Sorting Out Lateral Knee Pain in the AthleteSports physicians, physical therapists, and athletic trainers often hear these symptoms from athletes: I have pain along the outside of my knee, swelling, and sometimes the knee locks up on me or gives way from underneath me. What is causing this?
The examiner takes a patient history with standard questions about possible injuries or trauma to the knee. He or she will ask the patient questions what makes it better, what makes it worse, and are there any other symptoms? Conducting a physical examination and performing specific tests help in sorting out what could be causing the problem.
X-rays may be ordered and all possibilities are considered. The most common problem causing this type of clinical presentation is a lateral meniscus tear. The meniscus is a thick U-shaped piece of cartilage inside the knee joint. Anything inside the joint is referred to as intra-articular.
But there can be other causes coming from outside the joint mimicking a meniscal tear. These would be considered extra-articular and include: 1) iliotibial band syndrome (ITBS), 2) proximal tibiofibular joint instability, 3) snapping tendons (either the biceps femoris or the popliteus tendons), and 4) peroneal nerve compression or inflammation.
This article was written to help the examiner recognize the subtle differences between intra-articular meniscal tears and extra-articular causes of lateral knee pain. The typical history, symptoms, and test findings are presented for each one.
Drawings, X-rays, and photographs are provided to help show each of these conditions and how they differ from a lateral meniscal tear. A brief review of the most common treatment for each condition is also offered. Since the treatment varies with each type of problem, an accurate diagnosis is needed to get these athletes back on their feet and in the game as quickly as possible.
Let's take a quick look at each one. First and probably the most common condition to mimic a lateral meniscal tear is the iliotibial band syndrome (ITBS). This connective tissue structure runs along the entire outside of the thigh from hip to knee with several points where it inserts or connects to the knee.
Runners and cyclists have the most trouble with this problem because of the repeated knee flexion (bending) and extension (straightening). A special test called the Ober test is used to look for tightness of the iliotibial (IT) band.
X-rays don't show positive findings for IT band problems. But they are used to look for tumors, arthritis, and fractures. MRIs are better at showing changes (e.g., thickening, fluid collection) in the connective tissue.
A second mimicker of a lateral meniscal tear is the presence of tibiofibular joint instability. The tibiofibular joint is along the outside of the knee where the tibia (larger of the two lower leg bones) connects to the fibula (smaller of the two lower leg bones).
Instability usually tells us the joint is loose or shifts either into subluxation (partial dislocation) or into a fully dislocated position. This can be caused by small but significant anatomic variations.
Even slight changes that alter the natural angle of this joint can allow the fibula to slip out of the groove that holds it in place. Or a traumatic injury damaging ligaments and connecting soft tissue can damage the joint resulting in the same type of instability.
Instability may keep the athlete from putting weight on that leg. The examiner compares the unaffected knee to the painful one and looks for changes in how the joint moves. Any unnatural shifts in the fibula as it moves against the tibia (called joint translation) will be evaluated with more specific tests (e.g., apprehension test, Radulescu test).
The third extra-articular source of lateral knee pain comes from snapping tendons. Tendons that insert into the fibula near the knee may slip back and forth over the bone causing a painful snapping sensation.
The symptom is most noticeable during knee motion. A larger than normal fibular head (round top of the fibula) can contribute to the problem. Sometimes releasing the tendon surgically and/or removing some of the bone and reshaping the fibular head are necessary to end the problem.
And finally, the common peroneal nerve located along the outside of the knee and lower leg may be irritated either from compression (pinching) or neuritis (nerve inflammation). Like all the other problems discussed nerve compression or inflammation can cause lateral knee pain. With nerve involvement, there are usually sensory (numbness, tingling) and/or motor changes (muscle weakness) to help direct the examiner in finding the problem.
Helpful clues to nerve involvement include history of trauma to the outside edge of the knee (where the nerve is located), pressure on that spot from crossing the leg, sudden weight loss (the protective fat pad gets too thin), or ankle/foot injury that stretches the nerve.
Special tests to look for nerve compression or neuritis include Tinel sign (tapping over the nerve causes nerve pain), electromyogram (EMG) studies, and nerve conduction studies. X-rays are used to look for bone spurs, fractures, or tumors putting pressure on the nerve.
In summary, more and more athletes are showing up at doctors' and physical therapists' clinics with lateral knee pain. It is necessary to examine carefully to identify the involved structures in order to direct treatment to the specific problem.
Intra-articular (inside the joint) problems must be differentiated from extra-articular (outside the joint) causes of symptoms. The authors of this article provide a step-by-step approach to completing such an exam with photos and descriptions of recommended test procedures for each of four separate conditions that can separate out intra-articular meniscal tears from other extra-articular injuries that can mimic meniscal tears.
Joseph U. Barker, MD, et al. Extra-Articular Mimickers of Lateral Meniscal Tears. In Sports Health. January/February 2011. Vol. 3. No. 1. Pp. 82-88.
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