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Avulsive cortical irregularity - "tug lesion"

Summary

Tug lesion, also known as avulsive cortical irregularity is an overuse injury that occurs in the knees of children. It can be mistaken for a tumor.

Children between 11 and 14, depending on bone age, get this lesion.
Symptoms are knee pain with athletic activity
On xrays, at the distal posterior medial end of the femur, just above the growth plate, a cortical irregularity is seen.
Treatment is rest and observation
Complete Information on this Tumor
Introduction and Definition: 

This overuse injury occurs when a child is intensely active, in running sports or basketball or similar sports, and the medial head of the gastrocnemius muscle, which attaches along with distal medial portion of the femur just above the femoral growth plate, as a result of repetitive forceful muscle traction at the muscle-bone junction, causes a reactive process in the surface of the femur which can be apparent on x-rays.

Incidence and Demographics: 
In children and adolescents. Most cases occur in very active children, typically children who are participating in multiple sports are participating in frequent activities over a period of months. Typically both sides are somewhat involved a the one side may be more symptomatic.
Symptoms and Presentation: 

Patients present with knee pain and a bone lesion. One or both sides may be symptomatic.

X-Ray Appearance and Advanced Imaging Findings: 
On xrays, at the distal posterior medial end of the femur, just above the growth plate, a cortical irregularity is seen, either with lucency, reactive bone formation, sclerosis, or a combination of these.
Special and Unusual Features: 
This lesion has been mistaken for a malignancy, both on radiographs, as well as on histopathology. In patients with worrisome radiographic findings, or worrisome clinical history such as a history of other malignancy, additional concern arises because avulsive cortical irregularity lesions take up F-18 FDG and are thus PET positive.