MRI-Detected Bony Lesions Common – and Benign – in Young Athletes’ Knees

In a study out of Switzerland, published today in Radiology, investigators revealed that these tumor-like abnormalities – called distal femoral cortical irregularities (DFCI) – are frequently found on routine knee MRIs conducted on teen-agers. Even though they can frequently be confused with cancer or some other infection, they are actually no cause for alarm.

Understanding what these lesions are and being able to identify them is important, said lead study author Christoph Stern, M.D., a musculoskeletal radiologist at Balgrist University Hospital in Zürich, Switzerland, because more and more adolescents are having MRI exams.

“Our goal was to better understand the pathogensis of DFCI and to reduce uncertainty in the diagnosis of this benign condition, which should not be mistaken for malignancy,” he said.

Oftentimes, these abnormalities are asymptomatic, and they are self-limiting over time. If radiologists and referring providers have a better comprehension of these bony lesions, young adults could avoid unnecessary invasive diagnostic procedures, such as biopsies, he said.

Typically, these lesions are found on the distal femur, the area of the thigh bone just above the knee, and they affect the dense outer surface of the bone known as the cortical bone. Stern’s team chose to investigate these lesions in competitive young alpine skiers because they frequently experience high levels of physical activity and loading patterns to the knee that can affect the bones and the joint’s connective tissue.

In this first-of-its-kind study, the team compared unenhanced 3T knee MRI scans from 105 skiers to images from 105 young adults who do not ski. The analyzed images, collected between 2014 and 2019, were evaluated for the presence of DFCI at two tendon-bone attachment areas: the ones between the gastrocnemius (the major muscle in the calf) and the femur, as well as the ones between the adductor magnus muscle in the inner thigh and the femur.

According to the results, Stern said, more than half of the competitive skiers (58.1 percent) had a DFCI found on MRI. In contrast, the bony lesions were found in only slightly more than a quarter – 26.7 percent – of non-skiers. Most DFCIs identified in both groups were found at the attachment sites of tendons with the most common location being the inside head of the gastrocnemius muscle.

These lesions are most frequently associated with repetitive mechanical stress to those attachment sites. The most widely accepted theory about DFCI is that it is a “tug lesion” that is the result repeated stress placed on spots where the tendons attach to bone. Consequently, they should be not misinterpreted as a malignancy or any type of intraarticular damage.

“According to histologic results of DFCI, which have identified a reactive process, we assume there must be increased bone modeling with resorption and fibrous proliferation at the site of the tendon attachment that is pronounced in young competitive athletes,” Stern explained.

It is possible, Stern said, that these findings could be applied to other young athletes who repetitively strain their gastrocnemius muscles, particularly through jumping.

“This would apply to basketball and volleyball players,” he 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.”

Although DFCI are benign, follow-up MRI could be warranted, he advised, particularly in the rare situations where DFCI prompts pain or any other symptoms.