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I'm a little nervous because I hurt my knee and have to have it tested in case I need surgery. The physician's assistant who first saw me after the injury said I might have posterior and lateral instability -- not the typical anterior cruciate ligament (ACL) knee injury. Now I have to see an orthopedic doctor. What can you tell me about this kind of injury and what kind of tests will be done?
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The anterior and posterior cruciate ligaments hold the knee stable from inside the joint where they form a criss-cross. The anterior cruciate ligament keeps the tibia (lower leg bone) from sliding too far forward under the femur (thigh bone). The posterior cruciate ligament does the opposite: it keeps the tibia from sliding too far backwards under the femur. It sounds like maybe those two ligaments are okay but the surgeon will probably double check them just in case. The tests are simple hands-on done by the surgeon while you rest quietly.
There are other ligaments that hold the knee together from the outside. These will be tested as well. Three ligaments that provide posterior (to the back) and lateral (to the side) support and stability to the knee include the fibular collateral ligament (FCL), popliteus tendon (PLT), and popliteofibular ligament (PFL). Instead of keeping the bones in the knee from sliding too far forward or too far backward (the job of the cruciate ligaments), these posterolateral structures protect the knee from bowing out to the side too far or the tibia from externally rotating too far under the femur.
The fibular collateral ligament connects the top of the fibula (bone along the outside of the lower leg) to the bottom of the femur (thigh bone). It gives lateral (side) support to the knee to keep it from bowing out too far. The popliteus tendon starts midway along the bottom portion of the femur and angles back to connect to the back of the upper tibia (shin bone in the lower leg). This tendon supports the knee and keeps it from rotating too far in one direction. And the popliteofibular ligament connects the back of the tibia to the back and side of the fibula. The fibula and tibia sit side by side as the two bones in the lower leg.
Tests used to make the diagnosis may include imaging studies such as X-rays, MRIs, and/or CT scans. The surgeon will perform additional hands-on tests to look at joint movement, feel for tenderness around the joint where each ligament attaches, and assess strength. Pressure applied against the joint will show any excess gapping of the bones from weak or damaged ligaments that would normally hold the joint together and prevent excess movement.
With posterolateral instability, there is a widening of the joint space along the outside (lateral edge) of the knee when pressure is applied in that direction. There may be an increase in external rotation of the tibia under the femur and a positive posterolateral drawer test. The drawer test is done by applying pressure to the lower leg (tibia) and seeing or feeling too much backward movement of the tibia under the femur. Sometimes there is even a clunk as the bone shift too far back. This occurs because the ligaments are damaged and don't hold the tibia in place as they should.
The surgeon uses all of these tests and measures to make a diagnosis. It's always good to let the doctor know that you are a bit nervous. Don't be shy about asking for an explanation of the tests done and what to expect. This can help you understand what is going on and the results as you see and feel them yourself during the exam -- and good luck!
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*Disclaimer:*The information contained herein is compiled from a variety of sources. It may not be complete or timely. It does not cover all diseases, physical conditions, ailments or treatments. The information should NOT be used in place of visit with your healthcare provider, nor should you disregard the advice of your health care provider because of any information you read in this topic. |
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