Pain in Medial Knee • Xray of the Week 2016 • Week #43
This 14 year old bent over while showering and felt sudden “pop” with pain in the medial knee. What is the diagnosis?
Figure 1. Coronal PD with fat saturation image with red arrow showing the avulsion fragment and donor site. There is surrounding bone marrow edema (green arrows). Sagittal T1 weighted image shows avulsed fragment at attachment of medial gastrocnemius (orange arrow).
Figure 2. Axial image shows the avulsed fragment (red arrow). Note the cortical defect indicating a fracture (green arrow). Sagittal T2 “fat sat” image shows 2 mm of distraction (orange arrows).
Figure 3. Five weeks after conservative management, there is healing with no physeal bar.
Avulsion fracture of the gastrocnemius muscle is a rare injury caused by traction on the origin of the medial head of the muscle on the medial femoral condyle. As in this case, MRI demonstrates a fracture of the medial femoral condyle with mild distraction of the avulsed fracture fragment [Fig. 1-2]. Invariably there is associated bone marrow edema which resolves over time [Fig. 2-3]. A previous case report was of a patient who had an avulsion fracture of the medial head of the gastrocnemius muscle due to a skiing injury. The fracture was successfully treated with open reduction and internal fixation with a screw. A second case of case of a 14-year-old male wrestler presented with a radiographically occult avulsion fracture of the medial gastrocnemius tendon sustained during competition. This was treated conservatively with return to competition after non-operative management. Other more common avulsion fractures of the knee are described in detail by Gottsegen et al .
1. Maehara H, Sakaguchi Y. Avulsion Fracture of the Medial Head of the Gastrocnemius Muscle: A Case Report. The Journal of Bone & Joint Surgery. 2004; 86:373-375
2. Patterson, J.T., Jokl, P., Katz, L.D. et al. Isolated avulsion fracture at the medial head of the gastrocnemius muscle. Skeletal Radiol (2014) 43: 1491. doi:10.1007/s00256-014-1915-5
3. Gottsegen C, Eyer B, et al. Avulsion Fractures of the Knee: Imaging Findings and Clinical Significance. RadioGraphics 2008; 28:1755–1770
Phillip Tirman, MD is the Medical Director of Musculoskeletal Imaging at the Renaissance Imaging Center in Westlake Village, California. A nationally recognized expert in the applications of MRI for evaluating MSK and spine disorders, Dr. Tirman is the co-author of three textbooks, including MRI of the Shoulder and Diagnostic Imaging: Orthopedics. He is also the author or co-author on over sixty original scientific articles published in the radiology and orthopedic literature.
Kevin Rice, MD is president of Global Radiology CME and also a radiologist with Renaissance Imaging as the Chair of the Radiology Department at Valley Presbyterian Hospital in Los Angeles, California.
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