In this feature, AAOS Now publishes a series of images, challenging readers to diagnose the condition depicted.

The images for this month’s challenge were submitted by Trey Nichols, DO, primary care sports medicine fellow at the University of Mississippi Medical Center.

Dr. Nichols writes that an 11-year-old boy was seen for complaints of left leg pain and a nonhealing fracture. The boy’s mother reported that several months ago he complained of aches and pains in his leg following an illness. Radiographs ordered by his pediatrician showed a left fibula shaft fracture. His mother denied injury at that time and reported that he was assumed to have had a stress fracture.

The patient was treated with a walking boot and healed clinically over a few weeks, but had persistent changes on his radiographs. A physical examination of the left leg revealed no swelling or tenderness, but subtle fullness was found along the lateral calf without pigmentation changes. The ankle had full range of motion and was clinically well-aligned. Anteroposterior (Fig. 1) and lateral (Fig. 2) radiographs of the left tibia and fibula were obtained several months after the youth was initially seen. What’s your diagnosis?

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Do you have a challenging case you’d like to submit for publication? Email a short case description and any accompanying images to aaoscomm@aaos.org

Find the answer to this month’s challenge below.

Answer
According to Trey Nichols, DO, who submitted the case, the diagnosis is congenital pseudarthrosis of the fibula.

“Congenital pseudarthrosis of the fibula is a rare type of nonunion that frequently is not diagnosed until childhood or adolescence,” explains Dr. Nichols. “Its cause is unknown, but it is often seen in patients with neurofibromatosis. It typically involves the distal shaft of the fibula and may have associated subtle changes of bowing or medullary narrowing in the tibia. Thickened fibrous tissue and limited vascular ingrowth is seen surrounding the area.”

Forms of fibula pseudarthrosis may include the following:

• bowing of the fibula without pseudarthrosis
• fibular pseudarthrosis without ankle deformity
• fibular pseudarthrosis with ankle deformity
• fibular pseudarthrosis with latent pseudarthrosis of the tibia.

“Up until skeletal maturity, treatment usually involves ankle stabilization with an ankle-foot orthosis and may include a medial tibia hemi-epiphysiodesis for ankle valgus,” says Dr. Nichols. “After maturity, a significant deformity can be treated with a supramalleolar osteotomy and possibly a distal tibia/fibula synostosis.”