Case 72 - Great toe sesamoids: osteonecrosis versus stress fracture

Summary

Imaging description

Stress fractures of the great toe have been reported as occurring most commonly in the medial sesamoid. Stress fractures of the medial great toe sesamoid can be difficult to diagnose on radiographs since they are typically seen only on the AP view and can mimic a multipartite sesamoid. CT with multiplanar reconstructions can readily show the rough fracture edges of a stress fracture compared with the smooth edges of a multipartite sesamoid (Figure 72.1). If there is still confusion on CT images, MRI can be used to demonstrate abnormal bone marrow-like edema within the medial sesamoid.

Osteonecrosis of the great toe has been described as occurring primarily in the lateral sesamoid of the great toe. Osteonecrosis can be seen on axial sesamoid views of the foot as sclerosis and collapse/fragmentation of the sesamoid (Figure 72.2). It can also be seen on MRI as bone marrow-like edema within the lateral sesamoid with normal signal in the adjacent first metatarsal. It has been reported that bone marrow-like edema can be seen in the sesamoid from osteoarthritis; however, one will also see bone marrow-like edema in the subjacent first metatarsal head when osteoarthritis is the cause of the abnormal signal.

Importance

It is important to diagnose sesamoid pathology with medical imaging as it can be difficult to diagnose injuries or osteonecrosis of the great toe sesamoids based solely on history and physical exam findings. If there is clinical concern for possible great toe sesamoid pathology, the radiologist should be careful to not diagnose multiple sesamoid ossifications as a multipartite or bipartite sesamoid as both stress fractures and osteonecrosis can lead to fragmentation of the sesamoids. In these cases, CT and MRI are useful in diagnosing sesamoid stress fractures or osteonecrosis. Because of the difficulty in diagnosing these entities clinically, quick diagnosis of a multipartite sesamoid without questioning a stress fracture or osteonecrosis can lead to a delay in diagnosis.