Stress fracture of the first metatarsal after total knee arthroplasty: two case reports using gait analysis.

Stress fractures after total knee arthroplasty (TKA) occur mainly in patients with considerable deformity of the knee. In addition, the majority of these fractures after TKA involve the hip joint. We present two cases of stress fractures of the first metatarsal after TKA in patients with severe varus deformity. Correction of leg alignment and pain reduction obtained by TKA lead to stress fracture of the bone. Gait analysis was carried out for both cases in order to clarify the gait characteristics of the stress fracture. As a result, side-to-side differences of the distance between first metatarsal and foot center of pressure in the coronal plane were observed using gait analysis in these patients. Fortunately, conservative treatment was successful for these patients. Stress fractures should be considered when a patient who had a considerable severe deformity of the knee preoperatively complains of foot pain on the affected side. Contrary to stress fractures at the hip joint, patients with the fracture of the first metatarsal can be treated without surgery.