I want to know what got hurt.
Dear Reader: The knee is the largest joint in the body, and it’s one of the most complex. It's a hinge joint with a network of muscles, tendons and ligaments. These connect it to the femur (thigh bone) above, and to the tibia (shin bone) below. Although designed for bending and straightening the leg, the anatomy of the knee also allows for some slight rotation. All of this provides the strength and stability needed for all the demands we make on this hard-working joint as we walk, run, turn, crouch, jump and balance.
From your description of the event, it sounds like you sustained a mild injury to the medial collateral ligament, or MCL. This is the band of tough, fibrous tissue that anchors the femur and the tibia to the inner, or medial, side of the knee joint. This type of soft tissue injury can happen when you get hit on the inner part of the knee while your leg is extended. It can also occur when your foot is planted on the ground, which is why this is a fairly common injury in sports such as soccer, football and rugby.
Force to the medial side of the knee can also cause other injuries. A bump to the knee could affect the other three major ligaments, the four major tendons in the joint, the cartilage within the knee capsule, or the articular cartilage that coats the ends of the bones, the shin and the thigh. Repetitive impact can inflame the bursa within the knee. Bursa are small, fluid-filled sacs that act as a cross between cushions and shock absorbers. Bone bruises and strained or torn muscles are also possible.
In your case, because your thigh was supported by the couch, it stayed fairly still in this incident. But the bump from the dog -- and Labradors are pretty solid -- was forceful enough to shift the lower leg out of alignment for an instant. Ligaments, which provide stability, have limited elasticity. That sudden collision likely overstretched the MCL, causing your injury. Your recovery time of a week suggests a mild strain. This is when the ligament itself remains intact, but the tissue develops microscopic tears. It can cause the type of pain and limited range of motion you described.
The pain is a signal that the tissues need time to heal. Treatment for a mild strain begins with resting and elevating the joint. In the past, icing was advised. Newer thinking suggests this practice may slow healing. Anti-inflammatory medications can help manage the pain. Due to the complexity of the knee, it's a good idea to get a medical assessment of an injury, even when the injury is mild.
(Send your questions to [email protected], or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)
