A Wilson test is a medical screening procedure for the presence of osteochondritis dissecans of the knee. It is performed while the patient sits on a table with the legs and feet bent at a 90-degree angle and hanging freely. During the Wilson test, the medical examiner has the patient rotate the foot inward toward the other foot and slowly extend and straighten the leg. When osteochondritis dissecans is present, there is an increase of pain when the leg is about 30 degrees from extension. This pain is relieved when the leg is rotated outward.
Osteochondritis dissecans (OCD) is a medical condition where part of the bone of the knee becomes detached from the rest of the bone, allowing fragments of bone and cartilage to move loosely in the knee. This can cause pain and inflammation, especially when running or using stairs. OCD is a rare condition, but occurs most frequently in teenage athletes and more commonly in males. It usually occurs as a result of sports activity and repetitive stress of the knee.
During a physical exam, a physician will first observe the gait to see if the patient is compensating for painful movement. The physician will feel the knee for any lumps, swelling, or objects moving around the knee. A Wilson test is performed to further screen for the possibility of OCD in a particular area of the knee.
The classical location of an OCD is at the lateral edge of the medial femoral condyle. This is one of the two bony prominences at the lower end of the femur. Although OCD may occur in other locations around the knee and even in other parts of the body like the knee or elbow, a Wilson test can help determine if an OCD lesion is present at this location. The positioning of the knee and leg during the Wilson test puts pressure on bony fragments that may be present, causing pain.
If the physician determines that the patient has OCD, the patient may be referred for a magnetic resonance imaging (MRI) test, x-ray, or other testing to determine the exact location and extent of the injury. Young patients may heal on their own if they rest the joint and avoid high-impact activities. Physical therapy can help strengthen surrounding muscles and protect the knee from further injury. If the knee does not heal on its own, then surgery may be necessary to remove bone fragments and repair damaged areas.