KNEE

OSTEOCHONDRITIS DISSICANS

Osteochondritis dissicans generally indicates fragmentation and probable separation of a portion of the articular surface. The age of onset is variable but adolescence is most frequent. Patients may be entirely asymptomatic, however, pain, limited range of motion, soft tissue swelling, and the locking of the knee may be apparent.

The most typical location for osteochondritis dissicans is the lateral aspect of the medial femoral condyle affecting approximately 70 percent of cases. Men are typically more affected than women and the average age at the onset of symptoms is approximately 15 to 20 years although this is variable. Unilateral changes predominate over bilateral changes and there is a history of knee trauma and about 50 percent of cases.

The pathogenesis of osteochondritis dissicans of the femoral condyles has not been completely agreed upon. Most doctors agree that trauma initiates this condition, probably related to rotatory forces acting on a fixed weight bearing knee. Shearing forces and direct blows could also produce osteochondral fragments.

Radiographically, a purely chondral lesion requires advanced imaging for diagnosis. If an osseous component of an osteochondral lesion is present, routine radiography is very helpful. Sometimes a small osseous lesion is separated from the sclerotic base of the femoral defect by radiolucent crescent zone. It is also possible for the osteochondral fragment to produce a loose intraarticular osseous body which can cause joint locking clinically. Over time, the site of origin on the femur can be remodeled although a slightly flattened or at least irregular surface frequently lasts for a long period of time. Secondary degenerative joint disease also occurs in patients with osteochondritis dissicans much earlier in life than the usual osteoarthritis of the knee and is frequently associated with loose bodies.

The major differential diagnosis of osteochondritis dissicans is spontaneous osteonecrosis of the knee. Typically this lesion occurs in older persons with a sudden onset of clinical manifestations and almost always involves the weight bearing portion of the medial femoral condyle.

PATELLA - INFERIOR POLE

Sinding-Larson in 1921 and Johansson in 1922 independently described a syndrome which occurred most commonly in adolescence between 10 and 14 years of age consisting of tenderness and soft tissue swelling over the lower pole of the patella, accompanied by radiographic evidence of osseous fragmentation. Initially it was suggested that this was an "epiphysitis" or "apophysitis" but is now recognized that it is traumatic in origin. Its pathogenesis is very similar to that of Osgood-Schlatter's disease and is probably related to a traction phenomenon in which contusion or tendinitis in the proximal attachment of the patellar tendon is followed by calcification and ossification. In Sinding-Larson-Johansson disease, pain and tenderness are typically aggravated by activity. The small bony fragments may subsequently coalesce and become incorporated into the patella. The natural duration of the disease is approximately 3 to 12 months.

TIBIAL TUBEROSITY

Osgood-Schlatter's disease was described in 1903 as a disorder of the developing tibial tuberosity which each of the developers believed to be a manifestation of trauma. Other case studies were presented incorrectly emphasizing the possibility of "apophysitis" or osteonecrosis as the etiology of this condition. Osgood-Schlatter's disease typically occurs in adolescence boys between the ages of 11 and 15 years of age with the history of participation in sports and the rapid growth spurt prior to the onset of symptoms.

Clinically, there is typically local pain and tenderness which is aggravated with activity and relieved with rest. This disease is generally unilateral, however, bilateral alterations are detected on approximately 25 percent of cases.

Radiographic abnormalities in Osgood's Schlatter's disease are difficult to detect and because subtle soft tissue changes may be missed if the lateral knee films are over penetrated, a low kV technique is ideal. Initial radiographic abnormalities include subtle soft tissue swelling in front of the tuberosity with an indistinct margin of the patellar tendon and often times increased radiodensity of the infrapatellar fat pad. Multiple ossific irregularities in the region of the tibial tuberosity are also present, similar to the fragmentation of the inferior pole of the patella which occurs in Sinding-Larson-Johansson disease. Eventually the radiographic appearance can return to normal, however, it is not uncommon for ossific fragment to persist. MR imaging reveals evidence of patellar tendinitis and bursitis, however, again, this is not typically indicated.

To complicate things a little, it needs to be known that it's normal for one or more osseous centers to be present just anterior to the tibial tuberosity in children between the ages of approximately 8 and 14 years. Therefore, the most accurate way to diagnose Osgood-Schlatter's disease is based on both radiographic and clinical findings. If there is pain in the region of the tibial tuberosity in the right age group, especially with the history of repetitive stress, and the radiograph demonstrates soft tissue swelling, the diagnosis can confidently be made. Sometimes comparison views of the opposite, uninvolved side may be helpful.