Bony lesions on the distal femur are a common but benign finding on magnetic resonance imaging (MRI) in young alpine skiers and should not be confused with more serious conditions, according to a study from Switzerland published in the journal Radiology.
These tumor-like lesions affect the cortical bone and are referred to as distal femoral cortical irregularities (DFCI). The presence of DFCIs often leads to diagnostic uncertainty because they can appear to be cancerous lesions or areas of infection.
With an increasing number of MRI examinations performed in young patients, DFCI detection is likely to increase, said study lead author Christoph Stern, MD, a musculoskeletal radiologist at Balgrist University Hospital in Zürich, Switzerland, as MRI has a higher sensitivity for detecting lesions than radiographs, according to
“Our goal was to better understand the pathogenesis of DFCI and to reduce uncertainty in the diagnosis of this benign condition, which should not be mistaken for malignancy,” Dr. Stern said.
In the first study of its kind, Dr. Stern and colleagues investigated the prevalence of DFCI in 105 youth competitive alpine skiers versus 105 controls in the same age group. Competitive skiers are exposed to periodic high physical activity and loading patterns to the knee joint that are likely to affect the bones and connective tissue of the joint.
The researchers compared MRIs of the 2 groups to look for the presence of DFCIs at 2 tendon-bone attachment areas:
- Between the gastrocnemius and the femur
- Between the adductor magnus muscle of the inner thigh and the femur
They found DFCIs in more than half of the youth competitive alpine skiers (58.1%) and slightly more than a quarter of the controls (26.7%). DFCIs were observed predominantly at the inside head of the gastrocnemius muscle in both groups.
“DFCI are benign lesions, and occurrence around the knee joint is associated with repetitive mechanical stress to the attachment sites of tendons into bone,” Dr. Stern said. “DFCI should not be mistaken for malignancy and are not associated with intraarticular damage.”
The most common theory behind the occurrence of DFCIs is that of a “tug lesion” as a result of repetitive mechanical stress where the tendons attach to the bone.
“According to histologic results of DFCI, which have identified a reactive process, we assume there must be increased bone remodeling with resorption and fibrous proliferation at the site of the tendon attachment that is pronounced in young competitive athletes,” Dr. Stern said.
Similar findings are likely in other groups of athletes who place repetitive strain of the gastrocnemius muscles, such as those whose sports involve jumping. “This would apply to basketball and volleyball players,” Dr. Stern said. “It might also apply for weightlifters who are exposed to similar pretension states and eccentric loading of the gastrocnemius muscles as skiers during exercise,” he said.
The researchers recommend that invasive diagnostic procedures such as biopsies be avoided in these patients due to the benign, usually asymptomatic, and, over time, self-limiting character of typical DFCIs at the attachment sites of tendons. However, follow-up with MRI might be justified, they said, especially in the rare case where the DFCI causes pain and other symptoms.
Stern C, Galley J, Froehlich S Peterhans L, Spoerri J, Sutter R. Distal femoral cortical irregularity at knee MRI: increased prevalence in youth competitive alpine skiers. Radiology. 16 June 2020. Published online ahead of print.